Numerical Study of Sediment Management Strategies for Techi Reservoir

Abstract

Techi Reservoir built in 1974 has no sediment management strategy Accumulated sediment already exceeds 25% of reservoir capacity due to continuous sediment inflow Thence the power generation and reservoir storage have been severely impacted In order to maximize the use and extend the life of this reservoir a sustainable sediment management plan is needed In this study the 1D numerical model SRH1D was combined with the reservoir hydrological conceptual model to simulate a reservoir flushing operation In this simulation analysis we use recorded reservoir operation reports from 2008 to 2016 as input data and refer to the current reservoir operation rules to establish the hydrological conceptual model We simulated different operation scenarios adjusting factors such as the period of flushing the maximum operation water level during flushing the discharge capacity of the outlet as well as different regulation discharges during the flushing period By doing so we are better able to understand the influence of these factors on sediment release and reservoir geomorphology The results of the numerical model show that the longer the operation period and the lower the water level the more sediment release there will be However if the water level drawdown is incomplete for instance drawn down to only 1325meters instead of 1320 or bellow it is not advisable to implement longer flushing operation when considering water resource needs and conservation Although there is more sediment release with longer operation the flushing efficiency will be reduced due to the fact that water consumption per unit of sediment release has increased The efficiency of flushing operation was predicted by comparing flushed water to computed sediment ratio Results showed that modification of the bottom outlet by expanding the orifice area leads to more sediment flushing and improves flushing efficiency as the water level is able to be lowered more efficiently during the flushing period In addition increasing the regulated discharge from 86 to 115cms will flush more sediment but appears to reduce flushing efficiency The SRH1D simulations predicted that most scouring will occur on the reservoir delta Some scour sediment will not be flushed through the outlet but will deposit in the fore-set and bottom-set slope during the flushing process

Date of Award	2019
Original language	English
Supervisor	Hsiao-Wen Wang (Supervisor)