DES 606 : Watershed Modeling with

HEC-HMS

Module 5Theodore 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

Channels Reservoirs

Infiltration Loss

Snowpack

Rainfall, P(t)Snowfall

Snowmelt

Runoff 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

T

SOI

Upstream Hydrograph Downstream Hydrograph

Routing Hydrographs

SOIT )(

• 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

Run

off

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

Run

off

These two must transit the “rose” sub-basin

Run

off

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