# Engineering Hydrology Questions and Answers – Hydrologic Storage Routing (Level Pool Routing)

This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Hydrologic Storage Routing (Level Pool Routing)”.

1. Due to which of the following assumptions is hydrologic storage routing also known as level pool routing?
a) Reservoir storage is a function of outflow only
b) Level of water remains same throughout the process
c) Reservoir storage is a function of both outflow and inflow
d) The reservoir water surface is horizontal throughout the process

Explanation: One of the assumptions in hydrologic storage or reservoir routing is that the water surface remains horizontal even if the level is changing constantly. Due to this assumption, it is also called as level pool routing.

2. For a freely operating spillway, where does the peak of outflow hydrograph occur?
a) Before intersection of inflow and outflow hydrograph
b) After intersection of inflow and outflow hydrograph
c) At intersection point of inflow and outflow hydrograph
d) Cannot be predicted

Explanation: At the peak point of outflow hydrograph, the slope of tangent is zero.
⇒$$\frac{dQ}{dt}$$=0 , where Q = outflow discharge and t =time
So at this point, the reservoir elevation also remains same which means the storage also remains same.
⇒$$\frac{dS}{dt}$$=0 , where S = storage volume
From continuity equation, $$\frac{dS}{dt}$$=I-Q=0 ⇒I=Q
Therefore, the outflow hydrograph at its peak must intersect the inflow hydrograph.

3. Which of the following is true with respect to the rising limb of the inflow hydrograph of a reservoir used for hydrologic routing?
a) It is parallel to the rising limb of outflow hydrograph
b) It lies above the rising limb of outflow hydrograph
c) It lies below the rising limb of outflow hydrograph
d) It has a lower slope than rising limb of outflow hydrograph

Explanation: In the portion of the rising limb of inflow hydrograph, the outflow hydrograph lies below the inflow hydrograph. The slope of the rising limb of inflow hydrograph is more than that of the outflow hydrograph in reservoir routing.

4. What does the region between the falling limbs of inflow and outflow hydrographs represent in hydrologic storage routing?
a) Lost storage volume
b) Accumulated storage volume
c) Increased rate of storage decrease
d) Decreased rate of storage increase

Explanation: In the falling portion of the inflow hydrograph, the outflow hydrograph lies above the inflow hydrograph. This means that the outflow rate is more than the inflow rate, and hence a depletion in storage volume.

5. Which of the following is true with respect to the peaks of inflow and outflow hydrograph for hydrologic routing of a reservoir?
a) Both peaks occur at the same time and have different values
b) Both peaks occur at different times and have different values
c) Both peaks occur at same time and have same values
d) Both peaks occur at different times and have same values

Explanation: The most important characteristic of a reservoir in hydrologic flood routing is its storage effect. This leads to a different time of peak and magnitude of peak discharge of outflow hydrograph compared to the inflow hydrograph and allows for flood protection.

6. During hydrologic routing of a reservoir, the time to peak of inflow hydrograph was found to be ‘T’ hours. Which of the following is the most likely time to peak for the outflow hydrograph?
a) (T – 2) hours
b) T hours
c) 0.5T hours
d) 1.5T hours

Explanation: Due to the storage effect of a reservoir, the peak of the outflow hydrograph always occurs later than the peak of the inflow hydrograph. This is known as peak lag. The only option having a time to peak greater than T hours is 1.5T hours.

7. The peak outflow from a reservoir during hydrologic routing was found to be 63 m3/s. What would be the most likely value of the peak inflow?
a) 8.3 m3/s
b) 63 m3/s
c) 83 m3/s
d) 630 m3/s

Explanation: Due to the storage property of a reservoir, the peak of the outflow hydrograph will always be lower than that of the inflow hydrograph. This is known as peak attenuation. 83 m3/s and 630 m3/s are both greater than the outflow peak, but an inflow peak of 630 m3/s will give an implausible attenuation of (630 – 63) = 567 m3/s. Therefore, the most likely inflow peak is 83 m3/s.

8. The third order Runge Kutta method is used for hydrologic storage routing?
a) True
b) False

Explanation: The Runge Kutta methods are numerical method to efficiently carry out level pool routing of a reservoir. Any of the Runge Kutta methods may be used but the standard fourth order Runge Kutta method is the most accurate.

9. Which of the following is a pair of semi-graphical methods used for hydrologic storage routing?
a) Modified Pul’s and Muskingum method
b) Muskingum and Runge Kutta method
c) Runge Kutta and Goodrich method
d) Goodrich and modified Pul’s method

Explanation: There are many methods that are used to route floods through a reservoir, but all of them make use of the basic hydrologic continuity equation. In semi-graphical methods, modified Pul’s and Goodrich method are the most popular methods.

10. What is the basic difference between modified Pul’s and Goodrich method of flood routing?
a) Continuity equation and momentum equation
b) Arrangement of basic continuity equation
c) Use of partial derivatives
d) Graphical and numerical method

Explanation: Both the methods have the same principle and both of them are semi-graphical. The only difference between them is how the terms of the basic continuity equation are arranged and how the procedure is followed from thereon.

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