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(一) 概說: 由于大規模的羣众性水利工程及水土保持措施,显著地改变了流域自然面貌及逕流条件,对洪水逕流起了很大的控制作用。华北地区年雨量約70～75%集中于汛期,其河流属于干旱地区間歇性河流。汛期由于流域作了蓄水工程及各种水土保持措施,使河流汛期的洪水逕流量大为減少。这些減少的水量,一部分用于增加和补給河流枯季逕流,另一部分水量却形成深层地下水以及增加了水面蒸发、植物散发,因此枯季增加的逕流量要比
(I) General: Due to large-scale mass water conservancy projects and soil and water conservation measures, the natural appearance and runoff conditions of the watershed have been significantly changed, which has played a significant role in controlling flood runoff. About 70-75% of annual rainfall in North China is concentrated in the flood season, and its rivers are intermittent rivers in arid areas. During the flood season, due to the water storage project and various soil and water conservation measures, the flood runoff of the river during flood season is greatly reduced. These reduced amounts of water are partly used to increase and recharge dry season runoff of the river, while others form deep groundwater and increase water surface evaporation and plant emission, thus increasing the runoff during the dry season