Rainfall Losses: Difference between revisions
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“Evaporation data is usually required for reservoir studies, particularly for low-flow analysis. Reservoir evaporation is typically estimated by measuring pan evaporation or computing potential evaporation”.<ref name="EM 1110-2-1420">[[Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420) | EM 1110-2-1420 Hydrologic Engineering Requirements for Reservoirs, USACE, 1997]]</ref> | “Evaporation data is usually required for reservoir studies, particularly for low-flow analysis. Reservoir evaporation is typically estimated by measuring pan evaporation or computing potential evaporation”.<ref name="EM 1110-2-1420">[[Hydrologic Engineering Requirements for Reservoirs (EM 1110-2-1420) | EM 1110-2-1420 Hydrologic Engineering Requirements for Reservoirs, USACE, 1997]]</ref> | ||
“Evapotranspiration (ET) is difficult to estimate because it is a complex process. It is determined by the atmospheric demand for water vapor (potential ET) and the availability of water to be evaporated. ET is a sum of pure evaporation from free water surfaces, such as wet vegetation, puddles, and lakes, and the transfer of soil moisture through plants and out their leaves (transpiration). The former process depends only on the atmospheric conditions (temperature, humidity, wind), whereas the latter also depends on plant characteristics (stomatal resistance) and on soil moisture availability”.<ref name="NEH210-630-20">[[National Engineering Handbook | “Evapotranspiration (ET) is difficult to estimate because it is a complex process. It is determined by the atmospheric demand for water vapor (potential ET) and the availability of water to be evaporated. ET is a sum of pure evaporation from free water surfaces, such as wet vegetation, puddles, and lakes, and the transfer of soil moisture through plants and out their leaves (transpiration). The former process depends only on the atmospheric conditions (temperature, humidity, wind), whereas the latter also depends on plant characteristics (stomatal resistance) and on soil moisture availability”.<ref name="NEH210-630-20">[[National Engineering Handbook Hydrology: Chapter 20 Watershed Yield | National Engineering Handbook Hydrology: Chapter 20 Watershed Yield, NRCS, 2009]]</ref> | ||
“Many models are available for estimating potential evapotranspiration from meteorological data (Jensen, Burman, and Allen 1990; ASCE 1996). They vary in their assumptions, the processes described, the input data required, and the temporal scale for which they are appropriate. Potential ET can also be estimated from pan evaporation data if suitable pan coefficients are available” <ref name="NEH210-630-20" /> | “Many models are available for estimating potential evapotranspiration from meteorological data (Jensen, Burman, and Allen 1990; ASCE 1996). They vary in their assumptions, the processes described, the input data required, and the temporal scale for which they are appropriate. Potential ET can also be estimated from pan evaporation data if suitable pan coefficients are available” <ref name="NEH210-630-20" /> | ||
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==Best Practices Resources== | ==Best Practices Resources== | ||
{{Document Icon}} [[Flood Hydrology Manual|Flood Hydrology Manual (Bureau of Reclamation)]] | {{Document Icon}} [[Flood Hydrology Manual | Flood Hydrology Manual (Bureau of Reclamation)]] | ||
{{Document Icon}} [[ | {{Document Icon}} [[National Engineering Handbook: Chapter 7 - Hydrologic Soil Groups | National Engineering Handbook: Chapter 7 - Hydrologic Soil Groups (Natural Resources Conservation Service)]] | ||
{{Document Icon}} [[ | {{Document Icon}} [[National Engineering Handbook: Chapter 9 - Hydrologic Soil-Cover Complexes | National Engineering Handbook: Chapter 9 - Hydrologic Soil-Cover Complexes (Natural Resources Conservation Service)]] | ||
{{Document Icon}} [[ | {{Document Icon}} [[National Engineering Handbook: Chapter 10 - Estimation of Direct Runoff from Storm Rainfall | National Engineering Handbook: Chapter 10 - Estimation of Direct Runoff from Storm Rainfall (Natural Resources Conservation Service)]] | ||
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Revision as of 19:46, 21 October 2022
“Evaporation data is usually required for reservoir studies, particularly for low-flow analysis. Reservoir evaporation is typically estimated by measuring pan evaporation or computing potential evaporation”.[1]
“Evapotranspiration (ET) is difficult to estimate because it is a complex process. It is determined by the atmospheric demand for water vapor (potential ET) and the availability of water to be evaporated. ET is a sum of pure evaporation from free water surfaces, such as wet vegetation, puddles, and lakes, and the transfer of soil moisture through plants and out their leaves (transpiration). The former process depends only on the atmospheric conditions (temperature, humidity, wind), whereas the latter also depends on plant characteristics (stomatal resistance) and on soil moisture availability”.[2]
“Many models are available for estimating potential evapotranspiration from meteorological data (Jensen, Burman, and Allen 1990; ASCE 1996). They vary in their assumptions, the processes described, the input data required, and the temporal scale for which they are appropriate. Potential ET can also be estimated from pan evaporation data if suitable pan coefficients are available” [2]
“Even if potential ET is adequately estimated, the actual ET is less than or equal to this amount and depends primarily on soil moisture availability. Because of this interplay between the atmospheric demand and the soil moisture, determining the actual ET is problematic without a detailed hydrologic model operated at a short time step (i.e., a day or less). If adequate assumptions can be made, however, reasonable estimates of actual ET as a fraction of potential ET are possible”.[2]
Best Practices Resources
Flood Hydrology Manual (Bureau of Reclamation)
Citations:
Revision ID: 4000
Revision Date: 10/21/2022