The analysis of saltwater intrusion through Komesu underground dam and water quality management for salinity

Abstract

The Komesu underground dam is the first fullscale underground dam constructed to prevent saltwater intrusion in Japan. Although the cutoff wall of the dam effectively reduces the movement of saltwater into the reservoir area, saltwater masses remained behind the dam at the time of its completion, and saltwater can intrude beneath and diffuse through the wall, particularly when the reservoir level is below the sea level because of high pumping levels during the drought years. Therefore, it is necessary to estimate in advance whether the saltwater concentration in the pumped water is likely to exceed or not the permissible salinity level because of an increase in the residual saltwater mass as a result of saltwater intrusion and to take necessary measures to suitably manage the saltwater level behind the dam. To analyze saltwater intrusion, we first selected the optimal program suitable for the analysis of saltwater intrusion. Second, we examined the longitudinal dispersivity and the effect of the cone of depression around the pumping wells. Then we analyzed saltwater intrusion into the reservoir area in detail by using a two-dimensional convective-dispersive analysis. The results of the analysis make it possible to improve management of saltwater in the reservoir area behind the underground dam.

Management of Seawater Intrusion in Coastal Aquifers: A Review

“…Basri [35] performed simulation of a 2D vertical section of a hypothetical aquifer, and Nishikawa et al [36] simulated a 2D vertical section of Dominguez Gap coastal area of Los Angeles, California, using SUTRA (Saturated-Unsaturated variable-density ground-water flow with solute or energy TRAnsport) code developed by the United States Geological Survey (USGS). The Komesu underground concrete dam (cut-off wall) in Japan, with dimensions of 2320 m × 0.54 m and a depth of 70 m below mean sea level, can be considered as a good example of physical barriers successfully developed at a large scale to protect an aquifer from saltwater intrusion [37]. Through experimental and numerical simulations, Luyun et al [38] and Abdoulhalik and Ahmed [39] showed that the application of deep physical barriers located closer to the coast and in front of the toe location are more effective.…”

Science, society, and the coastal groundwater squeeze

“…“Hard‐engineering” approaches have also been developed and implemented, including the use of physical barriers to reduce the impacts of seawater intrusion. For example, the Komesu subsurface dam (Japan) has reduced seawater intrusion into fresh coastal groundwater [ Nawa and Miyazaki , ]. Perhaps the most ambitious and successful project to mitigate seawater intrusion impacts is the West Coast Basin Barrier Project (i.e., the Dominguez Gap and Alamitos Barrier Projects), where extensive artificial recharge to create hydraulic barriers against the salinization of water supply wells has been implemented in Los Angeles County (USA) [ Johnson and Whitaker , ].…”

Groundwater flow and transport and potential sources of groundwater nitrates in the Ryukyu Limestone as a mixed flow aquifer in Okinawa Island, Japan

“…In this area, two subsurface dams were completed in 2005 (Nawa and Miyazaki, 2009). Imaizumi et al (2003) demonstrated that caves and caverns in the Ryukyu Limestone aquifer had a significant effect on groundwater flow in the Komesu Subsurface Dam Basin.…”