沟塘组合除涝工程设计方法与应用

鉴于极端降雨事件增加和流域下垫面改变抬高排涝模数对传统沟道除涝工程形成挑战,该文结合塘堰滞涝功能提出了沟塘组合除涝工程技术及其设计方法。基于水文资料缺乏小流域的涝水形成规律,离散设计暴雨历时并假设离散时段内流量过程线符合三角形分布下,采用改进SCS模型和小流域汇流方程推求涝水流量过程线;采用水位-容积关系和堰流公式进行质量平衡演算设计塘堰工程规格。在淮北平原低洼区的农沟和斗沟尺度上组合堰宽分别为0.6和2 m的塘堰工程发现,3、5和10年一遇24 h设计暴雨下涝水流量峰值减少了25%以上,延迟了0.5~1 h,3或5年一遇设计暴雨除涝能力排水沟的除涝标准可分别提高到5或10年一遇。沟塘组合除涝工程为缓解排区和下游区域洪涝压力提供可选方案。

Design and application of drainage engineering in combination of ditch with ponds

Abstract: Drainage engineering technology combined with ditch and pond was proposed and its design method were developed to meet the challenge of increasing design discharge that had been caused by the increase of extreme rainfall events and variations of basin underlying surfaces. Considering drainage patterns and data shortage at small ungauged watershed, the design method consisted of the determinations of drainage criteria and drainage hydrograph, and the design of pond and weir sizes. Design storm amount was determined by the statistical analysis of long-term daily precipitation and local design return period, and the design storm duration, usually 24 h, was discretized based on storm temporal distribution (hourly) in local hydrology manual. Given that drainage hydrograph can be approximated by a triangular hydrograph at every discrete time interval, drainage hydrograph was synthetized each triangular hydrograph calculated with the improved SCS (soil conservation service-curve number) model and concentration equations every discrete time interval. Pond and weir sizes were estimated by the trial and error solution of the stage-storage function, weir equation and continuity equation, as the pond outflow rate was close to design drainage rate of the receiving ditch downstream. In the lowland of the northern Huaihe River Plain, the pond of 800 m2 was designed for combining with field ditch and installed with the weir of 0.6 m wide and weir coefficient of 1.28, which would be used to drain the runoff from the area of 0.06 km2. The pond of 26000 m2 was designed for combining with collector ditch and installed with the weir of 2.0 m wide and weir coefficient of 1.28, which would be used to drain the runoff from the area of 1.36 km2. The drainage engineering combined with the ditch and pond extended the time of concentration of 0.5 h for field ditch district and1 h for collector ditch district, respectively, under the return periods of 24 h storm of 3-year, 5-year and 10-year. The drainage engineering combined with the ditch and pond reduced peak storm flows of more than 25% under the return periods of 24 h storm of 3-year, 5-year and 10-year. Combined with the pond weir of 0.6 m wide and 0.7 or 0.85 m high, the drainage criteria of the field ditch could be increased from the return periods of 3-year or 5-year to the return periods of 5-year or 10-year, respectively. Combined with the pond weir of 2.0 m wide and 1.8 or 2.3 m high, the drainage criteria of the collector ditch could be increased from the return periods of 3-year or 5-year to the return periods of 5-year or 10-year, respectively. Drainage engineering technology combined with ditch and ponds could be an option to mitigate the flood damage of the drainage district and downstream. However, drainage engineering technology combined with ditch and ponds should be assessed for different weather and soil conditions, and the design parameters of ponds and weir should be evaluated to adapt different ditches and weather conditions. The effects of drought, flood and environment should be considered as the combined drainage engineering technology is used to control flood.