EFDC Hydrodynamic Model
Downstream Hydropower Impacts
DSI was contracted by THPC to perform a hydrodynamic modeling study of the Nam Hai-Upper Nam Hinboun and the Lower Nam Hinboun. This work was part of a larger assessment study of the Nam Hai-Upper Nam Hinboun river system in support of the Technical Feasibility Study for the Theun Hinboun Expansion Project. The objective was to conduct a study of the incremental impacts due to an existing hydropower facility and a proposed expansion on the downstream channel. Flooding and channel stability were evaluated and engineering analysis conducted. The flood conditions for the Mean Annual Flood for 10, 20, 50 and 100 Year return intervals were analyzed. Three scenarios were evaluated; Base Case (no hydropower discharge), Existing Case (Plant Q=110 m3/s) and the proposed expansion (Plant Q=220 m3/s). A 2D In-Channel hydrodynamic model had been built and calibrated that provided a detailed evaluation of the overall in channel flows, bed shears, and timing of releases. A 2D Floodplain model has been built and calibrated. This model allowed the assessment of flood durations, flood extents and flood depths to be assessed and compared for each desired flood event and THPP operational scenario. The following figure shows a plot of inundation areas for all three THPP scenarios assessed for the 20 Year Mean Annual Flood condition. This plot provides a quick visual assessment of area differences in flood extents.