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)

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

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

Routing Hydrographs Upstream Hydrograph Downstream Hydrograph Module 9

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

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

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

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

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

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

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

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.

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

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

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

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