Water Engineering Flashcards
What is evapotranspiration?
Evaporation from the ground, plus transpiration through plants.
Why can evapotranspiration be ignored?
Over short time scales (e.g. a storm event), negligible amounts occur. It is a slow process.
How is the Rouse profile derived?
Fall down = Diffusion up.
cbar * w_s = D_z dcbar/dz
What is a water budget?
Inputs-Outputs=Change in Storage
In a water budget, when must evapotranspiration be acconted for?
When storage > zero.
When is potential evaporation more than actual evaporation?
When storage = zero.
When is potential evaporation more than actual evaporation?
When storage = zero (or low)
Water order are storm pipes labelled in?
Start at largest upstream pipe (1.1), label downstream pipes(1.2), repeat for smaller pipes (2.1)
What is the Wallingford Procedure?
Used to estimate how intense a storm of duration D with return T, given an 5M60 storm.
What is a 5M60 storm?
Returns every 5 years, 60 minute duration.
What is a Wallingford Chart?
A chart of discharge, diameter, gradient and velocity, all for a specified pipe roughness.
Which pipe should you design first?
1.1, then 2.1, then 2.2 (i.e. start with entry pipes, and then move downstream, so that flow is known).
What is breakpoint chlorination?
Before acting as a disinfectant, chlorine reacts with other matter. The breakpoint is when it starts to be a disinfectant.
What shape is the BOD curve?
An exponential decay, with an additional nitrogenous demand after a few days.
What is nitrogenous BOD?
The O2 required to break down non-carbonaceous matter. It conceals the ‘useful’ BOD.
What is Returned Activated Sludge?
Sludge returned to the beginning of the system to kickstart aeration of new water.
What is aeration?
Violent agitation to mix and aerate water, so that organic matter is broken down.
What is sludge dewatering?
Sludge is left to ry so that it can be incinerated.
What shape is shear stress in the water?
A linear triangle, largest at the river bed.
What shape is reynolds-averaged velocity?
Parabolic-like, largest at the surface. For smooth flows it is more boxy, for rough flows it is more triangular.
What shape is the eddy viscosity coefficient?
Parabolic, zero at surface and at bed.
