Irfan A. Khan

River basin salinity management via the ASTRAN method: I. Model development☆

Abstract A new salinity management strategy for irrigated stream-aquifer systems, called the accelerated salt transport ( astran ) method, is described. It is based on the idea that the generally slow salt transport naturally occurring in the saturated zone of a groundwater basin can be augmented by using well pumpage on irrigated lands downstream of the well source. This controls excessive buildup of salts in the groundwater in any one area. An optimizing or screening model is developed for optimal basin-wide application of the astran method. Since the optimization problem is large-scale, it is proved that an efficient, sequential algorithm will yield optimal basin-wide solutions, under certain assumptions. A hierarchical algorithm links the optimizing model with quantity-quality simulation models of both the unsaturated and saturated zones in order to predict concentrations of important ions under astran management. A companion paper (Part II) describes the application of the astran method to a case study.

River basin salinity management via the ASTRAN method: II. Case study☆

Abstract The a ccelerated s alt tran sport ( astran ) method for managing salinity in an irrigated stream-aquifer system is applied to the lower San Luis Rey River basin in southern California. The hierarchical management algorithm developed in Part I is applied for optimally implementing astran over the basin. Three subbasins are included in the study; Pauma, Pala and Bonsall. Unsaturated and saturated zone models for water quantity and quality are calibrated for the area, including important ions such as Ca 2+ , Mg 2+ and Na + as well as SAR. Once the models have been satisfactorily calibrated, a 20-yr. planning period is selected which is divided into two 10-yr. model periods. Hydrologic, land-use, water-demand and water-supply projections are then made for each subbasin. The hierarchical algorithm is then applied, which results in a set of policies over a range of possible levels of total available imported water. For the same quantity of imported water, astran reduces the degradation rate by about one-fifth of what is projected under normal irrigation practice (called the no-management case). astran appears to perform best when the groundwater is allowed to degrade to higher, yet still usable, TDS levels.