中文摘要：

从湿周-流量曲线临界点的两种不同确定准则入手，分析湿周法推求河道内最小生态需水量（minimum ecological instream flow requirements，简称MEIFR）的不确定性。假设河道呈三角形断面和均匀流．得到湿周法的解析解表达式。表达式显示斜率法（曲线上斜率为1）和曲率法（曲线上曲率最大）二者所得的MEIFR结果迥异。当斜率法取斜率为0.39时，其相应的流量与曲率法结果一致。MEIFR对斜率临界值非常敏感．斜率法中的斜率临界值难以确定．相比而言．曲率法更可靠。这用近似具有三角形断面的南水北调西线一期工程调水区流域的实际数据得到证实。根据我们在该区实地观测和收集的6条河35个河道断面的水深和水宽资料．用解析解估算出各断面的MEIFR。曲率法所估算的MEIFR结果为多年平均流量的2．5％～23．7％．大部分数据溶在Tennant法的10％-30％的范围。斜率法为11％～105．7％．普遍偏大，超过这个范围。虽然采用较小的斜率临界点可使斜率法的估算结果变小．然而到底斜率临界点应取何值存在较大的不确定性．这进一步说明．在无法获得一个确定的斜率临界值的情况下，湿周法估算MEIFR宜采用曲率法确定临界点。本文的结果基于理想情况．更普遍的结论有待于对更多种河道断面的探讨。

英文摘要：

By comparing the two techniques to determine the critical point on the relationship curve between wetted perimeter and discharge for the estimates of the minimum ecological instream flow requirement （MEIFR）, the uncertainty of the wetted perimeter method is analyzed. Under the assumptions of the triangular cross section channel and the uniform stable flow, an analytical solution of MEIFR is deduced. It is clearly shown that the results of MEIFR based on curvature technique （corresponding to the maximum curvature） and slope technique （slope being 1） are significantly different. It is found that the slope of the transition point with the maximum curvature is 0.39 and the MEIFR varies prominently with the variation of the slope threshold. This notes that if a certain value of the slope threshold is not available in the slope technique, the results of MEIFR via curvature technique by the wetted perimeter method are more certain. By applying the analytical solution of MEIFR in the rivers of Western Route South-to-North Water Transfer Project in China, it shows that the MEIFR value via curvature technique is 2.5%-23.7% of the multi-year average annual discharge, while that for slope technique is 11%-105.7%. This paper starts the research from the simple triangular cross section channels. More general conclusions rely on the more detailed research on various sections.