Ecohydraulic modelling of Nestos River Delta under low flow regimes

Abstract The determination of a proper minimum environmental flow in a river basin is one of the most critical components of sustainable water resources management, with hydraulic and habitat modelling being the most advance methods for that analysis. The present study illustrates the ecohydraulic modelling of Nestos River Delta at the deltaic zone of a heavily modified watershed under various low flow scenarios, using the RIVER2D Model. RIVER2D is a two-dimensional, depth averaged hydrodynamic and fish habitat model, widely used in environmental flow assessment studies. A detailed digital model of the river channel and its surrounding area was developed, including all the morphological characteristics of the river channel, as well as its various sandy islets. Field surveys in combination with Digital Elevation Model data were used for the development of the digital terrain used as input to RIVER2D model. Several different steady state hydraulic simulations were conducted under typical low flow conditions, producing water depth and water velocity (direction and magnitude) maps for each discharge scenario, while results were verified with the use of field measurements. In the next step, RIVER2D was used for the fish habitat modelling of the study area, with the application of fish preference curves developed specifically for the study area. Finally, the fish habitat modelling was conducted for four different fish species, divided into two age groups, forced under the same five typical low flow conditions. Results reveal that the ecohydraulic modelling of river basins should be considered as an indispensable component in sustainable water resources management.