流域洪灾的形成直接受到地质、地貌条件的制约。洪灾是由洪水引发的，但洪水并不等于洪灾，由暴雨发展为洪水、洪灾是一种外动力地质作用过程。暴雨是一种气象现象，洪水是一种水文现象，而暴雨→洪水→洪灾，则是一种地质过程。因此，地质学在防洪、减灾中具有重要意叉。根据地质学原理，长江防洪策略为：① 沿江干堤不宜继续加高；② 干堤加固应因地(地质、地貌条件)制宜。要考虑到三峡工程可能引起的河流地质作用变化；③ 启用古河道分流泄洪；④“退田还湖”与“挖泥还湖”相结合；⑤ “平垸行洪”与“民垸蓄洪”结合；⑥ 实施有计划地开堤放淤工程，防洪与除渍结合；⑦ 区段综合治理与全流域系统治理结合。

The formation of flood disaster is restricted directly by the conditions of geology and geomorphology.Flood disaster is caused by floodwater,hut floodwater is not equal to flood disaster.The form of flood disaster is an outer dynamic geological process.Rainstorm is a meteorological phenomenon,flood is hydrological phenomenon,while the development from rainstorm to flood water to flood disaster is a geological process.So geology has important usefulness in the preventing and reducing flood.According to the principle of geology.the strategy of the preventing Yangtze River flood is:(1)the main bank along the river should not be heightened continuously:(2)the condition of geology and geomorphology and the fluvial geological effect caused by Three Gorge Project should he considered when the main bank is reinforced;(3)the old river ways should be used to discharge the flood;(4)combining “returning farmland to lake” with digging silt away in lakes;(5)discharge flood with polder an store flood in polder;(6)open bank and discharge the silt designedly;(7)combining the regional synthesis harnessing with all drainage area synthesis harnessing.