Estudo hidrológico em microbacia hidrográfica com regime de escoamento efêmero

Abstract

This study aimed to measure water balance, soil-moisture-related water uptake by plants, and the influence ofantecedem soil moisture on runofT and erosion, besides modeling the CN-SCS method for isolated rainfall events in a small-ephemeral watershed (1,03 ha). Data were collected from Nov/02 until April/03. Runoffwas evaluated using a Parshall flume with an automatic watersensor levei, meteorological data were measured using a compact weather station, soil moisture at the depths of 20, 50, and 80 cm were measured by electrical-resistance sensors, and the levei of water table, on the wetland área within the watershed, was monitored through piezometers. RunofT accounted only for 2.2% of the water balance, whereas evapotranspiration accounted for 51.6% of it. A logarithmic model relating water uptake by plants and soil moisture showed a criticai value at the soil moisture close to 76% of field capacity. Runoff and erosion were strongly affected by the antecedem soil moisture, with a maximum value of relative soil moisture at 0.90. CN-SCS method didnot produce goodaccuracy to estimate the runoffand peak discharge for individual rainfall events, resuking mean errors of 400% and 200%, respectively. The parameters of CN-SCS method showed high sensibility, meaning that they need some adjustment in order to be applied to individual rainfall events. Semi-conceptual models, based on rainfall characteristics and mean soil moisture on soil profile up to 80cm depth, were adjusted for initial abstraction, curve number, rising time, and ratio between falling time and rising time were applied to individual events, showing good accuracy. Those models can be reference for generating hydrological simulation models.