西南丘陵区小流域蓄水池优化选址

    Optimization of ponds allocation in small hilly watershed in Southwestern China

    • 摘要: 该文以保证蓄水池合适的汇水面积和实现最大程度自流灌溉为目标,同时考虑了丘陵地区地形高差的"天然优势",提出了丘陵地区蓄水池选址的方法。在研究区地形数据和研究时段降雨数据的基础上,以保证200 m3蓄水池汇流量和流域作物7至10月份灌溉需水量为目标,通过设置合理的集水工程选址约束条件,利用ArcGis水文分析、叠置分析及空间查询等空间分析工具筛选出65处适合修建200 m3蓄水池的位置。经计算得到蓄水池平均汇水面积为0.31 hm2,在当地降雨条件下能够保证200 m3蓄水池的汇水量。选址优化后蓄水池能够对流域内近50%的农田进行自流灌溉,较好地实现了保证蓄水池灌溉效用和降低灌溉成本的统一。该选址方法可指导丘陵地区土地整理项目规划阶段不同规格蓄水池的选址,也可为其他类型雨水集蓄工程选址提供借鉴。

       

      Abstract: Abstract: The annual rainfall in southwestern China is usually abundant in hilly areas. Nevertheless, due to the effects of terrain and disproportional rainfall distribution, the efficiency of rainwater use for farmland irrigation is actually low. Coupled with the weak storage capacity and the lack of water reservation projects, the severe shortage of water appears in some districts. As for ponds widely applied in hilly area, the phenomenon frequently occurs that large idle capacity and severe overflow lead to low irrigation utility. Moreover, gravity irrigation is regarded as a general requirement for newly-built ponds so as to reduce cost of pumping irrigation. This paper discusses an optimized allocation method of ponds under the primary goals of relatively adequate rainwater harvest for pond-irrigating and maximum gravity irrigation rate in a hilly watershed. The method takes the natural advantage of terrain elevation difference of hilly areas into account.Based on the actual situation of study area, the pond-irrigation was set to aim at meeting the water requirement of fruiters, vegetables and dry crops from July to October. With the terrain data, the hilly watershed was divided into 38 catchment areas by hydrological analysis tool in ArsGIS software. The crop irrigation schedule from July to October was determined by referring to technical code for rainwater collection, storage and utilization. Then the actual irrigation requirement in each catchment area could be calculated with the crop cultivated area being computed respectively. Given the local annual average rainfall from July to October, the minimum threshold was calculated to guarantee the rainwater harvest for 200 m3 pond, with which the catchment path of the small watershed was extracted based on the surface runoff-flowing model. Meanwhile, the appropriate number of 200 m3 ponds to build in each catchment area was figured out to meet the crop irrigation requirement from July to October with reference to the irrigation schedule. Finally, the allocation of ponds would be optimized by setting rational allocation constraints as follows: firstly, slope of the site should be smaller than 5 degree; secondly, the pond should be built within 500 m from rural residential areas, 100 m from crop areas and 100 m away from land for mining and industry; thirdly, the sites would lie along the first level catchment path to avoid the overlap of the water water-collecting area between the adjacent ponds and the higher position would be given priority to with the two constraints above satisfied. Fourthly, if the number of sites matching the first three constraints was larger than the appropriate number to be built, the higher position site would be preferred. The suitable pond sites are screened in the catchment path with ArcGIS spatial analysis. 65 sustainable sites for 200 m3 pond are selected using this method. The average water-collecting area of all the pond sites was estimated to be 0.31 ha and prospected to guarantee the relatively adequate rainwater harvest of 200 m3 pond under the condition of rainfall in study area. Furthermore, the gravity irrigation rate of farmland within the watershed came to nearly 50%, showing that the method contributes to reduce the irrigation cost. Additionally, the method can provide guidance for the allocation of pond in different specifications and reference for other kind of rainwater harvesting engineering in land consolidation project planning in hilly areas.

       

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