Calculation of the Ecological Water Demand of Plain Rivers Within Haihe River Basin Based on River Ecological Type Classification

SHI Wei,HOU Si-yan,CUI Wen-yan,LIU De-wen,LIN Chao(Haihe Water Conservancy Commission,Ministry of Water Resources,Tianjin 300170,China)

classification of ecological rivers;Haihe River basin;plain rivers;ecological water demand

The common ecological problems in the Haihe River basin were shortage and depletion of water,water pollution,siltation at river mouth,loss of biodiversity,and so on.In view of the current ecological status in the basin,the 21 plain rivers were classified into three groups: I water shortage or riverbed desertification,II water pollution,and III habitat deterioration.In the first group,a river dries up for not less than 300 days annually,and its riverbed desertificates seriously.Ecological restoration of these rivers was targeted at keeping enough wa-ter for growing grass at least.In the second group,the length of a river with COD concentrations of higher than 150 mg.L-1(or with DO con-centrations of lower than 0.4 mg.L-1)occupies two-thirds of its total length.Ecological restoration of these rivers was aimed at controlling discharged pollutants within the water environment capacity.Group 3 can be divided into two sub-groups depending on whether there is a dam or there are dams.Luan River is the only one without a dam.The target for the restoration of the river is to keep water depth over 0.6 m,which is the lower limit for fish.The target of ecological restoration for the second sub-group has to consider whether the river is a rural one and whether the river has to be navigable.The water depth of rural rivers was targeted at or above 0.8 m,and 1 m for urban rivers,and 1.5 m for navigable rivers.The ecological water demand was calculated by the use of four methods,they are vegetation water demand quota,mean flow in the driest month under 75% guaranteeing rate,the biological minimum space requirements and the channel storage.The result indicat-ed that the minimum ecological water demand of plain rivers within Haihe River basin′s was 1.812 billion m3,about 8.4% of the annual aver-age runoff of Haihe River basin.And finally,the above four methods were compared with the method of Tennant.The ecological water de-mand computed by the vegetation water demand quota was about 2.4%～5.5% of annual average runoff,much less than that computed by the method of Tennant.The ecological water demand by the mean flow in the driest month under 75% guaranteeing rate was about 15% of annual average runoff,being slightly larger than that by the method of Tennant.The ecological water demand by the biological minimum space re-quirements was about 6% of annual average runoff,close to the result by the method of Tennant.The ecological water demand by the channelstorage is closely related to the restoration goals.Methods used in this study can be applied to calculate the ecological water demand in Haihe River basin.