Minimum flow requirement for fish population affected by dam construction in temperate areas

Abstract

Dam construction on rivers and streams provide desired benefits such as freshwater, hydroelectric power, and fish. Dam-related operation includes flow augmentation procedures such as flow regulation, flood releases or fluctuating flow releases, all of which have a detrimental impact on the downstream aquatic habitat like benthic macroinvertebrate zooplankton, phytoplankton and fish. In order to avoid negative impacts, a minimum flow release downstream of the dam is recommended. Minimum flow is the planned release of small amounts of water for ecological sustenance. During summer, the river to the downstream of the dam becomes dry which is detrimental from the fishery point of view, as the migration of the fishes is disrupted. Fishes are accustomed to live in flowing river conditions, with their life cycle stages requiring the following factors: low silt content, well-oxygenated intra-gravel flows and minimum current, depth, velocity of water, dissolved oxygen. These factors are altered due to dam construction and restricted release of downstream flow. Fishes that feed on the invertebrate organisms like benthos and zooplankton are also affected by dam-manipulated flow. In order to maintain the aquatic habitat downstream of the dam, authorities recommend minimum flow according to the habitat. The significance of minimum flow is that it is needed to keep the streambed wet to an acceptable depth to support fish populations. This paper describes how minimum flow in the river, downstream of a dam, is the main requirement in the life cycle of fish with respect to feeding habit and reproduction. The paper also gives examples of various dam-related recommended flows with respect to the life cycle of the fish.