Key Technologies Of River Ecological Flow On Modified Tennant Method And Sensitive Ecological Requirements

River health changes with hydrological regimes. However, dramatic hydrological alterations have led to degradation of riverine ecosystem, and the lack of ecological water requirements (EWRs) has seriously restricted sustainable development of social economy. Naturally, ensuring ecological flow (EF) is the prerequisite of sustaining healthy river. Study on EF assessment methods has become the frontier issue in the field of river restoration.Aimed at general EWRs for maintenance of aquatic habitats and species diversity and EWRs in the middle-lower reaches of Hanjiang River for algalbloom controlling and fish spawning, research about universal EF assessment method and regional EF allocation scheme was then carried out, respectively. The main work and innovations list as follows.(1) Background and significance were explained from transition process of utilization framework of water resources, eco-hydrological effects of reservoirs and dams, and research requirements for ecological operation. Domestic and foreign achievements about theory and model for riverine EWRs was reviewed. This research focused on solving four key problems existed in the current EF criteria:poor monthly and inter-annual variability, weak spatial transferability, high sensitivity on extreme flow and highly subjective scalability.(2) The concept of EWRs was identified from the following five perspectives:runoff and flow, functions, critical value, requirement and use, sustainable river health. The characteristics of EWRs were analyzed from the following three aspects:temporal and spatial variability, unity of quality and quantity, optimality and threshold. Thus, monthly and year-to-year rich-poor variability, spatial transferability and objective scalability are necessary for EF assessment criteria.(3) To solve four key problems, this paper focused on developing a new modified Tennant method with universal EF criteria. Based on combined modified forms of average periodic flow, water period and percentage, modified Tennnat methods are comprehensively studied. The eco-hydrological characteristic of minimum flow, driest consecutive n-day average flow, base flow, flow under specific guaranteed rate in frequency curve and flow duration curve and average flow were analyzed. The MTMMHC method based on monthly division of water years, low flow, medial flow, monthly distribution and ecological grades was then proposed. Finally, five large rivers, two medium-sized rivers and three small rivers with different flow regimes were selected to provide for demonstrating the applicability and of rationality of MTMMHC method. The results show that multiple-level EFs calculated by MTMMHC method have synchronously monthly and inter-annual variability and spatial transferability, and avoid the influence of extreme year-to-year flow and uneven intra-annual distribution. The classification number and EF criterion for every level is objective, overcoming subjectivity existed in traditional methods.(4) The reason and influencing factor of algalbloom happened in the Hanjiang River were analyzed, and the critical velocity of algalbloom in the lower reach and EWRs in middle reach were both considered. Based on diverse water levels of Yangtze River in dry season, the corresponding EF scheme carried by water transfer of middle route project, water supplement of diversion project from Yangtze River to Hanjiang River, water release of Danjiangkou Reservoir, and various hierarchical aquatic habitat conditions of main streams and tributaries was proposed. The EF scheme can provide scientific basis for carrying out ecological operation of these projects.(5) Temporal-spatial evolution and spawning conditions of fish in the Xiangyang reach of Hanjiang River was analyzed. Based on water rising condition, appropriate ecological velocity, and contribution rate of eggs laid by four major Chinese carps made by discharge of Danjiangkou Reservoir and flood pulse of tributaries, an ecological flood scheme was proposed. Furthermore, its satisfaction on natural flow series and regulated flow series was evaluated. The results show that natural runoff in the driest year can provide good flood pulse process, however, the regulated runoff in dry and normal years cannot meet ecological flood scheme. Future research should focus on runoff and sediment ecological operation of Danjiangkou Reservoir, making water transparency, starting value, top value, rising rate and duration of peak flow meet the spawning need of four major Chinese carps.(6) The achievements and future orientations in this dissertation were summarized.