# What is unsteady flow in HEC-RAS?

## What is unsteady flow in HEC-RAS?

The unsteady flow computational program in HEC-RAS uses the same hydraulic calculations (cross section properties, bridge and culvert hydraulics, weirs, gated structures, etc…) that HEC developed for steady flow, however, the solution of the unsteady flow equations (Continuity and momentum equation) are solved using a …

In unsteady-flow analysis, internal boundary conditions are approximated as steady-flow relations because the special features generally are short enough that the changes in momentum and volume of water within the special features are small.

What is a HEC-RAS model?

HEC-RAS is a one-dimensional steady flow hydraulic model designed to aid hydraulic engineers in channel flow analysis and floodplain determination. The results of the model can be applied in floodplain management and flood insurance studies.

A flow that is not a function of time is called steady flow. Steady-state flow refers to the condition where the fluid properties at a point in the system do not change over time. Time dependent flow is known as unsteady (also called transient). This roughly means that all statistical properties are constant in time.

What is steady flow energy equation?

This expression represents the steady-flow energy equation in terms of energy per unit of mass of fluid [units of L2t−2]. The term p/ρw is the pressure energy per unit mass. The term gz is the potential energy per unit mass. Thus, in words, “the energy per unit mass is conserved along a streamline.”

What is the purpose of HEC-RAS?

Welcome to the Hydrologic Engineering Center’s (CEIWR-HEC) River Analysis System (HEC-RAS) website. This software allows the user to perform one-dimensional steady flow, one and two-dimensional unsteady flow calculations, sediment transport/mobile bed computations, and water temperature/water quality modeling.

## Why do we use HEC-RAS?

Usages. HEC-RAS is a computer program for modeling water flowing through systems of open channels and computing water surface profiles. HEC-RAS finds particular commercial application in floodplain management and [flood insurance] studies to evaluate floodway encroachments.

When to use unsteady flow with HEC-RAS?

However, the answer is not straightforward, requiring some elaboration. Under steady flow, the user specifies: (1) discharge at the upstream boundary, and (2) stage at the downstream boundary. The steady flow model proceeds to calculate stages throughout the interior points, while keeping the discharge constant.

What are the three types of HEC-RAS calculations?

The U.S. Army Corps of Engineers Hydrologic Engineering Center River Analysis System, for short, the HEC-RAS model, can perform three types of calculations: (1) steady flow, (2) unsteady flow, and (3) movable boundary flow. The steady flow component uses the standard step method for the solution of steady gradually varied flow.