Stream depletion in alluvial valleys using the SDF semianalytical model

Area of Science:

• Hydrogeology
• Groundwater Hydrology
• Water Resource Management

Background:

• The stream depletion factor (SDF) method, based on the analytic Glover model, is widely used for quantifying stream depletion from groundwater pumping.
• This method uses numerical model-derived SDFs to address non-ideal conditions like variable transmissivity and aquifer boundaries.
• Approximations in the SDF method can introduce errors, particularly near impermeable aquifer boundaries.

Purpose of the Study:

• To review the applicability of the SDF method in narrow alluvial aquifers.
• To present new stream depletion response curves for wells located within bounded aquifers.
• To propose a modification to the SDF method to accurately account for impermeable aquifer boundaries.

Main Methods:

• Review of the history and assumptions of the SDF method.
• Development of new stream depletion response curves based on well position in bounded aquifers.
• Proposal of a modification to modeled SDF values using image wells to account for impermeable boundaries without overcorrection.

Main Results:

• The proposed modification improves SDF-based stream depletion estimates in bounded aquifers.
• SDFs for well locations closer to the river than the aquifer boundary do not require modification.
• Boundary effects in other aquifer portions exhibit a predictable, removable pattern.
• Verification through comparison with a calibrated numerical model confirmed the modification's effectiveness.

Conclusions:

• The modified SDF method enhances stream depletion estimations in bounded aquifers.
• The approach retains the benefits of SDF maps for water rights administration.
• This improved method provides more accurate and reliable groundwater management tools.