敦煌莫高窟降雨分布及入渗特征研究

Research on the characteristics of rainfall distribution and infiltration in Dunhuang Mogao Grottoes

敦煌莫高窟文物具有唯一性和脆弱性,干燥环境是壁画和塑像长久保存的保障,降雨是病害发生诱因。为了弄清降雨对文物的损害机制,本研究通过气象监测数据分析和野外人工降雨模拟试验,分析莫高窟降雨分布特征和窟顶戈壁降雨入渗和产流规律,为开展洞窟内壁画病害发育机理分析和实施莫高窟洪水风险预控提供理论依据。25年气象监测数据分析表明,莫高窟区域多年平均降水量39mm,集中在5~8月,降雨类型主要为微雨和小雨,频现大于76%,大雨及暴雨均为突发性强降雨,频现仅为1.5%,常常伴随区域洪水的发生。降雨模拟试验结果表明,当平均降雨强度0.75mm/min,降雨历时160min时,入渗湿润锋迁移至深度80cm左右即趋于平衡。但是,高密度电阻率探测表明洞窟地层2~3m处,水分饱和度可达60%左右,极易带动可溶盐向壁画地仗层富集,致使病害发生发展。经计算,窟顶戈壁径流系数0.016,产流能力非常低。区域洪水主要来源于莫高窟周边戈壁及野马山地带降雨汇流。

The murals and statues of the Mogao Grottoes are unique and fragile. The dry environment is one of the key factors guaranteeing the preservation of the site over a long time. Rainfall can cause a lot of damage. Based on25 years of meteorological monitoring data,it is found that the average annual precipitation at the Mogao Grottoes is39 mm,most being atmospheric rainfall. The precipitation was not evenly distributed,May to August were the periods that received the most rain. For the most part,there were slight and small amounts of rain,counting for 76% of the total rainfall. The heavy rains and storms accounted only 1. 5% of the total,but they resulted in regional floods. A rainfall simulation experiment was done. The experiments show that when the average rainfall intensity is0. 75 mm / min and lasts for 160 minutes,the rainfall wetting front reaches a depth of 80 cm and then maintained and equilibrium. However,at adepth of 2m to 3m,the level of water saturation can increase to about 60%. This high saturation can drive the soluble salts enrich on the base layer of murals,causing damages to the wall paintings.The Gobi runoff coefficient in the roof of Mogao grottoes is 0. 016; It is inferred that the runoff capacity is very low.There would not be a regional flood if only the Mogao Grottoes area had a storm. Flooding is mainly caused by a confluence of rainfall in the Gobi area around Mogao Grottoes and in the Yema mountain region.