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Dames & Moore, 1999 - USDA Forest Service

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4.3.5 Basin Average Climatic Water Budgets<br />

Basin average monthly water balances or budgets were developed for the portion of the Railroad Creek<br />

watershed above Lucerne and the reach above RC-4 to evaluate the relationship between water inputs and<br />

outputs, including precipitation and glacial melt runoff (inputs), streamflow runoff and evapotranspiration<br />

(outputs). The water, budgets assumed that, over the long term. change in storage within the basin,<br />

consisting of changes in groundwater storage and storage as permanent ice and snow (glaciers) were<br />

negligible. The long term precipitation and temperature data for Holden Village were used to develop the<br />

long term water budgets, adjusted to represent either the entire watershed above Lucerne, or the watershed<br />

above RC-4. Table 4.3-6a presents the water balance results.<br />

The component parts of the water budgets are described by the equation:<br />

where:<br />

Q = streamflow runoff<br />

Q=P+M-ET-I+GW+CS<br />

P = precipitation<br />

. ,<br />

M = meltflow From glaciers and stored ice<br />

ET = evapotranspiration<br />

I - infiltration<br />

GW = groundwater<br />

CS = change in water storage in the watershed<br />

The change in storage within the watershed reflects groundwater recharge and discharge, and accumulation<br />

and melt of precipitation stored as snow. Within typical watersheds, storage conditions tend. to equalize<br />

over a period of years assuming climatic changes do not occur, or if so, the changes occur at a rate too slow<br />

to significantly impact watershed storage. Over the long term M, I, GW, and CS are assumed to equal zero.<br />

In completing an annual basin average water budget for Lucerne, some of the variables presented in the<br />

above equation were found not to be applicable. The annual basin average water budget was calculated<br />

based on long term average annual precipitation (USGS, 1984), and discharge measured at Lucerne was<br />

completed as a check on the monthly estimates bked on the following equation:<br />

where:<br />

P=Q+AET<br />

P = average annual precipitation for the basin (52 inches)<br />

Q = average annual streamflow runoff (42.5 inches)<br />

AET = average annual evapotranspiration (10.5 inches)<br />

G:\WPDATA\O05\REPORTSWOLDEN-ZUUbl-O.DOC<br />

17693-005-0 19Vuly 19. <strong>1999</strong>;4:S1 PM;DRAFT FINAL Rl REPORT<br />

DAMES & MOORE

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