杭嘉湖三府受天目诸山之水,或径注于海,或入太湖,其间地势高洼不等。平原地带居江滨湖,大部分农田,地势低洼,常遭水患,部分地势较高,又苦干旱,所谓“吴中之田,畏涝者十之七,畏旱者十之三。”至于丘陵山地,更患溪流干涸,又怕山洪暴发,明清两代封建政府与劳动人民,根据平原和山地的不同地势与水利资源,采取多种多样方式,进行农田水利建设,调节水量,力防旱涝,为发展农业生产创造条件。(一)疏通下流河江,导水归入于海。杭嘉湖据太湖上流,其水流注太湖而经三江,分流入海。疏通入江入海之下流,使太湖之水不致泛涨,是解决杭嘉湖水患的关键。明李惺《化湾陡门闸议》说:“治钱圹水患,不自钱圹治之也。天目诸水经余杭、汇具区,趋吴淞以入海。余杭南湖常浚,则有以留其势,而水不致奔溃;吴淞、刘河常通,则有以速其归,而水不至停蓄”。所以疏通 Hangjiahu Sanfu by the day of the mountain water, or diameter in the sea, or into the Taihu Lake, during which high-lying terrain varies. Most of the farmland, lying on the low land, is plagued by floods and some terrain is high. It is also bitterly droughty. The so-called “field of Wuzhong, ten of the floodwaters, and ten of the drought-hitters.” As for the hilly land , But also suffering from streams dried up, afraid of flash floods, the Ming and Qing dynasties feudal government and working people, according to the plain and mountainous topography and water conservancy resources, take a variety of ways to farmland water conservancy construction, water regulation, anti-drought , To create conditions for the development of agricultural production. (A) to clear the river downstream, water diversion into the sea. Hangjiahu Lake, according to the high Taihu Lake, the water injection Lake Taihu and Sanjiang, diversion into the sea. To clear the inflow of water into the sea, so that the water will not surge in Taihu Lake, is the key to solving the floods Hangjiahu. Ming Li Xing “steep gate of the gate of the Bay,” said: “cure money floods, not from the money 圹 governance of the. Tianmu water through Yuhang, WIP with Wusong into the sea. Its potential, and the water will not collapse; Wusong, Liu River often pass, then at its own speed, while the water can not stop saving. ” So clear