Question

could you help me with this exercise and write down the formula please?

6. A farm is to be serviced with irrigation requirements from a 30 cm diameter, fully screened, well I surficial aquifer. At present the water table is approximately 1.0 m below the ground surface and nearly horizontal. The aquifer consists of a sand and gravel material that is 15 m thick and sits on top of an impermeable till layer. Upon pumping the well at a constant rate for some time, the water level in the well reaches a constant level 5 m below the original water level while at the same time water in a monitoring well some 100 m away reaches a constant level some 0.1 m below its original static level. a. What is your estimate of the well pumping rate? b. What assumptions were required to answer part a? c. If the water being pumped is being returned to the land above the aquifer for irrigation purposes, how would you change your approach to part a?

Answer 1

Ground surface = 15 -|-0.1 = 13.9 m 4,9m ikk, 15 cm 42 5100 m (1) Using Thiems fermula for steady unconfined flow = Tk (H2-42) Tok (h3-4) in (M2/4) en (R/4w) = T ( 13.9² - 92) = 54,21 k (m2)

Since the aquifer consists of sand and gravel we can assume woefficient of pelumeability as around 10-3 m/sec Hence or 5.421 X10 x 103 m² / = 5.421 X10 2 m/s (6) Assumptions used in paket a 1) The flow is laminate and Darcy's law is valid. 2) The soll mass is isotropic A homogeneous 3) The well penetrates the entire thickness of aquifer. 4) The flow is steady 5) The wefficient of permeability remains constant throughout. 6) The flow towards the well is radial and horizontal 1) Natural ground watch regime remains constant (c) If the water being pumped is being retouned to the land above the aquifere then the ground water will get rechanged through infiltration. In that case, the formula used will change. Assuming a suchange of Rmls per meter length along