Calibration and Reliability in Groundwater Modelling: Credibility of Modelling

(Proceedings of ModelCARE 2007 Conference, held in Denmark, September 2007). IAHS Publ. 320, 2008, 214-219.

 

Saltwater dynamics due to cut-off wall installation in coastal unconfined aquifers: experimental and numerical studies

 

R. LUYUN, JR1,3, K. MOMII2, K. NAKAGAWA2 & S. FUJIYAMA2

1 United Graduate School of Agricultural Sciences, Kagoshima University, 890-0065 Japan

raluyunjr@ms.kagoshima-u.ac.jp

2 Department of Environmental Sciences and Technology, Kagoshima University, 890-0065 Japan

3 Land and Water Resources Div., University of the Philippines Los Ba–os, 4031 Philippines

 

Abstract In the construction of subsurface dams in coastal aquifers, investigations of the movement and removal of residual saltwater in the storage area are not usually carried out because of difficulties in monitoring. Experimental and numerical studies were thus performed to understand the saltwater dynamics due to the installation of cut-off walls. Experimental results for cut-off walls with opening on the upper part of the aquifer showed the initial advance, gradual retreat and attenuation, and complete removal of the residual saltwater. A shorter cut-off wall exhibited faster attenuation of residual saltwater than a higher cut-off wall. Numerical simulation using SEAWAT verified the experimental results. Flow patterns showed dispersed saltwater was carried by the freshwater discharge along the mixing zone and over the cut-off wall forming a circulation flow in the residual saltwater region, and eventually all the remaining saltwater in the storage area was flushed out. Numerical results also revealed a minimum cut-off wall height limit to achieve complete removal of the residual saltwater. For cut-off walls with opening on the lower part of the aquifer, experimental results showed that more effective attenuation of the saltwater wedge occurred with deeper cut-off wall penetration, which is in general agreement with numerical results.

 

Key words  coastal aquifer; cut-off wall; saltwater intrusion; SEAWAT; subsurface dam