Evaluation and Design of Irregularly-Positioned Relief Wells

Evaluation and remediation of existing levee segments with passive relief wells can present complexities that are not easily resolved using standard simplified approaches. This is especially true in urban areas where structures are often in proximity to the landside levee toe, as is the situation along the East Levee of the Sacramento River in Sacramento, California. Thus, traditional, simplified design procedures for lines of equally-spaced relief wells are not applicable. The current studies along the Sacramento River East Levee (SREL) required the use of less common relief well evaluation and design techniques. The area around Sacramento’s Pioneer Reservoir created such a scenario. The reservoir is in proximity to the levee with existing relief wells in localized areas of relatively low elevation near the landside toe. Based on the relief well configuration, it was judged that the most appropriate technique was a direct solution method using superposition and the Thiem equation as presented in USACE EM 1110-2-1914. The selected methodology allowed the existing relief wells to be modeled in their relative positions. The technique also allowed LiDAR elevation data to be overlaid on a map of the estimated aquifer heads to efficiently identify critical locations and optimize placement of new relief wells. Implementation of this approach included an evaluation of available procedures to evaluate the efficiency head losses that should be assumed for design. An approach for a line of relief wells, described in Guy et al. (2010), was generalized to the case of irregularly-positioned relief wells. This technique was compared to efficiency head loss estimates predicted using USACE EM 1110-2-1914 techniques to confirm the reasonableness of the results.