| Glacial lake outburst flood is large,with high peak 、 high speed 、 low temperature,and often accompanied by mudslides.If glacial lake outburst flood happens,it will be a devastating disaster to life 、property and ecological environment in downstream area.Recently, glacial lake outburst flood happens frequently,it has been the key problem of flood control and disaster reduction in Tibet.This paper selected a typical moraine lake and its downstream area in a river basin as the investigated subject, choosed different kinds of moraine dam failure modes,used dambreak model to calculate the occurrence and routing process of quasi outburst floods under different working conditions,analysised the inundation condition, combining with the spatial distribution of population and social economy, to zone the hazard risk caused by flood, and take a step further to put forward a series of glacial lake outburst flood disaster prevention countermeasures suitable for Tibet.Firstly,dam-break flood research was reviewed, Currently, it’s hard to accurately express the dyke erosion process while high strength sediment transport theory has not been established yet, and also the research about cascade dam-break floods and glacial lake outburst floods is rare.Seven aspects of glacial lake research were in particular introduced,this paper put forward a new expression for moraine dam failure mode.Theory and method of dam-break were learned, then selected a typical moraine lake and its downstream area as the investigated subject, choosed different kinds of moraine dam failure modes,used dambreak model to calculate the occurrence and routing process of quasi outburst floods under different working conditions.In the simulation of twodimensional flood routing,how to set roughnesses variated by terrain is studied,then a two dimensional roughness area has been built.According to flood routing results,this paper analysised the influence of different kinds of moraine dam failure modes on flood characteristics.Burst size is the main factor affecting flood characteristics,small burst size has a property of maintaining flood characteristics.The instantaneous and gradually collapse modes influence the flow process shape near the dam and emptying time of glacial lake. The a river runoff from upstream influences flood duration time.The peak flow under the most unfavorable condition of dam breach is 135741 m3/s. Once dam collapses,flood will arrive in A town in a few minutes,the shortest is only 3.5minutes,so people’s reaction time is really short.The time of flood peak arrived in A town will be about 15 minutes. The flood duration of A town is 2 hours and 8 minutes to 3 hours.The maximum flooding depth of A town on both sides of river is between 4-9m.Big flow velocity difference between b river and a river shows that glacial lake outburst flood will have a great impact on b river estuary.The maximum inundated area of each working condition is about 86-95 km2.Its emergence time is between 137-205.5 minutes.The inundated area reaches the top of 94.68 km2 at 137 minutes under the most unfavorable condition.The maximum inundated area of condition 10 is divided according to 8 water depth levels. Area corresponding to each water level depth is statisticed.The majority of water depth is between 3-7m,accounting for about 53%.Finally,the study area is divided into four hazard level: key protection area、important protection area、common protection area and safe area,safe road has been set.In the end,this paper put forward a series of glacial lake outburst flood disaster prevention countermeasures suitable for Tibet. |
