CVE 464/564 Groundwater Hydrology – HW3 (100)
Due: 6 pm, Oct 6 (W), 2021
1
CSU ID#: Last Name: First Name:
A. Attach this problem sheet as a cover on top of your separate answer sheets.
B. Clearly write your calculation procedures and answers in your answer sheets.
C. A
ange your answer sheet in order.
D. Your hard copy should be stand-alone to grade without supplementary material. If you have used a
worksheet (or program) in your calculation, you may upload the related worksheet file in Blackboard to
help grading.
1. Two rivers are separated by an unconfined aquifer as
presented. The water levels are 19 and 20 m,
espectively. The length of the aquifer is 1050 m,
hydraulic conductivity is 0.01 cm/s, the cu
ent
echarge rate is 365 mm/year, and the elevation of
ground surface is 22 m. It is required to maintain at
least 1 m thickness from the ground surface for crop
aeration in unsaturated zone. Perform the following.
(1) Compute the highest level of water table (m) and its location (m) in the aquifer under cu
ent recharge
ate.
(2) Compute the flow rate per unit width of aquifer to individual rivers under the cu
ent recharge rate.
(3) Compute the maximum possible recharge rate (mm/year) before not to violate the aeration
equirement of 1 m thickness.
2. A circular island with its diameter 1 km has an average effective recharge rate 146 cm/yr. The depth of
water su
ounding the island is maintained as 10 m and the bottom of this island is impermeable. A
pumping well (rw = 0.3 m) located at the center of the island discharges 600 m
3/d constantly. The
hydraulic conductivity is K=20 m/d. Perform the following.
(1) Compute the height of the water table at the center assuming there is no pumping.
(2) Compute the head drawdown (m) at the well (r=rw) while pumping.
(3) Compute the location of the water divide while pumping.
(4) Compute the height of water table at every 100 m from the well while pumping. And, also draw the
water table profile.
3. A fully penetrating well in a confined aquifer is pumped at a rate of 220 gallon per minute (gpm). After
1270 minutes of pumping, two observation wells showed no further drawdown. The first and second
observation wells are located 26 ft and 73 ft from the pumping well and show piezometric heads of 29.34
ft and 32.56 ft above the top of the aquifer, respectively. Find the aquifer transmissivity in ft2/d.
4. A fully penetrating well discharges 75 gpm from an unconfined aquifer. The original water table was 35
ft. After a long time period, the water table elevations in two observation wells were recorded as 20 ft and
34 ft, respectively. The two observation wells are located 75 ft and 2000 ft away from the discharging
well, respectively. Determine the hydraulic conductivity of this aquifer in ft/s.
19 m
20 m
22 m
1050 m
K = 0.01 cm/s
Recharge
CVE 464/564 Groundwater Hydrology – HW3 (100)
Due: 6 pm, Oct 6 (W), 2021
2
5. A confined aquifer has a transmissivity of 50 ft2/day and a storage coefficient of XXXXXXXXXXA well of radius 1
feet produces water at a rate of 5000 ft3/day.
(1) Use the Theis solution to compute the drawdown at the well and at observation wells that are located
at r=100, 500, 1000, 2000, 4000, and 10,000 ft from the pumping well after 5 days of pumping
(2) Draw the head drawdown profile using the results obtained from (1).
(3) Redo (1) and (2) using the Cooper-Jacob solution. If you can’t compute a drawdown for certain r
values, explain the reason.
6. A ground water well with a radius of 0.3 m supplies i
igation water at a rate of 1500 m3/day during the
growing season. The unconfined aquifer has a horizontal conductivity of 8 m/day, vertical conductivity
of 0.7 m/day, specific yield of 0.15, and an initial saturation thickness of 60 m.
(1) What is the drawdown at the well after four months of the growing season?
(2) Does this well interfere with another well located 2 km away? Please explain the reason.
7. A leaky confined aquifer has a transmissivity of 400 ft2/day. The aquitard has a hydraulic conductivity of
0.2 ft/day and a thickness of 20 ft. A well has a radius of 10/12 ft and pumps groundwater at a rate of
9600 ft3/day.
(1) Use the original solution (i.e., Bessel function) to compute the steady state drawdown at the well.
(2) Use the approximate solution to compute the steady state drawdown at the well.
(3) Compute the radius of influence.