Prepared By:

VISHVAM PANCHOLI

(130280712013)

ME-Water Resources & Management

L.D.College of Engineering,Ahmedabad-380061

Outline of seminar

*Basic Concept of modelling

*Introduction of modelling

*Introduction to HEC RAS Model

*Overview of HEC RAS Model

What is

Hydrological

modelling

Hydrologic models are simplified, conceptual representations of the

Hydrologic cycle.

Source:- U.S.D.S

Why Modelling is Required ?

Modelling has become an integral part of the decision making

process for water engineers and managers.

Recent research in hydrologic modelling tries to have a more global

approach to the understanding of the behaviour of hydrologic systems to

make better predictions and to face the major challenges in water

resources management.

Recently, Hydrological models have taken over the most important tasks in

problem solving in hydrology (UNESCO, 1985). It is valuable for studying

potential impacts of changes in land use or climate.

As one report of CSDMS ( Community Surface Dynamics Modelling

System) 56 Hydrological models are Present.

What are the use of a model?

Forecast / Prediction

Instead of expensive and time consuming measurements

What happens if’ questions

Summarize and test knowledge

Education

Hydrological Modelling

Black Box

Conceptual

Deterministic

Lumped

Semi-Distributed

Distibuted

1).Lumped models

Do not account for the spatial distribution of input variables or

parameters.

Do not require a digital elevation model (DEM) as input.

Also Known as “Low Rank” Models.

Ex- SRM (Snowmelt-Runoff Model), WATBAL etc.

2).Semi-distributed models

Models Parameters are partially vary in space by dividing the basin into

sub basins.

It has Two types

1) Kinematic wave theory models (KW models, such as HEC-HMS),

2) Probability distributed models (PD models, such as TOPMODEL).

The KW models are simplified versions of the surface and/or subsurface

flow equations

The PD models are accounted distributions of input parameters across the

basin.

Also Known as “Medium Rank” Models.

Ex-HEC-HMS,HEC-RAS, Storm Water Management Model (SWMM),

TOPMODEL.

3).Distributed models

Parameters are fully allowed to vary in space.

It require large amounts of (often unavailable) data.

Distributed models require a DEM as input.

Also Known as “High Rank” Models.

EX-MIKE11/SHE, WATFLOOD etc.

Introduction to HEC RAS

HEC-RAS(Hydrologic Engineering Centers River Analysis System)

HEC-RAS is a one-dimensional flow hydraulic model designed to

aid hydraulic engineers in channel flow analysis and floodplain

determination.

HEC-RAS program was developed by the US Army Corps of

Engineers to manage the rivers, harbors,other public works under

their jurisdiction.

HEC-RAS model offering a simple way to set model parameters and

a graphical user interface(GUI) to run the model and visualize the

results.

River Analysis

Water depth

Flow

Use of HES RAS

Water flowing through systems of open channels ;

Computing water surface profiles.

Floodplain management ;

Flood insurance studies to evaluate floodway encroachments.

Additional uses

Bridge and culvert design and analysis,

Levee studies,

Channel modification studies,

Dam breach analysis.

Graphical User Interface(GUI)

Data storage/management Graphics,

Tabular Output & Reporting

GeoRAS – GIS pre and post processor

Steady flow is the solution of the one-dimensional energy equation.

The momentum equation may be used (include hydraulic jumps,

hydraulics of bridges, and evaluating profiles at river confluences)where

the water surface profile is rapidly varied.

Unsteady flow is based on solution of 1-D Saint Venant Equation

using an finite difference method.

It is capable of modelling subcritical, supercritical, and mixed flow

regime flow along with the effects of bridges, culverts, weirs, and

structures.

Advantages :-

It support by the US Army Corps of Engineers, also acceptance by

many government agencies and private firms.

It is in the public domain and peer-reviewed,

available to download free of charge from HEC's web site.

Various private companies are registered as official "vendors" and

offer consulting support and add on software.

Limitations :-

Steep bed slopes (HEC RAS User's manual says >10%);

multi-dimensional flow characteristics;

complex pipe systems.

Large Data Accuracy Required

The HEC-RAS (4.1) Software New Features:

(1) Steady flow water surface profile computations;

(2) unsteady flow simulation;

(3) Movable boundary sediment transport computations;

(4) New RAS mapper floodplain delineation capabilities;

(5) Hydrologic routing reaches within an unsteady flow model run;

(6) Groundwater leakage for storage areas;

(7) Water quality modelling enhancements.

*

http://www.hec.usace.army.mil

http://csdms.colorado.edu/wiki/Hydrological_Models

http://en.wikipedia.org/wiki/HEC-RAS

http://www.forrex.org

http://www.eng.uwo.ca/research

http://www.fema.gov