This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Groundwater – Wells”.
1. When water is pumped from a well in a homogeneous and isotropic unconfined aquifer, what does the shape of the water table resemble?
a) Cylinder
b) Hemisphere
c) Cone
d) Helix
View Answer
Explanation: When a well is inserted into a homogeneous and isotropic aquifer with a horizontal water table and water is pumped from it, the water from the aquifer flows radially into the well and the water table assumes a shape similar to a cone.
2. What is the meaning of drawdown at a point in the concept of wells?
a) Drop of water table from initial elevation
b) Rise of water table from initial elevation
c) Depth of water table below the ground level
d) Height of water table above the impervious stratum
View Answer
Explanation: If the initial water table is assumed to be straight, it starts dropping as we move radially towards a pumping well inserted in the aquifer. At any point near the well, the height by which the water table has dropped with respect to the original is known as the drawdown at that point.
3. What is the conical shape of water table created around a pumping well in an unconfined aquifer called?
a) Cone of influence
b) Cone of deflation
c) Cone of drawdown
d) Cone of depression
View Answer
Explanation: Pumping wells in homogeneous isotropic unconfined aquifers start the attract inflow from the aquifer radially into them. This leads to the initially horizontal water table to assume a conical shape and this is known as the cone of depression.
4. What is the radius of the cone of depression called?
a) Radius of depression
b) Radius of influence
c) Radius of convergence
d) Radius of merging
View Answer
Explanation: The radial inflow of water into the well from the aquifer extends upto some radius around the well until the drawdown curve meets the original water table. This radial extent of the cone of depression is known as radius of influence.
5. Water is pumped from a well at a constant rate for a short period of time. What does this represent?
a) Unsteady flow
b) Steady flow
c) Horizontal water table
d) Sudden drawdown
View Answer
Explanation: When the rate of pumping from a well is constant, the drawdown curve develops slowly with time as the storage is being depleted. This represents an unsteady flow as the water table elevation at any point near the well is constantly changing due to drawdown.
6. Which of the following is not true with respect to prolonged pumping form a well in an unconfined aquifer?
a) Represents steady flow
b) Equilibrium is achieved
c) Drawdown at a point is fixed
d) Drawdown in main well is sudden
View Answer
Explanation: When a well is pumped for a long time, the rate of inflow into the well and rate of pumping reach an equilibrium state, in which the drawdown remains constant for any point in the zone of influence. At this stage, the well is under steady flow condition.
7. Recuperation time of an aquifer depends on the features and properties of the well.
a) True
b) False
View Answer
Explanation: Recuperation time is the time required for the depleted storage from the cone of depression to be restored by groundwater inflow till the original water table is reached. This process depends mainly upon the characterictics of the aquifer.
8. Which of the following is true with respect to the recovery process of aquifers after well pumping?
a) The original water table is never achieved
b) The accumulation of storage is sudden
c) It is an unsteady flow process
d) Drawdown in main well is recovered suddenly
View Answer
Explanation: When the pumping of a well is stopped, the groundwater inflow is allowed to gradually fill the depleted aquifer storage from the cone of depression. This is called the recovery or recuperation stage and it is an unsteady process as the drawdown level keeps decreasing gradually until it reaches the original static water table level.
9. What is the difference of a pumping well in a confined aquifer compared to that in an unconfined aquifer?
a) Drawdown curve does not represent water table
b) There is no cone of depression
c) The radius of influence is larger
d) The depletion is very slow
View Answer
Explanation: The well pumping activity in a confined aquifer is very similar to that in an unconfined aquifer. The only main difference is that the drawdown curve in a confined aquifer represents the piezometric surface instead of the water table surface.
10. Which of the following is true with regards to the recuperation of wells in confined aquifer with high piezometric head?
a) Very slow rate
b) Moderate rate
c) Very fast rate
d) Sudden recovery
View Answer
Explanation: When the piezometric head of the confined aquifer is very high, the recovery process of the aquifer and the well water takes place at a very rapid rate although it is not sudden.
Sanfoundry Global Education & Learning Series – Engineering Hydrology.
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