Analyzing the Effect of a Weir Construction on the Groundwater Flow System

Abstract

Visual MODFLOW, a three dimensional groundwater flow model, was used to analyze effects of a weir construction in an alluvial stream on the nearby groundwater flow system. A hypothetical conceptual model was developed to investigate how the groundwater level and the water budget could change after a weir construction depending on the location of tributary streams. A site example, dealing with the Juksan weir installed in the Yeongsan River, was also demonstrated to predict the effects of the weir construction. Model results show that impacts of a weir construction on the groundwater flow system greatly vary depending on how far a tributary is located and whether it is located downstream or upstream from the weir. Therefore, consideration of the location of tributaries in planning the location of a weir could effectively minimize the impacts of a weir construction on the groundwater flow system. It is also demonstrated that model results are highly dependent upon how the model is dealing with small tributaries and agricultural drainage channels, which can be easily found nearby the main streams, acting as major water bodies for groundwater discharge. The model for the Juksan area shows that the weir construction will change the direction of groundwater flow in some areas, leading to changes of groundwater quality and interaction of the Yeongsan River to the aquifer from a gaining to a losing stream. The model also predicted the areas where rise of groundwater level caused by the Juksan weir could adversely affect plant growth, and thereby suggested installing new drainage channels as a countermeasure to drawdown the groundwater level.

Spatio‐Temporal Variations in Stream–Aquifer Interactions Following Construction of Weirs in Korea

“…Similarly, the groundwater flow from the main stream to the channel also occurred within the old river channel. Jeong and Koo (2012) predicted similar results to our observations that the direction of groundwater flow in the Yeongsan River would be changed by the construction of the Juksan weir. Installation of new drainage channels was suggested as a countermeasure to drawdown the groundwater level.…”

“…This also affects groundwater discharge, thus a flood control effect is expected. Results of a groundwater flow model predicted the change of direction in groundwater flow in the Juksan area (Jeong and Koo ). This would lead to streams changing from gaining to losing streams, leading to changes in the groundwater quality and the water balance between the Yeongsan River and the local aquifer.…”

Changes in Stream–Aquifer Interactions Due to Gate Opening of the Juksan Weir in Korea

“…Figure 7 shows the groundwater level response rate following a change in the river level due to the opening of the four weirs. The response rate (R) was calculated as follows: R = r GW r SW (1) where r GW and r SW are calculated slopes of observed decline of water level change with time in groundwater and river water, respectively. The response rate increased with increasing transmissivity, which means that the transmissivity of the aquifer is an important factor for determining the response rate.…”

“…As part of the Four Major Rivers Restoration Project, 16 weirs were constructed on four major rivers in South Korea from 2010 to 2012, which helped to meet water demands during the dry season and control flooding. Many studies have shown that hydraulic structures such as weirs and dams are useful for replenishing groundwater resources [1,2]. Water filling at the weir caused an increase in the groundwater level during the dry season [3], while river level management at the Changnyong-Hamman weir in the Nakdong River resulted in a decline in the average groundwater level during the wet season [4].…”