闽江上游地区山洪灾害风险评估*

以1994年5月的山洪作为典型案例,分析了闽江上游地区存在山洪灾害风险的自然原因和人文原因。通过山洪灾害的强频分析和以灾变系数为指标揭示了闽江上游地区山洪灾害风险的空间分布规律,结果表明,同一频度的山洪强度量度都是从西北向东南减少,且其灾变性在源地附近较强,离源地越远越弱。

HAZARD ASSESSMENT FOR MOUNTAIN TORRENTSON THE UPPER REACH AREA OF MINJIANG RIVER

Mountain torrents often burst on the upper reach area of Minjiang River. Especially on May 1 of 1994 to May 3 of 1994, heavy mountain torrents at return period 100 year brought about great damages on this area. On this paper, we assess hazard for mountain torrents on the upper reach area of Minjiang River by the following steps: First, we describe triggering factor, propagating process of the mountain torrents and spatial distribution of damages caused by the mountain torrent. High intensity storm in short duration is triggering factor. Rainfall intensity on the storm center is 125.6 mm/2h. Flood propagated along Cuijiang River, Jiulongxi River and Saxi River to middle reach, lower reach of Minjiang River. Most serious disaster caused by the mountain torrents is on Linhua county, Qinliu county, Yongan city and Sanmin city. Damages on Linhua county and Qinliu county are mainly on countryside. Damages on Yongan city and Sanmin city is mainly on urban area. Second, we discuss reasons why hazard for mountain torrent exists on the upper reach area of Minjiang River. On the natural aspect, frequent storm and saturated runoff-yielding provide enough water sources; stair-like landform have advantages for fast routing of water, and fan-like drainage network increase flood hazard on the middle reach and lower reach. On the human aspect, settleland and farmland concentrated on river valley is liable to be suffered from mountain torrents, adjustment and management of reservoirs are an improtant influencing factor to flood hazard. Generally, reservoir is of function for flood-preventing. If water level on reservoirs is not lowered before storm begin, reserviors will increase hazard for disaster caused by mountain torrents. At last, spatial distribution-of hazard for mountain torrents is discussed by strength and frequency analysis of mountain torrents and the index;Disaster Variation Coefficient. The result shows that strength of moutain torrents for same frequency decreases from northwest to southeast and the variation weakens as distance to the source of river increase.