1. Routing-Hydrologic and Hydraulic
Routing simulates movement of a discharge signal (flood wave) through stream reaches.
Accounts for storage within the reach and flow resistance.
Allows modeling of a basin comprised of interconnected sub-basins
Hydrologic routing – uses continuity equation
Hydraulic routing – uses continuity and momentum (St. Venant Equations)

2. Hydrologic Routing
Hydrologic routing techniques use the equation of continuity and some linear or curvilinear relation between storage and discharge within the river.
Methods include:
Lag Routing (no attenuation)
Modified Puls (level pool routing)
Module 9

3. Routing-Hydrologic and Hydraulic
Problem:
you have a hydrograph at one location (I)
you have river characteristics (S = f(I,O))
Need:
a hydrograph at different location (O)
This is a “routing” situation.
The “river” can be a reservoir or some similar feature
Module 9

4. Routing Hydrographs
Upstream Hydrograph
Downstream Hydrograph
Module 9

5. Routing Hydrographs These “bar-heights” related by the routing table
Module 9

6. Routing Table Construction
Typically a hydraulic analysis used to build a storage-discharge table
Module 11

7. Subdivision The term subdivision occurs in two contexts:
Watershed subdivision into connected sub-basins
Stream channel subdivision into subsections with different properties (Roughness, shape, etc.)
This module refers to the first meaning:
Dividing a watershed into sub-basins
Module 11

8. Subdivision Watersheds are divided into sub-basins when
Ground conditions vary substantially within the watershed (e.g. part urban, part undeveloped)
Total area is so large that variations in precipitation depth within the watershed must be modeled
Other situations where treating the watershed as a lumped unit is unsuitable.
Module 11

9. Routing and Watersheds
Typically – multiple sub-basins. Routing to move outlet from a sub-basin to main outlet.
Module 11

10. Routing and Watersheds
Typically – multiple sub-basins. Routing to move outlet from a sub-basin to main outlet.
These two must transit the “rose” sub-basin
Runoff
Module 6
Time

11. Routing and Watersheds
Typically – multiple sub-basins. Routing to move outlet from a sub-basin to main outlet.
Composite
These two must transit the “rose” sub-basin
“routed” to the outlet
Runoff
Runoff
Module 6
Time
Time
Module 11

12. Routing-channel and reservoir
Reservoir routing
Account for storage in a reservoir
Unique storage-discharge relationship
Channel routing
Account for storage in channel as well as travel time
Storage-discharge relation in channel is non-unique (looped; HDM pp4-113)
Can treat channel as a series of reservoirs to mitigate looped effect.

13. Basic reservoir routing equations
From continuity equation, basic relationship is:
where DS = the change is storage during some time period Dt; Qin = the average inflow during the period; Qout = the inflow during the period
For application, rewrite as: It-1, It = inflow at times t-1 and t, respectively; Ot-1, Ot = outflow at t-1 and t; St-1, St = storage at t-1, t

14. Storage indication curve
Rather than trial and error with rating, convenient to create function relating O to [2S /t + O ]. Get from manipulating rating.
Then, knowing [2S /t + O ], find O. Proceed.
Moule 11

15. Rating curves to storage indication curve
Compute reservoir elevation-outflow curve – orifice and/or weir:
Outflow = CA(2gh)0.5 + CLH1.5
Compute elevation-storage curve based on shape of reservoir (e.g. surface area x depth)
Combine elevation-outflow and elevation storage to get storage-outflow
At each storage-outflow level, compute 2s/Δt+O using the same change in time as the inflow hydrograph ordinates. Make sure time converted to seconds!
Modle 11

16. Storage routing calculation table
Step It
It+It-1
2St/Dt - Ot
2St/Dt + Ot Ot
2St/Dt St -- 1 62
55-7=48 7
62-7=55 2
130 3
394 4
388
Look up in storage indication function
Compute if needed.
Compute with computed outflow and storage for this period
Mode 9