Boundaries and Superposition Groundwater Hydraulics Daene C. McKinney

Introduction Review Superposition Two Wells in an Aquifer Image Well Continuity in Aquifers Steady flow to a well in confined aquifer Superposition Two Wells in an Aquifer Image Well for an Impermeable Boundary for a Constant Head Boundary Multiple Wells in an Aquifer

Continuity in Aquifers Confined aquifer Unconfined aquifer Linear equations If h1 and h2 both satisfy a linear equation Then another solution is h3 = Ah1 + Bh2 where A and B are constants (For unconfined aquifer, everything is in terms of h2)

Steady Flow to a Well in a Confined Aquifer 2rw Ground surface Bedrock Confined aquifer Q h0 Pre-pumping head Confining Layer b r1 r2 h2 h1 hw Observation wells Drawdown curve Pumping well Point of interest (x,y) Well at = (xw,yw)

Superposition (2 wells pumping)

Superposition (n Wells pumping)

Steady Flow to a Well in an Unconfined Aquifer 2rw Ground surface Bedrock Unconfined aquifer Q h0 Pre-pumping Water level r1 r2 h2 h1 hw Observation wells Water Table Pumping well

Example x y

Example Q = 2x10-2 m3/s, T = 5x10-3 m2/s, Ho = 25 m, rw = 0.25 m y x

Example How much does the pumping in well 2 affect the head in well 1? With both wells pumping With only Well 1 pumping Difference = 1.54 m x

Superposition (n Wells pumping)

Image Well to Simulate Impermeable Boundary x y

Drawdown Near Impermeable Boundary

Image Well to Simulate Constant Head Boundary x y Todd, 1980.

Example - Constant Head Boundary

Example – Impermeable Boundary

Multiple Well Systems

Summary Review Superposition Two Wells in an Aquifer Image Well Continuity in Aquifers Steady flow to a well in confined aquifer Superposition Two Wells in an Aquifer Image Well for an Impermeable Boundary for a Constant Head Boundary Multiple Wells in an Aquifer

Well 1 pumping alone Well 2 Both wells pumping together