the development of a conceptual model to investigate the water … · 2012. 9. 8. · that are now...

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The development of a conceptual model to investigate the water level rise at

Sanctuary Moor, Knutsford

Kate Berry

This thesis is submitted in part fulfilment of the requirements for the B.Sc. degree in Environmental Science at the University of Lancaster.

January 2012

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Contents

1. Abstract ............................................................................................................................................................................ 4

2. Introduction ................................................................................................................................................................... 4

2.1 Aims ............................................................................................................................................................................ 8

2.2 The catchment ....................................................................................................................................................... 8

3. Residents Views ......................................................................................................................................................... 11

4. Methods ........................................................................................................................................................................ 13

4.1 Modelling .............................................................................................................................................................. 13

4.2 Subsidence ............................................................................................................................................................ 14

4.3 Precipitation ........................................................................................................................................................ 14

4.4 Run-off .................................................................................................................................................................... 15

4.5 Groundwater inflow and outflow ............................................................................................................... 16

4.6 Evapotranspiration ........................................................................................................................................... 17

4.7 Outflow of water from the River Lily ......................................................................................................... 18

5. Results .......................................................................................................................................................................... 20

5.1 Precipitation results ......................................................................................................................................... 20

5.2 Run-Off results .................................................................................................................................................... 21

5.3 Groundwater inflow and outflow results ................................................................................................ 22

5.4 Evapotranspiration results ............................................................................................................................ 24

5.5 Outflow of water from the River Lily results ......................................................................................... 25

6. Analysis ......................................................................................................................................................................... 26

6.1 Precipitation ........................................................................................................................................................ 27

6.2Run-off ..................................................................................................................................................................... 28

6.3 Groundwater inflow and outflow ............................................................................................................... 28

6.3Evapotranspiration ............................................................................................................................................ 30

6.4Outflow of water from the River Lily .......................................................................................................... 30

7. Overall picture ....................................................................................................................................................... 32

8. Sustainable Urban Drainage Solutions (SUDS) ............................................................................................. 34

9. Conclusion .................................................................................................................................................................... 36

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10. Further Work ........................................................................................................................................................... 37

11. Acknowledgments .................................................................................................................................................. 38

12.References .................................................................................................................................................................. 38

13.Appendices ................................................................................................................................................................. 40

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1. Abstract

Sanctuary Moor is a community owned wetland in Cheshire with a history of land drainage

issues. The water level is rising causing loss of land to the expanding pond which is

encroaching onto local residents’ gardens. The residents want to identify the cause of this

water level increase in hope that solutions can be found to save their gardens from being

permanently flooded. To identify possible causes of the water level rise a conceptual model

was created. This focused on the main input of precipitation, through direct rainfall and also

the precipitation reaching the wetland through the ground. The main model output was

identified as the drainage of the wetland by the small River Lily. The other outputs were

groundwater discharge and evapotranspiration. Precipitation data for the North West of

England was analysed using MATLAB to look for precipitation increases over the period of

the noticed water rise and also to find an average value to use in the model. Literature was

used to inform methods and estimate typical values for evaporation and transpiration.

Measurements were taken to estimate the average output of the River Lily. The storage was

calculated as 0.2% of the total input of water to the system. This suggests that if the amount

of water entering the wetland can be reduced by 0.2%, perhaps through less run off, then

the rise would stop. SUDS techniques could be implemented to reduce the total amount of

water entering the system. Another consideration would be to reduce the level rise by

increasing the amount of water leaving the wetland by increasing the amount of

evapotranspiration or increasing the River Lily’s capacity. The findings of this investigation

highlighted the importance of an integrated approach to hydrological issues as many factors

can affect the water level at this site.

Keywords – flooding, wetland, conceptual model, Knutsford, catchment management.

2. Introduction

Sanctuary Moor is an area of community owned wetland, lying within a 50m contour

depression in Knutsford, Cheshire (figure 1). Land drainage has been an issue here for some

time and in recent years the water level has significantly increased. Some residents are

losing areas of their gardens to permanent flooding which is causing concern. Potential

solutions need to be appropriate to the council categorisation of the site as a ‘Grade A Site

of Biological Importance’ (Sensagent, 2011).

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The River Lily is a narrow, shallow river. When flowing through Knutsford the river runs

alongside the road in a small trench. It has not been known to flood the road suggesting that

the river is not very flashy and the flow remains relatively constant.

In a natural environment when rainfall falls onto the land it slowly soaks away into the

ground or during heavy rainfall runs over the land through saturation overland flow into a

lake, pond or stream (Shaw et al, 2011). In man-made environments, such as urban areas,

when rain falls onto surfaces such as concrete it cannot soak away and runs over the land

into man-made drains. In the case of Sanctuary Moor the surrounding street’s surface drains

and the regional water company surface water drain (appendix 1) are discharged into the

wetland. Precipitation is likely to have a large impact on the area as this is a large input of

water to the moor. It affects the wetland through direct precipitation onto the area, as land

run-off and as surface drains.

Ragab (2003) states that on average 30% of rainfall is lost by evaporation and infiltration

with 6-9% infiltrating through road surfaces and 21-24% lost through evaporation. When

estimating these factors literature was consulted to get an average figure to make the value

more reliable. It also seemed unlikely that 6-9% of the rainfall would infiltrate through the

road surfaces in this area as the road surfaces are well maintained and appear largely

impermeable so water is more likely to run off the road surface. Although as tarmac is

slightly permeable, some water will seep through so a figure of 29% was used.

Sanctuary

Moor

250m

1km

Figure 1 – The location of Sanctuary Moor in Knutsford (Google, 2010).

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A major part of the hydrological cycle is precipitation. It can flow through soil, be intercepted

by vegetation and infiltrate through the ground. Precipitation can percolate through the soil

into the ground becoming recharge groundwater which could be a major input to the

wetland. Recharge is dependent on the availability of water which originates from

precipitation losing moisture along the way from evapotranspiration (Younger, 2007).

Three main causes of urban flooding relevant to this study are discussed by Fleming (2002):

culvert, drain and gully blockage caused by debris and sedimentation deposition of

organic material such as leaves;

bridge, tunnel or culvert capacity exceeded;

seasonal or long term change in groundwater levels.

In this study only two points of Flemings were investigated due to the studies confinements.

Firstly a visual site investigation took place but was not the only focus as due to the nature

of this flooding being long term it was unlikely that blockages would be the cause although it

may be exacerbating the problem.

Groundwater is another large input to the moor, with surface springs noticed by residents

that are now underwater. Darcy’s Law defines groundwater flow. It was calculated from

studies of water flow through a column of porous material as discussed in Hiscock (2005)

and Rushton (2006). Darcy’s Law states that the total flow through the column is

proportional to the difference in water height at each side of the experimental column. In

the case of Sanctuary Moor the pressure difference was estimated from the level of the

water table and the level of the water in the moor which was estimated from the change in

height of the surrounding land.

The area around Knutsford has previously been heavily mined for salt. The nearby area of

Northwich has had large subsidence issues resulting from this. It is possible that as this is

nearby it could be an issue at Sanctuary Moor. The water level may be remaining constant

but the land level may be falling due to subsistence from mining or the natural dissolving of

halite deposits, this issue was considered.

The ‘Flood and Water Management Act 2010’ states that Lead Local Flood Authorities

(LLFAs) are responsible for managing local flood risks including surface water flooding,

groundwater flooding, ordinary watercourses and small reservoirs. LLFAs are also

responsible for land drainage, designating vulnerable land and Sustainable Urban Drainage

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Systems (SUDS) on public land. As Sanctuary Moor is community owned this causes debate

as to who is responsible for carrying out actions to prevent the flooding. This needed

consideration when suggesting the next steps to try and stop the rising water level.

As there were many factors potentially impacting the water level at the site an integrated

approach was adopted. The main factors were explored including assessment of the

identifiable water inputs and outputs of the moor. It was anticipated this would indicate

imbalances in the system causing the level rise. As the issue at Sanctuary Moor is getting

progressively worse the underlying cause needs to be identified in an attempt to solve the

land drainage issues. Younger (2007) suggests using a conceptual model to understand

complex systems. This approach was adopted to assess the inputs and outputs of the

wetland (figure 2).

The model does not need to provide great accuracy, just broad estimates to enable better

understand the relative importance of the key parameters. The water balance concept was

used to:

1. Investigate and understand the physical processes at play,

2. Develop a basic model,

3. Estimate model parameters,

4. Create scenarios which might explain the water level rise and possible solutions.

Figure 2 - A conceptual model of Sanctuary Moor water balance

Lake Wetland Area

River

Lily

Outflow

Groundwater

Outflow

Ouflows:

Inflows:

Rainfall

Transpiration

From Plants

In Wetland Area

Change

In Water

Storage

In Lake

(resulting

In level

change)

Rainfall

Run-Off

From

Evaporation

From

Wetland Area

Groundwater

Inflow

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Modelling limitations due to the complexity of the situation and also missing data meant

that the model could not be relied upon to accurately identify the cause of the problem but

provided insights that could lead to finding the cause. Further information was obtained

from local residents, environmental consultants and literature reviews to reach conclusions

with respect to the likely reasons for the water level rise.

2.1 Aims

The aims of this study were to:

Obtain knowledge and information from a variety of sources including residents and

literature,

Create a conceptual model,

Estimate inflow and outflow to the moor,

Use the model to identify scenarios which would lead to the observed level increase,

Use knowledge of developments in the local area to identify the modelled scenarios

that would be consistent with these changes,

Use the model with other information to test success of potential solutions to the

problem.

2.2 The catchment

A large percentage of the catchment is rural land. The small area of urban land has

approximately doubled since 1950 with a lot of new building taking place in 1970 in the

immediate proximity of Sanctuary Moor (figure 3).

The topography of the area was examined to estimate catchment boundaries (figure 4).

The highest points in the area are between 60 m and 70 m with an area of

approximately 8.62km2.

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1950

1970

1990

Figure 3 – The growth of buildings from 1950 to 1990 showing an increase in building density in

the immediate area of Sanctuary Moor. Sanctuary Moor is shown in blue (Digimap, 2010).

1 km

1 km

1 km

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To simplify the model only the south catchment was looked at as the catchment converges

north of sanctuary moor forming a figure of eight shape. Contours here show this is a valley

shape, water in the southern half will be channelled through the narrowing of the catchment

to the north catchment. Therefore the model should only consider the south catchment as

water will pass from this to feed Tatton Mere. Figure 5 shows the new catchment break off

point, figure 6 shows a diagram of a cross section of the catchment from Sanctuary Moor

down to Tatton Mere with the cut off for the catchment shown. The output from the river

and groundwater here can be grouped as a system output.

Sanctuary Moor

Figure 4 – Sanctuary Moor catchment shown in pink derived from the

height of the land (Ordinance Survey, 2010).

1 km

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N

2.3Water level increase overtime

Figure 5 – Revised catchment, south of the blue line north of

Sanctuary Moor (Ordinance Survey, 2011) Y to X is a cut through of

the catchment.

Figure 6 – Cross section of y-x through the catchment showing the flow of water from

Sanctuary Moor to Tatton Mere.

NOT TO SCALE

Model Area

X

Y

Tatton Mere

Sanctuary Moor

Model Area

Catchment Area

General flow from

south catchment

across boundary

from Sanctuary Moor

towards Tatton

Mere.

1km

X Y

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Historical maps (figure 7) show an increase in the surface area of the pond with a larger

increase between 1970 and 1980 coinciding with significant increase in buildings. The

problem causing the rise is likely to have accrued before 1960 as the land here was once

marshy but with no surface water only the River Lily drain. The cause of the surface water

increase was exacerbated between 1970 and 1980 or possibly a new problem occurred

which increased the water level rise.

3. Residents views

Sanctuary Moor Residents Association was set up by homeowners affected by the water

level rise at the moor, they hold regular meetings. The opportunity to attend a number of

meetings enabled their views and observations to be collected.

The residents had not noticed seasonal fluctuations in the water level and claimed they had

only observed a gradual increase.

Concern was raised about the Lily Brook housing development downstream of the site. They

claimed the small bridge built at Lily Brook appeared to cause damming of the river resulting

in the River Lily’s flow stopping for a time. They felt this caused a temporary water level

increase in the wetland.

A house on the Lily Brook development, Eden Brook, created a water feature by diverting

the River Lily around the garden and blocking the natural river course with two concrete

blocks. The homeowners were asked to unblock the river here. They jetted a nearby culvert

and once this work was completed it resulted in the water level to decreasing by around

7 cm. The residents still feel that there may be some blockage at this location.

1960 1970 1980

Figure 7 – The area of open water at Sanctuary Moor over the period 1960 – 1980 showing the

increase over this 20 year period (Digimap, 2010).

200 m 200 m 200 m

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Residents also reputed problems with man holes overflowing. After many floods this

problem appears to have now been fixed by the local water company, United Utilities. The

residents also made known that there was a United Utilities pumping station on Croft Lane.

Upon query United Utilities confirmed that there is permission to discharge surface/storm

water from this during large rainfall events.

4. Methods

To carry out the investigation evidence was gained from local residents by asking for their

views and ideas about the water rise. It is recognised that this information needs to be

treated carefully as it is anecdotal evidence and may be inaccurate. Guidance and

suggestions from environmental consultants at Peak Associates was also sought and their

expertise drawn on. Background information was acquired from a literature review; this was

used to inform the methods for the construction of the conceptual model.

4.1 Modelling

Models can be used at the beginning or end of a study. Hiscock (2005) explained that

modelling at the beginning of an investigation is used for conceptualising the main

parameters controlling groundwater flow in a model. At the end of a project modelling is

useful for predicting the future of groundwater and its response to different conditions.

Conceptual models are constructed to demonstrate the current thinking on a situation

(Rushton, 2006). Usually these are used in the early stages of a project before inputting real

data. Another type of modelling is computational models as discussed by Rushton (2006).

These are very diverse, analytical models using mathematical expressions, and require

accurate data input into computer software used to create analytical solutions. This is

unsuitable for this study due to the lack of measureable data.

Todd and Mays (2005) discussed the availability of computers able to carry out numerical

modelling in the 1970s. This gave more accurate estimations although dependent on the

accuracy of the input parameters of the models.

A commonly used flow modelling programs is MODFLOW. Younger (2007) states this to be

three dimensional and reliable. This modelling does however need large quantities of field

data and calibration therefore unsuitable for this study.

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For this study a conceptual model is most appropriate and was constructed to explain the

current water balance and help explain changes over the last 60 years. It was used at the

start of the study then again at the end to work backwards and see what the inputs and

outputs were in the past to look at where the changes have come from.

4.2 Subsidence

There is the possibility of subsidence in this location which could account for some, if not all,

of the water level increase. This could occur from the presence of mining in the local area or

halite in the underlying geology being naturally dissolved.

The coal authority suggests that there are no records of mining in this area (Coal Authority,

2011) however records can be incomplete. A way of testing the water to see if it has flown

through an underground mine is to look for evidence of orange iron oxide. If this cannot be

measured it would suggest there has not been mining.

The bedrock at this location is halite which can be dissolved by water leading to subsidence.

This is possible as the water is likely to percolate through permeable layers of rock before

running along the bedrock and potentially dissolving it. There is no evidence of this in

research of the area. The buildings in the catchment do not appear to exhibit any signs of

subsidence and there is no warning on the coal authority database (including coal and salt

mining) for this area but it may be require further investigation.

4.3 Precipitation

Historical averages for annual precipitation in the North West was obtained (appendix 2).

Due to the format of the data downloaded from the MET office website (2011) it was

necessary to evaluate it using Matlab software. A script was written finding the 10 years of

greatest average rainfall over the 70 year period to identify any increase in the amount of

rainfall before the water level rise was noted. The previous 20 years of rainfall were also

examined for a recent increase in rainfall. Precipitation is measured in metres per year so

the amount of rainfall in metres for a given area can be easily found by multiplying the value

by the catchment area.

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4.4 Run-off

To investigate the run off from the area historical maps were used to assess the increase in

the area of impermeable surfaces from 1930 to present day. GIS software ArcMap GIS 10

was used to find the area of permeable surfaces at present day and 1990. Due to a technical

issue with the calculation of area using the GIS software AutoCAD was used to calculate the

area of the urban areas in 1930, 1950, 1970, 1990 and present day to check the values found

using the GIS software. The quantity of rainfall reaching the wetland is affected by the

amount of impermeable surfaces (figure 8 & 9). The numbers were adjusted to achieve

water balance.

Figure 8 – A diagram to illustrate a model of rainwater flow in to the wet

land.

To moor

y%

x2 % 1-x2 %

x3

%

To groundwater

1-y %

Rainfall

Infiltrates into Overland Flow

(Effected by

impermeable

surfaces)

Enters the

ground Surface

This value changes in

relation to the amount of

impermeable surfaces in

the catchment.

x1 % 1-x1 %

1- x3

%

1-x4 % X4

%

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4.5 Groundwater inflow and outflow

Darcy’s Law defines groundwater flow. It states that the total flow is proportional to the

difference in water height between two positions:

[1]

Q=total flow, K=hydraulic conductivity, A=cross-sectional area, dh/dl=hydraulic gradient

The hydraulic gradient term measures how easily water moves through a material. In coarse

grained material hydraulic gradient is high, but in fine material low (Hiscock, 2005). Typical

values are 100 cm h-1 in well drained topsoil and 0.001 cm h-1 in poorly drained subsoil (Shaw

et al, 2010).

This hydraulic gradient (dh/dl) is likely to be near zero as the water table is expected to be

the same as the pond water level. There will therefore be no drive for the water into or out

of the lake.

Groundwater may be transmitted from aquifers to Sanctuary Moor. Aquifers are bodies of

saturated rock that store and transmit significant quantities of groundwater (Young 2007).

Grain shape, size and arrangement all affect the rocks ability to store and transmit water.

Downing and Wilkinson (1991) discuss historical uses of aquifers in supplying water. At

Sanctuary Moor the water level within is likely to be at the same level as the natural water

table due to the geology which would lead to negligible groundwater flow.

Lake Groundwater

44.7% 52.3%

This value is

affected by the

run off

Figure 9 – A simplified diagram showing the estimated proportion

of rainwater that enters the wetland.

Rainfall

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Geological maps were used to explore the areas geology. This was then used to predict the

structure of the strata and to identifying the hydraulic gradient of the various rock types to

find a prediction for the amount of water passing through the rock to give an input and

output value for the groundwater. Although attempted the scope of this study did not allow

for obtaining a detailed geological map so a detailed geological cross section of the area

could not be constructed but was instead estimated from less detailed maps.

The areas bedrock was identified as impermeable, three superficial permeable rock types

were identified. The geological map was compared with the topography map to predict the

nature of the strata. A simple interpretation of the strata was made. This was then used with

Darcy’s Law to estimate groundwater inflow.

The hydraulic gradient, K, was assumed as 1x10-5 because the range for alluvium is between

10-5 and 10-2 m s-1 and between 10-7 and 10-3 for sand (Hiscock, 2005). This seemed a

reasonable estimate value for the initial calculations. This was varied slightly when carrying

out the calculations to ensure a water balance, this is discussed in the results section.

There is sand, gravel and alluvium beneath the river through which water will flow. The

vertical cross-sectional area of this river bed was estimated as a semi-circle with the radius

being half the width of the river (1.25 m) as it leaves Sanctuary Moor.

These values are then placed into the equation to give a value for the flow into the moor in

m3 s-1.

4.6 Evapotranspiration

Evapotranspiration includes rain intercepted by plants known as wet canopy evaporation

and water transpired from plants. Evapotranspiration is dependent on the vegetation type,

ability to transpire and water availability in the soil. Values can be difficult to quantify such

as wet-canopy evaporation and transpiration rates vary in different locations. It is also

difficult to establish the quantity of water drawn from the ground for plant use. Other

factors are also challenging to quantify that affect the rate of evapotranspiration such as

humidity, atmospheric pressure, nature of the evaporating surface and latent heat.

As there are many unknowns, to estimate the evapotranspiration the average evaporation

and transpiration for a similar area needed to be found. Literature was researched to find a

typical value for these. Forestry Commission (2005), Holmes et al (2002) and Hudson and

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Keatly (1997) gave similar ranges of values for evaporation and transpiration. Therefore the

value taken as typical transpiration was 500 mm yr-1 and evaporation 88 mm yr-1.

Once these values were found the area of the wetland was estimated. This allowed the

typical values to be calculated for this site.

4.7 Outflow of water from the River Lily

Measuring the flow of the River Lily leaving the moor explored Fleming’s (2002) issues:

Culvert blockage caused by debris and sedimentation deposition of organic material,

bridge, tunnel or culvert capacity exceeded.

The investigation of the water course and bridge explored the water’s ability to flow freely.

It was not possible to access all of the culverts upstream as they are on private land.

The river is very small and is surrounded by trees and shrubbery which caused difficulty in

obtaining a location where there was a clear viewing position to use as a reference point for

the survey. The river also has a large volume of soft silt on its bed which caused problems

measuring the depth of the water as the top of the silt was hidden due to the murky water.

These obstacles determined the choice of the survey to be implemented.

The most suitable survey was then carried out to estimate the flow.

Equipment list:

Tape measure,

Ranging poles,

Float,

Stopwatch.

One 12 metre stretch of the river before the bridge at Lily Brook (figure 10) was measured,

poles were located at four meter intervals. Eight metre after the bridge was also marked out

in four metre intervals.

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Figure 11 – The typical variation in velocity across the river channel (Hudson, 1993).

An orange was used due to its unique floating properties, as two thirds of the orange are

beneath the water surface error is reduced from wind acting on the object. The orange was

placed upstream of the first marker, when it passed the first marker the stopwatch started.

The times were recorded each time the orange passed a four metre marker. If the orange

got stuck the measurement was repeated.

The measured velocity was higher than a representative value as the surface velocity was

measured and the float experienced effects of friction from wind. Within the channel the

velocity varies as shown in figure 11. The measured velocity is faster than the velocity at the

sides and the bottom within the channel. To take this into account 0.8 of the measured

surface velocity is taken (figure 11, Hudson, 1993). This was multiplied by the average cross

sectional area of the section to give a discharge.

Two flow measurements were taken, June and October. To compare the sets of data and see

if they show a statistical difference a Mann-Whitney U test was carried out. This statistical

test was chosen as there are two sets of comparable data. Neither sets of data fit the

parametric assumptions (Wheater and Cook, 2000) as the method does not allow for

independent sampling. However the results should still be valid. Hypothesis for the test:

Figure 10 – Marked in blue the location of the measurement of the velocity of the River Lily.

(Google Maps, 2011)

8m

12m

bridge

20 m 40 m

20

Ho: There is no difference between the measured discharge in June and October.

Ha : There is a difference between the measured discharge in June and October.

∑

∑

To check that the calculation has been accurately performed equation 4 should be correct.

The values of n1 and n1 are used to read off Mann-Whitney tables the value of P=0.05.

5. Results

Input and output values in the model were critically reviewed to determine credible values

which would result in a water balance. Some values were best estimate within a range of

possible values, such as the groundwater flow estimates. The values that were amended and

reasons for change are identified and discussed in each section. Methods and results for

each parameter should be read together to make these reasons clear.

5.1 Precipitation results

The 20 wettest years recorded in the past 70 years (table 1) were extracted from the data

using Matlab software, trends in rainfall were also investigated. The average total rainfall

over the past 30 years was calculated as 1.283 m year-1. This was multiplied by the

catchment area to estimate the total rainfall volume within the catchment.

[2]

[3]

Mann – Whitney U Test equation where n1 = number of data points in sample 1, n2= number of data points

in sample 2, R1= Sums of the ranks in sample 1, R2= Sums of the ranks in sample 2.

[4]

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Year Total Yearly Rainfall /mm Years Ranked 1 highest to 10 lowest

1954 1689 1

2000 1651 2

2008 1549 3

2002 1465 4

1998 1455 5

1951 1441 6

1960 1435 7

1967 1420 8

1950 1429 9

1999 1406 10

5.2 Run-Off results

The results of average rainfall and the area measurement of the catchment were used to

calculate the volume of water falling on the catchment.

The volume of surface flow changes with the percentage of the catchment that is urban

surfaces. This value changes over the years. The percentages were adjusted to achieve water

balance in the model, it was found that the groundwater percentage was 45%.

Table 1 – The top 10 wettest years in the North West

Rainfall

Lake Groundwater

55% 45%

Total division of rainfall

determined by overall

run off effects.

Figure 11 – A simplified diagram of figure 8, showing the

proportion of rainwater that enters the wetland.

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Year Urban Area / m2 % of the

catchment

% of present

rainfall reaching

the Moor

Amount of

rainfall run-off

entering the

Moor /m3 y-1

Present 3229388 48 100 1988786

1970s 1036532 45 94 1864487

1950s 246112 37 77 1533023

5.3 Groundwater inflow and outflow results

Key

Till

Glaciofluvial Deposits, sand and gravel

Alluvium –Clay, silt, sand and gravel

Figure 12 - Geological map showing Sanctuary Moor and the surrounding

geology. (BGS,2011)

500m

Sanctuary Moor

Table 2 – The change in the amount of impermeable surfaces over the past 60 years.

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An estimation of the structure of the rock strata was constructed from geological maps

shown in figure 13.

It was assumed that the sub-layers at Sanctuary Moor are horizontal. This seems likely due

to the valley cutting through the layers. Water will infiltrate through the layers then run

laterally along the impermeable layer of halite.

Using Darcy’s Law and using the estimated values for the terms described in the methods

section 3.3, a flow value for the water leaving the Moor was calculated.

Q=K A dh/dl

where:

Q= ground water flow

K = 10-5m2 (best estimate)

A = 2.34m2 (best estimate)

dh/dl = 1 (due to the low head and length dimensions to the moor)

The values used in this estimation are:

Q=10-5m2 x 2.34 m2 x 1

Q=0.000234 m2s-1

x 31 536 000 m2year-1

The flow out of Sanctuary Moor through the ground water is estimated as 738m3yr-1.

This value should remain constant over time as hydraulic conductivity is unlikely to change

as it is a property of the rock type. The area may increase over time due to depth increase of

Alluvium –clay, silt, sand, gravel

GlaciofluvialDeposits, sand

and gravel

Till

Halite – Stone and mudstone

Figure 13 - A simple cross section of the land at Sanctuary Moor

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the water in the river channel but this is likely to be smaller than the error in the

assumptions of a semi-circular river channel cross section.

5.4 Evapotranspiration results

Evaporation

The amount of evaporation for this type of area was estimated at 0.088 m yr-1 from the

literature review. This was estimated as total evaporation from the open water on the site.

This gave a value of 3840.4m3

each year approximately 0.2% of the overall annual water

outputs. This value will increase slightly over time as the lake surface increases.

References give

typical value of

approximately

88 mm yr-1

(0.088 m yr-1

)

Lake surface

estimated from map

giving a surface area

of 43641 m2

Estimated volume = 0.088

x 48765

= 3840.4 m3

Figure 14 – Evaporation results for Sanctuary Moor

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Transpiration

The amount of evaporation for this type of area was estimated as 0.05 m yr-1. This was

estimated as a total evaporation from the whole site of Sanctuary Moor at 38,382.5 m3

each

year, 2.2% of the overall annual water outputs. This value should remain approximately

constant as the area of Sanctuary Moor will remain the same. The vegetation cover will

change slightly over time from loss to trees to water based plants and this will temporarily

reduce the transpiration during the transition. Evapotranspiration is a very minor

component of the water budget of the catchment.

5.5 Outflow of water from the River Lily results

Cross sections of the river were taken at a number of locations in the vicinity of the bridge

over the river at Lily Brook.

Cross sections of the river were taken by placing the tape measure across the river and

depths of the river measured across the width. The depth and distance across the river were

recorded. Care was taken as there was a large amount of silt on the river bed,

measurements were taken from the top of the silt, and some measurements of the silt were

taken and recorded. There were errors in this process as the cross-section constantly varied

as did roughness of the bottom of the channel and vegetation in the river.

Figure 15 – Transpiration results for Sanctuary Moor

Volume of water lost

to transpiration

= 0.5 x 76756

=38382.5 m3

Area of Sanctuary

moor estimated

from map giving an

area of 73641m2

References give

typical value of

approximately

500 mm yr-1

0.5 m yr-1

26

The complete set of results from the survey, including the cross section, can be found in

appendix 3.

The areas are averages across the sections that they represent, averaging the channel of the

bridge by an average of the cross section at each side. The river widened before and after

the bridge, these values were averaged by the cross section at each end of the four metre

intervals used for measuring velocity.

12-8m

before

bridge

8-4m

before

bridge

4-0m

before

bridge

Bridge

10.2m

width

0-4m

after

bridge

4-8m

after

bridge

Average 77.7 60.3 48.0 204.0 66.3 53.0

velocity (m/s) 0.04 0.05 0.07 0.04 0.05 0.06

volume (m2) 0.755 0.755 0.824 1.189 0.944 0.402

discharge(m3/s) 0.03 0.04 0.06 0.05 0.05 0.03

Average discharge 0.043m3/s

12-8m

before

bridge

Bridge

10.2m

width

0-4m

after

bridge

4-8m

after

bridge

8-12m

after

bridge

Average Time (s) 40.9 158.3 66.7 32.0 52.3

velocity (m/s) 0.08 0.05 0.05 0.10 0.41

volume (m2) 0.749 0.911 0.453 0.375 0.35

discharge (m3/s) 0.06 0.05 0.02 0.04 0.01

Average discharge 0.036m3/s

Table 3 – Results from measuring the flow of the River Lily as it leaves the Moor, June

Table 4 – Results from measuring the flow of the River Lily as it leaves the Moor - October

27

Discharge/ m3/s

12-8m

before

bridge

Bridge

10.2m

width

0-4m

after

bridge

4-8m

after

bridge

8-12m

after

bridge

June 0.03 0.05 0.05 0.03 Not measured

October 0.06 0.05 0.02 0.04 0.03

To test the relationship between the two sets of data a Mann-Whitney test was carried out.

The Mann-Whitney tables value of P = 0.05 is 80. The smallest U value is 104, as the U value

is greater than 80, P ≥ 0.05, the null hypothesis is accepted that there is no significant

difference between the two sets of data for the measured discharges in June and October at

the 5% significance level.

6. Analysis

6.1 Precipitation

The MATLAB analysis shows that there was an unusually wet period between 1950 and

1967, and another between 1998 and 2008. Four of the top five wettest years since 1950

have been in the past 12 years.

Looking at historical maps (appendix 4) of the area, the surface water appeared between

1930 and 1950 and looks to have remained constant until increasing in 1970. This suggests

that the increase in rainfall had a significant impact on the water level.

The precipitation may have been the initial cause of the water level issue. Between the wet

period of 1967 and 1998 the water level was still increasing, perhaps from a delay in the

system or another parameter. There may have been a delay in water passing through the

rock beneath the surface. Another reason for the delay could be explained by Ragab’s (2003)

study through loss of rainfall through evaporation and infiltration.

The rainfall data used here is data for the whole of the North West. It would have been more

accurate to use more local data from a local weather station but this was not available

within the scope of this study. It is unlikely that Knutsford precipitation would be

significantly different to the regional average. The model contains a lot of estimated values

Table 5 – Comparing results from June and October measurements

28

which are relatively uncertain and precipitation is no different to the other parameters in

this respect.

Although the data did not appear to show any patterns it is possible they were missed. As

this investigation requires the identification of high rainfalls or increases in rainfall over the

past 20 years, other patterns should not affect this greatly.

6.2 Run-off

There is uncertainty in the run-off percentage of the catchment and it is unrealistic to

assume that all the precipitation landing on urban areas will enter the wetland as run off. In

reality there is grass and surface drains that drain away from the wetland. However the

surface drains do go into the wetland. As previously discussed, Shaw et al (2011) states that

rainfall runs over the ground surface during heavy rainfall into ponds, therefore the

topography needed to be carefully considered.

The method for estimating run-off involved using a topographical map to estimate the

catchment boundaries, this involved error determining highest points between contours.

There is likely to be approximately ± 100 m error around the catchment perimeter.

There was also error when transferring the catchment perimeter to the base maps in both

GIS and AutoCAD, these two measurements varied from 7.98 km2 in the GIS software to 8.62

km2. This highlights the error in locating the catchment by eye. This also shows that there

will be error in the urban areas calculation, however these will have similar error to one

another and should still be correct relatively to one another.

AutoCAD and the GIS software used do not take into account the topography of the land,

this is another potential source of error. The topography in the catchment changes over the

30m stretch so there is scope for error here as this will increase the amount of available

surface.

It is considered that due to the nature of the study, these errors are acceptable as the

numbers obtained are recognized as not being exact numbers but numbers that are the

correct order of magnitude to look for the relationship between all the parameters.

29

6.3 Groundwater inflow and outflow

The bedrock of the catchment is halite-stone and mudstone. Halite loses porosity at 100m

burial depth (Warren, 2006). Mudstone is also impermeable (Broichhausen et al, 2005). The

superficial geology in the catchment is all impermeable, water will pass through the layers

then run laterally across the impermeable base rock and emerge at low points which in this

case may be Sanctuary Moor and Tatton Mere within this catchment.

The method for calculating inflow from groundwater contained significant error. The

greatest was the constant of proportionality, K , in the Darcy’s Law equation. The value of K

can be 10-7 - 10 -3 m2 for sand and 10-5 - 10 -2 m2 for alluvium. This is a range of five orders of

magnitude which would have a very large impact on the overall result. The 10-5 m2 middle

range value seems to be in line with the other parameters giving a value to the same order

of magnitude although it may be out by one order of magnitude either side as the value is

very large contributing one third of the overall output of the moor. This error only has a

small effect on the overall equation so is not very significant.

The area measurement also contains error as the stream outflow is simplified to a semi-

circle to include the sand, gravel and alluvium beneath the river that the water will be

flowing through. This area also includes that of the river but this is a very small amount and

the actual flow in the river is far greater than that through the rock so this effect should be

small.

The hydraulic gradient dh/dl is estimated to be one, as the head, dh, is thought to be very

small as the pond and the water table are likely to be very similar resulting in a very small

value for the head. The length, dl, is also likely to be very small. These two very small

numbers are likely to approximate to one in the dh/dl fraction. The hydraulic gradient is

unlikely to be larger than one but could be smaller than one, this then was estimated at the

largest it could be and therefore the largest outflow through the rock. The values selected

were consistent with those suggested by Hiscock (2005) and discussed in section 4.5.

Overall this is a very simple estimate of this factor. In reality there are a lot of parameters

that need to be measured and cannot be estimated in this way although measurement of

these is not within the scope of this investigation.

30

6.3 Evapotranspiration

The values for both evaporation and transpiration were taken from literature for similar

investigations. These all showed similar values so are likely to be representative given the

scope of this study. The area for transpiration is the whole of the moor. There may be large

trees beside the moor that are using water that is being taken away from the moor but the

overall effects of this are likely to be quite small.

6.4 Outflow of water from the River Lily

It was noticed that before the bridge in June there was a depth of 0.85 m, 350 mm of water

and 500 mm of silt before the concrete base was reached and 1.185 m above the water level

to the top of the bridge opening. At the downstream side of the bridge there was a 55 m

depth of water before the base and a height above the water of 1.25 m. This gives a total

height on the upstream side of 2.035 m and 1.305 m on the downstream side which suggests

that the base of the bridge slopes upwards. There was concern that it may be acting as a

dam. However this would need further investigation as some culverts are designed to slope

upwards to reduce the friction along the smooth base and to reduce the effect of erosion

after the culvert. This would need confirmation to ensure that there is no flow restriction

here although the results do not show a restriction.

The velocity measurements are subject to effects of wind on the float. There will also be

restrictions in flow from vegetation, changes in the river bed and changes in the channel

cross section causing eddy flows. The float followed the fastest flowing part of the surface

water, this should be accounted for in the 0.8 conversion factor due to the change in the

flow within the cross section shown previously in figure 11. The value for this conversion

factor, obtained from Hudson (1993), takes these channel velocity characteristics into

account. The float flowed between vegetation during some of the October measurements.

The flow here would be considerably restricted by this. As the measured results give a small

velocity they are vulnerable to being heavily affected by these issues.

It is also important to note that changes in the river channel can induce errors. A small

change in the measurement of velocity or area could then change the discharge. To try and

reduce this effect three velocity values were taken for each section. The area was measured

across the width of the river at least eight intervals to try and give an accurate estimate of

the cross section. Each section of river was four metres in length and the cross section was

taken at the start and end of the section. This was then used to estimate the whole section

of river which is unlikely to have been a completely accurate representation.

31

It is possible that in the past the River Lily could hold the required amount of water to

successfully drain the wetland, now that there is a greater water level it is causing a greater

flow in the River Lily and it may not be able to cope with the new load.

Further downstream the River Lily flows along side a road in an open man made channel. All

along are culverts (figure 16). The culverts appear to be at high capacity which will be

significantly restricting the flow. This is likely to have successfully drained the moor in the

past with a smaller flow but now the rivers capacity may not be great enough to drain the

moor at the required rate.

Figure 16 – A culvert as the River Lily passes through Knutsford,

alongside The Green before Knutsford Mere.

32

7. Overall picture

The calculated values for the inputs and outputs can now be combined into the model to

consider the overall water balance.

Inputs Water /m y-1

48% of rainfall as run

off 1988786

Total Input 1988786

Outputs

Evaporation 3840

Transpiration 38383

Groundwater outflow 773

River Outflow 1940532

Total Output 1983528

Storage 3116

Overall 2142

There is an overall imbalance of 2142 m. To make this zero the river outflow in the model

has to be scaled up by 1.32. This seems reasonable and realistic as the two samples of river

flow may not be representative of the average annual flow rate.

The two main uncertainties in the model are river flow and run off as these two values are

the two estimates that are best estimates to make the water balance. Initially there was only

one outflow measurement so the average flow was assumed by scaling up the measured

flow by a percentage of 1.32 as the measurement was taken in June when it was likely to be

lowest.

The run-off percentage in the model was also assumed in order to create a balance. This was

initially set to 48%. This suggested that there were a number of combinations of the two

main assumptions that could lead to a water balance. It was then decided that a second flow

measurement would be taken to get a better estimate. The average flow was found to be

the same despite being during a very wet period the second time, it is therefore likely that

the flow scaling factor in the model should be set closer to 1.00 rather than 1.32. This

restricts the number of scenarios for the water balance making the model more reliable.

Table 6 – The overall inputs and outputs to the moor

33

With the river flow scaling factor set to 1.00 (i.e. river flow equal to the average flow

measured), the run off scaling factor had to be set to 38.6% to achieve a water balance (i.e.

61.4% of the precipitation within the whole catchment area flows into the lake).

Inputs Water /m y-1

38.6% of rainfall as

run off 1600217

Total Input 1600217

Outputs

Evaporation 3840

Transpiration 38383




Storage 3116

Overall 0

The greatest output is river out flow and this will vary with the level in the moor. To see how

things have changed over time the same was calculated for a different run-off percentage.

This was then used to calculate what the flow would have been to give an idea of how the

balance has changed over time. The evaporation factor has increased over time as the over

water surface has increased. Transpiration was calculated for the whole of the moor area

throughout the years.

The storage is calculated from the water level increase over the past 20 years, this is only

0.2% of the water flow in the model of the present day. This suggests that if the input could

be reduced by this amount or an output increased by this amount the issue could be

resolved.

Groundwater is likely to be smaller but in this model this is not accounted for as this cannot

be appropriately estimated. As this is such a small value it is unlikely to have a large effect on

the overall balance. The pond was approximately a quarter of the size in 1950 than it is now

showing a very large increase in the last 60 years.

Table 7 – Adjusted figures for the overall inputs and

outputs to the moor

34

1970s

1950s

Inputs Water /m3 y-1

Inputs Water /m3y-1


run off 1499359


run off 1232806

Total Input 1499359

Total Input 1232806

Outputs

Outputs

Evaporation 1920

Evaporation 960

Transpiration 38383

Transpiration 38383







Storage 1558

Storage 779

Overall 0

Overall 0

The run-off value greatly affects the amount of rainfall entering the pond, this is estimated

to have increased by 8.7% since 1950. This has increased the amount of water entering the

moor over time, increasing the open water evaporation figure over time due to the increase

in the surface area of the lake. Similarly the storage was estimated to also have increased in

proportion to the surface area from historical maps. Transpiration is judged to have

remained constant over the whole area of Sanctuary Moor.

Table 8 shows that the river outflow has increased by approximately 22% between 1950 and

1970. This is an overall increase of 30% between 1950 and present day. It is possible that the

river cannot increase more than this to cope with the extra load. If the man-made channel

was designed for smaller flow in the past it may now be restricting the greater flow resulting

in increased storage.

Table 8 – Comparing the water balance between the 1970s and 1950s

35

8. Sustainable Urban Drainage Solutions (SUDS)

It is evident that run off has a large effect on the total input to the moor. This study shows

this is likely to be the main cause of the water level rise. One way of reducing this is by

implementing SUDs in the area. The ultimate aim of SUDs is to mimic natural processes to

move water away from man-made environments and therefore reducing flood risks and

improving the local water quality.

The Environment Agency aims to ‘promote SUDs as a technique to manage surface and

groundwater regimes sustainably’ (EA website, 2011). They have both primary and

secondary objectives, the primary is to incorporate SUDs as normal practice as suitable for

all new developments in England and Wales. The secondary is to apply SUDs in a retrofitting

scheme to reverse any changes caused to surface water drainage which has affected the

environment.

There are a few main SUDs options but not many are suitable for this area due to the large

amount of work involved and subsequent costs.

The simplest solution but perhaps the most difficult to implement due to the large number

of individuals involved, appears to be rainwater harvesting (Environment Agency, 2007). This

is collecting rainwater from roofs and impermeable surfaces such as car parks, roads and

driveways. This water is then stored and used to water plants and in some cases stored for

uses such as flushing toilets (EA website, 2011). Simply harvesting all the rainfall from

residents’ roofs may reduce the run off by a large enough percentage to have an overall

effect on the water level.

A useful SUDs technique is permeable paving (Environment Agency, 2007). The water would

percolate through the paved structure instead of running off as is currently the case. This

water would then percolate into the ground and soil when the conditions permit and enter

the water system in a more natural way. This would be difficult to put into practice at

Sanctuary Moor as it would require extensive construction and costs.

There is choice of other SUDS but would be more difficult to implement as they would need

to be placed in the surrounding roads. These are infiltration trenches and basins which are

trenches lined with a geotextile then filled with stone. This creates small storage trenches

for storm water to infiltrate into the subsoil in a controlled way. This method is highly reliant

on the permeability of the soil and the water table depth at the location. In this model this

36

would only delay the water reaching the moor rather than reducing it so this method may

not be suitable here.

A more suitable type of SUDS here may be permeable conveyance systems. These slow the

run off water as it enters the moor allowing it time to infiltrate and evaporate on the way

potentially reducing the amount of water entering the moor. Most popular of these is filter

drains, similar to infiltration trenches with a geotextile lines trench, this method also traps

sediment and organic matter.

9. Conclusion

The aims of this study were met, information was collected from a variety of sources and a

conceptual model created. Plausible estimates for all the inputs and outputs of the moor

were successfully derived and potential solutions to combat water level rise were identified

and discussed. As found from the literature review it was necessary to construct a

conceptual model due to the complex nature of the system with all the inputs and outputs.

The potential errors within the investigation are acceptable within the scope of the study

and the values are accurate enough to draw conclusions.

The overall increase in the water level at Sanctuary Moor is only a small percentage of the

total water in the system, suggesting that the water level can be decreased by reducing the

input, run-off precipitation or increasing the outputs. As all the factors discussed may have

an effect on the water level here they need to be managed in an integrated way. Calculated

percentages of the total water balance indicate a small reduction in any input or a small

increase in any output could reduce the water level to its former level as the percentage of

total water stored is only 0.2% of the total water passing through the system.

The main change over time noticed is the increase in impermeable surfaces in this locality

causing more water from precipitation to enter the moor. This study suggests this is likely to

be the main reason for the water level increase. The River Lily is then unable to cope with

this extra load as it was constructed, along with its’ culverts, for a smaller flow. This is

supported by the investigation of the River Lily as there was no difference in the flow found

between the June and October samples, supporting the theory that the river is at its full

capacity.

SUDS could help reduce the amount of water entering the moor from the highest input,

precipitation. A suitable suggestion would be rainwater harvesting. The bridge over the River

37

Lily as it leaves the moor also needs further investigations carried out to test whether this is

acting as a dam as this study is inconclusive.

The outcome is inconclusive for the homeowners affected by the issue, findings were

reported back to them (Appendix 5) in the hope of providing information and guidance for

the next stage of their management of the area.

This study shows that an increase in run-off resulting from increased urbanisation is likely to

be the main cause of the water level rise at Sanctuary Moor. However in a complex water

system it is possible that a combination of factors could cause this outcome. This highlights

the importance of an integrated approach to the management of the catchment area as

changing one factor may have an effect on another and perhaps a mixture of changes would

have a greater effect. Some possible changes would be too costly and difficult to achieve

but more easily implemented changes could be acted upon that may ease the problem.

10. Further Work

Due to project constraints a full solution has not been found and to aid finding a full,

integrated solution these further areas need investigation. The inputs and outputs can be

researched to see how much each can be increased or decreased to help reduce the water

level issue. As only 0.2% of the total water in the system needs to be removed only small

changes need to be made. The run-off value can be reduced by implementing Sustainable

Urban Drainage Systems (SUDS), the most suitable for these for the area needs to be

determined.

The evapotranspiration can be increased by planting certain types of plants that transpire

more than others. This would increase the amount of water leaving the moor.

The largest output of the moor is the river output. This could be increased by clearing the

river of debris and de-silting the river, beginning at the north end so that any debris does not

flow onto block cleared areas. It may also be worth looking into the feasibility of widening

the river as it leaves the moor or creating another river channel to meet the existing river at

the Lily Brook bridge.

The bridge also needs investigation and a more in depth analysis of the base of the bridge

needs to be carried out. If this is then still found to be sloping the upwards it may need to be

corrected to enable a greater flow.

38

A measurement of the water level could be kept to monitor the situation to see if it becomes

any worse.

A geological cross section may be worth looking at to look the abundance of groundwater in

case something was missed in the assumptions in the groundwater section.

It may be worth testing the water for chlorine in case any salt is being dissolved into the

water. This is unlikely to be a major cause but could me a minor contributor.

11. Acknowledgments

I would like to thank my supervisors Nick Hewitt and Rob McKenzie for their help and

guidance on this project. I would also like to give a special thanks to Paul Pallgrave, Matt

Brennan, Mike Matthews and the other staff at Peak Associates who have helped me with

this project. I wish to acknowledge the members of Sanctuary Moor Residents Association

who have been very helpful and supportive with this project.

12. References

(1991) Land Drainage act 1991.

British Geological Survey (2011)

http://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/makeamap/home.html

15/06/2011

Broichhausen, H. R., Littke, T. Hantschel (2005) Mudstone compaction and its influence on overpressure generation, elucidated by a 3D case study in the North Sea, International Journal Earth Science, 956 – 978. Coal authority (2011) https://www.groundstability.com 20/06/2011

Digimap (2011) http://edina.ac.uk/digimap/ 10/05/2011

Downing, R. A. and W. B. Wilkinson (1991) Applied Groundwater Hydrology. Clarendon Press,

Oxford, England.

Environment Agency (2007) Site handbook for the construction of SUDS. South Wales: MWL

Fleming, G. (2002) Flood Risk Management. Thomas Telford Publishing, London

Forestry Commission (2005) T. Nisbet, Water Use by Trees, Forestry Commission, Edinburgh. http://www.forestry.gov.uk/pdf/FCIN065.pdf/$FILE/FCIN065.pdf Accessed 21/08/11

Google maps (2011) http://maps.google.co.uk/maps?hl=en&tab=wl 10/06/11

http://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/makeamap/home.htmlhttps://www.groundstability.com/http://edina.ac.uk/digimap/http://www.forestry.gov.uk/pdf/FCIN065.pdf/$FILE/FCIN065.pdfhttp://maps.google.co.uk/maps?hl=en&tab=wl

39

Hiscock, K. (2005) Hydologeology Principles and Practice. Blackwell Publishing, Oxford,

England.

Holmes, M. G. R, A. R. Young, A. Gustard and R. Grew (2002) A new approach to estimating mean flow in the UK, Hydrological and Earth System Science, 6(4), 709 – 720,

Hudson, N.W. (1993) Field measurement of soil erosion and run off, Food and Agricultural

Organization of the United Nations. Rome

Hudson, I.L and M.R. Keatly (1997), Phenological Research: Methods for Environmental and Climate Change Analysis, Springer, London.

MET office website (2011) www.metoffice.gov.uk/climate/uk/ 15/06/11

Rainfall data

http://www.metoffice.gov.uk/climate/uk/datasets/Rainfall/date/England_NW_and_N_Wale

s.txt 15/06/11

Ragab, P. R. (2003) Experimental study of water fluxes in a residential area: 2. Road

infiltration, runoff and evaporation. Hydrological Processes , Volume 17, Issue 12, 2423–

2437.

Rushton, K. R. (2006) Groundwater Hydrology Conceptual and Computational Models. John

Wiley & Sons Ltd, West Sussex.

Sensagent (2011) Definition Site of Biological Imporatnce

http://dictionary.sensagent.com/site+of+biological+importance/en-en/ 5/6/11

Shaw, E.M., K.J.Beven, N.A. Chappell & R. Lamb (2010) Hydrology in Practice. Taylor and

Francis.

Todd, D.K. and L. W. Mays (2005) Groundwater Hydology. Hoboken, John Wiley & Sons Inc,

USA.

Warren, J.K. (2006) Evaporites: Sediments, Resources and Hydrocarbons, Springer, New York

Wheater, C.P and P.A. Cook (2000) Using statistics to understand the environment. Routledge, London, England.

Younger, P. L. (2007) Groundwater in the Environment. Blackwell Publishing, Oxford,

England.

http://www.metoffice.gov.uk/climate/uk/http://www.metoffice.gov.uk/climate/uk/datasets/Rainfall/date/England_NW_and_N_Wales.txthttp://www.metoffice.gov.uk/climate/uk/datasets/Rainfall/date/England_NW_and_N_Wales.txthttp://dictionary.sensagent.com/site+of+biological+importance/en-en/

40

13.Appendicies

Appendix 1 – United Utilities surface drain map

41

Appendix 2 – Rainfall data for North West between 1910 and 2010

45

Appendix 3 – Results from river surveys

June 2010

49

October 2010

54

Appendix 4 –Historical Maps

1960

1670

1980

55

Lake Wetland Area

River

Lily

Outflow

Groundwater

Outflow

Ouflows:

Inflows:

Rainfall

on

Transpiration

From Plants

In Wetland

Area

Change

In Water

Storage

In Lake

(resulting

In level

change)

Rainfall

Run-Off

From

Evaporation

From

Wetland Area

Groundwater

Inflow

Appendix 4 – Summary of findings produced for SMRA

Sanctuary Moor Investigation

Summary of Findings

Conceptual Model of Sanctuary Moor

From constructing a conceptual model the inputs and outputs of the moor could be

calculated. It was found that the run-off value greatly affects the amount of rainfall entering

the pond and this is estimated to have increased by 8.7% since 1950. In the model, the

storage was estimated to increase in proportion to the surface area visible on historical

maps.

The river outflow was estimated to have increased by approximately 22% between 1950 and

1970 and by only a further 8% between 1970 and the present day. It is possible that the river

cannot increase its capacity much more than this to cope with the extra load being put upon

it. The man-made channel was designed for the smaller flow in the past so it may now be

restricting the greater flow resulting in increased storage.

Solutions

SUDS (Sustainable Urban Drainage Systems)

The ultimate aim of SUDs is to mimic natural processes to move water away from man-

made environments therefore reducing flood risks and improving the local water quality.

The simplest solution is rainwater harvesting, this is collecting rainwater from roofs and

impermeable surfaces such as car parks, roads and driveways. This water is then stored

and used to water plants and in some cases stored for uses such as flushing toilets

Simply harvesting all the rainfall from residents’ roofs may reduce the run off by a large

enough percentage to have a significant effect on the water level.

56

Permeable paving is another useful SUDS solution, however this would be difficult to put

into practice at Sanctuary Moor as it could consist of a lot of construction and costs. The

water would percolate through the paved structure instead of running off as is currently

the case. This water would then percolate into the ground and soil when the conditions

permit and enter the water system in a more natural way.

Evapotranspiration

Evapotranspiration could be increased by planting certain types of plants that transpire

more than others. This would increase the amount of water leaving the moor.

River Flow

The largest output of the moor is the river output. This output could be increased by

clearing the river of debris and de-silting, beginning at the north end so that any debris

does not flow and re-block cleared areas. It may also be worth looking into the feasibility

of widening the river as it leaves the moor or creating another river channel to meet the

existing river at the Lily Brook bridge.

The bridge also needs further investigation including more in depth analysis of the base

of the bridge which may lead to adaptation enabling a greater flow.

Further Investigations

The flow was measured during June and October and showed very similar flow rates without

seasonal variation. It is possible that in the past the River Lily could drain the required

amount of water from the wetland. Now that there is a higher water level it is causing a

consistent maximum flow in the River Lily which may not now be able to cope with the

additional load. The constant river flow suggests evidence to support this theory. Periodic

measurements of water level and flow need taking throughout the year to monitor the

situation systematically to increase the reliability of the modelling of the water balance. This

would also be useful to see how effective particular solutions were as they are being tried.

In summary my investigations found a complex situation with many factors influencing the

water balance. Addressing one may improve the situation but it is likely that an integrated

response would have more chance of positive results.

Comments from my tutor and Peak Associates after reading my draft dissertation suggested

two main options:

Accept the flooding will continue and adopt a plan of managed retreat from the land

at risk,

Campaign for an integrated approach to management of the moor that involves a

sustainable improvement in drainage.

Kate Berry, Lancaster University 2011

the development of a conceptual model to investigate the water … · 2012. 9. 8. · that are now...

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