Runoff characteristics and influence of antecedent precipitation in Zhaitang Reservoir basin of the Yongding River

The “23·7” basin-wide rainstorm and flood process revealed certain correlation between incoming water at Zhaitang Reservoir on Qingshui River (a tributary of Yongdinghe River) and previous rainfall in the basin． To clarify the law between runoff yield and concentration of reservoir and previous rainfall in the basin, a hydrological model of Zhaitang Reservoir basin was constructed with HEC-HMS software． Runoff yield and concentration process of historical rainfall and flood events was simulated and analyzed． Data show that previous rainfall has a decisive impact on the timing of runoff yield． Average rainfall threshold for runoff yield in the basin is 45 mm, which this fluctuates depending on previous soil moisture content． Drier the previous soil is, larger the threshold becomes． Determination of critical rainfall threshold for runoff yield of the reservoir has important reference significance to understand the following: runoff yield and concentration law of the basin, rapid judgment of incoming water of the reservoir, flood dispatch and timing of related defense work arrangements．