围湖垦殖对湖泊调蓄功能的累加效应分析

计算了长湖、洪湖在围垦前后湖泊容量在水位变化时的容量增长率和四个涝灾年份降雨条件下汛期湖泊水位逐日增加值，对四湖流域尚存的18个湖泊的围垦强度与容量损失情况进行了分析。结果发现，围垦后的长湖容量平均增长率、相对增长率、最大增长率分别从1.8436、0.1834、2.4979(10^8m^3/m）减少到了1.4321,0.1802,1.7569(10^8m^3/m0，洪湖容量平均增长率、相对增长率、最大增长率分别从5.8506、0.3000、6.5095(10^8m^3/m）减少到了3.3970、0.2900、3.4440(10^8m^3/m），围垦导致的湖泊容量损失随着水位上升呈加速增加趋势，随着围垦强度的增加呈加速增加趋势，围垦后这两个湖泊在同样降雨条件下的水位逐日增加值都有不同程度的增加且这种增加值随着雨量和围垦强度的增加而增加。18个湖泊容量变化率随着围垦强度的增加而增加且在围垦强度为40％左右时表现出门槛效应。表明围湖垦残对湖泊调蓄功能的影响具有明显的累加效应。从累加效应的角度对四湖流域围湖垦残的合理性和退田还湖问题进行了讨论。

CUMULATIVE EFFECT OF LAKE RECLAMATION UPON THE FLOOD STORING IN CHANGHU AND HONGHU LAKES

The increase rate of the volume of Changhu and Honghu before and after reclamation was calculated with the determination of the change of the rate in relation to daily water levels in four bigger flood periods. The correlation between the reclamation intensity of the 18 lakes remained in the Sihu basin and their loss in volume was analyzed. We can see that the mean increase rate in volume of the Changhu, as the water levels increase, change from 1.843 6, 0.183 4, 2.497 9(10\+8m\+3/m)to 1.432 1, 0.180 2, 1.756 9(10\+8m\+3/m)respectively after reclamation, and in Honghu, from 5.850 6, 0.300 0, 6.509 5(10\+8m\+3/m)to 3.397 0, 0.290 0, 3.444 0(10\+8m\+3/m). The losses in volume induced by reclamation accelerate increase as the water levels and the reclamation intensity increase. The daily increase in water level of the two lakes increase after reclamation under same conditions of rainfalls, and the increase continues with the increase of falls and reclamation intensity. The rate of loss in the volume of the 18 lakes increase with the reclamation intensity, and there is one marked threshold when the reclamation intensity is about 40%. So it was proved that there were cumulative impacts on the floodwater storing in the lakes after the reclamation of these lakes. Evalations as how to reclaim and to restore the lakes were discussed.