mike novotney, p.e. (md) center for watershed protection

Putting It All Together Integrated Natural Resource Protection, Stormwater Management and Site Design

Mike Novotney, P.E. (MD)Center for Watershed Protection

Stormwater & Site Design Criteria

Flood

Control

Channel

WQV

Runoff Reduction

Flood Control

Aquatic Resource Protection

Water Quality

Meeting the Stormwater & Site Design Criteria Satisfying these criteria requires the successful

integration of natural resource protection and stormwater management with the site planning and design process

This integration can be accomplished by using an approach to the site planning and design process that:

(1) identifies and protects valuable natural resources(2) limits land disturbance and the creation of new impervious and disturbed pervious cover (3) reduces and manages post-construction stormwater runoff rates, volumes and pollutant loads

Natural Resource Protection & Stormwater Management Practices & Techniques This approach involves the use of two distinct, but

complementary groups of natural resource protection and stormwater management techniques:

Green Infrastructure Practices: – Natural resource protection and stormwater management

practices and techniques (e.g., better site planning and design techniques, low impact development practices) that can be used to help prevent increases in post-construction stormwater runoff rates, volumes and pollutant loads

– Used to protect natural resources from the direct impacts of the land development process, limit land disturbance and the creation of new impervious and disturbed pervious cover, and reduce post-construction stormwater runoff rates, volumes and pollutant loads

Stormwater Management Practices– Stormwater management practices (e.g., wet ponds,

swales) that can be used to manage post-construction stormwater runoff rates, volumes and pollutant loads.

How do I best use these practices during the site planning and design process?

Need guidance for the developer, site designer and plan reviewer– Stick with the existing process– But make sure that we consider

natural resource protection and stormwater management from the very beginning of process

Six-step stormwater management planning and design process

Prior to Site Assessment Have a project

idea or find a site that leads to an idea

Develop knowledge of all applicable constraints and requirements

Make a basic “go or no go” decision

Goal is to understand the site constraints

and possibilities without investing too

much time and money

Prior to Site Layout

Complete site assessment & natural resources inventory

Develop site fingerprint

Identify primary and secondary conservation areas and buildable area

Goal is to ID important resources and reduce impacts of land development

“by design”

Step 4: Prepare Stormwater Management Concept Plan

Can complete iterative process using Coastal Georgia Site Planning & Design Worksheet…

Let’s walk through an example

Peachtree Strip Mall

Our site is pretty basic:

PEACHTREE STRIP MALL – CONVENTIONAL DESIGN

Basic Site Analysis

Farm Field

Natural Vegetation

Small Pond

Peachtree Strip MallConventional Design


VL = (a . C) . P6

ParkingParking

ParkingParking

ShopsShops

ShopsShopsAnchorAnchor

RestaurantRestaurant

Sketch Plan

ConcentratedConcentratedParking AreaParking AreaConcentratedConcentratedParking AreaParking Area

Disturbed Disturbed PerviousPervious

AreaArea

Disturbed Disturbed PerviousPervious

AreaArea

DetentionDetentionPondPond

DetentionDetentionPondPond

Drugstore Shops Supermarket

Shops

Restaurant

DisturbedDisturbedPerviousPervious

AreaArea


AreaArea


Concept Plan

0 100 200

Peachtree Strip Mall Conventional Design

HSG B Soils Area = 18 acres Impervious Cover = 15.2

acres I = 84% impervious RRv =

(0.05+ 0.009*84)*1.2÷12*18 = 1.46 ac-ft Assume Tc = 15 min.

P = 3.6 in ARPv = 2.65 ac-ft

ConcentratedConcentratedParking AreaParking AreaConcentratedConcentratedParking AreaParking Area

Disturbed Disturbed PerviousPerviousAreaArea

Disturbed Disturbed PerviousPerviousAreaArea

DetentionDetentionPondPondDetentionDetentionPondPond

Drugstore Shops Supermarket

Shops

Restaurant


AreaArea


AreaArea


Concept Plan

0 100 200

We can probably do a better job protecting naturalresources and reducing stormwater runoff rates,volumes and pollutant loads…

Peachtree “Glen”Innovative Design Using Green Infrastructure Practices

Our site is pretty basic:

Basic Site Analysis

Farm Field

Natural Vegetation

Small Pond

Better Site Planning Technique:Preserve Secondary Conservation Areas

Better Site Design Technique: Reduce Parking Lot Footprint

Better Site Design Technique: Create Landscaping Islands in Parking Lot

Better Site Design Technique: Reduce Clearing and Grading Limits

Drugstore

Shops

SupermarketRestaurant

Shops

Shops

Sketch Plan

PEACHTREE GLEN – INNOVATIVE DESIGN


Drugstore

Shops


Shops

Shops

ReducedReducedClearing & Clearing &

GradingGrading

ReducedReducedClearing & Clearing &

GradingGrading

Parking Lot Parking Lot LandscapingLandscaping

IslandsIslands

Parking Lot Parking Lot LandscapingLandscaping

IslandsIslands

ReducedReducedParking LotParking Lot

FootprintFootprint

ReducedReducedParking LotParking Lot

FootprintFootprint

ConservationConservationAreasAreas

ConservationConservationAreasAreas

Concept Plan

0 100 200

Site Information

HSG B Soils Area = 18 acres Impervious Cover = 13.6 acres I = 76% impervious RRv == (0.009*76+0.05)*1.2÷12*18= 1.31 ac-ft Was 1.45 ac-ft

– 10% savings even before stormwater management “credits”

Next, apply “credits”…

Assume Tc = 15 min. P = 3.6 in ARPv = 2.35 ac-ft

– 12% savings

PEACHTREE GLEN – BETTER SITE DESIGN

Drugstore

Shops


Shops

Shops

3.9 A3.9 A

0 100 200

ConservationConservationAreaArea




Same number of parking spaces but with slightly narrower widthsSame number of parking spaces but with slightly narrower widths

After Better Site Planning/Design “Credits” RRv =

= (0.009*76+0.05)*1.2÷12*(18-3.9)

= 1.03 ac-ft Was 1.45 ac-ft, then 1.31 ac-ft

– 29% savings over conventional design with “credits”

Low Impact Development Practice Selection In general, the following information should be

considered when deciding what green infrastructure practices should be used on a development site:– Ability to Help Satisfy the Stormwater Management Criteria

(Table 7.1)– Overall Feasibility (Table 7.2)– Site Applicability (Table 7.3)

In addition, site planning and design teams should consider how the following site characteristics and constraints, which are commonly encountered in coastal Georgia, will influence the use of green infrastructure practices on a development site:– Poorly drained soils, such as hydrologic soil group C and D

soils– Well drained soils, such as hydrologic soil group A and B soils– Flat terrain– Shallow water table– Tidally-influenced drainage

Table 7.1: Ability to Help Satisfy the Stormwater Management Criteria Table 7.1: How Low Impact Development Practices Can Be Used to Help Satisfy the Stormwater Management Criteria

Low Impact Development Practice

Stormwater RunoffReduction

Water Quality Protection

Aquatic Resource Protection

Overbank Flood Protection

Extreme Flood Protection

Alternatives to Disturbed Pervious Surfaces

Soil Restoration

“Credit”:Subtract 50% of any restored areas from the total site area and re-calculate the runoff reduction volume (RRv) that applies to a development site.

“Credit”:Subtract 50% of any restored areas from the total site area and re-calculate the runoff reduction volume (RRv) that applies to a development site.

“Credit”:Assume that the post-development hydrologic conditions of any restored areas are equivalent to those of open space in good condition.



Site Reforestation/ Revegetation

“Credit”:Subtract 50% of any reforested revegetated areas from the total site area and re-calculate the runoff reduction volume (RRv) that applies to a development site.

“Credit”:Subtract 50% of any reforested/revegetated areas from the total site area and re-calculate the runoff reduction volume (RRv) that applies to a development site.

“Credit”:Assume that the post-development hydrologic conditions of any reforested/revegetated areas are equivalent to those of a similar cover type in fair condition.



Soil Restoration with Site Reforestation/ Revegetation

“Credit”:Subtract 100% of any restored and reforested/ revegetated areas from the total site area and re-calculate the runoff reduction volume (RRv) that applies to a development site.

“Credit”:Subtract 100% of any restored and reforested/ revegetated areas from the total site area and re-calculate the runoff reduction volume (RRv) that applies to a development site.

“Credit”:Assume that the post-development hydrologic conditions of any restored and reforested/ revegetated areas are equivalent to those of a similar cover type in good condition.



Table 7.2: Overall Feasibility

Table 7.2: Factors to Consider When Evaluating the Overall Feasibility of Green Infrastructure Practices

Green Infrastructure

PracticeDrainage Area Area Required Slope Minimum Head Minimum Depth

to Water Table Soils

Better Site Planning Techniques

Protect Primary Conservation Areas

N/A

10,000 SF minimum* to

receive stormwater management

“credits”

No restrictions N/A N/A No restrictions

Protect Secondary Conservation Areas

N/A



“credits”

Protect slopes >15% N/A N/A

No restrictions; protect erodible

soils

Better Site Design Techniques

Reduce Clearing and Grading Limits N/A No restrictions No restrictions N/A N/A No restrictions

Reduce Parking Lot Footprints N/A N/A No restrictions N/A N/A No restrictions

Low Impact Development Practices


Soil Restoration N/A No restrictions 10% maximum N/A 1.5 FT C/D or disturbed soils

Site Reforestation/ Revegetation N/A



“credits”

No restrictions N/A N/A No restrictions

Table 7.3: Site Applicability

Table 7.3: Factors to Consider When Evaluating the Applicability of Green Infrastructure Practices on a Development Site

Green Infrastructure Practice Rural Use Suburban Use Urban Use Construction Cost Maintenance

Better Site Planning Techniques

Protect Primary Conservation Areas Low Low

Protect Secondary Conservation Areas Low Low

Better Site Design Techniques

Reduce Clearing and Grading Limits Low Low

Low Impact Development Practices


Soil Restoration Medium Low

Site Reforestation/ Revegetation Medium Low

Alternatives to Impervious Surfaces

Green Roofs High High

Permeable Pavement High High

“Receiving” Low Impact Development Practices

Conservation Areas Low Low

Vegetated Filter Strips Low Low

Grass Channels Low Medium

Practice Selection:

We might have picked grass channels or dry swales for conveyance– But we protected the natural drainage

features as a secondary conservation area We might consider green roofs or

permeable pavement We might also think about rainwater

harvesting or stormwater planters Let’s start with bioretention areas and

sheetflow to conservation areas– Can use distributed landscaping areas to

“receive” stormwater runoff


Drugstore

Shops


Shops

Shops





BioretentionBioretentionAreaArea


BioretentionBioretentionAreasAreas


Area 14.7 acArea 14.7 ac

Area 21.5 acArea 21.5 ac Area 3

3.8 acArea 33.8 ac

3.9 ac3.9 ac

0 100 200

Sheetflow toSheetflow toCons. AreaCons. Area

Sheetflow toSheetflow toCons. AreaCons. Area 1.8 ac1.8 ac



0.4 ac0.4 ac

Bioretention

Area 1

Areas 2 & 3

Apply Runoff Reduction “Credits”

Target RRv = 1.03 ac-ft Apply runoff reduction “credits”

for each of our low impact development practices– Site Planning & Design Worksheet

helps automate this process, so let’s go there…

Check Stormwater Management Criteria

If we haven’t completely satisfied the criteria, we may want to go back to the concept plan to apply additional low impact development practices to further reduce post-construction stormwater runoff rates, volumes, and pollutant loads…

Apply Stormwater Management Practices

If we determine that the criteria cannot be satisfied exclusively through the use of green infrastructure practices, the next step is to apply stormwater management practices to the site– Let’s try a stormwater pond to satisfy

the remainder of the criteria…


Drugstore

Shops


Shops

Shops









Area 14.7 acArea 14.7 ac

Area 21.5 acArea 21.5 ac Area 3

3.8 acArea 33.8 ac

3.9 ac3.9 ac

0 100 200

Overland Overland Flow AreaFlow AreaOverland Overland Flow AreaFlow Area 1.8 ac1.8 ac

StormwaterStormwaterPondPond

StormwaterStormwaterPondPond

Stormwater Pond

Moving on to Final Design

Discuss concept plan with local development review authority

Further develop stormwater management plan

Include details about green infrastructure and stormwater management practice design

mike novotney, p.e. (md) center for watershed protection

Documents

site constraints

site designer

site assessmenthave

better site planning

site designmike novotney

design techniques

design processprior

design processthis integration