Hydrology – 18 WATER BUDGET – LIMITS OF ACCURACY

Hydrology of Crater, East and Davis Lakes, Oregon by Kenneth N. Phillips
 CRATER LAKE

 

WATER BUDGET

LIMITS OF ACCURACY

The water budget was computed chiefly on the basis of hydrologic data for the water year ending September 30, 1962. Some of the factors are based in part upon personal judgment and are subject to some error even for 1962. The relationships found are subject to further error when extended to other years and other lake stages. For a single year, the relationships given may be in error as much as 10 percent, but on the average they are probably accurate within 5 percent. Hydrologic data obtained in the year ending September 30, 1963, were used in the following table to test the overall accuracy of the water budget deduced from the data of 1962.

Test of water budget for Crater Lake, year ending September 30, 1963
 index.8

On the basis of observed precipitation and estimated seepage loss and evaporation, the computed rise in lake level for the 12-month period was 0.18 foot, exactly the same as the actual recorded rise. Such a close agreement is fortuitous, because the water budget can never be known so closely. Similarly, a computation of the water budget for the year ending September 30, 1964, showed a computed decrease of 0.34 foot in water level (actual decrease, 0.58 ft). For 1965, the computed rise was 2.16 feet (actual rise, 1.83 ft). These errors for each year are less than 4 percent of the gross water supply.

The accumulation of additional hydrologic data will provide a means of refining the water budget given herein. Continuous records of lake level are needed, especially at very high and very low stages.

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