8. Channel Routing Flashcards
1
Q
What steps are involved in channel routing?
A
- determine catchment boundary
- determine sub-catchments according to the stream network & topography (should be roughly the same size)
- insert catchment nodes (open squares) for each sub-catchment at either: i) the point on the stream closest to the centroid, ii) when no stream present, the centroid of the shape
- insert nodes (solid circles) at each sub-catchment outlet
- draw links between upstream & downstream nodes
- draw triangles on the links that require routing i.e. the ones where storage is present (either point storage e.g. reservoir/dam, or long narrow storage e.g. river)
2
Q
What are 2 main equations used in the Muskingum method?
A
S = K ( x.I + (1-x).O ) O(t+∆t) = C1.I(t+∆t) + C2.I(t) + C3.O(t)
3
Q
What are the key features of the channel routing hydrograph?
A
- peak of outflow curve occurs AFTER the intersection of inflow and outflow curves
- point of max storage occurs at intersection of inflow & outflow curves
4
Q
What are the steps to calculate outflow from a given inflow using the Muskingum method?
A
- calculate C1, C2 and C3 from K and x (must add to 1)
2. calculate O(t+∆t) using equation and initial condition (usually steady state i.e. I = O)
5
Q
What are the steps to calibrate K for a given inflow & outflow using Muskingum method?
A
- calculate (I - O)∆t for each time step
- using water balance equation, calculate S (initial condition S=0)
- calculate x.I + (1-x).O for each time step
- graph S vs. x.I + (1-x).O, and choose a value for x that gives the best linear representation
- calculate K as the slope of the line of best fit
6
Q
What are the Muskingum-Cunge approximations for K and x
A
K = L/c
L: length of the reach [m]
c: celerity of the flood peak [m/s]
x = 0.5 [ 1 - Qavg/(Bavg.s.L.c)]
Qavg: average Q along the reach [m3/s]
Bavg: average channel width [m]
s: average bed-slope
7
Q
When is Muskingum-Cunge method used?
A
In the absence of hydrograph data
