GIS Applications for Water, Wastewater, and Stormwater Systems - Chapter 13 pdf

LEARNING OBJECTIVESThe learning objectives of this chapter is to understand how GIS can be applied in developing sewer system hydraulic models, and to understand how GIS can beused to pr

CHAPTER 13 Sewer Models

GIS saves time and money in developing sewer system models for simulating flows and depths in the collection system GIS also helps

to prepare maps of the model results, which can be easily understood

by nonmodelers

GIS-based sewer models bridge the gap between information and its recipients.

2097_C013.fm Page 257 Monday, December 6, 2004 6:08 PM

LEARNING OBJECTIVES

The learning objectives of this chapter is to understand how GIS can be applied

in developing sewer system hydraulic models, and to understand how GIS can beused to present modeling results

MAJOR TOPICS

• Representative sewer models

• Storm Water Management Model (SWMM)

• Graphical user interface (GUI)

• SWMM applications

• Data preparation

• Interface development steps

• GIS application case studies

LIST OF CHAPTER ACRONYMS

CMOM Capacity, Management, Operations, and Maintenance

CSO Combined Sewer Overflow

DSS Decision Support System

EPA (U.S.) Environmental Protection Agency

GUI Graphical User Interface

HEC Hydrologic Engineering Center

HGL Hydraulic Gradient Line

LTCP Long-Term Control Plan (for CSOs)

NMC Nine Minimum Controls (for CSOs)

NPDES National Pollution Discharge Elimination System

ODBC Open Database Connectivity

OLE Object Linking and Embedding

SHC System Hydraulic Characterization (for CSOs)

SSO Sanitary Sewer Overflow

SWMM Storm Water Management Model

MAPINFO ™ AND SWMM INTERCHANGE

In the late 1990s, Portland’s Bureau of Environmental Services (BES) developed asuite of GIS and database tools to develop data for SWMM models Model data were

Application area Basement flooding modeling using the Interchange

GIS Linkage Method described in Chapter 11 (Modeling Applications)

GIS software MapInfo Modeling software SWMM Other software Microsoft Access GIS data Sewer pipes, aerial photographs, buildings and

parking lot polygons GIS format Raster and vector Study area City of Portland, Oregon Organization Bureau of Environmental Services, City of Portland,

Oregon

2097_C013.fm Page 258 Monday, December 6, 2004 6:08 PM

developed from maps and databases with automation of many of the steps for dataextraction, variable assignments, and model building Detailed collection-system models

of basins were developed to analyze local areas These models contained essentially all

of the pipes in the collection system and utilized two subcatchment definitions to placerunoff into the system in the correct location Surface water subcatchments were defined

as the areas that flowed into the sewer through street inlets in the public right-of-way.Direct connection subcatchments were defined as the areas that contributed to sanitaryand stormwater drainage through service laterals

A GIS tool was developed to predict flooding of individual parcels by overlayingmodeled hydraulic gradient lines (HGLs) with estimated finished floor elevations obtainedfrom a DEM Detailed SWMM RUNOFF and EXTRAN models were developed fromfacility maps and photogrammetric data with the use of a MapInfo GIS and a MicrosoftAccess database The SWMM model showed that many of the system capacity problemswere in the local areas at the upstream ends of the system and that the local collection systemtended to hold water back from the downstream trunk sewers in the system This betterunderstanding of where flooding was likely to occur and where system capacity constraintsactually occurred allowed BES a top-down view of the basin during alternatives analysis.Local inflow control alternatives were considered first, and pipe upsizing along with passingthe problem downstream was the second alternative Figure 13.1 shows a thematic mapshowing flooding risk and historical complaints (Hoffman and Crawford, 2000)

GIS APPLICATIONS FOR SEWER SYSTEMS

GIS applications for sewer systems include (Shamsi, 2002):

• Performing H&H modeling of collection systems, including:

• Automatic delineation of watersheds, sewersheds, and tributary drainage areas

Figure 13.1 Thematic map showing flooding risk and historical complaints (map courtesy

of Computational Hydraulic Int.).

2097_C013.fm Page 259 Monday, December 6, 2004 6:08 PM

• Model simplification or skeletonization to reduce the number of manholes and sewers to be included in the H&H model

• Estimating surface elevation and slope from digital elevation model (DEM) data

• Estimating dry-weather sewage flow rates from land use, census data, and billing records

• Estimating wet-weather sewage flow rates from land use, soil, surface ousness, and slope

impervi-• Creating maps for wastewater National Pollution Discharge Elimination System (NPDES) permit requirements (as described in Chapter 9 [Mapping Applica- tions]), such as:

• U.S Environmental Protection Agency’s (EPA) combined sewer overflow (CSO) regulations, such as System Hydraulic Characterization (SHC), Nine Minimum Controls (NMC), and long-term control plan (LTCP)

• U.S EPA’s sanitary sewer overflow (SSO) regulations, such as capacity, agement, operations, and maintenance (CMOM)

man-• Documenting field inspection data (as described in Chapter 15 [Maintenance Applications]), including:

• Work-order management by clicking on map features

• Inspection and maintenance of overflow structures and manholes

• Television (TV) inspection of sewers

• Flow monitoring and sampling

• Smoke-testing, dye-testing, and inflow/infiltration (I/I) investigations

• Performing and planning tasks such as assessment of the feasibility and impact

of system expansion

In this chapter, we will focus on the sewer system H&H modeling applications

of GIS

SEWER SYSTEM MODELING INTEGRATION

Tight integration between a sewer model and a GIS is highly desirable.

The GIS applications in sewer system modeling are developed by using the threeapplication methods (interchange, interface, and integration) described in Chapter

11 (Modeling Applications) These methods facilitate preparation of model-inputdata and mapping of model output results similar to their application for watersystem models described in Chapter 12 (Water Models)

Transfer of data between a GIS and a sewer model is handled differently bydifferent software vendors Some products offer nothing more than a manual cut-and-paste approach for transferring data between a GIS and the model Others offer

a truly integrated package Obviously, tight integration between the sewer modeland the GIS is desirable However, it should not be assumed that a tightly integratedmodel is the best modeling tool For example, the interchange or interface capability

of a comprehensive sewer model might be more useful for some users comparedwith a tightly integrated model having limited modeling capability to simulatecomplex situations such as surcharged sewers

2097_C013.fm Page 260 Monday, December 6, 2004 6:08 PM

SOFTWARE EXAMPLES

Sewer system modeling software is used to compute dry- and wet-weather flowfor hydraulic analysis and design of collection systems and wet-weather controlfacilities such as storage tanks and equalization basins

Table 13.1 lists representative sewer system modeling packages and their GIScapabilities, vendors, and Web sites The salient GIS features of some programs aredescribed in the following subsections

What is common among the recent software developments is a transferability

of fundamental database information, also referred to as a decision supportsystem (DSS) Under a DSS framework, neither the GIS nor the model is central

to the process Both perform satellite functions for a central master database.(Heaney et al., 1999)

SWMM

Numerous hydrologic models were created in the U.S during the 1970s,including the U.S EPA’s legacy computer program SWMM and the U.S ArmyCorps of Engineers’ Hydrologic Engineering Center’s HEC series of models(HEC-1 through 6) Two of the most popular models, HEC-1 and HEC-2, havebeen updated and renamed HEC-HMS and HEC-RAS

Collection system hydraulics can be characterized by using an H&H computermodel such as SWMM SWMM is a comprehensive computer model for analysis

of quantity and quality problems associated with urban runoff Both continuousand single-event simulation can be performed on catchments having sanitary

Table 13.1 Representative Sewer System Modeling Software

Software

GIS Linkage

SWMM Interchange U.S Environmental

Protection Agency (EPA)

www.epa.gov/ceampubl/ swater/swmm/index.htm

CEDRA AVSand Integration CEDRA Corporation www.cedra.com

H2OMAP Sewer

H2OVIEW Sewer

Interface and Integration

MWH Soft www.mwhsoft.com

InfoWorks CS

and InfoNet

Interface and Integration

Wallingford Software

sewers, storm sewers, or combined sewers and natural drainage, for prediction offlows, stages, and pollutant concentrations.

SWMM is one of the most successful models produced by EPA for the water environment SWMM was developed from 1969 to 1971 as a mainframecomputer program and has been continually maintained and updated Versions 2,

waste-3, and 4 of SWMM were distributed in 1975, 1981, and 1988, respectively Thefirst batch-mode microcomputer version of SWMM (Version 3.3) was released byEPA in 1983 The first conversational-mode user-friendly PC version of SWMM,known as PCSWMM, was commercially distributed in 1984 by ComputationalHydraulics, Inc., of Guelph, Ontario (Computational Hydraulics, 1995) The first

PC version of EPA’s SWMM was Version 4, which was distributed in 1988 (Huberand Dickinson, 1988; Roesner et al., 1988) An excellent review of SWMM’sdevelopment history can be found in the book by James (1993)

SWMM is regarded as the most widely used urban H&H model in the U.S.(Heaney et al., 1999) SWMM continues to be widely used throughout the worldfor analysis of quantity and quality problems related to stormwater runoff, combinedsewers, sanitary sewers, and other drainage systems in urban areas, with manyapplications in nonurban areas as well From 1988 through 1999, the EPA Centerfor Exposure Assessment Modeling in Athens, Georgia, distributed approximately

3600 copies of SWMM The University of Florida distributed roughly 1000 copies

of SWMM in the late 1980s Third-party interfaces for SWMM, such as SWMM, PCSWMM, and XP-SWMM, have several thousand users The number

MIKE-of subscribers to the SWMM Users Group Internet discussion forum (Listserv) onthe Internet is nearly 10,000 (EPA, 2002)

The current version (4.3) was released by EPA in May 1994 for the 16-bitMS-DOS operating system Professor Wayne Huber of Oregon State University,one of the authors of SWMM, has developed several updated versions of SWMM

4 His latest version (4.4H) was updated in March 2002 All of these and previousSWMM versions were written in the FORTRAN programming language None

of them have a user interface or graphicalcapability Users must provide ASCIItext input and rely on ASCII text output EPA is currently developing an updatedversion of SWMM referred to as SWMM 5 Written in the C++ programminglanguage, SWMM 5 will incorporate modern software engineering methods aswell as updated computational techniques The modular, object-oriented com-puter code of SWMM 5 is designed to simplify its maintenance and updating

as new and improved process submodels are developed The new code will alsomake it easier for third parties to add GUIs and other enhancements to theSWMM engine This approach follows the same approach used by the highlysuccessful EPANET model from EPA (described in Chapter 12 [Water Models]),which analyzes hydraulic and water quality behavior in drinking water distribu-tion systems (Rossman, 2000)

SWMM simulates dry- and wet-weather flows on the basis of land use, graphic conditions, hydrologic conditions in the drainage areas, meteorologicalinputs, and conveyance/treatment characteristics of the sewer system The modelercan simulate all aspects of the urban hydrologic and quality cycles, includingrainfall, snow melt, surface and subsurface runoff, flow routing through drainage2097_C013.fm Page 262 Monday, December 6, 2004 6:08 PM

network, storage, and treatment Statistical analyses can be performed on term precipitation data and on output from continuous simulation Figure 13.2shows a conceptual schematic of SWMM This figure shows that SWMM is acomplex model capable of modeling various phases of the hydrologic cycle usingdifferent blocks (modules) such as RUNOFF, TRANSPORT, and EXTRAN.SWMM can be used both for planning and design Planning mode is usedfor an overall assessment of the urban runoff problem or proposed abatementoptions SWMM is commonly used to perform detailed analyses of conveyancesystem performance under a wide range of dry- and wet-weather flow conditions.These days, SWMM is frequently used in the U.S for modeling wet-weatheroverflows including CSO, SSO, and stormwater discharges from collection sys-tems As such, it is the model of choice for use in many collection-systemmodeling studies For example, SWMM can be used to develop a CSO model

long-to accomplish various tasks leading long-to the development of a CSO Plan of Actionsmandated by EPA These tasks include characterizing overflow events, develop-ing the CSO vs rainfall correlation, maximizing the collection-system storage,and maximizing the flow to the treatment plant The CSO model can also beused to develop the EPA-mandated LTCPs to evaluate various CSO controloptions Sizing of CSO control facilities such as a wet-weather equalization tankrequires CSO volume and peak discharge, both of which can be modeled usingSWMM

The use of SWMM to model wet-weather overflows is particularly advantageousfor the following reasons:

• SWMM produces estimates of present and future dry- and wet-weather flow rates Flow estimates can be prepared based upon present and future land-use

Figure 13.2 SWMM conceptual schematic.

2097_C013.fm Page 263 Monday, December 6, 2004 6:08 PM

conditions, topography, sewer characteristics, and selected meteorological ditions The model can be calibrated against measured flow rates.

con-• SWMM models the performance of the conveyance system under a range of dynamic flow conditions.

• Using SWMM, it is possible to assess hydraulic capacity in response to weather input This characteristic can be very useful for analyses related to abatement of overflows.

wet-SWMM is flexible enough to allow for different modeling approaches to thesame area An approach that adequately describes the service area and accuratelycomputes and routes the flows at reasonable computing time and effort should beadopted The following modeling strategy is generally used for modeling wet-weather overflows:

• Delineate sewersheds (the drainage areas tributary to overflows, also referred to

as subareas or subbasins).

• Use the TRANSPORT Block to generate sewershed dry-weather flows.

• Use the RUNOFF Block to generate sewershed wet-weather flows.

• Combine dry-weather and wet-weather flows to generate combined sewershed flows.

• Use the EXTRAN Block to route the flows through the collection and interceptor system.

USEFUL SWMM WEB SITES

SWMM Graphical User Interface

Most users have now become accustomed to modeling in a point-and-clickcomputing environment that provides a user-friendly graphical user interface(GUI) A GUI is a computer program that acts as an interpreter between usersand their computers It is designed to minimize (but not eliminate) the need forhuman experts and to guide the modeler through the intricacies of a particularnumerical model A GUI provides a suite of tools to create a decision supportsystem for the numerical model that has been adopted It also stimulates userinterest and facilitates interpretation of model results A GUI improves produc-tivity by increasing the efficiency of data entry, eliminating data errors throughexpert-checking, and the use of decision-support graphics and interpretation tools

It replaces difficult-to-remember text commands by interactive computer graphicsconsisting of menus, dialogue boxes, input and output windows, and icons Themain goal of using GUIs is to develop user-friendly computer applications or to

Oregon State University ccee.oregonstate.edu/swmm/

SWMM-Users Internet Discussion

Forum

www.computationalhydraulics.com/Community/ Listservers/swmm-users.html

2097_C013.fm Page 264 Monday, December 6, 2004 6:08 PM

add user-friendliness to existing command-line-driven applications For example,Microsoft Internet Explorer is a GUI for user-friendly access to the Internet.Modern software offer pull-down menus, toolbars, icons, buttons, dialogueboxes, hypertext, context-sensitive online help, etc., which are not available in legacycomputer programs including SWMM 4 Many commercial modeling packages nowoffer on-screen point-and-click drawing and editing of drainage network maps, butunfortunately some legacy programs still rely on ASCII text input and output files.SWMM was developed in an era when input files were created on punched cards.After 30 years, SWMM 4 now runs on personal computers, but it is still a text-based,nongraphical DOS program It reads ASCII input to produce ASCII output, which ismost suitable for mainframe line printers SWMM’s ASCII format output is long,boring, difficult to interpret, and not very useful for nonmodelers Creating computermodels and reviewing the model results is often slowed by our inability to see thesystem being modeled It is up to the modeler to review SWMM’s voluminous outputand construct a mental image of the physical system being modeled Often, thelimitation in understanding the model output has been the modeler’s own comprehen-sion of the output, not the model itself Quite frequently, it is impossible for the modeler

to absorb the large amount of information contained in the model output (TenBroekand Roesner, 1993)

A GUI and a GIS can be employed to overcome SWMM’s input/output ciencies Two types of GUIs can be employed for GIS applications in SWMMmodeling (Shamsi, 1997; Shamsi, 1998):

defi-• An input interface (also called a front-end interface or preprocessor) extracts SWMM input from GIS layers and creates SWMM’s traditional ASCII text input file The input GUIs can also provide graphical tools to draw a network model that is subsequently converted to SWMM’s ASCII input file For example, an input interface may extract sewer-segment lengths and manhole coordinates from the sewer and manhole layers.

• An output interface (also called a back-end interface or postprocessor) converts text to graphics It can convert SWMM’s traditional ASCII text output file to graphs, charts, plots, and thematic maps that can be easily understood by everyone.

With the help of these GUI/GIS tools, everybody can understand the modeloutput These tools help one to see storm-surge progress through the sewer systemand pinpoint areas of flooding and surcharging More than just reams of computerpaper, such models become automated system-evaluation tools Other benefits ofGUI/GIS tools are:

• Preparation of network schematics is not essential Digitized plots of sewers and subarea boundaries can be used to create a drainage network diagram on a com- puter screen.

• Zoom and pan features make it possible to display even the largest networks conveniently on the screen.

• Connectivity data errors are easily detected and can be edited while still in the program Instabilities in the model output, often the most difficult errors to find, are also easily located.

2097_C013.fm Page 265 Monday, December 6, 2004 6:08 PM

• Flow and depth data from SWMM output can be displayed in either plan or profile view, providing an animated display of the HGL during the simulation time steps.

• Flow and HGL time-series plots can be displayed for any conduit or node in the hydraulic network.

• Field-collected flow and depth data can be displayed along with the model output for model calibration and verification.

• Network graphics and modeled hydrographs can be exported to word processors

to aid in report preparation.

XP-SWMM and XP-GIS

XP-SWMM by XP Software (Belconnen, Australia and Portland, Oregon) is

a full-fledged 32-bit Microsoft Windows application The program has beenenhanced by the addition of a graphics database, and an adaptive dynamic wavesolution algorithm that is more stable than the matrix method used in the originalSWMM The program is divided into a stormwater layer, which includes hydrologyand water quality; a wastewater layer, which includes storage treatment and waterquality routing for BMP analysis; and a hydrodynamic/hydraulics layer for sim-ulation of open or closed conduits (Heaney et al., 1999)

XP-SWMM is also included in Visual SWMM from CaiCE Software Corp.(Tampa, Florida) Basically, XP-SWMM and Visual SWMM are GUI programsfor SWMM The user-friendly GUI is based upon a graphical representation of

Figure 13.3 Visual SWMM screenshot.

2097_C013.fm Page 266 Monday, December 6, 2004 6:08 PM

the modeled system using a link-node architecture It provides a shell that acts as

an interpreter between the user and the model It facilitates on-screen development

of a SWMM model in the form of a link-node network Figure 13.3 shows a VisualSWMM (Version 7) screenshot

Because the links and nodes are set up on a coordinate-system basis, files can

be translated between most CAD and GIS software systems using the interchangemethod CAD or GIS files can also be used as a backdrop for the system beingmodeled Although XP-SWMM is not linked or integrated to a GIS package, itprovides an optional utility called XP-GIS to extract model input data from theexisting GIS database tables XP-GIS is a module for linking XP-SWMM to GISdatabases Its main purpose is to facilitate the import and export of modeling datafrom GIS and other data sources such as spreadsheets, asset management software,and OLE/ODBC compliant databases It also allows for the inclusion of Shapefiles

as background layers and for data to be viewed and manipulated in an XP-SWMMgraphical environment

GIS Data for SWMM

GIS layers for land use, elevation, slope, soils, and demographics can be cessed to extract model parameters for input to various SWMM Blocks and othercollection system models The basic input parameters to be assembled into theRUNOFF Block input files include sewershed area, overland flow slope, overlandflow width, percent imperviousness, roughness coefficients, and soil infiltrationparameters Area, slope, and percent imperviousness can be computed from the GISlayers Table 13.2 shows sample sewershed RUNOFF data extracted from GIS layersusing the interchange method for a study area in Pennsylvania

pro-GIS layers can also be used to estimate inputs for sewershed population, ulation density, number of houses, average family size, average market value ofhouses, average family income, and the predominant land-use type for the TRANS-PORT Block Table 13.3 shows sample sewershed TRANSPORT data extractedfrom GIS layers using the interchange method for a study area in Pennsylvania

pop-Estimating Green-Ampt Parameters Using STATSGO/SSURGO GIS Files

Based on their resolution, there are three types of U.S Natural Resources servation Service (NRCS) (formerly the U.S Soil Conservation Service or SCS)soils data that are useful in GIS applications:

Con-• National Soil Geographic (NATSGO)

• State Soil Geographic (STATSGO)

• Soil Survey Geographic (SSURGO)

SSURGO provides the highest resolution soils data at scales ranging from1:12,000 to 1:63,360 This resolution is appropriate for watersheds a few squaresmiles in area STATSGO data are digitized at 1:250,000-scale, which is useful when2097_C013.fm Page 267 Monday, December 6, 2004 6:08 PM

Table 13.2 Sample GIS Data for SWMM’s RUNOFF Block

Sewershed

Area

(Acres)

Mean PI

Mean % Slope

Land Use (Acres)

O.S = Open Space; and S.W = Surface Water.

Copyright © 2005 by Taylor & Francis

analyzing large regional watersheds NATSGO data describe variations in soil type

at the multistate to regional scale, which is not suitable for wastewater and water modeling applications (Moglen, 2000)

storm-The steps for estimating Green-Ampt parameters using STATSGO GIS data aregiven in the following text:

1 Download the STATSGO database files from the NRCS Web site ( www.ftw.nrcs.

usda.gov/stat_data.html ).

• comp.dbf — Attribute HYDGRP has Hydrologic Soil Groups (A, B, C, etc.)

• layer.dbf — Attribute TEXTURE2 has soil texture (S [sand], SIL [silt], etc.)

2 Join the soils layer to the preceding tables using the MUID attribute that provides

a common link between the soils layer and the STATSGO database files.

Table 13.3 Sample GIS Data for SWMM’s TRANSPORT Block

Sewershed Population

Population Density

Family Size

Family Income

Market Value Houses

3 Perform an overlay of soils with subareas layer to estimate:

• Percentage of HYDGRP in each subarea

• Percentage of TEXTURE2 in each subarea

4 Calculate the Green-Ampt parameters (saturated hydraulic conductivity KS, initial moisture deficit IMD, and average capillary suction SU) for each subarea using the look-up tables shown in Table 13.4 These look-up tables are based on the data provided in SWMM’s users manual (Huber and Dickinson, 1988).

GIS APPLICATIONS FOR SWMM

Representative GIS applications in SWMM modeling are given in the followingsubsections

AVSWMM

Shamsi (1997) developed an ArcView GIS interface called AVSWMM forcollection-system and wet-weather overflow modeling Both RUNOFF and EXT-RAN Blocks were included The interface was developed by customizing ArcView3.2, using Avenue Avenue is ArcView’s native scripting language and is built intoArcView 3.x Avenue’s full integration with ArcView benefits the user in two ways:(1) by eliminating the need to learn a new interface and (2) by letting the user work

Table 13.4 Sample EXTRAN Input Data

AVSWMM RUNOFF Extension

When the extension is loaded, a menu named SWMM is added to the ArcViewinterface as shown in Figure 13.5 The SWMM menu has seven calculators andtwo functions that calculate various RUNOFF Block parameters for subareas (sew-ersheds) A polygon layer for subareas is required to use this extension ArcView’sSpatial Analyst Extension is required for the analysis of raster data layers Eachcalculator prompts the user for the layer containing the subareas and the layercontaining the data from which the model parameter is to be extracted Eachcalculator adds the calculated input parameters to fields in the subarea layer Thefields are created if they do not exist Various functions and calculators of thisextension are described in the following text:

1 Average Slope Calculator

Function Assigns average slope to subareas

Input Layers Subarea polygon layer

Slope grid Output Adds or updates MEANSLOPE field in subarea layer

2 Census Parameter Calculator

Function Assigns total population and housing counts to subareas

Figure 13.4 ArcView 3.x integrated programming interface for writing avenue scripts.

2097_C013.fm Page 271 Monday, December 6, 2004 6:08 PM

Input Layers Census block polygon layer

Subarea polygon layer Output Adds or updates total population and housing fields to subareas

Pop100 Total Population

PopDens Population density per acre HouseDens Households density per acre MnFamSize Mean family size

3 Land Use Calculator

Function Calculates area of each land use class for subareas

Input Layers Landuse grid layer

Subarea polygon layer Output Adds fields for each land use type to subarea layer

Calculates area for each land use type

Figure 13.5 AVSWMM RUNOFF Extension.

2097_C013.fm Page 272 Monday, December 6, 2004 6:08 PM

4 Percent Imperviousness Calculator

Function Assigns percentage of percent imperviousness for each subarea.

The calculator will add a percent impervious field to the landuse polygon layer and will prompt for the percent impervious value for each land use type.

Input Layers Landuse grid layer

Subarea polygon layer Output Adds or updates field containing percent impervious, PERIMP, to

subarea layer

5 Set Soil Look-up Tables Function

Function Joins the look-up tables for soil infiltration parameters for the

Green-Ampt method (Huber and Dickinson, 1988) IMD Initial moisture deficit

KS Saturated hydraulic conductivity or permeability

SU Capillary suction Additional information is presented below Input Layers Soils polygon layer

IMD.dbf look-up table

KS look-up table

SU look-up table Output Joins the look-up tables to the soils layer

6 Soil Parameter Calculator

Function Calculates Green-Ampt infiltration parameters, IMD, KS, and SU

for subareas The user may also select any numerical fields of the Soils layer to average.

InputLayers Soil polygon layer

Subarea polygon layer Output Adds or updates average soil parameters to subarea layer

7 Manhole Elevation Calculator

Function Assigns elevation to manholes based from a DEM

Input Layers DEM grid

Manhole point layer Output Adds or updates ELEV field containing elevation to Manhole layer

8 Make Curve Number Grid Function

Function Prepares a grid layer for runoff curve numbers

Input Layers Land use layer

Soil polygon layer Subarea polygon layer Output It overlays the land use and soil layers to make a curve number

grid The values of the grid are based on each unique combination

of land use and hydrologic soil group.

9 Curve Number Calculator

Function Calculates subarea runoff curve numbers Although EPA’s SWMM

release does not use runoff curve numbers for input, many logic models (e.g., HEC-HMS) and some SWMM GUI programs, 2097_C013.fm Page 273 Monday, December 6, 2004 6:08 PM

hydro-Input Layers Curve number grid

Subarea polygon layer Output Calculates the average curve number for each subarea The values

are added to the CURVNUM field of the Subarea layer.

AVSWMM EXTRAN Extension

Development of the AVSWMM EXTRAN Extension required the two main tasks

described below:

Task 1: Create EXTRAN input file

This task requires that ArcView-compatible GIS layers (themes) exist with

attribute fields for all model input parameters The interface fetches the model input

parameters from the GIS layers and exports (copies) them to an ASCII text input

file specified by the user The user should create a header file containing the model

control parameters The control parameters are entered on the A1 line (title) and

on B0 to B9 lines (solution and printing instructions) The interface automatically

appends this header file to the input file A simplified example is given in the

following text:

Given Data:

1 ArcView GIS layer for manholes

Manholes layer attributes:

• ID

• Bottom elevation

• Top elevation

• Inflow rate

2 ArcView GIS layer for sewers

Sewers layer attributes:

• ID

• Upstream manhole

• Downstream manhole

• Type (circular, rectangular, etc.)

• Depth (diameter for circular pipes)

• Width (not required for circular pipes)

• Length

• Material

• Date installed (material and date installed can be used to automatically calculate Manning’s roughness coefficient)

• Upstream invert elevation

• Downstream invert elevationData To Be Created: An ASCII text input file containing the following parameters:

• Junction (usually manhole) data:

• Data type (D1 for junctions)

• Manhole number

• Top elevation (GR-EL)

2097_C013.fm Page 274 Monday, December 6, 2004 6:08 PM