Water-Surface Evaporation in Reservoir Vitoon Thititanapak December 1999

Acknowledge Dr. David G. Tarboton Mark Winkelaar

Objective To study the effect of evaporation in reservoir. To apply GIS technique in the analysis of the water-surface evaporation.

Conceptual Map Theory Study Data collection TOOL Arc View 3.0 SINMAP The role of evaporation in reservoir ( water-surface evaporation) The method for measuring the evaporation Data collection DEM from USGS RF1 from EPA Dam site from GIS DATA DEPOT and EPA Pan – evaporation data from NOAA Technical Report NWS 33 TOOL Arc View 3.0 SINMAP TARDEM

Theory study Estimating Free-Water Evaporation 62 % of precipitation fall on the land - 97 % is evapotranspiration - 3 % is open-water evaporation Estimating Free-Water Evaporation - Water-Balance Approach - Mass-Transfer Approach - Energy-Balance Approach - Penman or Combination Approach - Pan-Evaporation Approach ( Class-A pan)

Data collection - DEM grid file from USGS http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html - rf1 shape file and Dam site shape file from EPA http://www.epa.gov/OST/BASIN/ - Dam location USGS digital raster graphics http://www.gisdatadepot.com/ - Pan evaporation data from NOAA technical report NWS 33

Step 1: Study area Middle Bear Basin Cutler Dam The Albers Equal-Area projection Middle Bear Basin Cutler Dam

Step 2: Add DEM grid files

Step 3:Locating Dam as outlet grid Newton Dam

Step 4:Find water-surface area

Step 5:Calculate water-surface evaporation Evaporation = Number of cell count x cell size x pan coefficient x Class-A pan evaporation data * from National Oceanic and Atmospheric Administration Technical report, Office of Hydrology National Weather Service, June 1982 **Map 4: Map of coefficients to convert Class A pan evaporation to free water surface evaporation for May - October

Evaporation in Cutler Dam, Utah U.S.A. Result Evaporation in Cutler Dam, Utah U.S.A. At elevation +1344.00 m Number of cell count = 13910, Cell size = 30 x 30 m.

Conclusion We can apply GIS technique to find water-surface area in reservoir at the design water level. This technique is limited on GIS data (DEM elevation grid data) to find water-surface area. This method can apply to find the reservoir area in the dam construction project planning.

THE END THANK YOU