CN Approach to Water Budgets for Small Watersheds

Westphal, Jerome A.; Thompson, David B.; ,

CN Approach to Water Budgets for Small Watersheds

by Jerome A. Westphal, Univ of Missouri-Rolla, Dep of Civil, Engineering, Rolla, MO, USA,
David B. Thompson, Univ of Missouri-Rolla, Dep of Civil, Engineering, Rolla, MO, USA,

Document Type: Proceeding Paper

Part of: Water for Resource Development

Abstract:

In some states, issuance of a surface mining permit is dependent upon an assessment of the current hydrologic baseline of the area to be mined and of the probable future impacts of mining and reclamation. The approach described establishes an artificial baseline predicated on normal annual rainfall, normal annual evapotranspiration (ET) and a Soil Conservation Service Curve Number (CN) which is representative of pre-mining watershed conditions. The method involves Monte Carlo generation of daily rainfalls each month until the commensurate monthly normal is achieved. The CN equation is then used as a forcing function to determine a CN which makes runoff events sum to the difference between annual rainfall and annual ET. Computed monthly ET surpluses and deficits are taken to be changes in soil moisture storage. Limited tests of this procedure using Missouri data yielded CN's within the expected range.

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