rational road drainage environment

8/6/2019 Rational Road Drainage Environment

1/40

RURAL ROAD DRAINAGE DESIGN FORENVIRONMENTAL PROTECTION

by P. J. Griffiths, A.B. Hird and P. Tomlinson

Unpublished Project ReportPR/INT/192/00


2/40

PROJECT REPORT PR/INT/192/00

Rural Road Drainage Design For Environmental

Protection

by P J Griffiths, A B Hird and P Tomlinson

Subsector: Transport

Theme: T2

Project Title: Rational Road Drainage Design For Unbound Pavement Materials

Project Reference: R6990

APPROVALS

Project Manager Quality reviewed

Copyright Transport Research Laboratory March 2000.

This document is an output from an DFID-funded technology development and researchproject, carried out for the benefit of developing countries. It is an unpublished report andmust not be referred to in any publication without the permission of the DFID. The viewsexpressed are those of the author(s) and not necessarily those of the DFID.

Transport Research Foundation Group of CompaniesTransport Research Foundation (a company limited by guarantee) trading as Transport Research Laboratory. Registered in England, Number3011746.TRL Limited. Registered in England, Number 3142272. Registered Offices: Old Wokingham Road, Crowthorne, Berkshire,


3/40

TABLE OF CONTENTS

EXECUTIVE SUMMARY .......................................................................................................... i1. INTRODUCTION ............................................................................................................. 1

1.1 Environmental Impact Assessment.............................................................................. 1Category B Projects/Components ....................................................................................... 2Category C Projects/Components....................................................................................... 21.2 Environmental Good Practice for Rural Road Drainage Design .................................. 3

2. IDENTIFICATION OF SENSITIVE ENVIRONMENTS .................................................... 63. SITE SURVEY AND DATA ASSEMBLY ......................................................................... 9

3.1 General Objectives....................................................................................................... 93.2 Watercourse Surveys................................................................................................. 103.3 Meteorological Data ................................................................................................... 113.4 Land Use.................................................................................................................... 123.5 Geotechnical Survey .................................................................................................. 12

3.5.1 Soil Erosion......................................................................................................... 12

3.5.2 Pollution .............................................................................................................. 123.5.3 Sediment Loadings ............................................................................................. 123.6 People........................................................................................................................ 133.7 Fish and Wildlife Surveys........................................................................................... 133.8 Mitigation.................................................................................................................... 14

4. ROAD ALIGNMENT ...................................................................................................... 155. ROAD DESIGN.............................................................................................................. 16

5.1 River Crossings.......................................................................................................... 165.2 Drainage Design ........................................................................................................ 16

5.2.1 Drains.................................................................................................................. 165.2.2 Culverts............................................................................................................... 175.2.3 Channel Alterations............................................................................................. 18

5.3 Storm Water, Erosion and Pollution Control .............................................................. 185.4 Enhancing and Reconstructing Natural Environments............................................... 26

5.4.1 Riverbanks.......................................................................................................... 265.4.2 Water Features ................................................................................................... 26

5.5 Vegetation.................................................................................................................. 276. CONSTRUCTION OPERATIONS ................................................................................. 29

6.1 Scheduling of Construction Activities ......................................................................... 296.2 Borrow Pits and Quarrying......................................................................................... 296.3 Erosion and Sediment Control ................................................................................... 306.4 Pollution Control During Construction........................................................................ 316.5 Waste Management ................................................................................................... 32

7. MAINTENANCE............................................................................................................. 33

8. REFERENCES.............................................................................................................. 349. WEB SITES ................................................................................................................... 35


4/40

TRL LIMITED Rural Road Drainage Design For Environmental Protection

EXECUTIVE SUMMARY

International Aid Agencies and National Governments recognise that good drainage in ruralroads is critical to the success of road construction. If drainage is inadequate, maintenancecosts can be increased, the life span of the road can be reduced, and adverse impacts onthe environment and local communities can result. Such impacts can include increasedhealth risks, damage to food and water supplies, depletion of natural resources and harm tolocal economies.

Although it is possible to mitigate some impacts after construction, it is acknowledged thatsuch retrospective measures are not as effective as, and generally more expensive than,measures taken during the planning, design and construction phases. In some cases,problems can be avoided altogether by making slight changes to e.g. Route alignments ordesigns. It is important, however, that those involved in the early stages of rural roadplanning, design and construction are aware of the full range of potential impacts that road

drainage can have so that appropriate information can be collated and used in the decisionmaking processes.

A wealth of guidance and associated literature already exists on formal EnvironmentalImpact Assessment (EIA) procedures. However, many rural road projects do not require aformal EIA and consequently little, if any, importance is given to environmental issues duringplanning, design or construction. Such situations have resulted in detrimental impacts notonly to the natural environment but also the road and local communities.

This report gives a comprehensive checklist of good practice procedures for road engineersof rural road drainage projects; projects that do not require a formal EIA, but would stillbenefit from consideration of environmental issues in the manner described above. It is not

intended to provide detailed designs for all eventualities - indeed it is probably impossible todo so, but it gives an overview of the approach to be taken.

Firstly, sensitive environments that might warrant special protection, or need to be avoidedcompletely, are identified. These include Mangrove coastlines, coral reefs, wetlands, aridregions, mountain regions and rain forests. Notable (environmentally valuable) featureswithin each type of environment are highlighted along with possible impacts roadconstruction may have in such areas. Sources of further information relating to these areasare provided.

Secondly, site survey and data assembly activities are described to ensure that the roadengineer gains a full understanding of the existing value of the local environment. This

includes identification of existing water quality and quantity, climate, land use, soil andgeology, communities, and wildlife. Methods for collecting this information are suggested,including identification of external sources of information. Following establishment of this'environmental baseline' the engineer can then go on to identify potential problems andbenefits that road construction will have on the surrounding area.

Thirdly, methods of mitigating potential adverse effects through informed decision making atthe road planning and design stages are presented. The report gives a checklist of issuesthat either need to be avoided or considered carefully when aligning and/or designing a road.Methods of enhancing or reconstructing natural environments are also provided forconsideration at the design stage.

Finally, ways of ensuring decisions made during the design stage are carried forward intothe construction and maintenance phases are presented.

Rational Road Drainage Design For Unbound Pavement Materials R6990 i


5/40


This report is one of a series of reports concerned with the design of roads and roaddrainage features; others provide more detailed information on the engineering.

Rational Road Drainage Design For Unbound Pavement Materials R6990 ii


6/40


1. INTRODUCTION

1.1 Environmental Impact Assessment

Good drainage design in rural roads is critical to the success of road construction. If

drainage is inadequate, maintenance costs can be increased, the life span of the road canbe reduced, and adverse impacts on the environment and local communities can result suchas increased health risks, damage to food and water supplies, and depletion of naturalresources. Many of these problems can be avoided if consideration is given to the design,construction and maintenance of adequate road drainage. The time and expense needed toimplement adequate road drainage more than off-sets the greater costs of trying to mitigateproblems after construction, and is much more effective in the long term.

Environmental Assessment (EA) or Environmental Impact Assessment (EIA) is therecognised technique used for ensuring that the environmental effects of any newdevelopment are fully understood, and taken into account, before the development is

allowed to go ahead. The UN Environment Program (UNEP) has adopted goals andprinciples to be considered for use as a basis for EIA (UNEP, 1987). Its first goal is:

States (countries, including their competent authorities) should not undertake orauthorise activities without prior consideration, at an early stage, of theirenvironmental effects. Where the extent, nature or location of a proposed activityis such that it is likely to significantly affect the environment, a comprehensiveenvironmental impact assessment (EIA) should be undertaken in accordancewith the following principles (it goes on to list the minimum requirements of anEIA).

The criteria and procedures for determining whether an activity is likely to

significantly affect the environment, and is therefore subject to an EIA, should bedefined clearly in legislation, regulation, or other means, so that subject activitiescan be quickly identified, and EIA can be applied to the activity as it is beingplanned.

The World Bank has an Operational Policy on Environmental Assessment (World Bank,1999) which mandates an environmental assessment for all projects that might have asignificant negative impact on the environment, so that problems can be tackled early in theproject phase. From 1991 all projects were placed in one of three environmental assessmentcategories (see Box 1.1). Those falling into category A require detailed environmentalassessments; those falling into category B require a limited assessment; those falling intocategory C did not require an environmental assessment.

Rational Road Drainage Design For Unbound Pavement Materials R6990 1


7/40


8/40


The World Bank stipulates that these examples are only illustrative; it is the extent of theimpacts, not the sector, that determines the extent of the environmental assessment and,hence, the category. Consequently, a road design team should always check withappropriate government departments and regulatory authorities to determine whether an EIAis required. If found to be necessary, the reader is directed towards more formal EIAguidelines and requirements, a full listing of which is given by the International Institute forEnvironment and Development (IIED, 1998).

1.2 Environmental Good Practice for Rural Road Drainage Design

For small rural road projects, unless the road proposal adversely affects a nationallyprotected area or an area protected under international conventions, it is unlikely that aformal EIA would normally be required. This, however, does not mean that all forms ofenvironmental assessment should be disregarded. The principles underlying theInternational Aid Agencies environmental assessment guidelines can be translated intoGood Practice procedures and applied to even the smallest project. For rural road projects,good practice will identify the significant environmental impacts of the road project during theplanning stage. This knowledge can then be used by the road engineer to plan and design

the road to protect the natural environment, and preserve social and community activities.Such design will also prevent costly road maintenance activities after construction.

The steps that make up good practice when incorporating hydrological considerations intothe road planning and development processes are outlined by the World Health Organisation(1997). These are highlighted in Figure 1.1, and summaries of the activities to be undertakenin each step are given in Box 1.2.

The following chapters in this report give more detailed guidance on good practiceprocedures for road engineers of rural road drainage projects; projects that do not require aformal EIA. Firstly, sensitive environments that might warrant special protection areidentified, along with their notable features. Secondly, site survey and data assembly

activities are described to ensure that the road engineer gains a full understanding of thepotential problems and benefits road construction will have on the surrounding area.Proposed activities have been accommodated with existing recognised operations, such assite surveys and desk studies. Thirdly, methods of mitigating potential adverse effectsthrough informed decision making at the road planning and design stages are presented.Finally, ways of ensuring decisions made during the design stage are carried forward intothe construction and maintenance phases are presented. This report will demonstrate thatconsideration of the environment at an early stage in road planning and design will not onlyimprove the local natural environment but also increase he longevity of the road, reduceoverall maintenance costs, and reduce adverse impacts on local communities by protectinglocal drinking water supplies, and maintaining valuable natural resources.



9/40


Determine Sensitivityof the LocalEnvironment

Specify EnvironmentalPlans in Construction

and MaintenanceActivities

Undertake CarefulPlanning and Designof Water Crossin s

Develop MitigationPlans

Make InformedAlignment Choices

Collect Relevant Data

Figure 1.1. Good Practice Procedures in Road Drainage Design



10/40


Box 1.2. Summary of Good Practice Activities in Road Drainage Design

1. DetermineSensitivity Of The

Local Environment:

Identify sensitive environments in the proposed road corridor anddetermine whether these can be adequately protected, or need to be

avoided

2. Collect RelevantData:

Identify the main potential impacts, working from basic data on thedrainage basin, nature and frequency of flooding, water quality, wateruse, fauna species and habitats. Identify the sensitivity of the road andsurrounding area to erosion, instability and contamination. Soil type,vegetation and land use are particular points to consider. Health risksshould also be identified, especially diseases and movement of water-borne disease vectors. Assess the likely modification of existingconditions arising from construction of the road.

3. Make InformedAlignment Choices:

Minimise water crossings and avoid sensitive areas wherever possible,including those with a high risk of erosion or slope instability

4. Select PreferredDesign Which LimitsErosion:

Take account of design changes which concentrate or speed up flows,lower the water table, or increase flood risks. Factors to be consideredinclude horizontal and vertical alignment, cross section, slopes,drainage of subgrade and surrounding area, as well as restoration ofnatural surface and underground flow and replanting of vegetation.Give priority to mitigative measures which are easy to implement andrequire only local materials

5. Undertake CarefulPlanning AndDesign Of WaterCrossings:

Planning and construction of water-crossings needs to be co-ordinatedwith local aquatic conditions such as flow regimes, fish movement, andhuman use. Inadequate planning can have severe long-term effects;for example an improperly sized bridge culvert could cause floodingbringing economic losses, impaired fish migration, erosion andsiltation.

6. Develop MitigationPlans:

Mitigation plans include proposals for specific technical measures,such as planting of cleared areas, installation of flow-speed dissipatersand slope retaining structures, sediment control measures, andrecommendations for subsequent maintenance. Scheduling, anddictating the manner in which works are undertaken, may also beincluded.

7. Specifications InContract

Documents:

Environmental specifications for contractors should cover road design,bridge and culvert construction, drainage installation and any work site

plans which may affect water flows and quality, including fuel storageand re-fuelling areas.



11/40


2. IDENTIFICATION OF SENSITIVE ENVIRONMENTS

Road drainage can affect the natural environment in a variety of different ways, dependingon the characteristics of the local environment. Rural road engineers need to be able toidentify those types of environment that are of particular importance, and understand whythey are of importance, to enable them to decide how they could/should be considered in thedesign of road drainage. Environments identified as being of particular importance by theInternational Aid Agencies have been identified in Boxes 2.1-2.6, along with a brief summaryof their importance in terms of the natural environment and social/community activities. Formore detail on each of these environments, the reader is referred to the World BanksOperational Policy on Natural Habitats (World Bank, 1994) and DFIDs Guidance Note onInternational Environmental Agreements (DFID, 1998). When encountering any of thesesensitive environments along a proposed road corridor, careful thought must be given towhether it is possible to avoid these areas and , if not, the measures required to ensurethese areas are adequately protected.

Box 2.1. Mangrove Dominated Coastlines

Mangrove forests occur at the fringes of tropical coastlines and are typified by soils that arefrequently flooded and waterlogged. These areas provide food for small aquatic animals that in turnsupport fish and wading birds that could well have an economic value to the local or nationalcommunity. Mangroves also provide protection from storm erosion and provide valuable productssuch as wood for charcoal.

Given their value to national and local economies, mangroves should not be diked or permanentlyflooded. Normal tidal flooding should not be restricted and the network of circulatory streams should

be protected. Also, fine sediment should not be allowed to flow into the flooded forest area. Forthese reasons it is usually best to locate roads away from these areas.

Box 2.2. Coral reefs

Coral reefs provide a habitat for diverse populations of fish and other aquatic life. In a similarmanner to mangrove forests, they reduce wave energy which not only provides protection fromstorms but, in this instance, can also provide conditions beneficial for sport, commercial fishing,recreational diving and other activities with an economic value to the local community. Growth of the

reef is slow, and it is easily damaged by poor water quality resulting from sediment/pollutiondischarges. Consequently, road construction on nearby shores should avoid drainage, or release ofsediment, into such areas.



12/40


Box 2.3. Wetlands and Estuaries

Like mangrove forests and coral reefs, wetlands provide nursery habitats for many species of fishand wildlife that may also be of value to local communities. By temporarily storing large quantities of

water, wetlands also play an important role in reducing flooding problems and recharging groundwater supplies. They help to maintain water quality by filtering out pollutants and sediments, andserve to control erosion by trapping soil washed from nearby uplands.

Estuaries are among the word's richest and most productive environmental areas. Sunlight in warmshallow waters and nutrients from rivers and the ocean encourage the growth of algae and marshvegetation. This in turn provides cover for fish, birds and mammals. Consequently, estuaries areimportant habitats for migratory waterfowl and fish. They may also provide productive farmland,drinking water and recreational areas.

Wetlands and estuaries can easily be damaged through water diversions and pollution.Consequently, roads crossing wetlands and deltas should be located at the narrowest point. Thecrossing should be designed to alter the existing nature of the aquatic environment as little aspossible, and the construction process should be carefully planned to avoid excessive discharges.Methods to reduce flow velocities and trap excessive sediment should be incorporated into roaddesign and construction activities where necessary.

Box 2.4. Arid Regions

About one-third of the earth's land mass is arid to semiarid. Typically, rainfall occurs in brief intervalsand is unpredictable from year to year. Because of these conditions, deserts are among the most

fragile ecosystems on the planet. Biological and economic resources, notably soil quality,freshwater supplies, and vegetation are easily damaged, mainly due to a combination of climatevariability and unsustainable human activities (especially poor irrigation practices).

Roads in these areas should be carefully located to avoid dry valleys prone to flash flooding. Careshould be given to the consequences of secondary development resulting from road construction,especially as it may put pressure on already limited natural water supplies. By careful design of theroad drainage system, however, it might be possible not only to protect these sensitive areas, butalso enhance natural water supplies and encourage the development of sustainable economicactivities by encouraging retention and use of flood water.



13/40


Box 2.5. Mountain Regions

Mountainous regions, especially those experiencing humid climates, are unstable landscapes.Intense and prolonged rainfall leads to locally high groundwater tables, saturated soils and large

quantities of surface runoff during the wet season. Land slides, erosion, river flooding and periodicearthquakes usually compound these problems. In hot humid regions, rapid rock weathering andheavy rainfall act to induce erosion and land slides. Cultivatable land is in short supply in suchregions and has a high local economic and community value.

Mountain regions are difficult places in which to construct and maintain roads. Frequently,topography, slope stability, flood hazard and erosion potential will be the most significant controls onthe choice of alignment and design of cross-section. Road construction can lead to impoundment orchange of drainage pattern with increased erosion potential. Consequently, road geometry,earthworks, retaining structures and drainage systems must be designed to cause the least impacton the stability of the surrounding slopes and natural drainage systems. Excessive blasting, cutting,side tipping of spoils and concentrated or uncontrolled road drainage must be avoided as this willoften lead to accelerated instability and erosion.

Box 2.6. Rain Forests

Although tropical rain forests cover only 7 percent of the earth's land area, they contain about one-half of the 1.9 million named species in the world, as well as innumerable species yet to be properlyidentified. This degree of biodiversity is seen as a valuable resource which, as yet, remains largelyuntapped. The special characteristics of tropical woods also makes them valuable as a source ofindustrial wood, with an immediate commercial value. Tropical rain forest has a much greaterinfluence on the global climate and carbon dioxide levels than the other main types of forest(tropical dry forests and temperate forests). Moreover, they are the most fragile forests in that theirsoils are easily degraded once deforested, and experience to date indicates that even ifreforestation or selective felling is attempted, the original ecosystems cannot be fully renewed orsustained. De-forestation has accelerated in recent years for three reasons:

The pressure of population on the natural resource base has grown sharply in many countries.

Income opportunities in settled agricultural regions have deteriorated in some countries, leadingto increased migration and encroachment on forested land.

Access to the forest frontier has increased dramatically in some areas because of infrastructuredevelopment, especially road building.

If rain forest areas cannot be avoided when planning a new road, careful consideration must begiven to indirect effects, including the long-term effects of secondary development, in these areas.



14/40


3. SITE SURVEY AND DATA ASSEMBLY

3.1 General Objectives

This chapter addresses the field survey and data assembly activities that should be

incorporated into scheduled engineering surveys and studies to enable an environmentalbaseline to be established. This information is then used to inform choices made during thedesign and construction of a road to ensure the best environmental option is chosen, whilestill meeting the objectives of the road scheme.

An understanding of the characteristics of an area through which a road is being constructedenables the engineer not only to identify potential engineering problems and benefits to roadconstruction (location of raw materials, unstable geology etc), but also the potentialenvironmental problems and benefits. This environmental baseline information is used as areference point from which potential changes, arising from construction, operation andmaintenance of the road, can be identified. Much of this baseline information is gathered by

conducting field surveys within, and collating existing data on, the road corridor. Box 3.1summarises the objectives of site survey and data collection.

Box 3.1 Objectives Of Site Survey And Data Collation

1. Determine the wildlife features of the road corridor in terms of quality, quantity and visualqualities that will determine the importance of the area. If necessary, locate similar geographicalareas with data suitable for transfer into the geographical area of interest.

2. Identify issues relevant to local communities (land use, heritage, cultural issues).

3. Determine the water quality, quantity and visual qualities of the road corridor to use as abaseline to compare possible changes caused by construction (including groundwater data thatinfluences surface waters, abstraction points for drinking water supplies, commercial fisheriesetc).

4. Identify the nature and quantity of existing discharges to watercourses.

5. Identify any future land use changes planned for the road corridor that could influencewatercourses.

6. Forecast what mitigation measures should be included in the design, construction andmaintenance activities to protect the surface waters (using worst case scenarios).

The first activity in collating this information is to carry out a walkover study of the roadcorridor and make a preliminary identification of watercourses and other possible sensitiveareas (see Chapter 2) that may be affected by construction of the road. Most of theremaining information can be carried out through desktop studies. If there is a deficiency ofpublished information it might be necessary to carry out field studies or it may be possible totransfer data from another similar geographical area. Early co-ordination with expert bodiessuch as water resource sections of government departments, wildlife agencies andgovernmental planning agencies should be undertaken to assist in the identification of allpertinent laws and regulations regarding environmental protection, and in the identification ofprotected and/or sensitive areas. Liaison with the local communities is also necessary toassist in identifying detailed characteristics of the road corridor, including cultural/heritagesites. Time constraint issues are identified in Box 3.2.



15/40


Box 3.2 Time Considerations In Data Assembly

When deciding how much time to spend the following should be considered:

Sensitivity of the road and the surrounding area;

Time constraints: restrictions imposed by project schedules will affect the level of data collected;

Resource availability e.g. sufficiently qualified personnel, necessary equipment, and projectfunds; and,

Site accessibility.

All data collection should be taken during a stable time i.e. not just after a drought or flood,and should encompass the entire geographic area affected by the road (not just limited tothe road right-of-way). Again, the use of experts may be required to determine theseboundaries.

To establish an adequate baseline, and determine the potential impacts of the proposedroad on the surrounding environment, the data collected should be adequate to describe:

existing water quality and quantity

climate

land use

soil and geology

people

wildlife

The detailed information required for each of these topics, and methods of collection, isdescribed below.

3.2 Watercourse Surveys

Watercourse information will include: changes arising from the elimination or change in thesize of a surface or groundwater feature; the effect on floodplains and wetlands; effects onflood control; and the duration and limits of flooding. Water quality and quantity controlrequirements and information on protected/sensitive areas within the study area may befound in laws and regulations. A review of previous studies and reports concerning waterquality and quantity in the area will help to identify other problems. Sources for thisinformation are:

educational institutions, governmental agencies at all levels, and

quasi-public bodies.

Useful information for determining the effect of the road upon watercourses is given in Table3.1 below. The table is separated according to information obtained from an initial walkoversurvey, desk studies and field surveys.



16/40


Source Aspects to consider

Note where boundaries are intersected by route alternatives

Identify any exposed groundwater that may be affected

Identify any features that would allow the surface water to affectgroundwater

Note the presence of e.g. lakes, marshes, bogs, wetlands, streams andrivers, especially those with unique surface water character andaesthetics

note existing water surface areas, volumes and stream lengths.

Identify groundwater recharge areas

Identify flood control facilities

Identify past, existing and future sources of pollution, and their points ofdischarge

WalkoverSurvey

Identify current water use e.g. fishing, recreation, water supply, culturalassociations

Locate water supply reservoirs and facilities (intakes)

Identify water rights and type of water use e.g. agricultural, municipal,industrial, recreational, religious etc

Is there any information on water quality

What are the downstream water uses e.g. abstraction points

What is the current flood risk

What fish and animals are dependant on local surface water supplies, andwhat are their migratory habits

DeskStudies

What are the future planned uses for the area.

Where channel crossings are necessary, sufficient information is needed

to describe the channel upstream and downstream of the crossingEstablish normal flow depths and volumes associated with variousseasonal discharges

Determine natural sediment discharge rates for various seasons.

Field Data

What is the estimated temporary and permanent volume of runoff from theproposed road

Table 3.1. Information Required In Watercourse Studies

3.3 Meteorological Data

Climatic considerations include seasonal variations in temperature, precipitation, and windstrength/direction. Knowledge of the climatic conditions is necessary for:

Effective design of stormwater drainage,

Predicting likely erosion patterns/rates, and

Determining when best to carry out certain construction activities.

Data will vary in availability and format, but both current and historical climatological datamay be used. Data from outside the geographic area of interest should only be used whendata is unavailable from within the study area, and be supported with local knowledge.



17/40


3.4 Land Use

Clearly any new road construction will displace existing land uses and affect adjacent landuse patterns. Consequently, a study should be carried out to determine present and futureland use activities that might be influenced by road construction. The following land usefeatures of the study area should be identified:

Protected/designated sites;

Other environmentally sensitive areas (see chapter 2);

Sources of pollution e.g. waste sites, areas of contamination;

Productive farmland, including details of irrigation;

Recreational land;

Features with an unusual aesthetic value;

Archaeological sites; and

Heritage sites.

Most of this information will come from desk studies, but valuable information can also be

gained from consultation with local residents and landowners.3.5 Geotechnical Survey

There are three geotechnical areas for which the possible impact of the road needs to beidentified: soil erosion, pollution and sediment loadings. This information is normallycollected as part of the geological survey, but is specified here to indicate the environmentalimportance of these features.

3.5.1 Soil Erosion

Soils prone to erosion, either because of textural or slope characteristics, need to beidentified and adequate protection measures incorporated in both the road design and roadconstruction plan to reduce the amount of erosion. Relevant information includes:

Soil type (texture) in terms of susceptibility to erosion.

Main topographical features, such as cliffs, terraces etc;

Natural slope angles;

Uninterrupted length of slope;

The stability of slopes; and

Cuts, fills and other earthwork features for the proposed route alternates

3.5.2 Pollution

Rural road projects, by virtue of their low traffic volumes and low percentage of freight traffic,should not constitute a pollution problem during use. Although unlikely, geologicalexploration and evaluation of proposed construction areas should also determine whetherharmful minerals might be transported to adjacent surface waters during excavation of rawmaterials. The main source of pollution however, is likely to come from constructionactivities, mainly in the form of sediment in run-off.

3.5.3 Sediment Loadings

Information on sediment is needed in order to estimate the existing sediment loading withinlocal watercourses, and to assess the effect that sediment from road construction will haveon surface waters. Where information is not available, information should be collected sothat pre-construction sediment discharge can be estimated and seasonal fluctuationsidentified. Watercourses with periods of low natural sediment discharge will be more

susceptible to a large influx of construction sediment. During periods of high naturalsediment discharge the sediment added from construction activities may have negligibleeffects. Road construction activities should be planned accordingly.



18/40


3.6 People

Construction and operation of a road can alter the life style of communities in thesurrounding area, particularly in remote areas. The effects could be short term, for theconstruction period, or long term if the project results in secondary activity and development.Watercourses serve local communities in several ways:

Water supply;

Recreation;

Agriculture;

Transportation;

Waste disposal.

If the road construction requires a temporary labour force to be accommodated in the localarea, or if secondary development is a possibility, the following questions should beaddressed by the survey and considered in the road design:

Will traditional rights and needs be considered in a just and fair manner?Does the area support, or will it support, significant commercial fisheries and willthese be affected?

Will potable water supplies be affected in terms of quality or quantity?

Will there be the capacity to increase water abstraction if the populationincreases?

Are sufficient controls in place to limit disease e.g. mosquito controls.

This information should be obtained by discussions with local government officials, localresidents and walkover surveys.

3.7 Fish and Wildlife Surveys

Wildlife are dependent on many physical, chemical and geometric features of watercourses,such as water quality, water depth, riffles and pools. The walkover survey should identifythose characteristics that will be affected by road construction. Aspects to consider whenassessing impacts to the aquatic environment and surrounding wildlife are set out in Table3.2 below.



19/40


Stage Aspects to consider

Walkoversurvey:

What are the vegetative patterns in the river corridor.

Will sensitive wildlife habitat and features be damaged or lost?

Critical areas include: feeding areas; protective cover, spawning andbreeding grounds, nesting and nursery areas, and dry or wet seasonrefuge areas.

Desk Study Is there any existing information on local wildlife and habitats?

Are there any endangered species and are they dependent upon thearea permanently or at particular times of the year?

Are there any areas protected by Government legislation etc?

Expert Advicewill required toidentify:

What is the relative seasonal abundance and distribution of wildlifewithin the area?

What are the migration patterns and timings of various species?

What are the critical periods (e.g. nesting period of waterfowl;

spawning and nursery periods of fish)?

Will the road disrupt the area and will natural processes be able torepair the damage?

Will animal or plant species be lost?

Will pests and pathogens e.g. mosquitoes become more common?

Table 3.2 Information Required In Fish And Wildlife Surveys

3.8 Mitigation

Once all the baseline data has been collected it will be possible to assemble an inventory toindicate the interrelationships between watercourses and the other study area featuresinvestigated. This will help to summarise the changes that road construction and use mayhave on the environment. Ways of mitigating adverse impacts and enhancing positiveimpacts can then be incorporated into the planning, design, construction and/or maintenanceof the road. The earlier that adverse changes are identified, the more options an engineerhas to address them, resulting in more effective methods of mitigation and reducedmagnitude of the effect. Five ways to mitigate losses are listed below, in order of priority:

Avoid the effect altogether by not taking a certain action or part of an action;

Minimise the effect by limiting the degree or magnitude of the action and itsimplementation;

Rectify the effect by repairing, rehabilitating or restoring the affectedenvironment;

Reduce the effect over time by preservation and maintenance operations duringthe life of the action; and

Compensate for the effect by replacing or providing substitute resources orenvironments.

Methods of mitigating the changes caused by road construction should be used to informdecisions regarding the alignment of the road, the drainage design, construction practicesand maintenance practices. This is addressed in more detail in the following chapters.



20/40


4. ROAD ALIGNMENT

Good choice of road alignment can avoid many potential environmental problems. Wherepossible the road should be located to avoid recognised sensitive environments, and notdisrupt natural surface waters or aquatic habitats. It is appreciated that, in many cases, it willnot be possible to avoid all sensitive areas. In such circumstances, roads should be locatedto minimise the number of river crossings and channel alterations. Those areas that shouldideally be avoided during road alignment studies are given in the Table 4.1 below.

Areas to Avoid Other considerations

Recognised sensitive environments (seeChapter 2)

Avoid sensitive areas by 1km if possible.

Watercourses and dry channels identified inthe route survey

If necessary to cross water courses,minimise number of water crossings andlocate crossings at narrowest points of

watercourse where there is no evidence ofactive bank erosion.

River flood plains and other low-lying areasthat might be inundated by storm surges

Areas susceptible to erosion. Minimise land disturbance and do notexceed a road grade of 12% or 5% iflocated near riverbanks.

Edges of watercourses and lakes, rivermouths, lake outlets.

Locate to provide a buffer strip of at least100 m of undisturbed land between the roadand any water body. Crossings should not

be placed within 450m of a river mouth orlake outlet.

Important fisheries and fish spawning areas.

Groundwater recharge areas.

Table 4.1. Environmental Issues Influencing Road Alignment Choices

Where river crossings and channel alterations are necessary, adverse changes to theenvironment can be reduced by incorporation of appropriate mitigation techniques into theroad drainage design.



21/40


5. ROAD DESIGN

Like good road alignment, good design can also avoid many environmental problems arisingat a later date during construction, operation and maintenance.

5.1 River CrossingsFollowing the order of preference for mitigation given in Section 3. 8, river crossings shouldbe avoided wherever possible by appropriate choice of road alignment. Where watercrossings cannot be avoided, they should be designed to minimise interference with naturalriver conditions through bridging or culverts. Issues to consider are outlined in Box 5.1.

Box 5.1. Road Crossing Design Criteria

The design and scheduling of approaches to river crossings should maintain stability of valleywalls and river banks and minimise changes that could lead to slope failures, gullying, andrelated disturbances;

The scheduling, location, and design of watercourse crossings (temporary and permanent)should enable safe upstream and downstream passage of fish;

The impact of crossings on runoff, bank erosion, migration of stream channels, ice jams,upstream ponding and streambed scouring should be mitigated;

Include design and/or maintenance procedures to prevent the crossing from being clogged byfloating debris.

5.2 Drainage DesignConventional drainage networks are designed to facilitate the efficient collection and rapidtransport of water away from the road. Unfortunately this often results in heightened peakrunoff volumes and increases in erosion and pollution problems in natural rivers andstreams. Groundwater recharge may also be restricted. Good road drainage design shouldconsider, therefore, not just the removal of runoff water, but also maintenance of sensitiveenvironments, public health, natural water resources and the cost effectiveness of futuremaintenance activities. For example, in very dry areas, road drainage can be designed toretain water in small dams or maintain a high water level that will increase the availability ofwater for wildlife and local inhabitants and recharge local aquifers. In areas prone toflooding, road works can incorporate retarding basins to reduce runoff peaks, or they canimprove drainage in residential or farming areas that are excessively sensitive to flood

damage.

5.2.1 Drains

Surface water drains should be designed to carry uncontaminated rainwater to a localstream, river, pond, detention pond or soakaway. Nothing that could cause pollution shouldbe allowed to enter these drains.

Roadside table drains should follow natural drainage lines where possible, to reduce watervelocity and therefore erosion. They can be sown with grass and maintained by mowing, sothey trap silt efficiently. Cut-off drains can be used to divert runoff water before it reachescritical areas, and diverting drains avoid excessive concentration of flow. Concrete or wooddissipation structures will slow fast running storm water in drains and hence reducedownstream erosive potential.



22/40


5.2.2 Culverts

Culverts should be provided as necessary to prevent a road from disrupting or changing theexisting natural drainage regime. The ideal location for installation of a culvert is where theriver or stream gradient is as close to zero as possible, and where there are no suddenincrease in water velocity. Culvert shapes vary, and are listed below in order of their positive

environmental attributes:

Shelved: Good for wildlife passage.

Arched: This may have an open or a closed bottom. The open bottom typeallows for natural riverbed material to be retained.

Horizontal Ellipse: By lowering the culvert invert below the stream bed elevationit is possible use the wide middle portion of this culvert for maintaining streamflow width and maintain natural river bed material in the culvert. Small barrierdams placed on the culvert bottom will provide some protection against thematerial washing out.

Circular: This is the most familiar culvert shape but may restrict fish passage ifnot installed correctly. This, and other issues to be considered when designingculverts are listed in Box 5.2.

Box 5.2. Culvert Design Criteria

Culvert inverts must be laid a minimum of 15cm below normal streambed elevation.

Design to prevent sag. Sag in a non-cambered culvert can impose a passage problem for fishdue to the increased culvert gradient on the upstream side of the sag.

Gradient should be as close to a 0% gradient as foundations and stream conditions permit, aslong as upstream velocity barriers are not formed as a result. The maximum culvert slope that

should be installed when employing a baffle configuration is 5%.

The culvert should have sufficient capacity to pass the design flood (generally a 1 in 50 yearflood) with no backwatering or ponding at the upstream end of the culvert. There should also besufficient allowance for passage of debris.

If construction procedures permit, the bolt connections should be installed with the bolt head onthe culvert interior to prevent fish being damaged.

The streambed at the downstream end of the culvert may require armouring with heavy riprapmaterial to prevent bed scour. This should extend at least 2 pipe diameters past the culvertoutlet. Such controls must allow for fish and floating debris passage.

When installing multiple culverts, a minimum distance of 1.8m between adjacent culvert walls in

the arrangement will provide a backwater area (downstream end) in which fish can rest beforepassage.

Water flow entering or leaving a culvert generally undergoes an abrupt and localised changein water surface elevation, this causes an increase in water velocities that can form alocalised velocity barrier to upstream fish movement. To avoid this the maximum "drawdown" through any section of the culvert should not exceed 0.3 metres. Culverts should bedesigned so that the average cross-sectional velocity through any section does not exceed0.9 m/s during fish migration periods. Alternatively the culvert design should include aselected region, continuous throughout the length, where velocities are low enough to permitfish passage.



23/40


5.2.3 Channel Alterations

The aim when making channel alterations is to control erosion and flooding while stillproviding good habitat for wildlife. If the cross sectional shape of the original channel isstable with desirable low flow depths, velocities and adequate minimum flow requirements,efforts should be made to keep modified channels the same in terms of profile, shape, and

vegetative cover. It is likely therefore that any new or altered channel will not have a straightalignment and will vary in width, depth and gradient. This will allow the new or alteredchannel to return to a relatively stable condition with less total erosion. Further information isgiven in Box 5.3. For low flow channels the formation of overhanging banks, and otherstream enhancing features is encouraged (see section 5.4).

Box 5.3. Issues To Be Considered When Reducing The Environmental Effects OfChannel Modifications.

A relocated stream channel should carry approximately the same discharge as the original

natural channel. Usually this will be a discharge in the range of the 50% chance flood to the10% chance flood.

Shortening the length of the stream often causes channel instability. This may start a cycle oferosion that can cause damage upstream and downstream. Therefore preserve the naturalgradient by making the new channel the same length as the original. If the channel must beshortened building check dams to absorb some of the elevation difference can preserve theoriginal gradient. In some cases, the channel may be made rougher (e.g. using rocks) to offsetthe steeper gradient.

Some bank erosion will occur as an essential part of the channel forming process, however inareas where the road or land needs protecting riprap bank protection should be used.

Provide stream grade control structures to preserve the natural channel profile or increase the

channel change length by constructing an artificial meander. Grade control practices havedisadvantages. Drop structures and culverts in natural channels may be easily and quicklybypassed as a result of a stream's natural meander tendency. They may also inhibit themigration of aquatic wildlife. To minimise these problems, it may be necessary to routinelyprovide remedial erosion protection.

5.3 Storm Water, Erosion and Pollution Control

Stormwater, erosion and pollution control efforts should include one or more of the followingtechniques:

Reducing the amount of erosion and therefore sediment available for transportinto runoff;

Measures which will remove the sediment from the runoff, prior to release intowater courses (by means of sedimentation, filtration, biological uptake, and/or soiladsorption); and/or

Siting pollution risks away from watercourses.

Temporary erosion and stormwater controls will be employed during the constructionprocess and afterwards removed or converted to permanent measures. The design shouldensure that the flow leaving the site during construction is no greater in pollution loading,velocity, or quantity than it was before construction started. All temporary conveyance

systems should be sufficiently stable to withstand a 2-year storm event. Most projects withearthworks will require at least one control measure to retain sediments on the site. Table5.1 gives existing options that should be evaluated for their suitability to the project.



24/40


Permanent erosion and stormwater control measures are put in place to control erosion andrunoff after construction has been completed. Table 5.2 gives options that should beconsidered. Temporary controls should be converted to permanent controls where practical.For instance ponds used for sediment control during construction can be designed and builtas the detention facilities to control stormwater runoff. A pond used for temporary sedimentcontrol during construction must be cleaned before it becomes a part of the system. Pondsthat are designed to include infiltration must not be used as a sedimentation pond duringconstruction since there is no way to clean the trapped particles from within the soil.Conveyance channels during the construction phase can be utilised as permanentconveyance or even swales, if they are cleaned and seeded as required. The preferredstormwater control measure is an infiltration pond since it not only reduces potential floodingbut also recharges the local ground water table.

Road-generated sediment in runoff will often occur for brief periods even though sounderosion control practices are employed. Consequently, sensitive environments and locationssuch as municipal water supplies, recreational areas, industrial water supplies, may require

additional erosion and sediment control. These should be included in the design.

Permanent erosion control features can also provide environmental enhancements in theform of additional water supplies, groundwater recharge and recreational areas. Table 5.2outlines the potential advantages of these permanent features, however, consultation withlocal communities and relevant government departments should be undertaken at an earlystage in planning and design to ensure that the feature is appropriate to the surroundingenvironment and community.



25/40


26/40

TRL LIMITED Rational Road Drainage D

Practice Definition Conditions Where PracticeApplies

Advantages

Dust Control Use of water or approved dust palliative

to reduce surface and air movement ofdust during land disturbing, demolition,and construction activities.

In areas subject to surface and air

movement of dust where damage islikely to occur

Reduces risk of respiratory problems.

Reduces loss of good quality top soil.

Filter Fence A temporary sediment trap consisting ofa filter fabric stretched across andattached to supporting posts andentrenched. Constructed of stakes andsynthetic filter fabric with a rigid wirefence backing where necessary forsupport.

Below disturbed areas where runoff mayoccur in the form of sheet and rill erosion;wherever runoff has the potential toimpact downstream resources.Perpendicular to minor swales or ditchlines for contributing drainage areas upto 0.5 hectare in size.

Downstream bank side and in strhabitat will not be damaged by sedimdeposits originating from development.Flexible siting.

Table 5.1 contd. Temporary Erosion Control Techniques

Rational Road Drainage Design R6990


27/40


28/40


29/40


30/40

TRL LIMITED Rational Road Drainage D

Practice Definition Conditions Where PracticeApplies

Advantages

Buffer Zones An undisturbed area or strip of naturalvegetation or an established suitableplanting that will provide a living filter toreduce soil erosion and runoff velocities.

Natural buffer zones are used alongstreams and other bodies of water thatneed protection from erosion andsedimentation. Vegetative buffer zonescan be used to protect natural swalesand incorporated into natural landscapingof an area.

Low maintenance and effectivcontrolling and filtering runoff.

Provide critical habitat adjacenstreams and wetlands. Bualong streams and other wbodies also provide a protearea where wildlife can move fone place to another.

Act as a visibility screen.

The filtering action of the grasmoderately effective in remoparticulate pollutants.

Interceptor Dikeand Swale

A ridge of compacted soil or a swale withvegetative lining located at the top orbase of a sloping disturbed area. Thisintercepts storm runoff from drainageareas above unprotected slopes and

directs it to a stabilised outlet.

Where the volume and velocity of runofffrom exposed or disturbed slopes mustbe reduced. When placed above adisturbed slope, it reduces the volume ofwater reaching the disturbed area by

intercepting runoff from above. When it isplaced horizontally across a disturbedslope, it reduces the velocity of runoff byreducing the distance that the runoff canflow directly downhill.

Low maintenance and effective of controlling and filtering runoff.

Provides a practical, inexpenmethod to divert runoff from ero

situations.

Table 5.2 contd. Permanent Stormwater and Erosion Control Prac

Rational Road Drainage Design R6990


31/40

TRL LIMITED Rational Road Drainage Design For Environmental Protection

5.4 Enhancing and Reconstructing Natural Environments

It may be necessary to reconstruct habitat damage caused during construction works topreserve the natural environment for the local plant and animal species and localcommunities. It may also be possible to increase the environmental, economic and socialvalue of an area.

5.4.1 Riverbanks

Overhanging areas provide habitats for both fish and wildlife. The most economical methodto create overhanging banks is to excavate to provide near vertical banks and ensure thatnatural vegetation becomes established. Natural river flow processes will then encouragethe formation of stable banks. Where a new uniform channel has been installed, banks canbe created using wire-enclosed rock or the embedding of culverts in banks with one endprotruding. Riprapped banks should be partially covered with soil to provide a toehold forgrasses and plants.

Care must be taken when locating overhanging banks: the location must have slow currents

to deliver oxygen and food to fish population. They should not become isolated from thestream by sediment deposition during low flows. In a newly constructed channel it issometimes difficult to determine reliable locations for artificial overhanging banks. Thereforeit may be better to wait several seasons before installation as alterations made by the streamchannel will make it easier to locate conditions suitable for overhanging banks.

The construction of riverbanks should be suitable for local community activities as well asthe natural environment. For example:

Small craft such as canoes prefer a relatively shallow, gradual slope forbeaching;

Motored craft, except for launch areas, prefer a deeper shoreline;

Certain aquatic species depend on both overhanging banks and shallowshorelines where wetland-type vegetation can be found for cover, breeding,nurseries and for food supplies;

Farm animals and wildlife that feed in the water are dependent on shallowshorelines.

These should all be considered when designing new or re-constructed riverbank areas.

5.4.2 Water Features

Riffle and Pool Sequences

Riffles and pools develop as a feature of natural stream erosion in areas where the stream

bed material is relatively coarse (riffle-pool sequences will not develop in streams with sandor silt beds). The pool and riffle sequence is a valuable feature to fisheries, the riffles beingimportant food producing areas. They can be constructed artificially using clusters of large(48 inches or greater) rocks or cribs, or wire gabions of smaller rock or logs. Artificial pooland riffle features can be very sensitive to large floods, bed load material and other streamforces.

Steam Velocities Check Dams

Check dams decrease the slope and velocity of a stream to control erosion. Plunge poolsbelow the check dam can also provide excellent fish habitats. Check dams can be made outof logs, gabions or timber. They should be embedded in the streambed at least 0.6m and theend should extend into the banks about 3m beyond the low water line. Riprap bank

protection is essential to prevent washout. They should be placed far enough apart so thatthe pool below a dam is above the backwater of the next dam downstream. Care should be

Rational Road Drainage Design R6990 26


32/40


taken, however, to ensure the dam does not block fish migration. Expert advice should besought where necessary.

Wetlands

The creation of wetlands can provide a range of uses for both the natural environment andthe local community. The four most common ways of creating wetland habitats are as

follows:

Use of ditches and culverts: Use of roadside ditches as wetlands provide abenefit to the environment by trapping road pollutants and providing cover, foodand breeding areas.

Borrow pits: either newly constructed or depleted borrow pits may be convertedto productive wetlands with proper management and design; similar practicescould be used to provide lake or pond habitats.

Disposal of dredge spoil, and

Use of selective excavation.

Weirs, commercial hydraulic brakes and spillways can be designed to regulate culvert flows.This may:

provide an intermittent stream with a supply of water constant enough during drymonths to support aquatic fauna.

create shallow marshes suitable for waterfowl and mammals

prevent the draining of existing wetlands, or

sustain ecosystems that rely on intermittent dry and wet conditions.

Consultation with relevant government departments and local communities will be requiredto ensure that the wetland is appropriate to the surrounding environment and community.Careful design and landscaping will also be required to ensure that the newly created

wetland calls for a little maintenance as possible.

5.5 Vegetation

Vegetative cover shields soil from the impact of rain, holds the soil particles in place,maintains voids in the soil to allow absorbance of water, and physically slows the velocity ofwater thereby providing erosion and stormwater control. Vegetation also provides food andcover for wildlife and should be replaced and encouraged wherever possible. Box 5.4 liststhose issues to be considered when selecting appropriate plants.

Box 5.4. Issues To Be Considered When Selecting Plants For Re-Vegetation

When selecting plants to use the following should be considered:

Successful local plant species should be used where ever possible

High degree of resistance to heat, cold, insects and diseases

Potential for rapidly proliferating root system

Potential for nitrogen fixation by root system

Low maintenance requirements

High drought resistance

Responsiveness to fertilisers

Attractiveness to wildlife

Shrubs and trees can control erosion on slopes over 30-40%.

Should be compatible with the site soil typeShould fit with the desired engineering function.



33/40


Vegetation in watercourses can be provided to enhance local wildlife. In-stream vegetationshould not be located where sediment and debris will bury it, or where it will be damaged byscour or other abrasive transport characteristics of the watercourse. Wire enclosed ortethered devices might need to be protected from metal corrosion, depending on the pH ofthe watercourse. In-stream devices such as large boulders, or rock-filled gabions, should besecured to resist hydraulic forces, or located in a protected area within a stream. To ensurethe stream/river remains suitable for fish populations any changes should still leave:

sufficient depth during minimum flows,

pools to furnish resting velocities, and

sufficient current to bring oxygen and food into the cover areas.



34/40


6. CONSTRUCTION OPERATIONS

Although adequate road drainage design aims to alleviate environmental problems, andpossibly even enhance existing areas, road construction activities often result in temporarybut significant adverse environmental impacts. Consequently, every effort should be madeduring construction of the road to minimise the disruption to aquatic and other surroundingecosystems. Good practice procedures in road construction should be identified during thedesign stage, and be stipulated in construction contracts in the form of a site managementplan. This plan should include instructions for:

Scheduling of construction activities

Management of borrow pits

Methods of site clearance

Sediment and pollution control, and

Waste management

6.1 Scheduling of Construction Activities

Ideally construction activities should not be planned for seasons where high rainfall ormonsoons are likely to occur. Recognising that this is not always practical, those activitiesgenerating greatest potential ground disturbance should be scheduled to avoid periods ofhigh rainfall intensity.

Scheduling of ground clearing and transportation route construction should be planned sothat there is no long interval between the two operations. Construction activity schedulesshould also contain flexibility to allow construction to cease during periods critical to fish,wildlife, or waterfowl. By constructing roads and modified channel concurrently it might bepossible to dispose of the channel excavations as road fill.

6.2 Borrow Pits and Quarrying

Use of local materials will reduce transportation costs and subsequent environmentalimpacts. If local material is going to be quarried certain guidelines, however, should befollowed:

Beach singles should only be used if they can be removed without destabilisingthe coastline

Coral reefs should not be used to provide roadstone

Gravels taken from river systems can deplete or destroy fish stocks.

Consequently, agreement from relevant government departments and or regulatoryauthorities should be sought before extraction is undertaken.

Borrow pits should be located and operated so that any aquatic and other surroundingenvironments are not affected. Topsoil from borrow pit should be stripped and stockpiled forlater distribution on disturbed areas. Stockpiles should be placed uphill to reduce or divertrunoff. Borrow areas should be shaped, covered with topsoil and seeded to control erosion.Separation from streams or lakes by a buffer zone of at least 100m is desirable.

The occurrence of tropical diseases such as malaria and bilharzia can be increased by anincrease in standing water at construction sites. The site management plan should focus onelimination of casual water through good housekeeping practices. This should include

ensuring that stormwater runoff does not accumulate in borrow sites and become stagnant.



35/40


There are other mosquito control methods, including temporary artificial flooding andcarefully designed ditching, which prevent mosquitoes from breeding successfully.

Using borrow sites for stormwater retention, recharge, and sediment collection will havebeen considered at the design stage, and plans for post-construction use included in the sitemanagement plan.

6.3 Erosion and Sediment Control

Temporary and permanent erosion and sediment control features have already beenoutlined in Tables 5.1. Appropriate techniques identified at the design stage will be specifiedin the construction site management plan. In addition to these structural features, however,other controls can be implemented to ensure that erosion and sediment pollution are kept toa minimum. Issues to be addressed are outlined in Box 6.1.

Sediment from construction sites can also arise from the washing of vehicles. Vehiclesshould not be washed in natural water courses nor should water from equipment or materialstaging areas be allowed to drain directly in natural water courses without adequate

sediment and/or pollution controls specified in the design. Work in watercourses should beminimised to the extent practicable as it may cause habitat damage, erosion and introducepollutants. Guidelines for work in watercourses are outlined in Box 6.2.

Box 6.1. Erosion And Sediment Control Measures During Construction

These should include, but should not be limited to, the following measures:

Disturb as little of the site for the shortest possible time.

Minimise the amount of exposed ground and stockpiles. Stockpiles can be seeded or coveredand silt fences constructed.

Where possible, organic debris and topsoil removed should be stored for use during site

restoration. Such stockpiles should be located away from water courses/bodies and coveredwith coarse material or seeded to minimise wind and water erosion.

Design cut and fill slopes to reduce the amount of area exposed to weathering and erosion.

Use gentle side slopes; some slope can be beneficial for drainage; however, if they are toosteep there will be erosion and scouring problems.

Repair eroded sites by preparing the soil with fertilisers and/or mulches and replanting.

Control overland drainage to prevent channelling and sediment transport by diverting flows fromareas where soils are exposed, and/or by providing filter barriers or settling basins to removesediment before the runoff is discharged to surface waters.

Re-vegetated areas and areas subject to erosion must be monitored and maintained duringproject operation.

The upper 3m of sloped surface should be compacted to 90% of maximum density ascompaction will reduce the potential for erosion.

Water velocity in ditches should be reduced by limiting ditch gradient and by designing the ditchwith an appropriate cross section. V-shaped ditches are prone to erosion and should only beconsidered if protected with coarse granular material.

On sand dunes, cut slope and embankment surfaces should be capped with a silt-clay materialapproximately 2 cm thick wherever possible or, if economically unfeasible, re-vegetate.

Where possible prevent water from entering excavations.

Silty water arising from excavations, exposed ground, stockpiles, plant and wheel washing andsite roads should not be pumped directly into a watercourse or drain.

Retain sediments containing oil and other pollutants on the construction site and dispose ofsafely.

Minimise contamination of water resources by stormwater runoff by directing into settlingbasins.

Use only clean fill materials around watercourses, such as quarried rock containing no finesoil.



36/40


Box 6.2. Guidelines For Works In Watercourses

New channels for stream locations should be excavated in the dry if possible. Where work mustbe done in the existing channel, for example when starting a retaining wall, work should be

scheduled during extreme low water periods, and the stream diverted.Minimise in-stream construction activities during known migration and spawning periods.

Pipeline/cable placed beneath riverbeds should be covered with backfill similar to dredgedmaterial.

Fill should not be taken from elsewhere in the streambed nor should it contain debris.

Section above the low water mark on each side of the river should be completely backfilled andall underwater contours re-established.

Excavations on land should terminate at least 15 m from water crossings, leaving adequateplugs of undisturbed material at each bank. Plugs should be left in place until excavation iscompleted.

Stockpile dredging spoil on riverbanks within dyked areas to prevent sediment from washingback into river.

Pump particularly silty water from the trench into an upland area well back from riverbank.

Use impervious clay plugs around pipes to avoid sluicing of backfilled material. Slope riverbanksto natural contours after pipe is installed using rip-rap if erosion is a problem; above rip-rap,terrace according to the natural gradient and soil wherever it is necessary to catch runoff andprevent sediment from entering watercourse.

6.4 Pollution Control During Construction

Many chemicals are used during construction which have the potential to pollute watercourses, including: solvents, paints, oils, fuels such as gasoline, diesel oil, kerosene,lubricating oils, and grease. When used or stored improperly, most of these chemicals will

adhere to soil and sediment particles, possibly become mixed with storm water and carriedinto local water courses as runoff. Standard erosion and sediment control techniques willencompass most of the pollution control measures needed. By storing such chemicals in theappropriate manner, however, and applying them in a proper manner, pollution problemscan be reduced still further. Guidelines for the proper storage of hazardous chemicals aregiven in Box 6.3.

Box 6.3 Storage of Hazardous Materials

Storage and liquid impoundment areas for chemicals and waste products should be designedwith secondary containment, such as dikes, to prevent contamination of the surrounding

environment.Contents should be clearly marked on the container,

Store products in weather-resistant sheds where possible.

Create shelter around storage area with cover and wind protection,

Keep containers off the ground.

Keep lids securely fastened.

A staging area should be specified for vehicle maintenance activities, located away fromdrainage courses.

All storage facilities and equipment should be regularly monitored for leaks and repaired asnecessary.

Storage at or above roof level should be avoided.

Sites of all fuel, lubricant and petrochemical depots should be located a minimum of 200m from

any lake, stream or river, preferably 300m.Fuelling of equipment should not take place within 100 m of river, lake or stream.



37/40


6.5 Waste Management

The correct handling, storage and disposal of waste materials are vital to avoidenvironmental harm. During construction, every opportunity should be made to minimise thewaste created. Any useful materials should be salvaged and recycled. For instance,masonry waste can be used for filling borrow pits; and trees and brush from land clearingcan be converted into wood chips through mechanical chippers and then used as mulch ingraded areas.

The major control mechanism to prevent pollution is to provide adequate disposal facilities.The correct method of disposal will vary with the material. Wash-up waters from water-basedpaints may go into a sanitary sewer, but wastes from oil-based paints, cleaning solvents,thinners, and mineral spirits must be collected and disposed of through proper incineration.Disposal of concrete products, additives, and curing compounds depends on the product.Guidelines are given in Box 6.4

Box 6.4. Waste Management Guidelines

Leaking or empty oil drums must be removed from the site immediately and disposed of.

All wastes must be stored in designated areas that are isolated from surface drains.

Collected solid waste should be removed and disposed of at authorised disposal areas. Wastecontainers should be labelled and located in a covered area.

Skips should be covered to prevent dust and litter being blown out and rainwater accumulation.

If plant maintenance is carried out on site, used oil should be stored in a bunded area forcollection.

Untreated human sewage should not enter watercourses.

Organic wastes should be oxidised in a controlled manner before discharge or released in such

dilute quantities that no damage will occur.Slurries and fine particulates e.g. bauxite should be disposed of on land.



38/40


7. MAINTENANCE

Maintenance extends the life of roads and consequently has significant financial benefits. Aroad system that is well maintained also brings important social and environmental benefits.When designing a road, thought should be given to the future maintenance requirements,who will be responsible for carrying out this work, and how it will be funded. Thesemaintenance practices should be identified in the form of a maintenance management plan.

A level of priority should be given to each maintenance activity to ensure the whole roadsystem is adequately maintained. For example:

Routine maintenance (required continually): includes grass cutting, drain clearing,recutting ditches, tree pruning and culvert maintenance.

Recurrent maintenance (required at intervals during the year with a frequency that

depends on traffic volume): on unpaved roads it includes repairing pot-holes and ruts,dragging and grading. On paved roads it includes repairing pot holes, patching, repairingedges and sealing cracks.

Periodic maintenance (required only at intervals of several years): includes re-gravelling of unpaved roads, resealing (surface dressing, slurry seal) and re-gravellingshoulders.

Urgent Maintenance (required in response to emergencies): calls for immediate actionwhen a road is blocked either as a result of an accident or a natural event. Tasks includeremoval of debris and other obstacles.

Neglected drainage rapidly leads to deterioration of the road. The execution of this workshould therefore be monitored at regular intervals to ensure it is carried out effectively.However, although the effects of poor road drainage maintenance activities on the road arefrequently highlighted in road maintenance manuals, the implications for the environment arenot. Consequently, if indirect impacts are located away from the road, where they are notdirectly visible, a false sense of complacency can develop. The importance of theenvironment therefore needs to be emphasised in future maintenance management plans.Guidance is also required on the level of priority given to the various mitigation measuresthat can be incorporated, such as the cleaning of retention ponds and maintaining thediversity of habitat within a drainage channel, especially if funds are limited.



39/40


8. REFERENCES

American Association of State Highway and Transportation Officials (1992). Guidelines forEvaluating Road Effects on Surface Water Environments. AASHTO, Washington, DC.

Australian Road Research Board (1997). Biological Diversity in Transport Corridors - RoadDrainage Management. Transport Research Report ARR302. ARRB, Victoria, Australia.

Department for International Development (1998). Guidance Note on InternationalEnvironmental Agreements. Available on the DFID web site.

Environment Agency (1999). Working at Construction and Demolition Sites. PollutionPrevention Guidelines (PPG6). Environment Agency, London.

Washington State Department of Transport, Environmental and Engineering Service Centre

(1995). Road Runoff Manual: M31 -16. WSDOT, Washington.

International Finance Corporation (1998). Environmental, Health and Safety Guidelines forRoads and Highways. IFC, Washington.

International Institute for Environment and Development (1998). A Directory of ImpactAssessment Guidelines. llED, Nottingham.

International Union for the Conservation of Nature and Natural Resources (1974). The Useof Ecological Guidelines for Development in the American Humid Tropics. IUCN publicationsServices Unit, Cambridge.

Morris, J. M (1995). Earth Roads (Second Edition). Avebury Ashgate Publishing Limited,Aldershot.

Odum, W. E (1976). Ecological Guidelines for Tropical Coastal Development. InternationalUnion for the Conservation of Nature and Natural Resources (IUCN). New publication seriesNo 42, IUCN, Morges, Switzerland.

Transport Research Laboratory (199?). Principles of Low Cost Road Engineering inMountainous Regions. Overseas Road Note 16. Transport Research Laboratory,Crowthorne, UK.

Parks Canada, 1981. Manual on the Application of the Environmental Assessment and

Review Process within Parks Canada. Parks Canada, Quebec.

Tsunokawa, K. and C Hoban (1997). Roads and the Environment: A Handbook. World BankTechnical Paper No 376. World Bank, Washington, DC.

US Department of Transportation (1979). Restoration of Fish Habitat in Relocated Streams.Federal Highway Administration, Washington, DC..

World Bank (1994). Natural Habitats. World Bank OP/BP 4.04. World Bank, Washington,DC..

World Bank (1995). Environmental Assessment Sourcebook: Volume II - SectoralGuidelines. World Bank Technical Paper No. 140. World Bank, Washington, DC..



40/40


World Bank (1997). Pollution Prevention and Abatement Handbook: Toward CleanerProduction. World Bank, Washington, DC..

World Bank (1999). Environmental Assessment. World Bank OP/BP 4.01. World Bank,Washington.

9. WEB SITES

www.aashto.orawww.arrb.orq.auvvww.environment-agency.gov.ukwww.wsdot.wa.govwww.worldbank.org/ifcwww.worldbank.orgwww.iucn.orn

www fhwa.dot.povwww.dfid.gov.ukvvww.who.orn