Chapter 4 - Flora and Fauna and their Habitats 4.3 Water Ecosystems 4.3.1 Issue Rivers, streams, waterbodies, wetlands and their margins have many ecological values such as habitats, physical systems, recreational resources and amenity values, and use of water resources may affect these values. Many different fauna and flora, both indigenous and exotic have their habitat in the water environment. Rivers form ecological corridors linking the sea and other parts of the land for fish, birds and plant life. Different parts of different rivers also provide specific habitat for particular flora and fauna. A summary of the values associated with freshwater resources can be found in Appendix A to this volume. 4.3.1.1 Water Abstraction Water abstraction reduces the flow or levels in rivers and lakes which in turn affects the water flow or levels, instream habitat, instream and amenity values, depth, width, velocity and temperature or quality; especially at times of river low flows. Significant abstractions occur on the Waihopai (to Gibson’s Creek), Omaka and Awatere rivers. A less obvious “abstraction” is the Wairau Diversion that takes a large proportion of Wairau River flows without any specific control structure. 4.3.1.2 Damming and Diversion This completely alters habitat upstream of the dam and often alters the flow regime downstream. Fish passage can be detrimentally affected. Significant damming has occurred on the Branch and Waihopai Rivers for hydro-electric purposes, on the Upper Opawa River to block off Wairau flows, and on the Opawa Loop to reduce Upper Opawa and Taylor flows into the loop, and the Taylor flood detention dam. 4.3.1.3 River Control Works These can directly damage fauna or flora or alter the physical channel form and substrate, and thus the habitat provided. River control works on the Wairau have narrowed the normal channel width making it a deeper channel. This has been done by strong bank edge protection works in the form of rocks and trees which in themselves provide more cover for fish. The extensive bank edge tree planting significantly changes the riparian habitat. Unmaintained willows or other vegetation can lead to choking of the river channel downstream. 4.3.1.4 Gravel Extraction Gravel extraction will affect channel form and thus habitat provided and its operation can directly affect fish spawning or bird nesting areas. It may also discolour water downstream if carried out in flowing water. 4.3.1.5 Barriers Floodgated culverts and drop structures block fish passage or create artificially high velocity that prevent or inhibit fish passage. 4 - 7