Part 1: Steady Radial Flow Questions

Transcription

1 Islamic University of Gaza Water Resources Management EENV 4359 First Semester ( ) Instructors: Dr. Yunes Mogheir Eng. Wael Salem Eng. Israa Abushaban Question 1 (text book) Part 1: Steady Radial Flow Questions The initial piezometric surface in a confined aquifer of 20 m thickness is 34 m above the bottom. After a long period of pumping, the piezometric surface stabilizes at 29.3 m above the bottom. The hydraulic conductivity of the aquifer is 12.2 m/day. If the radius of the well is 0.5 m and the radius of influence of the pumping is 500 m, what is the steady state well discharge?

2 P a g e 2 Question 2 The following drawdowns were observed in a pump test. The drilling log indicated silty clay up to a depth of 20 m underlain by a 25 m thickness of medium sand followed by fine sandy and clayey sediment. The well screen was installed over the whole thickness of the aquifer (medium sand). A discharge Q of 150 m 3 /hr was pumped for 15 hours till the drawdown became steady. Dtermine the aquifer hydrulic conductivity K. Oservation well at (m) Drawdown (m) Sol. 1- Steady Radial Flow (OR: Pumping for a long period). 2- Unconfined Aquifer (medium sand), H=25m. 3- Calculate K.

3 P a g e 3 Question 3 (text book) After a long period of pumping from an unconfined aquifer at a constant rate of 850 m 3 /day, the cone of depression reaches equilibrium. The aquifer has an initial saturated thickness of 20 m and a hydraulic conductivity of 8.65 m/day. During the equilibrium, the water levels in an observation well 50 m away and in the pumping well are measured as 18.4 and 9.9 m. Determine: 1- The radius of influence of the pumping. 2- The radial distance where the steady drawdown is 5 cm. 3- The expected drawdown in the pumping well (r w = 0.4 m). 4- The total well losses.

4 P a g e 4 Question 4 (text book) A well with a radius of 0.5 m pumps at the rate of 15 L/s from an unconfined aquifer that is uniformly recharged at a rate of 0.6 m/day. Without pumping from the well, the water table is nearly horizental and the aquifer thichness is 30 m. the hydrulic conductivity of the aquifer is 20 m/day. Determine the radius of influence of the well and the approximate drawdown at the well location near steady state condition.

5 P a g e 5 Question 5 A 30 cm diameter well fully penetrates an unconfined aquifer K is 10 m/day having a saturated thickness of 30 m. Dtermine the discharge for a drawdown at the well of 5 m if rainfall penetration is 0.1 cm/hour. Assume steady state condition.

6 P a g e 6 Question 6 Part 2: Unsteady Radial Flow Questions Drwadown in an observation well 100 meters away from a well fully penetrating a confined aquifer of 20 m thickness and pumping at a steady rate of 30 m 3 per hour are listed in the table below. Determine the aquifer transmissivity and storativity using Theis, Jacob and chow method of solution and compare between results. t (min) s (m)

7 P a g e 7 Question 7 Assume that the pump of the well of Question 6 was stopped at 960 minutes. And residual drawdowns were observed in an observation well 100 m from pumped well which are recorded in the table below. Dtermine the Transmissivity of the aquifer. (Use Recovery method). t (min) s (m)

8 P a g e 8 Question 8 (text book) A fully penetrating production well pumps from a confined aquifer at a constant rate of 64 L/s. If the coefficients of transmissiviy and storage of the aquifer are 1240 m 2 /day and 4 * 10-4, respectively. Estimate the drawdown at a distance of 200 m from the pumping well for pumping period of 8 hours, 30 days, and 6 months using: 1- Theis equation (Non-equilibrium equation). 2- Cooper-Jacob method of solution.

9 P a g e 9 Question 9 Calculate the drawdown in an observation well 100 m from a pumped well which completely penetrates an unconfined aquifer. The aquifer properties are K = 20 m/day, H = 100 m, and S = The well is pumped at 5027 m 3 /day. Calculate s for t = 0.08, 0.32, 3.2, 8, 32, and 80 days.

10 P a g e 10 Question 10 An aquifer has been pumped for 240 min and at this time the drawdown was determined to be m, Aquifer transmissivity is equal m 2 /day, and the aquifer was pumped at m 3 /min. 1- What should be the drawdown have been at 100 min of pumping. 2- At what time the drawdown of 0.61 m should been occur. 3- Find the aqufier storativity S if an observation well was at a distance of 50 m. Hint: Use Cooper-Jacob method.

11 P a g e 11 Question 11 A completely penetrating well in an unconfined aquifer is pumped at a rate Q of 4000 m 3 /day. At time t equal to 360 min the drawdown s was determined to be 0.9 m in an observation well at distance r = 500 m. Also the aquifer transmissivity T is equal to 2000 m 2 /day. 4- Calculate the drawdown s for t = 160 min of pumping. (Hint: Use Time-Drawdown (Cooper-Jacob) method) 5- Calculate the distance r of an observation well with a drawdown s equal to 1 m. (Hint: Use Distance-Drawdown method) Sol. 1- s = 0.77 m. 2- r = 266 m.

12 P a g e 12 Question 12 A completely penetrating well in an unconfined aquifer is pumped at a rate of 5072 m 3 /day. The aquifer constants are T = 2000 m 2 /day and S = Calculate the drawdown s in observation wells, 50, 100 and 200 m from the pumped well after 0.01, 0.025, 0.1, 0.25, 1, 2.5, 10, 25, and 100 days of pumping. Calculate the difference between drawdown s for the wells at 50 and 100 m from the pumped well, and plot this difference against log t for the above t values. Use the calculated s-vs-t data for observation well 100 m distance from pumped well to determine T and S of the aquifer using Theis OR Jacob method. Compare calculated values of T and S with known values of both.

13 P a g e 13 Question 13 You are asked to design a pump test for a confined aquifer in which the transmissivity is expected to be about 1.4 * 10-2 m 2 /s and the storativity about 1.0 * What pumping rate would you recommend for the test if it is desired that there be an easily measured drwadown of at least 1 m during the first 6 h of the test in an observation well 150 m from the pumping well.

14 P a g e 14 Question 14 For transmissivity T = 2500 m 2 /day, storativity S = 1.0 *10-3, and a pumping rate Q = 500 m 3 /day, calculate drawdowns in a confined aquifer for r = 10, 50, and 100 m at t = 150 min.

15 P a g e 15 Question 15 Values of drawdown and distance in a pumping test in a confined aquifer are listed in the following table. Determine the hydrulic parameters of the aquifer using the distance straight-line technique. Assume that t = 105 min, and Q = m 3 /day. Distance (m) Drawdown (m)