1. Water-Surface Evaporation in Reservoir
Vitoon Thititanapak
December 1999

2. Acknowledge
Dr. David G. Tarboton
Mark Winkelaar

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

4. 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

5. Theory study Estimating Free-Water Evaporation
62 % of precipitation fall on the land
- 97 % is evapotranspiration
% 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)

6. Data collection - DEM grid file from USGS
- rf1 shape file and Dam site shape file from EPA
- Dam location USGS digital raster graphics
- Pan evaporation data from
NOAA technical report NWS 33

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

8. Step 2: Add DEM grid files

9. Step 3:Locating Dam as outlet grid
Newton Dam

10. Step 4:Find water-surface area

11. 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

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

13. 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.

14. THE END
THANK YOU