Loxton Salt Interception Scheme Trial Horizontal Drainage Well: Well and Aquifer Response to Pumping, and Effectiveness in Controlling Groundwater Flux Discharging to the River Murray

摘要

The Loxton irrigation area is located adjacent the River Murray in the northwest region of the Murray Basin. In-river surveys indicate that a groundwater driven salt load of -98 t/d enters the river in the Loxton reach at river flows of less than 5,000 ML/d, and this may double to 188 t/d at flows of 20,000-30,000 ML/d. The construction of a salt interception scheme (SIS) was proposed to intercept the flux of saline groundwater (and therefore the salt load) before it enters the river. The Department of Water, Land and Biodiversity Conservation (DWLBC) in partnership with the Murray Darling Basin Commission and SA Water, have designed and constructed the SIS floodplain wellfield component of the SIS, and have undertaken preliminary investigations in relation to the application of horizontal drainage wells in the highlands. This paper details the results of a long-term (18 month) pumping test conducted on the Loxton trial horizontal drainage well. Interpretation of the test results, in terms of the well and aquifer response to pumping, and operational issues are discussed. This paper also discusses numerical groundwater modelling that predicts the effectiveness of the trial well, and various theoretical horizontal well construction scenarios, at intercepting the groundwater flux discharging to the river through a 1,300 m long aquifer strip. A general review of the design of the AUS$1.2 m trial well, which has a total length of 500 m and an operational horizontal production zone 250 m in length, is given. Recommendations are provided in relation to well design and construction.