Rainfall runoff modelling Flashcards
What is the benefit of using rainfall record to assess design flood over discharge data?
There are far more rain gauges than river gauges
Rainfall records are longer than river flow records
How is absolute humidity defined?
The mass of water in a unit volume (kg/m3).
How is time of concentration defined?
Tc is the longest time required for a water particle to travel from the remotest point in the catchment to its outlet.
Why is it important to check generalised PMP chart data against local rainfall record?
The Flood Estimation Handbook (FEH) provides generalised probable maximum precipitation in the UK.
▪ However, you should check the maps against local historical data.
▪ Sometimes, the actual 100 year rainfall can be greater than PMP, so reliability is still a problem.
What is the major limitation of using the rational method of assessing runoff?
The rational method cannot provide hydrograph. Its is only able to cope with constant rainfall intensity over the time of concentration. Different modelling techniques are needed to deal with variable rainfall with time and more realistic catchment responses.
Discuss the impact of soil permeability and land cover type on runoff (essay).
ESSAY –> THINK
What is the precipitable water equation?
Integral between 2 limits, of absolute humidity X area wrt dz
What do we use to estimate rainfall?
Probable Maximum Precipitation approach
What is effective rainfall?
Effective rainfall (or net rainfall) is the part of the total rainfall that contributes to runoff.
What is the loss model?
Calculates the effective rainfall
The loss model uses Probability Distribution Model (PDM). Conceptually, the PDM
assumes the catchment to consist of a number of individual storage
elements, each of a random soil moisture capacity C arising from a statistical distribution
What is the routing model?
The routing model depends on the unit hydrograph concept
What is the baseflow model?
The baseflow model uses the linear reservoir concept
The baseflow model implemented in the ReFH model is based on the linear reservoir concept, with a characteristic recession defined as an exponential decay. The approach, discussed by Appleby (1974) allows the separation of total flow in baseflow and surface flow without knowing the rainfall input.
