Ecological flow considering hydrological season and habitat suitability for a variety of fish

Maintaining the ecological flow of rivers is necessary to resolve the contradictions between water resource development/utilization and ecological protection. To investigate the ecological flow of the mainstream of the Si River in Shandong Province, China, the ecological flows in reaches from Sishui Sluice to Shuyuan Station and from Shuyuan Station to Longwandian Sluice were calculated using the habitat simulation method. First, the indexes of relative importance calculated using the results of a fish survey identified Carassius auratus, Pseudorasbora parva, and Misgurnus anguillicaudatus as the most prevalent and therefore the target fish species for this analysis. A model of the fish habitat was subsequently constructed using the River2D software and the relationship curves between different flow conditions and the weighted usable area of fish habitat were plotted for each of the three target fish species. Finally, the ecological flows for the non-flood to pre-flood period (October to June) at Sishui Sluice and Shuyuan Station were determined to be 1.4 m3/s and 1.8 m3/s, respectively, and those for the flood period (July to September) were 6 m3/s and 10 m3/s, respectively. The rationality of the habitat simulation method results was subsequently confirmed by comparison with the results obtained using four hydrological methods. Finally, the results indicated that water resource management and regulation of the Si River mainstream should be strengthened during the dry period (April to May) to improve the ecological flow guarantee rate and thereby ensure the connectivity of the fish habitat and sustain fish lifecycles.