Numerical Modeling of Salt‐Water Intrusion at Hallandale, Florida

Abstract

ABSTRACT The City of Hallandale, located on the east coast of Florida, has documented over the past decade an increase in chloride in the monitoring well network surrounding its wellfield. Data indicate that the salt‐water front is currently located within 1,200 ft of the wellfield and is still moving inland. Suspected causes of the intrusion are: (1) increased pumpage by Hallandale, (2) increased pumpage from neighboring wellfields, (3) cumulative deficiency in rainfall over the past decade, and (4) reduction of canal stages that control water‐table elevations. The inability of standard methods to characterize the salt‐water intrusion led to the use of numerical modeling to aid in understanding the processes occurring at Hallandale. A series of three models were used in the study. A cross‐sectional model was used to conceptualize the flow system, and a regional model synthesized input for the third model, the wellfield model. The wellfield model was eventually used to assess the relative merits of proposed water management alternatives. Although the modeling did not isolate a specific cause of the intrusion, it did show the extreme sensitivity of the hydrologic system. Long‐term water‐level declines of only a few tenths of a foot were shown to result in a significant movement of the salt‐water front. There is a distinct time lag, however, between lowering of the hydraulic heads and movement of the salt‐water front, which has many implications for water management decisions and in the construction and calibration of a numerical model. These observations, as well as others made in the course of this study, can be applied generally to coastal water management programs.