| Guizhou lies in subtropic mountainous region which consists of plateau karstlandforms and karst canyon. Guizhou belongs to humid subtropical monsoon climate,with the annual average temperature of15℃to18℃and annual rainfall of1100mm to1400mm. However, the exceptive mountainous topography of Guizhou leads to lowavailability of water resources. As a result, agriculture in the mountain area still heavilyrelies on the rainfall. The water conservancy facilities constructed in the last century areaging and lost their usefulness, which can not meet water demands at present. To solvethese problems, we can make use of karst depression as the reservoir basin and buildflood ditch to collect flood water from surrounding moutain, and use water-savingirrigation methods. This paper shows the design of the Dangba Reservoir project atQiaojia Town,Yanhe County, Guizhou Province to prove this layout..The Dangba Reservoir project is located in an area of the typical karst mountainoustopography, where catchment concaves of different sizes develop and no surface riverflows. Considering water demand of the Qiaojia town and the local hydrogeologyconditions, the Dangba concave with suitable size is chosen as the reservoir basin. Thedrainage area upstream the dam site is0.812km2, with an average annual inflow of413000m3that is far from meeting water demand of7706people and3100muirrigation farmland. Therefore, four diversion canals were designed to collect waterfrom adjacent mountain spring and flood with the recurrence period of five yearstoincrease the reservoir inflow. Tatal length of diversion canals is10.98km, thecatchment area is1.85km2, and average annula inflow is751000m3. As a result, annualwater suppy of the Dangba reservoir can increase to845300m3. Three karst conduit(K1, K2and K3) and one aven (K8) develop in the left bank of the reservoir, and oneaven in the right bank (K5). Most areas on the right bank and the bottom of reservoirhave a weak karst water-resisting layer,安and there is no problem of karst leakage.However, the left bank and tail area of the reservoir have strong to moderate karstdevelopment layer, and reservoir leakage can occur through the karst conduits andfractures. Therefore, reservoir seepage control design adopts the comprehensivetreatment measures of blocking the bank slope fracture, plugging holes, and localcurtain wall ". There is no natural watercourse for flood drainage. In order to ensure the security of production and living of downstream residents, and to prevent soil erosioncaused by flood, flood will be drained through the spillway chute in the left bank to theunderground river (K7), then to the Erdang River. Water resource in the reservoir isextremely valuable, and the water will be transfered through the pipeline. Although theproject investment increased, the water transfer through pipeline will increase the wateruse efficiency and water security.This study would contribute to improve the water use efficiency in karstmountainous areas which can not build medium-sized water conservancy project. |
