Flow to Wells - 1 Groundwater Hydraulics Daene C. McKinney

Summary Steady flow to a well in a – confined aquifer – to a well in an unconfined aquifer – capture zones

Steady Flow to a Well in a Confined Aquifer

Flow to a Well in a Confined Aquifer

Flow to a Partially Penetrating Well in a Confined Aquifer

Steady Flow to a Well in a Confined Aquifer rwrw Ground surface Bedrock Confined aquifer Q h0h0 Pre-pumping head Confining Layer b r1r1 r2r2 h2h2 h1h1 hwhw Observation wells Drawdown curve Q Pumping well

Example - Steady Flow to a Well in a Confined Aquifer Q = 400 m 3 /hr b = 40 m Two observation wells, 1.h 1 = 85.3 m r 1 = 25 m) 2.h 2 = 89.6 m r 2 = 75 m) Find: Transmissivity ( T ) rwrw Ground surface Bedrock Confined aquifer Q h0h0 Confining Layer b r1r1 r2r2 h2h2 h1h1 hwhw Q Pumping well

Steady Flow to a Well in a Confined Aquifer Head Drawdown h(r = R) = h 0

Example - Steady Flow to a Well in a Confined Aquifer 1-m diameter well Q = 113 m 3 /hr b = 30 m h 0 = 40 m Two observation wells, h 1 = 38.2 m r 1 = 15 m) h 2 = 39.5 m r 2 = 50 m) Find: Head and drawdown in the well rwrw Ground surface Bedrock Confine d aquifer Q h0h0 Confining Layer b r1r1 r2r2 h2h2 h1h1 hwhw Q Pumping well Drawdown

Example - Steady Flow to a Well in a Confined Aquifer rwrw Ground surface Bedrock Confine d aquifer Q h0h0 Confining Layer b r1r1 r2r2 h2h2 h1h1 hwhw Q well Drawdown at the well

Steady Flow to a Well in a Confined Aquifer rwrw Ground surface Bedrock Confined aquifer Q h0h0 Pre-pumping head Confining Layer b r1r1 r2r2 h2h2 h1h1 hwhw Observation wells Drawdown curve Q Pumping well

Steady Flow to a Well in a Unconfined Aquifer

Flow to a Well in an Unconfined Aquifer

Steady Flow to a Well in an Unconfined Aquifer rwrw Ground surface Bedrock Unconfined aquifer Q h0h0 Pre-pumping Water level r1r1 r2r2 h2h2 h1h1 hwhw Observation wells Water Table Q Pumping well

Given: – Q = 300 m 3 /hr – Unconfined aquifer – 2 observation wells, h = 40 m r 1 = 50 m) h = 43 m r 2 = 100 m) Find: K Example – Steady Flow to a Well in an Unconfined Aquifer rwrw Ground surface Bedrock Unconfined aquifer Q h0h0 Prepumping Water level r1r1 r2r2 h2h2 h1h1 hwhw Observation wells Water Table Q Pumping well

Steady flow to a Well in an Unconfined Aquifer with Recharge Recharge rate = W Flow to well increases

Example - Steady flow to a Well in an Unconfined Aquifer with Recharge r 50 m 25 cm diameter well to maintain lowered water table K = 1x10 -5 m/s (0.864 m/d) Bottom of aquifer is horizontal at 20 m bgs Water table is 1 m bgs Unconfined aquifer is recharged at W = 0.06 m/d Water table must be lowered 3 m over site Drawdown at corners must be at least 3 m r=35.35 m Solve by iteration: r 0 = 70 m, Q w = 924 m 3 /d

Capture Zones

Well Pumping in Uniform Flow “capture zone” = zone from which a well is drawing water in an aquifer When a well is in an aquifer with a uniform regional flow, we can calculate the capture zone by superposing the uniform flow on the well flow “groundwater divide” = boundary of the region providing inflow to the well

Example – Capture Zone ).5 m radius well pumps at 15 L/s from a 35 m thick confined aquifer with a hydraulic conductivity of 20 m/d. Distance and head drop between 2 well are 1000 m and 3 m before the well. Find: longitudinal and transverse limits of water entering the well.

Summary Steady flow to a well in a – confined aquifer – to a well in an unconfined aquifer – capture zones