Assessment of Artificial Recharge Dams and Improvement of Their Groundwater-Recharge Capacity

Abstract

Construction of recharge dams across highly permeable beds of alluvial streams is one of the most important techniques used for artificial groundwater recharge from muddy surface runoffs. To assess recharge dams, the Meymand and Tangeriz recharge dams located in southern Iran were studied. More than 90% of the Tangeriz recharge dam capacity was artificially created by excavating two vertical sidewall pits behind the dam. During the most extreme recorded rainfall in the study area, the ratio of inflow runoff volume to reservoir capacity was equal to 1.43 and 16.59, respectively, for the Meymand and Tangeriz dams. The Meymand dam was overflowed, while the Tangeriz dam was not overflowed and stored runoff in the pits was quickly recharged. To interpret the large recharge capacity observed in the Tangeriz recharge dam, a theory of vertical ponded flow in two-layered soils with a low-permeability upper layer was developed. Theoretical development supported by numerical modeling and laboratory/field observations showed that vertical infiltration in reservoirs of recharge dams is mainly controlled and limited by sedimentation of a low-permeability silt layer on the reservoir bed. In contrast, due to negligable sedimentation, lateral infiltration through vertical sidewalls is not influenced by siltation. Therefore, excavation of vertical sidewall pits inside the reservoir of recharge dams is proposed as a novel method for improvement of artificial groundwater recharge. A high lateral recharge rate through the vertical sidewall pits of the Tangeriz recharge dam confirms the effectiveness of the proposed method.