DES 606 : Watershed Modeling with HEC-HMS Module 5 Theodore G. Cleveland, Ph.D., P.E 29 July 2011

Module 5: Routing Routing simulates movement of adis 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

Module 5: Routing Previous modules –Storage : similar ideas, recall HMS is NOT a hydraulic model. Routing used to connect sub-basins together into an integrated hydrology model.

Rainfall-Runoff Process Watershed –Losses –Transformation –Storage –Routing Precipitation –Meterology, Climate Runoff –Fraction of precipitation signal remaining after losses Hydrologic and Simplified Hydraulics HMS – Basin Component

HEC-HMS Hydrologic Cycle Components in HEC- HMS (circa 2008) Land Surface and Vegetation ChannelsReservoirs Infiltration Loss Snowpack Rainfall, P(t) Snowfall Snowmelt Runoff Percolation Loss Evapo- transpiration Discharge, Q(t)

Routing Hydrographs Routing is the process of predicting temporal and spatial variation of a flood wave as it travels through a river (or channel) reach or reservoir Two types of routing can be performed: –Hydrologic routing –Hydraulic Routing We will concern ourselves with hydrologic routing

Routing Hydrographs Hydrologic routing techniques use the equation of continuity and some linear or curvilinear relation between storage and discharge within the river. –Lag Routing (no attenuation) –Modified Puls (level pool routing) –Muskingum Routing

Routing Hydrographs Hydraulic routing techniques solve full versions of the St. Venant Equations for 1-dimensional free surface flow. Generally these are handled in HEC-RAS, but a subset (simplified hydraulics) available in HMS –Kinematic wave –Muskingum-Kunge

Routing Hydrographs Applications of routing techniques: –Flood predictions –Evaluation of flood control measures –Assessment of effects of urbanization –Flood warning –Spillway design for dams –Detention pond design Vital for multiple sub-basin systems simulations

Routing Hydrographs 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

Routing Hydrographs Upstream Hydrograph Downstream Hydrograph

Routing Hydrographs These “bar-heights” related by the routing table (like the storage-discharge table in prior module)

Routing As a process diagram: Routing Model Inflow (t) Outflow (t) Stream resistance properties Stream geometric properties Wedge and Prism Storage

Routing Table Construction Typically a hydraulic analysis (external to HMS) used to build a storage-discharge table

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

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

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

Routing Hydrographs The routing relationships are usually developed external to HEC-HMS –Like rainfall and external hydrographs, use external tools to develop the storage- discharge relationships

HEC-HMS Example 5 – Illustrate Routing Data Entry –Ash Creek Watershed Subdivide into three sub-basins –Parameterize each sub-basin –Use Lag Routing (simplest model) –Examine results.

Summary Routing is of two types: –Hydraulic –Hydrologic Routing tables built outside HMS, then information imported. May need hydraulic programs to develop routing tables