9532

• UCREFRP Catalog Number: 9532
• Author: Anderson, R. and G. Stewart.
• Title: Riverine Fish Flow Investigations.
• USFW Year: 2000.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

flows including very small discharges, it became necessary to create artificial rectangular

channels at both ends of the modeled reaches. These artificial channels allow the model to

have stable boundary conditions that never go dry while still allowing for the modeling of

flows that would otherwise dry out elements at the inflow and outflow boundaries of the

mesh. HEC-RAS was used to develop stage discharge relationships for the artificial

rectangular channels. HEC-RAS output was also calibrated against known water surface

elevations to estimate a Mannings n for the channel, to determine the wetted perimeter at the'

highest modeled discharge for use in creating the mesh, and for evaluating wetted perimeter

(I-D) vs. wetted area (2-D) as stated in the objectives.

HEC-RAS is a I-D hydraulic flow model created by the Hydrologic Engineering

Center of the U.S. Army Corps of Engineers (Brunner, 1998), and is based on solution of the

one-dimensional energy equation (1).

O!;.

a V 2 a v2
y. +z +~ = Y. +Z +--1..l..-+h
2 2 2g 1 1 2g e

(1)

where Yl'y2 = depth of water at cross. sections
21,22 = elevation at cross sections
Vl,V2 = average velocities (total discharge/total flow area)
al,a2 = velocity weighting coefficients
g = gravitational acceleration
he = energy head loss

h = LS + Ca2Vz2 _ al~2
e f 2g 2g

(2)

'";' r i.;.

where L
Sf
C

= discharge weighted reach length
= representative friction slope between two gross se~.ti<?,ns
= expansion or contraction loss coeffiecient

Water surface profiles are computed from one cross section to the next by solving the

energy equation with an iterative procedure called the standard step method. The steady flow

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