Characteristic of variations of surface runoff and groundwater recharge in the middle Helhe River valley, northwestern Gansu, China

Integrated stuay of a wealth of data from investigations indicates that, when the influence coefficient of human activities exceeds 37%, the surface runoff process changes from a natural process to a process influenced mainly by man-made interference, thus not only resulting in the considerable decrease of surface runoff in the lower reaches of the Heihe River but also causing the loss of the natural character of groundwater recharge and significant reduction of the recharge amount in the middle reaches. In addition, the groundwater runoff process is also influenced and its overflow decreases continuously, Furthermore, the eco-environment of the lower reaches is more severely short of water and degraded due to above variations, The key to solving the problem of the eco-environment in the lower reaches of the Heihe River valley is to regulate and control the safe water-diversion volume and improve the structure of plantation and develop water-saving agriculture in the middle reaches,