john jacob, ph.d. ricardo lópez, m.s

Houston, TXHouston, TXMay 8-210, 2006May 8-210, 2006 The AWRA 2006 Conference on GIS & Water RThe AWRA 2006 Conference on GIS & Water R

esources IVesources IV

AWRAAWRA11

Higher or Lower Density?Higher or Lower Density? What Gives the Best Bang for the What Gives the Best Bang for the Buck for Mitigating the Effects of Buck for Mitigating the Effects of

Development?Development?

Higher or Lower Density?Higher or Lower Density? What Gives the Best Bang for the What Gives the Best Bang for the Buck for Mitigating the Effects of Buck for Mitigating the Effects of

Development?Development?

John Jacob, Ph.d.John Jacob, Ph.d.Ricardo López, M.S.Ricardo López, M.S.



AWRAAWRA22-30-30

Low Impact DevelopmentLow Impact DevelopmentVs.Vs.

Urban SprawlUrban Sprawl

Low Impact DevelopmentLow Impact DevelopmentVs.Vs.

Urban SprawlUrban Sprawl Low Impact Development (LID)

Increase the amount of perviousness in developed areas

Smart Growth Increase density (and

therefore imperviousness), but save more open space overall



AWRAAWRA33-30-30

GoalGoalReport the results of a Report the results of a

modeling effort comparing modeling effort comparing the two approaches in a the two approaches in a hypothetical watershedhypothetical watershed



AWRAAWRA44-30-30

Impervious land coverImpervious land cover Impervious land coverImpervious land cover

Impervious surface features are those that Impervious surface features are those that prohibit water from naturally infiltrating the prohibit water from naturally infiltrating the ground (concrete, pavement, etc)ground (concrete, pavement, etc)

Urban Landscapes:Urban Landscapes: Concrete, pavement, rooftopsConcrete, pavement, rooftops Swimming PoolsSwimming Pools

Impervious Land CoverImpervious Land Cover: essentially the area that : essentially the area that is not “green” is not “green”

Impervious surface features are those that Impervious surface features are those that prohibit water from naturally infiltrating the prohibit water from naturally infiltrating the ground (concrete, pavement, etc)ground (concrete, pavement, etc)

Urban Landscapes:Urban Landscapes: Concrete, pavement, rooftopsConcrete, pavement, rooftops Swimming PoolsSwimming Pools

Impervious Land CoverImpervious Land Cover: essentially the area that : essentially the area that is not “green” is not “green”



AWRAAWRA55-30-30

Pop. Density Vs. Pop. Density Vs. Impervious Land CoverImpervious Land Cover

Total Population:100,000

5,000 Pop/Sq. Mile

Total Study Area:50 Sq. Miles

10,000 Pop/Sq. Mile

Total Study Area:50 Sq. Miles

Developed Area:20 Sq. Miles

Developed Area:10 Sq. Miles

May 8-210, 2006May 8-210, 2006 The AWRA 2006 Conference on GIS & Water ResouThe AWRA 2006 Conference on GIS & Water Resources IVrces IV

66

GoodGood

FairFair

PoorPoor

Watershed Impervious CoverWatershed Impervious Cover

Str

eam

Qu

ality

Str

eam

Qu

ality

Sen

sit

ive

Imp

acte

d

Non-Supporting

Urban Drainage

Impervious Cover Model Impervious Cover Model

10% 25% 40% 60% 100%

Center for Watershed Protection

May 8-210, 2006May 8-210, 2006 The AWRA 2006 Conference on GIS & Water ResouThe AWRA 2006 Conference on GIS & Water Resources IVrces IV

77

City of League City, TXCity of League City, TX 2002 Aerial Photo2002 Aerial Photo



AWRAAWRA88-30-30



AWRAAWRA99-30-30

100,000 new residents



AWRAAWRA1010-30-30


8.3 sq mi @ 12,000 pop / sq mi



AWRAAWRA1111-30-30


3.4 sq mi @ 30,000 pop / sq mi



AWRAAWRA1212-30-30

League City Area: 53 Sq. MilesPopulation: 50,000 (2000)

BogotaArea: 160 Sq. MilePopulation: 6,500,000 (2000)

BOGOTA, COL160 Sq. mi. @ 40,000 pop/sq mi



AWRAAWRA1313

Pollutant Load Pollutant Load CalculationsCalculations



AWRAAWRA1414-30-30

Pollutant Load Model (1)Pollutant Load Model (1)Input: LULC Input: LULC VectorVector format format

ArcGIS 9 Model BuilderArcGIS 9 Model Builder



AWRAAWRA1515-30-30

Pollutant Load Model (2)Pollutant Load Model (2)Input: LULC Input: LULC RasterRaster format format

ArcGIS 9 Model BuilderArcGIS 9 Model Builder



AWRAAWRA1616-30-30

Pollutant Load ModelPollutant Load ModelSimplified, GIS-based applicationSimplified, GIS-based application

Developed in ArcGIS 9.x (Model Builder)Developed in ArcGIS 9.x (Model Builder)

Raster data model Raster data model

Estimates total pollutant loads (NPS) in lbs / yr, for any Estimates total pollutant loads (NPS) in lbs / yr, for any user-specified pollutantuser-specified pollutant

Based on the empirical Based on the empirical Simple MethodSimple Method developed by developed by Schueler (1987) for estimating pollutant export from Schueler (1987) for estimating pollutant export from small urban watersheds small urban watersheds



AWRAAWRA1717-30-30

Model Input DataModel Input Data

Geo-spatial Data Geo-spatial Data Watershed BoundariesWatershed Boundaries Land-Use/Land-Cover (LULC) - VLand-Use/Land-Cover (LULC) - Vectorector or or

rasterraster

Tabular DataTabular Data Event Mean Concentration (EMC) table - Event Mean Concentration (EMC) table -

TextText (csv) (csv) Imperviousness factors table - Imperviousness factors table - TextText (csv) (csv)



AWRAAWRA1818-30-30

Runoff Coefficient RVU *Runoff Coefficient RVU *

RVU = 0.05 + (0.009 * IU)RVU = 0.05 + (0.009 * IU)Where: Where: • RVU = Runoff Coefficient for land use RVU = Runoff Coefficient for land use

type u, inches(runoff) / inches(rainfall) type u, inches(runoff) / inches(rainfall) • IU = Percent ImperviousnessIU = Percent Imperviousness

* Schueler 1987 (Washington D.C.)



AWRAAWRA1919-30-30

IMP - Imperviousness valuesIMP - Imperviousness values(%)(%)



AWRAAWRA2020-30-30

Total Pollutant Load (lb/yr) *Total Pollutant Load (lb/yr) *

LP = Σ U (P * PJ* RVU * CU* AU * 2.72 / 12)LP = Σ U (P * PJ* RVU * CU* AU * 2.72 / 12)Where: Where: • LP = Pollutant load, lb/yrLP = Pollutant load, lb/yr• P = Precipitation, in/yr (assumed 46 for study area)P = Precipitation, in/yr (assumed 46 for study area)• PJ = Ratio of storms producing runoff (default = 0.9)PJ = Ratio of storms producing runoff (default = 0.9)• RVU= Runoff Coefficient for land use type u, RVU= Runoff Coefficient for land use type u,

inches(runoff)/inches(rainfall)inches(runoff)/inches(rainfall)• CU = EMC for land use type u, mg/lCU = EMC for land use type u, mg/l• AU = Area of land use type u, in acresAU = Area of land use type u, in acres

* Schueler 1987 (Washington D.C.)



AWRAAWRA2121-30-30

Event Mean Concentration (EMC)Event Mean Concentration (EMC)Event Mean Concentration (EMC)Event Mean Concentration (EMC)

An EMC is defined as the total An EMC is defined as the total constituent mass discharge divided by constituent mass discharge divided by the total runoff volume (EPA 1983)the total runoff volume (EPA 1983)

EMCs were developed by the EPA’s EMCs were developed by the EPA’s Nationwide Urban Runoff Program Nationwide Urban Runoff Program (NURP) (1983) to serve as a national (NURP) (1983) to serve as a national measure of the magnitude of urban measure of the magnitude of urban runoff, specifically pollutant loadingsrunoff, specifically pollutant loadings

An EMC is defined as the total An EMC is defined as the total constituent mass discharge divided by constituent mass discharge divided by the total runoff volume (EPA 1983)the total runoff volume (EPA 1983)

EMCs were developed by the EPA’s EMCs were developed by the EPA’s Nationwide Urban Runoff Program Nationwide Urban Runoff Program (NURP) (1983) to serve as a national (NURP) (1983) to serve as a national measure of the magnitude of urban measure of the magnitude of urban runoff, specifically pollutant loadingsrunoff, specifically pollutant loadings



AWRAAWRA2222-30-30

EMC - Event Mean Concentration values EMC - Event Mean Concentration values for TSS, BOD, TN and TP in mg/lfor TSS, BOD, TN and TP in mg/l(Houston Area EMC Database)(Houston Area EMC Database)

GBNEP – 15March 1992



AWRAAWRA2323-30-30

ScenariosScenarios

No development Full buildout at 4000 people/mi2 (Status Quo) Same population as full buildout but at 12,000

people/mi2 Same population as full buildout but at 30,000

people/mi2 Full-buildout scenario at 4000 people/mi2 with

the addition of best management practices (BMPs or “LID”) treating 20% of the area with a 65% effectiveness.



AWRAAWRA2424

ResultsResults



AWRAAWRA2525-30-30



AWRAAWRA2626-30-30

Pollutant Loads - Comparison ChartPollutant Loads - Comparison Chart(lbs / year)(lbs / year)

Total Nitrogen Total Phosphorus

Biochemical Oxygen Demand Total Suspended Solids



AWRAAWRA2727-30-30

ConclusionsConclusions The BMP scenario reduced pollutant loadings

from the conventional-density, full-buildout scenario by 13-15%.

Holding the population constant and increasing density 3-fold to 12,000 people/mi2, decreased pollutant load overall by 50-75%.

Clearly, density should be considered as a BMP in its own right when considering development scenarios.

But the LID approach remains valid in the low density developments that are destined to remain with us.



AWRAAWRA2828-30-30

Texas Sea Grant / Tx. Coop. ExtensionTexas Sea Grant / Tx. Coop. ExtensionTexas A&M UniversityTexas A&M University

www.urban-nature.orgwww.urban-nature.orgRicardo A Lopez M.S.Ricardo A Lopez M.S.

17000 El Camino Real, Suite 30117000 El Camino Real, Suite 301Houston, TX 77058Houston, TX 77058

(281) 218 0570(281) 218 0570E-mail: E-mail: [email protected]



AWRAAWRA2929

AppendixAppendix



AWRAAWRA3030-30-30

What is Urban Sprawl?What is Urban Sprawl? To spread out in a way that is not organized.To spread out in a way that is not organized.

www.inhs.uiuc.edu/chf/pub/virtualbird/glossary.htmlwww.inhs.uiuc.edu/chf/pub/virtualbird/glossary.html

Haphazard growth or outward extension of a city Haphazard growth or outward extension of a city resulting from uncontrolled or poorly managed resulting from uncontrolled or poorly managed development.development.www.co.monterey.ca.us/gpu/glossary2.htmwww.co.monterey.ca.us/gpu/glossary2.htm

Current development patterns, where rural land is Current development patterns, where rural land is converted to urban uses more quickly than needed to converted to urban uses more quickly than needed to house new residents and support new businesses, and house new residents and support new businesses, and people become more dependent on automobiles. people become more dependent on automobiles. www.smartgrowth.org/bibliographies/greenlit_search/glwww.smartgrowth.org/bibliographies/greenlit_search/glossary.htmlossary.html



AWRAAWRA3131-30-30

BASINSBASINS

BASINSBASINS: Better Assessment Science Integrating : Better Assessment Science Integrating Point and Nonpoint Sources – U.S. Environmental Point and Nonpoint Sources – U.S. Environmental Protection Agency (EPA)Protection Agency (EPA) Multipurpose environmental analysis system designed Multipurpose environmental analysis system designed

to perform watershed and water quality-based studiesto perform watershed and water quality-based studies Makes it possible to quickly assess large amounts of Makes it possible to quickly assess large amounts of

point source and non-point source datapoint source and non-point source data Geographic Information System (GIS) tool developed Geographic Information System (GIS) tool developed

as an extension to ArcView software program as an extension to ArcView software program (Environmental System Research Institute – ESRI)(Environmental System Research Institute – ESRI)



AWRAAWRA3232-30-30

Watershed BoundaryWatershed Boundary WatershedsWatersheds define the areas for which the define the areas for which the

pollutant loads are calculatedpollutant loads are calculated Available from local Available from local government agenciesgovernment agencies in most in most

moderate- to high-density urban areasmoderate- to high-density urban areas May be derived using standard GIS or BASINS May be derived using standard GIS or BASINS

tools and the United States Geological Survey tools and the United States Geological Survey (USGS) (USGS) Digital Elevation ModelDigital Elevation Model (DEM) data files (DEM) data files (See appendix)(See appendix)

Dataset must have a code field containing Dataset must have a code field containing unique unique identifiersidentifiers for each watershed for each watershed

Vector format, projected CS, same projection and Vector format, projected CS, same projection and datum, stored in meters (map units)datum, stored in meters (map units)



AWRAAWRA3333-30-30

LULC DatasetLULC Dataset

Defines Land-Use/Land-Cover types for the Defines Land-Use/Land-Cover types for the study areastudy area

Dataset must encompass the entire watershedDataset must encompass the entire watershed Essential for calculating the pollutant loads.Essential for calculating the pollutant loads. Available from local Available from local government agenciesgovernment agencies in in

most moderate- to high-density urban areasmost moderate- to high-density urban areas If available in If available in rasterraster format (grid of cells), must format (grid of cells), must

be converted to be converted to vectorvector format (polygon spatial format (polygon spatial features)features)



AWRAAWRA3434-30-30

Imperviousness & EMCImperviousness & EMCTablesTables

DATASET: imp_csv: Imperviousness table Attributes: LUCODE: Land use unique identifier Imperv: Imperviousness factor (Percentage in percent

fraction format)

DATASET: emc_csv: Event mean concentrations table

Attributes: LUCODE: Land use unique identifier TN: Total Nitrogen (mg/l) BOD: Biochemical Oxygen Demand (mg/l) TSS: Total Suspended Solids (mg/l) TP: Total Phosphorus (mg/l)



AWRAAWRA3535-30-30

Software ReferencesSoftware References

P-LOADP-LOAD (ArcView extension to (ArcView extension to BASINSBASINS (Better (Better Assessment Science Integrating Point & Nonpoint Assessment Science Integrating Point & Nonpoint Sources – U.S. Environmental Protection Agency - Sources – U.S. Environmental Protection Agency - EPA):EPA):

BASINS 3.1 Description:BASINS 3.1 Description:http://www.epa.gov/waterscience/ftp/basins/system/http://www.epa.gov/waterscience/ftp/basins/system/BASINS3/areadb3.htmBASINS3/areadb3.htmDownload BASINS 3.1 program and data:Download BASINS 3.1 program and data:http://www.epa.gov/waterscience/basins/index.htmlhttp://www.epa.gov/waterscience/basins/index.html

john jacob, ph.d. ricardo lópez, m.s

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