Study On Hydrologic And Hydraulic Characteristics Of Fish Habitat In Middle And Lower Lancang River

Habitat protection is an important method to protect the ecological system in China’s hydropower construction projects. It is suggested to be the most suitable and efficient fish protection method, as it can both preserve the original river habitat and protect aquatic creatures. Based on the relevant historical data and field investigation results, this paper discusses the feasibility of applying tributary habitat alternative protection method in Luosuo River, a tributary of Lancang River, by studying fish species similarity and hydrologic condition similarity between Luosuo Rvier and Lancang River. Through field investigating and monitoring of fish spawning sites, the spawning reach of Tor sinensis in Luosuo River is confirmed. Taking Tor sinensis as a target fish species, this paper analyzes the fish demand on hydrologic and hydraulic charateristics in its critical life period, and presents objective scope of hydrologic and hydraulic index in order to better protecting endemic fish species of Lancang River.The main contents and conclusions are as follows:Fish species lists for both Luosuo River and the middle and lower Lancang River are gained via a two-year field fish investigation and a historical data study.62 fish species, including 20 endemic species, are recorded in both two reaches. Calculation result of species similarity index between two reaches is 67.39% and endemic species similarity is 66.67%. Similarity study of hydrologic condition between middle and lower Lancang River and Luosuo River is carried out on the basis of daily runoff data of Yunjinghong and Manan Hydrologic Station from 1959 to 1985. The results show that interannual and annual variation of hydrologic regime and flow rising condition in flood seasons are consistent in both reaches. In summary, Luosuo River is suitable to applying tributary habitat alternative protection to reduce the impact of hydropower structure on fish assemblages in middle and lower Lancang River.In order to better quantify the hydrological and hydraulic characteristics for protecting the endemic fish in Lancang River, Tor sinensis is set to be a target species. Based on the field monitoring results, reaches, starting from 500 m downstream Manan Station and ending at 500 upstream the junction of Nanxing River, are identified as spawning reach of Tor sinensis.Daily runoff data of Manan Hydrologic Station from 1959 to 1985 are used to calculate 33 IHA (Indicator of Hydrologic Alteration) hydrologic indices, which are important hydrologic indices for fish habitat protection. The acceptable ranges of these indices are set to be smaller than mean value plus standard deviation and larger than mean value minus standard deviation. The results show that among the 33 IHA indices,17 are thought to be more important than others. And flow rising is found to be an essential stimulus for fish spawning. Number of flow rising process varies in [3.1,4.2] and average duration of each rising process varies in [3.2,3.7], showing that flow stimuli of nature reserve in Luosuo River is in several times but not lasting for long.Riverbed topography of Tor sinensis spawning reach was measured in December,2012. 3 pools and 4 riffles are identified according to the measured results by bed differencing technique. Average distance between adjacent pool and riffle is 0.66 km and distribution density of pool or riffle in this reach is 1.40 individual per kilometer. The measured topographic data is used in a two-dimensional hydrodynamic simulation in Delft 3D software. The results show that, with flow discharge rising from 237 m3/s to 1273 m3/s, average velocity varies in [1.29, 2.24], water depth varies in [2.36,5.18] and Froude number varies in [0.31,0.41] in the whole simulated reach. For the pools, average velocity varies in [0.53,1.53], water depth varies in [5.40,8.46] and Froude number varies in [0.10,0.19]; and for the riffles, average velocity varies in [1.88,3.51], water depth varies in [0.95,3.56] and Froude number varies in [0.61,0.71]. The average velocity, water depth and Froude number variation scopes of the whole reach, pools and riffles are used here to represent the hydraulic characteristics of Tor sinensis spawning reach and they could also provide materials and technical support to other Lancang endemic fish habitat protection.