chapter 5. hec-ras user's guide

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CHAPTER 5. HEC-RAS USER'S GUIDE

This chapter provides a general view of the tool including a description of the technological approach and a quick start guide (tutorial).

5.1 Introduction

In the recent years HEC-RAS (USACE-HEC 1995) model has become a crucial tool in the hydraulic and fluvial engineering modeling.The development of remote sensing technologies has provoked an impressive increase in the topographical information availability. This

evolution has forced to create a powerful link between hydraulic models, like HEC-RAS, and GIS (Geographic Information System)

tools.

GIS constitutes the optimum framework to manage and combine the wide range of available information, it also provides a common

interface to interact with such amount of heterogeneous data, including aerial pictures, satellite images, geological maps, topographical

grids, land use info, etc. Most of the data sources mentioned above are relevant to hydraulic modeling, therefore, in order to construct a

hydraulic model of a natural landscape, GIS become mandatory.

In this framework a couple of tools exist that link GIS and HEC-RAS. The most famous one is the free tool HEC-geoRAS developed by

the HEC-RAS producers (USACE HEC). Hence the performance of the tool and its interaction with GIS and HEC-RAS would make it

the best choice.

The main dawback of this tool is that it works as an ESRI ArcGIS extension; therefore a complete set of ESRI licenses should be ownedto use HEC-geoRAS. GISWATER is the open source alternative to HEC-geoRAS which is presented here. The aim on the background of

this project is to create a serious alternative to the proprietary software required by HEC-geoRAS. Therefore all the software is released

as open source and supported by GITHUB (https://github.com/Giswater/giswater).

GISWATER Association is in charge of the bug control and updates of the tool.

5.2 Software overview

At the first stages of this new tool of design and implementation, a couple of questions emerge, however the most relevant one was

related to the selection of the open source GIS software used as the target platform. The concern was that once the GIS software is

selected, the tool must be developed constrained to GIS platform requirements. This GIS software acts as a container and the GISWATER

tool behaves as a kind of extension or plugin.

The analysis of the existing GIS open source projects reveals that it is a dynamical area where different projects coexist and most of

them just for a short period of time. So there is an important uncertainty in the GIS tool life cycle and expectancy. After realizing these

facts a brainstorming of the tool designers (GITS-UPC, TecnicsAssociats) concludes in a new proposal for the development platform. In

this case the PostgreSQL (Stonebraker & Rowe 1986)/PostGIS (Regina O. Obe 2011) combination was considered.

The key features that exist in PostgreSQL database that are of great importance for hydraulic tools, inventories and collections are

naturally included in an object oriented database. These inventories can include multiple elements of a hydraulic model such as bridges,

pipes, gage stations etc all these elements are essential parts of the hydraulic model.

From the system architecture point of view the database environment provides a rational way to share the information and store it.

Concurrent access to information makes it interesting for team work.

Another crucial element of the PostgreSQL which important for its selection is the PostGIS extension.

PostGIS is an open source extension intended to include geometrical/geographical information in a database. It also includes more than

200 spatial functions to interact with the geographical data. From topology to metrics everything is included in the extension. Also since

version 2.0 PostGIS launch, there is the ability to manage raster datasets and allows interaction between vectorial/raster information. This

was a major requirement in GISWATER development for HEC-RAS, where the terrain role is crucial. Therefore as described here the

PTER 5. HEC-RAS USER'S GUIDE http://www.giswater.org/book/expor

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tool landscape is represented by a DTM (Digital Terrain Model) which is stored within the database as a standard table.

Almost all the existing open source GIS have a driver to interact with a PostgreSQL database, therefore all of them become a useful

interface to the tool. As has been described previously all the information is collected in the database, and this database includes all the

necessary spatial algorithms, therefore the GIS becomes just a graphical interface to view/edit the information but processing is

performed in the database. This means that light GIS viewers are capable of running the tool, neither a simple intersection command is

necessary in the GIS platform.

As a consequence of these facts, using a simple SQL console pointing to the database is all you need to create the HEC-RAS geometry

file, but the support of any GIS tool improves the user experience and the tool becomes user-friendly. In the following three different

examples of GISWATER interfacing will be presented, GRASS, gvSIG and QGIS, but this are three examples in a long list.

Figure 1.GISWATER database loaded into GRASS GIS.

In the Figure 1 the GRASS GIS interfacing to the tool is presented. This is one of the first open source GIS developed. It has some

constraints in working with PostgreSQL. In the version 6 the layers coming from the database could not be edited, just shown, the table

views are not accepted as a layer.

Figure 2.GISWATER Database into gvSIG GIS.

In Figure 2 the gvSIG interface to the database is also presented, this software has a great strength in the community. It was able to

interact to the whole tool but the stability of the platform accessing a Postgres database was poor.


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Figure 3.GISWATER Database into a QGIS platform.

In the Figure 3 the QGIS interface is presented. It was selected as the best tool to run the model. The stability and the power of thesoftware was its main advantage. The driver is complete and works in both direction read/write.

Therefore, most of the commands and processes of the HEC-RAS tool are included into the database. Standard HEC-RAS users are far

from being database experts, hence a JAVA interface is provided in order to trigger the main tool commands. Most of the tool

practitioners will use the tool without any direct contact to database working in the background. For advanced users, accessing the

database is a way to tune and customize the tool.

As it is known the PostgreSQL database is based in the schema paradigm. This means that the database is decomposed in parts, each one

named schema. This is a kind of organization system.

Following this idea and, to take advantage of its strength, these schemes are used in the developed tool. Each schema in the database is

considered as a case. A case is a group of tables that contains all the geographic information necessary to construct a HEC-RAS GIS

file (sdf).

Therefore, every time a case is stored in the database it creates a new schema using the name provided by the user. This philosophy is

coherent with the fact of a database being used. One single database is able to contain all the cases developed by a user or a group of

users.

5.3 Quick start tutorial

The complete process to generate a HEC-RAS model could be divided in two different phases. The first phase involves creating theproject case database, loading the topographical raster and finally exporting the HEC-RAS GIS import file (sdf). The second phase is

carried out inside the GIS and it involves the delineation of the involved lines, checking the topology, etc. It is mainly supported by the

editing tools provided by the GIS software. In this case the QGIS will be the selected platform.

Most of the processes are developed inside the database, GISWATER acts just as an interface to trigger processes in the database, but any

other database-interfaces are valid. A Postgresql console could be used to launch the commands or a SQL console as well. The list of the

database commands is described in the "Functions description" document section.

5.3.1 JAVA GISWATER Interface


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As has been commented in the previous section, GISWATER JAVA user interface provides a simple way to manipulate the Postgres

database and including the following essential steps:

0) Start GISWATER

1) Create project

2) Add DTM to the project

3) Generate GIS project

4) Export projecto to HEC-RAS

GISWATER works linked to a database. There two general approaches to work with database are firstly the user could have an installed

postgres database, in a corporative server or in a local computer. GISWATER could connect to this existing database. The second

approach is to use the GISWATER distributed database, named "portable postgres". Depending on the selected installation file the

porstable database is installed or no.

In case of having a portable database it is started by GISWATER on launch. If the portable database is used is mandatory to have it active

during project development, otharways the databse is not available for adding/editing process. During the development of the tool there

has been several issues concerning database and Windows OS. Depending on the OS version new issues emerge. Bug report is provided

in GISWATER, the address is [email protected]

Due to this issues the portable database is stored in the user's folder in the Windows file system,a folder named "giswater" could be found

in this directory.

A project in the database is a list of information tables. The tables contain data field and spatial information as well. When a project is

created the user should select the type of project. The last GISWATER release includes the EPANET, SWMM and HEC-RAS interface.

5.3.2 Why using GISWATER for river analysis?

Giswater is an open source software connecting spatial data with water analysis software such as EPANET, EPA SWMM and HEC-RAS.

Also it is possible to create an SDF file in order to import terrain data from GIS to other GIS tools such as HEC-RAS.

In the latest case of the using it as a tool to facilitate the river study in HEC-RAS, it could be used for

a) Flooding analysis

b) Risk assessmentc) Options appraisal

d) Risk management

Firstly the area under investigation needs to be identified with the areas having more flood risks problems as well. Then the river system

needs to be specified including the source, the pathway and the receptors and the different risks associated with this system. In the past

such studies were only based on traditional hydrological modeling, but nowadays more information is necessary in order to produce a

more accurate model of the system which is closest to reality and hence produce more relevant and accurate results. Hence river systems

are now being modeled using different sources of information such as cadastral, topographical, hydrological and meteorological data with

the use of Geographic Information Systems (GIS) in order to create flood risk assessment maps. This kind of data is easier to interpret

and include much more information for the interested parties.

The problem arises in connecting GIS software to river analysis software. The methodology to toggle the problem is by using Giswater

which is able of connect to a GIS, a river analysis software using a geospatial database.

5.3.3 Methodology

The case scenario is the river Onyar in Girona, in Catalonia Spain begins at the Guilleries massif and it joins river Ter at the city of

Girona. The river has flooded in the past creating devastating damages to the city. Analyses on the vulnerable areas of the city have been

carried out in the past. However, the case developed below would show the areas affected with different flow regime of the river and the

vulnerability to flooding without any specifications on land use.

The GISWATER platform involves four main elements, the GISWATER interface, the database, the GIS and the HEC-RAS software.

First of all the GISWATER interface should be started using the desktop icon. GISWATER would try to connect to an existing database in

your system or an external one, stored in the default preferences. If a database is not found in your system or configured in the default

settings, it would try to launch the portable version included in the all-in-one distribution. In case that a database connection is not


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obtained, the first task of the user is to manually configure it. Once the connection is successful, the settings are stored in the default

project or they could also be saved as a new project.

The methodology of how to connect to GIS using a database and then importing it to HEC-RAS (river analysis software) would be

described below. In order to facilitate the procedure the case scenario of river Onyar above would be used. The following steps are to be

followed after opening Giswater in order to successfully create the case scenario

1. Edit project preferences

2. HEC-RAS preferences- configuration of the project

3. Setting up the river scenario using GIS

4. Export SDF file

5. Set up the river analysis study

5.3.3.1 Edit project preferences

The first step is to set up new/edit project preferences. The user interface of Edit project preferences is shown below.

Figure 1. Edit preferences user interface

1. Water softwareis to be chosen between EPANET, EPA SWMM and HEC-RAS. In this case we should choose HEC-RAS for a river

study.

2. Data storagechoose between Database and DBF (filename extension). In this case choose Database.

3. Database storageensure that the connection to the database storage is open.

4. Project Data Managementhere the GIS project is created. Click on create. A screen shown on figure 2 below would appear.

5. Finally, at the end of the page click on accept to finalize the edition of the project preferences. This would lead you to the user interface

of HEC-RAS preferences.


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Figure 2. Create project interface

Set the Project name and project title taking into account that it should be a name that it is easy to remember, it does not have any weird

characters like accents, question marks or any other characters which is not widely used. Also ensure that the SRID (Spatial Reference

System Identifier) is the correct one for the study of interest. Click on accept and close to create the project.For this project the project

name chosen was hec_demo and the project title was Onyar from the name of the river.

5.3.3.2 HEC-RAS preferences - configuration of the project

In the HEC-RAS preferences, the Digital Terrain Model (DTM) of the area under study is to be loaded. The HEC-RAS user interface is

shown below in figure 3.


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Figure 3. HEC-RAS preferences

Giswater accepts any file type of DTM including GDAL (geoTIF,img, asc, txt..). After finding the file, click on accept in order to connect

to the database. This step takes a while to execute. This step is vital in order to successfully create the GIS project. Then return to the

previous screen by clicking on Edit Project Preferences at the bottom of the page.

At the bottom left corner of the interface there is a button Create Gis Project, click on the button in order to create a new QGIS project.

A screen would pop-up shown in figure 4 below.

Figure 4. Create GIS project interface

Choose the location which the file would be located, name the Gis Project and click on accept to create the new project. The following

screen shown on figure 5 would pop-up. Click on Yes.

Figure 5. Pop-up message to create a new GIS project

This process might take a few minutes. Then it asks if you want to open the new file created. The GIS software then opens with the new

project which was created with the data specified in the previous steps such as the SRID and the DTM.


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5.3.3.3 Setting up the river scenario using QGIS

Once the file created by Giswater opens, it should be noted that it contains the layers which are vital in order to set the project. They are

grouped in two blocks: input and output. Both blocks are strongly connected because some of them correspond to the same database table

(i.e. view_banks and banks). They are collected into groups because in the group input includes just the layers and fields which are

compulsory to the user. In the input group, the layers are named views as the layers are only partially presented, hence in a database

view, not a table. The output group includes all the project layers and every layer contains all the fields, with some of them being internal

fields to the tool. The layers which were created include view_banks, view_flowpaths, view_xscutlines and view_river. The Gis

project generated is shown in figure 6 below.

Figure 6. New QGIS prohect- hec_demo

These layers need to be drawn. In order to draw these layers it is essential to load the raster layers of the area including the orthophotos,

the DTM (Digital Terrain Model) and the cartography to facilitate the task. Even though by default the terrain layer is included in theoutput group with the name mdt, the performance is reduced if the user uses this layer. This is due to the fact that if the database is in

the cloud every pan movement or zoom involves a new terrain download for the database, adding a delay. In order to reduce the delay it

is recommended to load the QGIS table of content (ToC) a new terrain layer, linked to a local version of the terrain raster, avoiding the

active visualization of the mdt layer of the data base. Also it is recommended to generate a layer demonstrating the terrain relief and

hence depict the most possible path of the river. When loading all the layers necessary for the study the map canvas should look as the

figure below.


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Figure 7. Area under study

The next step is to start drawing the layers which were generated in the Gis project. Using the orthophoto and in conjunction with the

elevation and shadow layers all the layers should be drawn starting with the view_river, ensuring that the line follows the river flow in the

middle of the channel. Note that after drawing the river, the data in the attribute table should be entered as shown below. Failing to

include this data, the model would be incomplete.

Figure 8. Attribute table for river_view layer

Following the view_river, the view_flowpaths should be drawn. In this layer there are three different lines which should be drawn for the

three different flows which could exist such as normal flow regime, over flooding the banks of the river both on left and right sides of the

river. Note that the normal flow regime should be the same as the view_river and also the other two lines on the left and side of the river

should be drawn in such a way that the flow is the easiest path that the water could follow taking into consideration the relief of the

terrain as well as possible obstacles which could be found such as buildings, trees. The flow paths should look relatively the same as in

the figure below.


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Figure 9. Flow path of the river for 3 case scenario flows

Then each line should be specified on the attribute table. There are three different line types, channel, left and right. In order to correctly

specify each line consideration should be given in the direction of the flow of the river as shown below. For this, it is essential to know

the direction of the river and that the left bank is the one on the left-hand side if watching at the same direction as the flow of the river

and the same implies for the right side.

Figure 10. Classification of river flow paths

Then the next layer to be drawn is the view_banks. The river banks are the borders of the river during normal flow regime (depth of the

river has not reached maximum river flow and hence no risk of flooding). The river banks are shown in the figure below. Note that all the

layers which were drawn up to this point should not cross each other at any moment except from the channel in the flow paths and the

river which should be the same.


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Figure 11. River banks of area under study

The last layer to be drawn is the view_xscutlines. This layer includes various lines which are cut all the above layers. These are the

sections of the river at different locations and depending on the length of the river under study they should be placed equidistance from

each one, in this case the distance between each section is approximately 30m. The final results of all the layers being drawn are shown

below.

Figure 12. GIS project of the study area

5.3.3.4 Export SDF file

After finishing the Gis project on the GIS software, the project should be exported in a format which is acceptable by HEC-RAS. In order

to do this, Giswater should be used. In the HEC-RAS user interface inside Giswater (see figure below), specify the location and the name

of the file which would be created. In this case the folder is Results and the name of the file hec_demo (the same as the Gis project).

Finally click on Accept in order to create the SDF file. This might take some minutes. When the file is created, the river study could be


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performed using HEC-RAS.

Figure 13. Exportation of SDF file

5.3.3.5 Set up the river analysis study

The river analysis study would be performed using HEC-RAS hence the tool should be opened. The main window of HEC-RAS is shown

below.

Figure 14. HEC-RAS main window- Edit menu

The first step in HEC-RAS is to enter the geometry data of the area under investigation. In order to do that click on Edit/Enter geometric

data, a new window would pop-up. Then you should go to file, import Geometry Data and GIS Format (as shown in the figure below).


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Figure 15. Geometry data import - SDF file

The Geometry Data to be imported as a GIS Format is the SDF file which was created in Giswater. The following window would open,

locate the location of the file, choose the file and click on OK.

Figure 16. Import Geometry Data-SDF file

Note that HEC-RAS would ask with what units the analysis should be performed (as shown in figure below). For this case choose

SI(metric) units, then Next and Finish- Import Data.


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Figure 17. Unit specification

The geometry would be imported in the window. This saves a lot of time in performing a river analysis as the geometry is inserted

directly without having to insert it manually. Then from the main menu, go to file and Save Geometry Data As. The next steps are to

configure the Mannings coefficient, the boundary layers. For this, go to Tables, Mannings n or k values (Horizontally varied) (see

figure 18 below).

Figure 18. Configuring Manning's coefficient

In the columns n#1 and n#3 set the value of Mannings coefficient at 0.06 which it is the value for the left and right bank respectively. In

column n#2 set the value at 0.04 which is the value at the channel of the river. In order to set the values first select the column to be filled

(the column would be colored on lilac), click on Set values, fill in the black with the corresponding values; all the values would be set

therefore you should not fill in the blanks one by one. Then click on OK.


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Figure 19. Manning's coefficient for banks and channel

The next step is to enter the steady flow data. In order to bring up the steady Flow data editor, select the Steady Flow Data icon from the

Edit menu on the HEC-RAS main window. The steady flow data editor should appear as shown in the figure below. Fill in the blank

box named PF1 with 400.

Figure 20. Steady Flow Data Editor

Then the Boundary conditions should also be set; click on Reach Boundary Conditions and a new window will appear as shown in the

figure below.


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Figure 21. Steady Flow boundary conditions

The Boundary conditions should be set for both Upstream and Downstream locations; in this case choose for both of them CriticalDepth. Choosing the Critical Depth does not require entering any further information. The program will compute critical depth for all

the profiles and this would be used as the boundary condition.

Finally click on Perform a steady flow simulation, choose the flow regime Mixed. The window which would appear is shown in the

figure below. Click on Perform to compute results.

Figure 22. Steady Flow analysis

In order to view the results, click on Close on the new window that appears, go to the main menus of HEC-RAS and click on View 3D

multiple cross section plot. The following screen would appear showing the results of the analysis.


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Figure 23. Results in a 3D multiple cross section plot

5.4 References

Regina O. Obe, L. S. H. (2011), PostGIS in action, Greenwich, Conn.

Stonebraker, M. & Rowe, L. (1986), The design of postgres, in Proc. ACM-SIGMOD Conference on Management of Data.

USACE-HEC (1995), HEC-RAS, River Analysis System, Hydraulics Reference Manual. CPD-69, Hydrological Engineering Center,

Davis, CA.


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