WAMView - A GIS/LAND SOURCE BASED APPROACH TO

WATERSHED ASSESSMENT MODEL

Del Bottcher, Ph.D., P.ESoil and Water Engineering Technology, Inc.3448 NW 12th Ave, Gainesville, FL 32605

andJeffrey G. Hiscock, P.E.

Mock, Roos & Associates, Inc.5720 Corporate Way, West Palm Beach, FL 33407

ABSTRACT

An interactive GIS Watershed Assessment Model (WAM), which has been applied to over30,000 km2 of northern Florida and New Zealand, has been adopted for the ArcView platformmaking it more user-friendly and accessible to engineers and planners. The model simulatesspatial water quality loads based on land use and soils and then routes and attenuates thesesource cell loads through uplands, wetlands and streams to watershed outlets. The model isalmost entirely GRID based providing a higher resolution of results than models that rely onpolygon coverages. This new version of the model includes a menu interface written in ArcViewAvenue with the Spatial Analyst extension to let the user create modified land use scenarios andcompare the results side-by-side with the results of the existing land use.

KEY WORDS

WAM, WAMView, Water Quality, Watershed, Attenuation, GLEAMS, Arc/Info, ArcView, Grid

WATERSHED ASSESSMENT APPROACH

Watershed Assessment Model (WAM) is a Geographic Information System (GIS) based modelthat allows engineers and land use planners to interactively simulate and assess theenvironmental effects of various land use changes and associated land use practices. WAM wasoriginally developed with an Arc/Info interface for the entire Suwannee River WaterManagement District (SRWMD - 19,400 km2 of northern Florida) (SWET, 1998) and has sincebeen customized for the St. Johns River Water Management District (SJRWMD) in northeastFlorida (SWET, 2000) and the National Institute of Water and Atmospheric Research in NewZealand (NIWA, 2000) to accommodate their special regional and geological characteristics.The SJRWMD version (called WAMView with ArcView interface) provides hourly time seriesof flow, total suspended solids (TSS), and nutrients for all the contributing watersheds to theLower St Johns River. These data are used as boundary conditions for a main-stem river modelbeing developed by the US Army Corps of Engineers.

The GIS based processing and user interface in the WAM/WAMView models allows for anumber of user options and features to be provided for grid sizes down to 0.1 ha, featuresinclude:

• Source Cell Mapping of TSS and Nutrient Surface and Groundwater Loads• Tabular Ranking of Land Uses by Constituent Contributions• Overland, Wetland, and Stream Load Attenuation Mapped Back to Source Cells• Hydrodynamic Stream routing of Flow and Constituents with Annual, Daily or Hourly

Outputs• Optional Index Model for Toxins, BOD, and Bacteria for Source Cell Mapping• Wetland Indexing Model for Wildlife Diversity Impacts• Flood Proneness Model• User Interface to Run and Edit Land Use and BMP Scenarios

The water quality parameters (impact parameters) simulated within the models include: Waterquantity, soluble nitrogen (N), particular N, groundwater N, soluble phosphorus (P), particulateP, groundwater P, sediment, biological oxygen demand (BOD), coliform bacteria, andtoxic/hazardous materials. Additional fractionation of N and P for refractory forms and theaddition of organic carbon are currently being added to the model.

The water quality assessments within the models are accomplished using two methods. The firstprovides spatial assessment using impact indices, and the second utilizes detailed hydrologic andcontaminant transport modeling. The method used depends on the watershed assessmentparameter of interest. The indexing approach is used for assessment parameters (BOD, coliformbacteria and toxins) that are hard to quantify and directly associated with pollutant transport,while the modeling approach addresses the major pollutants of sediment and nutrients. Bothapproaches provide outputs at both the source cell, sub-basin, and basin outlet level.

Two approaches are used to reflect the relative importance of the various impact parameters andtheir ability to be modeled using available data. Based on current and anticipated future landuses, it is estimated that nutrients (N and P) and sediment have the greatest potential for causingadverse impacts in the streams, wetlands, rivers and estuaries within the areas to which themodel has been applied thus far. The fact that only hydrologic/nutrient transport models havebeen effectively tested for use in watershed assessments supported the decision that only thewater, nitrogen, phosphorus and sediment loads would be simulated dynamically. Theseparameters may vary for other regions and the model would be adjusted accordingly.

˚The indexing and modeling approaches are similar because both use the watershed characteristicdata from existing GIS coverages to select the appropriate input data (indices for index approachand model parameter sets for the modeling approach). These data are used to calculate thecombined impact of all the watershed characteristics for a given grid cell. Once the combinedimpact for each unique cell within a watershed is determined, the cumulative impact for theentire watershed is determined by first attenuating the constituent to the sub-basin outlets andthen calculating an area-weighted ranking/index for the attenuated load generated at each cell.Constituents are attenuated based upon the flow distances (overland to nearest water body,

through wetlands or depressions and within streams to the sub-basin outlet), flow rates in eachrelated flow path and the type of wetland or depression encountered.

The wetland wildlife diversity indexing model provides a means to assess the influence ofsurrounding land uses and wetland type on various types of wildlife. Grid cell neighborhoodfunctions are used to calculate the average value of land use arial influences within a block ofcells surrounding each wetland cell. The cells of each wetland are then averaged to produce anadjusted wetland index value.

The hydrologic contaminant transport modeling is accomplished by first simulating all of theunique grid cell combinations of land use, soils, and rain zone (New Zealand version adds landslope) by using one of several source cell models including GLEAMS (Knisel, 1993), EAAMOD(SWET, 1999 & 2000), a wetland module, and an urban module. The time series outputs for eachgrid cell is then routed and attenuated to the nearest stream and then through the entire streamnetwork of the watershed. The figure below shows a flow diagram of the hydrologiccontaminant transport modeling component of the overall WAM model.

Field Model Parameters Files

Unique LU/SoilGrid Cell

Coverages

CellLoads

CumulativeLoads

SJR-WAMINTERFACE(Algorithms& SubModelsExecuted)

SJR-WAMOutputs andIntermediatefiles

Data InputsDatabases

GIS Coverages

AttenuationCoefficients

DistanceCoverage

Land Use Topography

Unique Parameter

Sets

Land Attenuation PreProcessing

Stream Reach Flow Rates &

Concentrations

GIS Coverage

ASCII Datefile

Interface Operation

Stream Routing Network

River Outlet Stages

Hydrography Subbasins

Land Use(LU)

Soils

Rainfall Zone (new)

Land Use

Soils

Default Values

BUCSHELL BLASROUTE

Create/Link Model

Parameter Sets

Simulate UniqueCells for Load

Estimates

Overlay Coverages

Attenuate toStreams

Stream Routing

Fortran SubModel

LEGEND

Edit Land Use& Display I/O Files

Generate Attenuation Distances

Climatic Data

Dynamic Modeling Process

GIS MODEL INTERFACE

Getting Started

The WAM interface has been documented inprevious publications. WAMView was developedto bring WAM to the average personal computeruser. WAMView was written for ArcView 3.2 (orhigher) with Spatial Analyst 1.1 (or higher). Theprogramming language known as Avenue isprovided by ArcView and allows complexfunctions and menu manipulation. ArcView itselfcomes with many features that users have becomeproficient on and accustomed to. The concept ofWAMView is to leave the existing functionality ofArcView for the more experienced users and to add the WAM functions that were developed inthe original Arc/Info version of WAM. The ArcView interface is modified in a way, however,that simplifies its use and does not require extensive experience with ArcView.

The interface begins with a dialog box that shows the user a list of previously saved projectsalong with the attributes of each project. This is called the Project Manager and provides a meansto track, delete, open or create new projects. Pertinent information is stored about each projectincluding the name, basin, date, user name and a project description. When creating a newproject the user is prompted for this information. After the project information is entered, the

user is then prompted to graphically select a primary basin for analysis. A map (or coverage) ofthe available primary basins is presented for the selection. A primary basin is defined as acollection of subbasins that discharge to a common waterbody via a network of streams, sloughs,ditches, etc. The user simply clicks on to the desired primary basin.

When the primary basin is selected, an ArcView layout appears that includes dual view ports,legends and a tool palette. The dual view ports are provided to allow for side by sidecomparisons of land use scenarios, but could also be used to compare land use or soils withmodel output to visually observe the relative effects each have on the model results. By default,subbasins are shown with existing vs modified land use scenarios. The tool palette provides basicpanning, zooming and other mapping options including overlaying base maps such as roads,county boundaries, etc. The zooming and panning tools are designed to perform simultaneouslyon both view ports.

The Map Options tool allows the user tochange the GIS coverages in the display. MapOptions includes two basic choices for eachview port. The land use scenario can beexisting or modified. By default, when a newproject is opened, the modified land usemodel output coverages are equal to theexisting land use scenario and will remainsuch until the land use is modified by the userand the model has been run.

In Map Options the map coverage can be avariety of GIS coverages including modeloutput for several pre-run water quality parameters. The user can display any two of the providedcoverages such as subbasins, land use, soils, or topography. The user can view output in a varietyof coverages as discussed later in this paper.

WAMView includes all of the standard tools and optionsfamiliar to most ArcView users. A new menu item,however, has been added to provide functions specific toWAMView and familiar to WAM users. The optionsbegin with three methods to create a modified land usescenario. The remaining options allow the user to runthe model and view the output.

Modifying Land Use

There are three methods providedto create a modified land usescenario. One or all three methodscan be applied to create a news c e n a r i o . S e v e r a l B e s tManagement Practices (BMPs)can be applied that are developedspecifically for individual regions.BMPs may include reducedfert i l izer applicat ions orstormwater retention, for example.The available BMPs are land usedependant and may includeseveral BMPs per land use.

Land use swapping is useful forassessing government incentiveprograms to encourage landowners to change their land use orpractices. Both options (ApplyingBMPs and Land Use Swapping)apply changes at a global scalewithin the selected primary basin.The changes are applied by altering the land use code numbers.

The final option to modify land use involves editing individual land use with a variety of tools.Paint shop type tools are provided to allow the user to literally paint on a selected land use.

The user can select from a list of available land uses and draw shapes onto the existing (orpreviously modified) land use coverage. Land uses with BMPs can also be selected and added tothe coverage which provides a means to include land uses both with and without BMPs. The filltool can be used to change an individual land use with one click of the mouse button. BMPs toindividual agricultural or urban developments can be added with the same ease and specificity.

Creating and Viewing Model Output

After the desired land use changes are made, the water quality model can be run. This isaccomplished from the WAM functions on the main menu. WAMView creates a list of uniqueland use, soil and rainfall zone combinations based on the modified land use coverage. Theinformation is compiled into a format needed for the BUCSHELL and BLASROUTE models.The models are then run sequentially. A DOS window will appear showing specific screenoutput for each model and a prompt will appear in ArcView instructing the user to press ’OK’when the models are complete. This pauses the interface while the models are running. TheDOS window will close when the models are complete.

There are three basic options for viewing model output maps, tables and graphs. Map Optionscan be used to begin viewing the results as GIS coverages. Output coverages include SolublePhosphorus (P), Soluble Nitrogen (N), Total Suspended Solids (TSS), Sediment P and SedimentN. When selecting an output coverage, two sets of options are available: Attenuated vs.Unattenuated and Average Subbasin Load vs. Source Load. Attenuation represents loadreduction (in most cases) based on the physical processes that occur as the runoff moves viaoverland flow wetland conveyance. Selecting Unattenuated provides the estimated load at the

source of the runoff. Average Subbasin Load represents the mean value of a parameter overeach subbasin. The resulting map will include one value per subbasin. Selecting Source Loadprovides a map with values placed on the grid cell where the runoff originated (attenuated orunattenuated).

The table manager provides a means of viewing the results in tabular form. The table managerincludes features to list, view, create and delete tables specifically created in WAMView. Themanager itself keeps track of tables specifically created by WAMView and will list them as

Currently SavedTables. There aretwo basic choiceswhen creating atable. The averageannual loads reflectsummaries of theoutput coverages.The reach timeseries includeshydro-dynamically

modeled output fora selected streamreach. The averagea n n u a l t a b l e sinclude choices tosummarize the databased on subbasinsor land use ,

attenuated or unattenuated. The user then selects a parameter. The resulting table includes ac o m p a r i s o n o fexisting and modifiedland use scenarios

The time series tablesinc lude choicesregarding land uses c e n a r i o a n dreporting interval.The user can enter areach number, ifknown, or pressselect reach and

select from a varietyof reaches availablewithin the primary

basin. The resulting table includes a complete list of the modeled parameters along with theestimated flows.

The final output option includes graphs of the time series data. Because of ArcView s limitedgraphing capabilities, WAMView has been designed to open the graphs in Excel. The user isagain provided with a means to enter or select a reach. After the reach is selected, the model willautomatically open Microsoft Excel and apply a macro to insert the model output datasets intopre-configured graphs of runoff, nitrogen, TSS and phosphorus.

SUMMARY AND CONCLUSIONS

WAM, a GIS watershed model, developed to perform water quality, wetland and flood pronenesswatershed assessments, has been compiled for ArcView users on a standard PC desktop.WAMView allows engineers and planners to create new modified land use coverages bychanging site specific land uses and/or applying Best Management Practices through the use ofgraphical user interface. The user can then run water quality models and compare the results

and WAMView or contact SWET, Inc. tollfree at (888) 881-8507 for additional information.

REFERENCES

Cooper, A.B. and A.B. Bottcher. 1993. Basin Scale Modeling as a Tool for Water ResourcePlanning. Journal of Water Resources Planning and Management, Vol. 119. No. 3. pp306-323.

Bottcher, A.B, J. Hiscock, N.B. Pickering, and R.T. Hilburn. 1998a. WAM-WatershedAssessment Model. Proceedings of Watershed Management: Moving from Theory toImplementation. Water Environment Federation, Alexandria, VA

Bottcher, A.B, N.B. Pickering, and A.B. Cooper. 1998b. EAAMOD-FIELD: A Flow andPhosphorous Model for High Water Tables. Proceedings of the 7th Annual DrainageSymposium. American Society of Agricultural Engineers, St. Joseph, MI.

Knisel, W. G. 1993. GLEAMS: Groundwater Loading Effects of Agricultural ManagementSystems. UGA-CPES-BAED Publication no. 5.

Mock, Roos & Associates. 1997. Quantification of P-enriched Tributary Sediment Report.Deliverable #7. Report to the South Florida Water Management District.

NIWA. 1999. Sediment Runoff from the Catchment of Okura Esturary. National Institute ofWater and Atmospheric Research Ltd. Hamilton, New Zealand. NIWA Client Report: ARC90241/1.

SWET. 1998. GIS Watershed Assessment. Final Report to the Suwannee River WaterManagement District. Live Oak, FL.

side-by-side with other land use scenarios. The model provides maps, tables and graphs forvarious nutrients.

WAM provides an excellent tool for regional planners to determine and rank current areas underenvironmental stress, estimate future impacts of land use management decisions, set achievablepollution load reduction goals and establish Total Maximum Daily Loads (TMDLs).

ADDITIONAL INFORMATION

Please visit our website at www.swet.com to download PowerPoint demonstrations of WAM

SWET. 2000. Development of Grid GIS Based Simulation Models for Lower St. Johns RiverBasin (LSJRB) Hydrologic/Water Quality Assessment. Phase 2 Final Report to the St.Johns River Water Management District. Patlaka, FL. Report includes a User Manual.

SWET. 1999. EAAMOD Technical and User Manuals. Final Reports to the EvergladesResearch and Education Center, University of Florida, Belle Glade, FL. Also availablefrom www.swet.com.