4waterbalance&globalhydro1

4waterbalance&globalhydro1 - A water budget is an...

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Water Budgets A water budget is an attempt to “follow the water” or account for the movements and transformations of water in a watershed or region.
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Input (precipitation, groundwater inflow) Storage (soil, Surface waters Groundwater) Output (evapotranspiration streamflow, groundwater outflow) Mass Balance: Input – Output = Change in Storage
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Physical Hydrology , Dingman 2002 Major terms of a water budget Precipitation and stream flow are routinely measured in many areas, reported in inches (or mm) and cubic feet per second (or cubic meters per second) Evapotranspiration is measured in a few places and can be estimated from meteorological data. It may be reported in a range of units, including watts per square meter. Changes in storage are not routinely reported but can be estimated from changes in lake levels, changes in soil moisture, etc. Continued…
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Terms of a water balance, continued Groundwater flows are measured in a few places, based on monitoring wells, tracer studies and flow models. Results are not routinely reported and may be reported in any of a number of different units. Constructing a complete water budget is not a trivial exercise: 1) water inputs and outputs are often reported in different units of measure and different time periods 2) data on some important flows may not be available The problem of different units of measure is relatively easy to deal with. Addressing information gaps may require significant investment in measurement, but in some cases a partial water budget can provide an approximation of the unmeasured flows.
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Simplified Long-term Water Balance can be useful for estimating Evapotranspiration: Input – Output = change in storage Input = Precipitation + Groundwater input = P + G in Output = Evapotranspiration + Stream Flow + Groundwater Output = ET + Q + G out P + G in (ET + Q + G out ) = S In many, but not all, instances, the long term difference between groundwater inputs and outputs are is small compared to other terms, and in such conditions, the water balance can be simplified by assuming the difference between G in and G out is essentially zero. Change in storage (soils, reservoirs, lakes and
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This note was uploaded on 12/25/2010 for the course GLY 4288 taught by Professor Root during the Fall '10 term at FAU.

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4waterbalance&globalhydro1 - A water budget is an...

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