海河流域典型河口生态环境需水量

Study on the ecological water demands for typical estuaries in Haihe River Basin

在分析河口生态环境需水量类型及特征的基础上 ,采用水文学、生物学及水力学方法计算了海河流域中海河口、滦河口及漳卫新河口生态系统水循环、生物循环消耗水量及生物栖息地需水量。考虑不同生态功能需水量间的兼容性 ,得到各河口生态环境需水年度总量 ,以保持河口径流时间分布自然性为基础 ,确定了生态环境需水量年内时间分配。结果表明 ,即使不考虑污染物的排放 ,近年来海河口、漳卫新河口实际径流量已无法满足最低等级生态环境需水量 5 .97和 4 .96亿 m3的要求。相应河口生态系统已发生了不可自然恢复的退化。滦河口径流年度总量基本满足生态环境要求 ,其生态保护重点在于保持生态环境需水量年内时间变化的自然状况。通过比较不同河口间生态环境需水量结果 ,认为河口生态环境需水量空间差异性主要源于河口间气候和径流量的不同 ,时间差异性则受到河口地区年内季节间气候变化幅度的影响。保证污染物达标排放基础上 ,保持河口生态系统蒸发消耗。

Estuaries in Haihe River Basin are located at the east of Haihe River Basin and west of Bohai bay. In recent year, degradation of estuarine ecosystem has become common due to a high level of pollutant load and water resource utilisation in order to support a continuously increasing population and economic development in Haihe River Basin. In order to minimize the negative influence of a reduced river discharge, the ecological water demands for different ecological objective are calculated for Haihe, Luanhe and Zhangweixin estuaries in Haihe River Basin. Three types of water demands are included in the calculation of the estuarine ecological flows. These are water demands for water circle, the biological circle and for the habitat. Water demands for the water circle and the biological circle are consumed, whereas the demands for the other portions of the ecological flow (e.g. maintaining reasonable salinity, dilution of pollutant loads, sediment and nutrients transport, for habitat) are not consumed. These parts of the Ecological flow, which constitute the runoff to ocean, is compatible. The maximum value is considered as the Ecological flow.Evaporation and the water content of soil are considered as water demands for water circle of the estuarine ecosystem. Water demands for the biological circle in the estuarine ecosystem is defined as water content of biota and biomass. Methods of calculating water demands to sustain a required salinity that ensure certain habitat conditions are presented. The methods are based on the close relationship between freshwater inflow and salinity in estuaries. Water demands for sediment transport is affected by sediment carrying capacity and alluvial sediment in estuary. Hydrological, biological and hydraulic methods used are presented and parameters for different kinds of water demands are listed respectively.The problem of pollution can not be solved through dilution. At the existing pollution level this would require more water than can be made available. Required flows for such purpose are therefore neglected in the calculation. For considering complex responds of the ecosystem to nutrients loads, a more sophisticated model is needed. In this study, it is assumed that water demands for salinity and sediments transport will also fulfill the needs for water quality.Annual ecological water demands for different estuaries is calculated considering the compatibility of the water demands. In general, water demands for fulfilling the minimum and medium salinity objective also fulfill the requirements for sediment transport, but the water demands that fulfill the maximum salinity objective will not fulfill the requirements with respect to sediment transport. Maximum ecological water demands for runoff should in this case be determined by the requirements of sediment transport. The allocation of ecological water demands between the month of the year should be close to natural flow distribution.The basic annual requirements of ecological water demands in Haihe and Zhangweixin estuaries are 5.97 and 4.96×10~8m^3 respectively, which could not be fulfilled by river inflow in recent year. The estuarine ecosystems in Haihe and zhangweixin have degenerated completely and could not rehabilitate naturally. Annual freshwater water supply for Luanhe estuary is enough for the ecosystem. However to protect the Luanhe estuary it is highly recommended also to focus on the monthly variation in the discharge. Analysis for the estuaries of Haihe River Basin has shown that the seasonal variation of the natural flow is approximately in accordance with a normal distribution. Temporal variation of monthly ecological water demands are calculated based on normal distribution.Spatial variation in the ecological water demands is related to the difference between the local climate and fluvial flow regime of the estuaries. The temporal variation is influenced by climatic variation over the year. Maintaining water demands for evaporation and to ensure a reasonable salinity is recommended to be the key issue for the protect