梯田蓄水效益估算方法探讨

目的]综合考虑梯田土壤性质、梯田形态及降雨雨型的差异，构建梯田蓄水保水效益的估算方法及框架。方法]运用土壤水库计算模型与入渗模型，探讨蓄满产流和超渗产流模式下梯田土壤水分的预测方法；基于Richards方程，分析不同田坎边界的土壤水分入渗二维分异。在此基础上，进一步对前峰型、均匀型、后峰型、阶梯型4种降雨雨型下产生的单一产流模式或2种产流模式均存在时土壤水分运动进行情景分析。结果](1)提出梯田蓄水效益分布式估算方法，计算单个梯田田块土壤最大蓄水容量(W_M);(2)对不同田坎类型的梯田而言，浆砌石坎梯田防侧渗效果最好，土坎梯田防侧渗效果最差，且孔隙大、密度小、修筑时间短的新土坎梯田比修筑时间长的土坎梯田在发生侧渗时损失水分更多；(3)得出不同雨型下蓄满产流的临界时间(t)。结论]该估算方法可大幅度降低对野外设施、设备的依赖程度，降低投入成本，借助野外调查采样，基于模型模拟估算梯田蓄水效益。此外，该方法可根据单个梯田田块蓄水效益分布式计算数据，在区域尺度上估算梯田蓄水保水效益，以期为不同区域梯田的蓄水效益估算提供参考。

Discussion on Estimation Method of Water Storage Benefit of Terrace

Objective] On the basis of considering the differences of soil property, terrace form and rainfall type, we aimed to establish the estimation method and framework of water storage and retention efficiency of terrace. Methods] By using soil reservoir calculation model and infiltration model, we explored the prediction methods of soil water distribution in saturation-excess runoff and infiltration-excess runoff. Moreover, based on the Richards equation, we analyzed the two-dimensional infiltration of soil profiles at different field and ridge boundaries. On this basis, we constructed the scenario of soil water movement under single runoff generation mode or two runoff generation modes under four types of rainfall patterns, including pre-peak rainfall, uniform rainfall, post-peak rainfall, and stepped rainfall patterns. Results] We proposed the distributed estimation method of soil water storage efficiency of terrace field, and the maximum water storage capacity (W_M) of soil in a single terraced field was calculated. For different types of terraces, the anti-lateral seepage effect of stone walled bench terrace was the best, and the anti-lateral seepage effect of earth banked terrace was the worst, and the new soil ridge terrace with large pores, small density and short construction time lost more water than the soil ridge terrace with long construction time. The critical time (t) of full flow production under different rain patterns was obtained. Conclusion] This estimation method could greatly reduce the dependence on field facilities and equipment, and reduce the input cost. With the help of field investigation and sampling, the efficiency of terraced water storage could be estimated based on model simulation. In addition, the method could be used to estimate the water storage efficiency of terrace on a regional scale according to the distributed calculation data of the water storage efficiency of a single terrace field, and provided a reference for the estimation of the water storage efficiency of different regional terraces.