BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY

FLOOD PLAIN MAPPING

COURSE NAME: COMPUTER APPLICATION IN WATER

RESOURCES ENGINEERING

COURSE NO.: WRE 404

GROUP NO. : 10

GROUP MEMBERS :

1. TANVEER AHMAD (0816010)

2. RUBAYAT SOBHAN (0816020)

3. ARPAN PAUL (0816030)

INTRODUCTION :

Bangladesh lies in a flood plain zone since 100 or more years . It is most concern to the Water resources engineers to mitigate flooding from maximum discharge coming in the monsoon . Jamuna river and upto it’s lower reach along the river, houses , roads, villages, fertilizing lands are flooded every year . Bank protection , revetment, dam , drazing are established only the cause for flood. So for this reason mapping of flood in this river basin , most valuable for all engineers . the goal of performing a flood plain mapping is to determine the limits of mapping that will cause a specified change of water surface elevation.

CONCEPTUAL BACKGROUND :

Steady flow water surface profiles:

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 energy equation Is written as follows,

Where:

Z1 , Z2 = elevation of the main channel inverts

Y1 , Y2 =depth of water at cross section

V1 , V2 = velocity weighting velocity

a1 , a2 = velocity weighting coefficient

he = energy head loss

here

Where ;

L = discharge weighted reach length

= representative friction slope between two slopes

C = expansion or contraction loss coefficient

The distance L is calculated by,

Cross section subdivision for conveyance calculation:

Conveyance is calculated within each subdivision from the following form of Mannings equation:

Where;

K =conveyance for subdivision

n= Mannings roughness coefficient

A =flow area subdivision

R = hydraulic radius for subdivision

Flood plain mapping method:

There are five optional methods in flood plain mapping.

Method 1 :

Method 2 :

Method 3 :

Method 4 :

Method 5 :

METHODOLOGY:

The .tin data file is inputed in the GIS-9.3 . Using HEC-GEORAS with same compatibility for GIS-9.3 , we export .sdf file for HEC-RAS . Then putting steady , unsteady , quasi steady , sediment data onto it and then export the ultimate data for GIS-9.3 again . Using RAS MAPPING from HEC-GEORAS we found so many geological variety due to different maximum discharges .

Process:

Step 1 : At first opening GIS-9.3 and catalog . Adding .tin data file by pressing this button or from catalog

Then we found the view that

Step 2: Active the HEC-GEORAS tool from menu bar .

Step3: Creating layer setup from Ras Geometry and selecting terrain tin exchange of null. Then OK .

Step 4 : Then Ras Geometry Create Ras Layer Stream Centerline Naming “Jamuna River” OK .

Step 5 : From editor tool start editing sketch tool snapping on the centerline of river stop editing. We can found ,

Step6 : Ras Geometry Create Ras Layer banklines naming JamunaBanks ok .

From editor tool start editing sketch tool snapping on the bankline of river stop editing. We can found ,

Step 7: : Ras Geometry, Create Ras Layer, flowpath centerlines, naming flowpaths , ok.

Then From editor tool start editing, sketch tool ,snapping on the flowpathline of river, stop editing. We can found ,

Step 8: Pressing button and click on the stram center line .

Given the river name = Jamuna river

River reach name= upper reach.

Then pressing button and knock on the flow path lines ,

Middle line= channel

Left line= left

Right line= right.

Step9: Ras Geometry, Create Ras Layer, x-cul lines,naming crossection , ok.

Then From editor tool start editing, sketch tool ,snapping on the crossectionline of river, stop

editing. We can found

The attribute table of crossection may seem as like as ,

Maximum thing are null value showing .

Step10 : : Ras Geometry,Xs cut line attributes , all , ok .Now it can be seem asa like as .

The cross section become as like as using this tool .

Step11: : Ras Geometry,export ras data for HEC-RAS.

Step12: From the geometry , file,import gis data. We can see the project as like as ,

Step13: creating 10 steady flow profile of the discharge sequently 500,1000,1500,3000,4000,7000,10000,16000,22000,30000cumec.

Normal depth of 0.0005 .

Fig: For 500cumec Fig: For 10000cumec Fig: For 30000 cumec

EXPORTING HEC-RAS OUTPUT FOR GIS:

Step1: Exporting GIS data from the file of HEC-RAS.

All unselect option found, make them selected, the export data to a specific folder.

Step2: Going to GIS , HEC GEORAS tool, RAS mapping , Import RAS data icon to convert .sdf file to .xml file .then ok. New .xml file be created on the same directory .

Step3: RAS mapping, layer setup,and file will be shown as like as,

Then ok !

Step4: RAS mapping , import RAs data,ok. The feature will be created like that.

Step5: ras mapping,inundation mapping, water surface generation , select any profile . we can see the inundation as like as

Step6: RAS mapping, inundation mapping,flood plain delegation using ruster.

We can see the flood water delegation as like as,

Profile1 Profile 6

Profile10

Model result:

For profile of 500 cumec :

Fig: X-Y-Z perspective plot Fig : X-section at station 11

Fig: flood plain at 500 cumec

For profile of 30000 cumec :

Fig: X-Y-Z perspective plot Fig : x-section at station 11

Fig: flood plain at 30000cumec

Discussion :

It is almost close to the design against flood. We the engineers or designers, can perform more accurate decision and go ahead with the help of RAS mapping of flood plane . It assures us not to be disappointed about design.

Conclusion:

All output ruster datasets created by RAS mapper are stored in the FLT format. Along with the binary .flt a second header file (.hdr) will be created .Both files must be used together to define a raster dataset. This file format can be compressed for transmission of smaller file sizes. It is also a format that is widely supported and can be imported to other GIS analysis . In ARC-GIS, for instance, there are utilities to import and export the FLT format . Conversion from one file format to the next is not time consuming.

Recommendations:

We recommend about flood plain mapping that , it is natural about uncertainity of flood water . So for all of us ,we should try to get maximum information about discharge, water level, flood water velocity , against the river bank erosion. This design can also be done by various (five) methods and maximum safety would be taken .