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9th International Rainwater Catchment Systems Conference
"Rainwater Catchment: An Answer to the Water Scarcity of the Next Millennium."
Petrolina, Brazil - July 1999

Section 10: Rainwater Runoff Management

Paper 10.6

Practical Soil Science Applications for Estimating Runoff in Semiarid Regions

Flávio Hugo Barreto Batista da Silva, Antônio Cabral Cavalcanti & Lúcia Raquel Queiroz Nogueira
Embrapa Solos Nordeste
E-mail: cabral@embrapacnpsuep.com.br

Abstract

The evaluation of watershed water flow using traditional methods is a difficult task due to the high cost and the time needed to carry out the task. This work presents a safe and practical methodology by using the calculation of the L600 of a watershed taking into account the hydrological characteristics of the soils of Brazil's semiarid Northeast. The L600 coefficient corresponds to a model water depth with runoff on a specified soil class or map unit in this semiarid region, receiving about 600 mm of rain per year. This method allows a fast evaluation of the water resources in small watersheds in areas of Brazil's Northeast averaging less than 1,000 mm precipitation/year. The method is based on the determination of the runoff after applying a standard water depth (L600) on soil classes or soil map units present in a drainage watershed. The central values proposed for the L600 for the main soil classes of this region were obtained under an "average" natural condition. However, the calculation of L600 must be corrected for the vegetation cover, ponds upstream from the measuring station and other affecting factors, such as local subsurface geology, climate and landform characteristics. Experienced soil scientists are needed to adjust the measured results. One example for these adjustments, is the one for Planossolos where the standard results of 70 mm can vary from 10 to 125 mm when the variations on the depth of the A horizon is taken into account. This reduction is aggravated in a deeper and more exposed Planossolo found in the lower part of the toposequence.

PDF of full document (8pp, 190kb)


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