Abstract
The objective of this study is to evaluate the effect of increasing instream flow at Gapcheon stream of Daejeon city by considering two virtual reservoirs upstream, respectively; Geum-gok reservoir and Koe-gok reservoir upstream, respectively. The paralleled and cascaded reservoir operations were performed including the existing Jang-an and Bang-dong reservoirs. The results are summarized as follows. Firstly, from the Bang-dong and Geum-gok cascaded reservoir's water balance analysis, instream flow of $6.83Mm^3$ was able to be supplied to downstream, and water supply indexes of Geum-gok reservoir were analyzed to have the rate of water supply divided by watershed area of 403.4 mm, the rate of water supply divided by rainfall of 33.0 %, the rate of water supply divided by inflow of 96.4 %, the rate of water supply divided by storage capacity of 81.9 %, and the rate of inflow divided by storage capacity of 112.3 %. Secondly, from the Jang-an and Geum-gok paralleled reservoir's water balance analysis, flow durations at Gapcheon station were analyzed to have Q95 (the 95th high flow) of $4.806m^3/s$, Q185 (the 185th high flow) of $2.217m^3/s$, Q275 (the 275th high flow) of $1.140m^3/s$, and Q355 (the 355th high flow) of $0.887m^3/s$. Thirdly, inflow to Koe-gok reservoir was simulated including the Jang-an and Bang-dong paralleled reservoir's water balance analysis, instream flow of $49.60Mm^3$ was able to be supplied from Koe-gok reservoir to downstream, and water supply indexes of Koe-gok reservoir were analyzed to have the rate of water supply divided by watershed area of 246.5 mm, the rate of water supply divided by rainfall of 19.4 %, the rate of water supply divided by inflow of 40.8 %, the rate of water supply divided by storage capacity of 412.1 %, and the rate of inflow divided by storage capacity of 1,189.8 %. Fourthly, daily streamflows at Gapcheon stream were simulated including outflows from Koe-gok reservoir, flow durations at Gapcheon station were analyzed to have Q95 (the 95th high flow) of $4.501m^3/s$, Q185 (the 185th high flow) of $2.277m^3/s$, Q275 (the 275th high flow) of $1.743m^3/s$, and Q355 (the 355th high flow) of $1.564m^3/s$. The conclusion appeared that the effect of increasing instream flow at Gapcheon stream from Koe-gok reservoir was more higher than that from Geum-gok reservoir.
대전 3대 하천의 하나인 갑천의 유등천 합류전 지점의 하천유지유량 확보를 위해 상류 유역에 금곡지와 괴곡지를 각각 설치하는 경우 각각 장안지, 방동지의 기존 저수지를 포함하여 직렬, 병렬 연계 운영을 반영하여 목표 지점의 유량을 1966년부터 2007년까지 모의하여 효과를 분석한 결과 다음과 같다. 첫째, 방동지-금곡지 직렬 연계에 의해 금곡지로부터 용수공급능력을 분석한 결과 연평균하여 하천유지유량 공급량은 6.83백만 $m^3$, 용수공급량/유역면적은 403.4 mm, 단위유역 용수공급량/강우량 비율은 33.0 %, 용수공급량/유입량 비율은 96.4 %, 용수공급량/저수량 비율은 81.9 %, 유입량/저수량 비율은 112.3 %였다. 둘째, 장안지-금곡지 병렬 연계를 고려한 갑천지점의 유량을 분석한 결과 유황은 연평균하여 풍수량 $4.806m^3/s$, 평수량 $2.217m^3/s$, 저수량 $1.140m^3/s$, 갈수량 $0.887m^3/s$로 분석되었으며, 평균갈수량은 목표유량 $1.486m^3/s$보다 $0.599m^3/s$ 적게 나타났다. 셋째, 장안지-방동지 병렬 연계에 의해 괴곡지 유입량을 모의하였고, 괴곡지로부터 용수공급능력을 분석한 결과 연평균하여 하천유지유량 공급량은 49.60백만 $m^3$, 용수공급량/유역면적은 246.5 mm, 단위유역 용수공급량/강우량 비율은 19.4 %, 용수공급량/유입량 비율은 40.8 %, 용수공급량/저수량 비율은 412.1 %, 유입량/저수량 비율은 1,189.8 %였다. 넷째, 괴곡지 방류를 고려한 갑천 지점의 유량을 분석한 결과 유황은 연평균하여 풍수량 $4.501m^3/s$, 평수량 $2.277m^3/s$, 저수량 $1.743m^3/s$, 갈수량 $1.564m^3/s$로 분석되었으며, 평균갈수량은 목표유량 $1.486m^3/s$보다 $0.078m^3/s$ 높게 나타났다. 요약하면 괴곡지를 설치하는 것이 금곡지를 설치하는 것보다 갑천 지점의 하천유지유량을 확보하는데 효율성이 높은 것으로 분석되었다.
