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1. In reservoir routing, when the inflow and outflow coincide, the outflow is a maximum. Why?
Because storage is the area between inflow and outflow curves [S = ∑ (I - O) Δt].
At the point in time when outflow equals inflow, incremental storage is zero and total storage is a maximum.
Right after that, incremental storage becomes negative and total storage starts to decrease.
Since storage is directly related to outflow, maximum storage means maximum outflow.
2. In reservoir routing, there is no lag between the start of inflow and the start of outflow.
Why?
Because in an ideal reservoir, the water surface slope is zero, and the velocity of propagation of surface waves
is infinity. Thus, as soon as inflow is sensed by the reservoir, outflow starts to come out.
3. What is McCarthy's contribution to hydrology?
McCarthy developed the Muskingum method, which routes flood waves through channels. The method is the most widely used
method of flood routing in channels.
4. What is Hayami's contribution to hydrology?
Hayami developed the concept of diffusion analogy, which states that flood propagation can be modeled as a diffusion problem,
with a governing diffusion equation having a distinct coefficient of hydraulic diffusivity ν = (q)/(2S).
5. What is Cunge's contribution to hydrology?
Cunge found out that the Muskingum method is a solution of the linear kinematic wave equation, and that
its numerical diffusivity can be modeled with the diffusion wave equation. Thus, he was able to calculate the weighting factor K
of the Muskingum method in terms of measurable hydraulic parameters, making the method more predictable.
6. Give three definitions for flood wave (Seddon) celerity.
(1) c = dQ/DA (discharge-area rating)
(2) c = (1/T) dQ/dy (discharge-stage)
(3) c = βV (in terms of mean flow velocity)
7. What is the Courant number? Under what value of Courant number does the Muskingum-Cunge method
work best? Why?
The Courant number is the ratio of physical celerity to grid celerity (the latter is the mesh ratio Δx/Δt).
The Muskingum method works best under Courant numbers close to 1. This is because errors are minimized at Courant equal to 1.
8. Which situation, mountain flow or valley flow, diffuses the flow more? Why?
Valley flow, because diffusion is inversely related to prevailing channel slope. Valley slopes are typically smaller that mountain slopes.
9. Why does the time-area method overestimate the flood peak?
Because the time area method considers only translation, and not diffusion. Diffusion, or hydrograph spreading, is totally absent from
results calculated by the time-area method.
10. Why would you not use the method of cascade of linear reservoirs in an ungaged basin?
Because we would have no way to calibrate the results, since there are no field measurements.
11. Why are worms important in hydrology?
Worms work the soil and improve texture, increasing porosity and hydraulic conductivity, making possible more infiltration.
Thus, worms change the water balance from more runoff to more infiltration.
12. Why are cowboys important in hydrology?
Cowboys more cattle around, avoiding overgrazing of the land, and preserving the range.
Without cowboys, cattle have a tendency to remain near waterholes, resulting in overgrazing and the eventual
ruin of the range.
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