中文摘要：

通过长系列实测水文、地形资料分析,钱塘江河口上段河床具有大冲大淤和洪冲潮淤的演变特性,影响河口上段的潮汐强弱,进而影响盐水入侵。若年内丰水期径流量大,则河床出现＂大冲＂,河床容积增大,潮汐增强,导致秋季强潮期盐水入侵加剧;反之,若年内丰水期径流量小,河床容积较小,导致秋季强潮期盐水入侵减弱。结果表明,钱塘江径流对盐水入侵存在直接和间接影响：直接影响是盐水入侵与径流量成反比;间接影响是通过径流冲刷河床,引起潮汐增大,间接导致盐水入侵加剧,这是钱塘江河口大冲大淤以及对潮汐巨大反作用的特性造成的。

英文摘要：

Based on the long term hydrological and bathymetric analysis, the morphological evolution in the estuary features the significantly large riverbed change, that is, the great erosion in runoff-dominated periods and the great sedimentation in tide-dominated period in the upper reach of the Qiangtang River estuary. This morphdynamic charac- teristics results in the large variation of tide in the upstream section and therefore affects saltwater intrusion. With plen- tiful runoff during wet seasons, the riverbed suffers great erosion, leading to the increase of river convey volume and enhancement of tide. This results in the increase of saltwater intrusion in falls with strong tide. On the contrary, with small runoff during wet seasons, the river convey volume is small. Therefore, it results in weakening saltwater intrusion in falls. The results indicated that the runoff variation has direct and indirect impacts on saltwater intrusion in the Qiantang River estuary. The direct impacts are the common characteristics of tidal estuary, i.e. saltwater intrusion increases as runoff decreases. The indirect impact is that the large erosion caused by the large runoff results in the in- crease of tide, and therefore indirectly leading to intensified saltwater intrusion. This feature results from the character- istics of the large riverbed change and its great response of tide strength in the Qiantang River estuary.