Ecological Water Demand Estimation For The Restoration Of Groundwater System In The Lower Liaohe River Plain

Groundwater is an important part of the worldwide ecosystem, and is also is akey influence on the ecological system in arid and semi-arid regions of northwestChina, and is the primary source of water for human use in northern China. This paperchose a typical huge groundwater basin-the lower of Liaohe River Plain as the studyarea, with recent economic growth, rapid development of the groundwater resourcesin this region is occurring. The groundwater has been and is being seriously depletedand some hydrogeologcal problems in the system are becoming apparent, the area isexperiencing significant water shortages, and the ecological health of groundwatersystems has become a serious issue in ecology, and is receiving considerable attentionfrom the general public.On the basis of considering the evaporation characteristics in this area, thegroundwater table limit rules for the healthy state maintance of some ecosystems asnatural grassland, natural wetland and river are demonstrated, then the ecologicalgroundwater table were determined from the two aspects of hydrogeology andecology. For example, as for natural grassland, the burying depth of ecologicalgroundwater table in spring, summer and autumn is3~4m,2~3m and3~4mrespectively, and in winter, the burying depth of ecological groundwater table shouldonly meet the need of hydrogeologcal limit. As for natural wetland, the burying depthof ecological groundwater table in spring, summer, autumn and winter is0.5~0.8m,0.3~0.5m,0.5~0.8m and1.0m respectively. According to the comparison of theecological groundwater table and the actual groundwater table, the Golden surfersoftware was applied to calculate the ecological water demand for the restoration ofgroundwater system on the month scale. The month ecological water demand fromJanuary to December is40.32×10~8m~3、41.90×10~8m~3、42.41×10~8m~3、42.93×10~8m~3、44.07×10~8m~3、57.33×10~8m~3、48.93×10~8m~3、42.78×10~8m~3、40.85×10~8m~3、36.40×10~8m~3、37.49×10~8m~3、35.15×10~8m~3respectively, the most ecological waterdemand appears in June, in which the vegetation is luxuriant and the animal is activity,the lest ecological water demand appears in December, in which the vegetation iswithered and the animal is migrated or in hybernating state.This paper adopts the idea of guarantee rate method to delimit the five types ofthe ecological water demand for the restoration of groundwater system, which arewith the guarantee rates of90%,80%,70%,60%and50%. In order to obtain theprobability density of ecological water demand by the12data which is impossible by the traditional statistic model, so the information diffusion technique was applied, inthis technique, each data is regarded as a set of data, and has been proved as asuccessful and widely used method. Then the ecological water demand under differentGuarantee rates is obtained. Under each guarantee rate, the ecological water demandis divided into five grades, which are the100%,80%,60%,40%, and20%of theecological water demand corresponding to the related guarantee rates. The resultsshow that with the decrease of guarantee rate or increase of grade, the quantity ofecological water demand increased.This paper also discussed the recharge scheme of ecological water demand,given that the recharge periods are5,10,15,20,25years, under each guarantee rate, theyearly groundwater recharge volumes were calculated. For example, under theguarantee rate of50%, when the restoration grade are excellent, the yearlygroundwater recharge volume is8.58×10~8m~3, while the restoration grade isminimum, the yearly groundwater recharge volume is only0.34×10~8m~3.The resultsof this paper are of significance for the groundwater protection and healthy ecologymaintance in the lower Liaohe River Plain.