CURVE NO. DEVELOPMENT STEP 8 Soils data, land use data, watershed data, and CN lookup table are used to develop curve numbers for use in the SCS Curve Number Method. The soils data and land use data must both be in raster or vector format, but not both. The CN lookup table defines which soil type and land use equal which curve number. The user may use the default table or create one to be imported to the tool. This step calculates a curve number and average impervious cover for each sub-basin. Texas A&M University Department of Civil Engineering Instructor: Dr. Francisco Olivera CVEN 689 Applications of GIS to Civil Engineering ABSTRACT Traditional methods of calculating parameters for hydrologic analysis are tedious and time consuming. Commonly data is derived from contour maps (USGS or survey data), land use maps, and soil maps. This process may be greatly expedited by the use of a geographic information system (GIS) and hydrologic preprocessing tools. PrePro2004, developed by Dr. Francisco Olivera, is a preprocessing tool for ESRI’s ArcGIS 9.0 which uses the spatial capabilities of GIS to create input data for HEC- HMS. Tools such as PrePro2004 reduce the amount computation time, which may save hours of work and reduce the cost of hydrologic studies. This project investigates the use of PrePro2004 to develop a hydrologic model within HEC-HMS compared to compare common manual methods. PREPRO 2004 BASIC STEPS 1.Gather data 2.Fill sinks, create FDIR grid, create FACC grid 3.Construct stream network 4.Add inlet, outlet, and/or reservoir 5.Delineate watershed 6.Extract HMS elements 7.Calculate parameters 8.Calculate curve numbers 9.Export data to IDM 10.Export IDM to HMS 11.Setup HMS project Step 1: Project Study Area. DEM, mask, and stream vector data were used as primary input. Step 2: Flow direction grid based on 8-direction pour-point method. Each cell drains to one of 8 adjacent cells in direction of steepest decent. Step 5: Delineate watershed based on flow direction and flow accumulation grids as well as stream data developed in step 3. Step 11: Basin model successfully input into HEC-HEC by use of ASCII files. APPLICATION PrePro2004 was used to delineate streams and watershed for Spring Creek, prior to the confluence with Lick Creek, in College Station Texas. The use of ProPro2004 was done concurrently with hand delineation and input parameter calculations as part of a flood hazard study for the Castlegate Subdivision in College Station, TX. The DEM was obtained from the USGS seamless website. Stream vector data was downloaded from US EPA Lower Brazos arc data. A grid mask was made based on the hand delineated study area to reduce computation time. Soils and landuse vector data were obtained from the City of College Station GIS department. Zoning data was used for landuse data for this application. HSG soils data (blue and green) and land use (pinks) were obtained for College Station. Basin comparison: PrePro2004 v. Hand Delineation RESULTS It was found that PrePro2004 greatly reduced computation time for the development of watershed parameters of HEC-HMS on a large scale watershed system. Hand delineation and development of parameters took days, where PrePro2004 analysis only took a few hours. Although the hand delineation and calculation of parameters will always be slightly different due to its ability of capture storm drainage pipes and curb and gutter systems, it is interesting to note that the two methods yielded similar watershed outlines (Figure 14). Other parameters, such as average slope and curve number, also were extremely similar for the two methods. CONCLUSION PrePro2004 works best for large non-urbanized systems. Urban settings may be more correctly modeled by adding more user defined outlets, creating additional sub-basins. It is difficult to accurately define watersheds with PrePro2004 on a small, development scale and for highly urbanized settings. Using a preprocessing tool such as PrePro2004 greatly reduces the time to develop watershed parameters for use in a hydrologic modeling system. Time saved in development of hydrologic models may reduce the overall project costs, increasing the profit margin for hydrologic studies. Study Area Pond: Greens Prairie SH6 HEC-HMS electronically simulate precipitation- runoff processes of dendritic watershed systems