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RGDSS Memorandum <br />Final <br />TO: Ray Bennett <br />FROM: Ed Armbruster, Hydrosphere <br />SUBJECT: RGDSS Surface Water, Task 6.1 -Define Drainage Areas, Develop <br />Proration Factors and Prepare Basin Map <br />DATE: November 4, 1999 <br />CC: Randy Seaholm <br />Introduction <br />This memorandum represents delivery associated with Task 6.1, Define Drainage Areas, Develop <br />Proration Factors and Prepare Basin Map. The objective of this task is as follows: <br />Develop Arc Uiew coverage that shows the drainage area associated with each key <br />streamflow station. Identify ungaged locations where streamflow data is required, and <br />develop proration factors. <br />The RGDSS StateMod model requires the development of baseflows at key locations within the <br />Rio Grande basin. These locations include stream gage stations as well as ungaged points at <br />which stream flows are required for simulation. <br />Baseflows at gaged locations are computed using a mass balance computation. The mass balance <br />calculation adjusts the observed flow at a gage by removing the effects of all upstream diversions, <br />return flows, imports, exports, change in reservoir storage content, and evaporation. <br />Baseflows at ungaged locations are calculated by prorating the observed gains between upstream <br />and downstream gages. This proration is based on the basin area and historical average <br />precipitation at the gaged and ungaged locations. <br />Therefore, the basin area and average basin precipitation must be developed for each gaged <br />baseflow location, and the incremental basin area and incremental basin precipitation must be <br />developed for each ungaged baseflow location. <br />The following is a description of the methods and information used to determine drainage basin <br />areas, average precipitation and the resulting proration factors. <br />Topographic, Streamflow Station, and Precipitation Mapping <br />The primary files used by Hydrosphere for the Geographic Information System (GIS) mapping of <br />basin areas, baseflow areas, stream gages and other baseflow points included: <br />• riversd3.shp <br />• contours.shp <br />• gages.shp <br />• headgates.shp <br />• precip_d3.shp <br />C:\cdss\Task6-l.doc Drainage Areas and Pro <br />geographic location of rivers, streams, creeks <br />topographic contour lines <br />geographic location of stream gages <br />geographic location of diversion headgates <br />average annual precipitation <br />ration Factors November 4, 1999 -Page 1 of 1 ] <br />