SUMMERY

Hydrological analysis using Geographical Information System has been performed by taking the

case study of 2010 floods in district Charsadda of Khyber Pakhtunkhwa province, Pakistan.

After agriculture revolution flooding has become the most potential natural hazard in the world.

Pakistan being the sixth largest population of the world and having huge irrigation system is

facing this problem severely in recent decades. Flooding is a recurrent event in Khyber

Pakhtunkhwa districts which are settled along the river Kabul. In 2010, monsoon season brought

unusually large amount of rainfall and completely destroyed many villages and Charsadda

district was also the most severely affected district. Flash floods are due to River Swat while

riverine flooding is caused by high discharge of River Kabul. These floodplains are densely

populated and there is a need to identify flood hazard risk zones to prevent further damages

caused by such floods. The present study aims to prepare flood hazard risk zones of District

Charsadda by performing hydrological analysis in ArcGIS 10.1 Hydrological Analysis is

performed using Digital Elevation Model. Sinks, basins, flow accumulation, flow length, flow

direction, watershed, catchments and stream network of District Charsadda have been generated

using hydrology tool in arc toolbox. Flood risk potential zones around the rivers are identified by

buffering along the stream network.

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CHAPTER 1

INTRODUCTION

Flooding is a temporary layering of water on land that may be caused by high rainfall or surface

waters evading from their normal limits. Flood hazards are the most common and harsh of all

natural disasters and are a regular risk to human life and property. Flood is a global phenomenon

affecting rich and poor, the prepared and unprepared alike.

The major causes of flood disasters include the combining effect of land inundation from heavy

rainfall, climate change, and blockage of drainages with refuse, construction of buildings

across drainages, inadequate drainage networks, and population increase in urban areas.

These factors independently do not cause floods but the combination of several of these usually

cause flood disaster. Construction on natural drainages, increase in the population, and

conversion of natural vegetation, agricultural land, and wetlands due to urbanization threaten

the lives of people living in flood vulnerable areas such as flood plains and river beds.

1.1Study Area

District Charsadda lies between 34o03' to 34o38' north latitudes and 71o53' to 71-28’ east

longitudes. The district is 32 kilometer away from Provincial Capital Peshawar and is divided

into three tehsils i.e. Charsadda, Tangi, and Shabqadar. The total geographical area of district

Charsadda is 996 square kilometers (243753 acres). According to 1998 the total population of

Charsadda was 1,022,364, having Urban population was 18.86 % while rural population was

81.14 %. Population density of the study area was 1,026.5 per Sq. Km. The annual rainfall in

district Charsadda is about 400 to 600 mm. June is extremely hot and dry, and the temperature

rises to over 40oC while the months of July and August are hot and humid. The winter rainfall

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shows a high record during the months of March and April and the summer rainfall is in the

month of August. Charsadda is the land of rivers. River Swat, River Kabul along with the upper

and Lower Swat canals, Michini Dalazak Canal and Doaaba feeder Canal are the main sources of

irrigation. The three rivers then connect and join the Indus River. The surrounding area of River

Swat and River Kabul is called Doaaba having a great importance in the District . From the west

the Kabul River flows in the district of Charsadda. The Swat River is the important tributary of

the Kabul River. It enters the district near Abazai village and flows to Kabul in a south-easterly

direction till it joins Kabul River. River Kabul forms the boundary between district Charsadda

and district Peshawar. In the south of the district Warsak dam has been constructed on River

Kabul. The land of Shabqadar tehsil is very fertile because it is surrounded by three branches of

river Kabul. Canals are the main source of irrigation as 72% of the rural mouzas are irrigated by

canals while 23% irrigation is done by the rivers and 27% are irrigated by tube wells. Reference

map of Charsadda is shown in figure 1 below.

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Figure 1: Reference map of District Charsadda

1.2 Problem Statement

Charsadda district is covered by 81% of agriculture land so these regularly occurring floods

affect the livelihood of small farmers. Floods need to be quickly monitored during and after the

flood for rapid flood management and this can only be possible by using modern techniques like

hydrological analysis.

1.3 Research Objective

1.4 Main Objective

The main objectives of the study is flood risk assessments using hydrological analysis tool.

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1.5 Specific Objectives

1. DEM analysis

Fill

Basin classification of the study area

Flow direction of the study area

Flow length of the study area

Flow accumulation of the study area

Sink

Snap pour point

Stream link

Stream order

Stream to feature

Catchment classification

Delineation of Watershed area

2. Buffer analysis of stream network

1.6 Scope of the Study

The main scope of the study is to propose a GIS based methodology using hydrological analysis

for flood risk assessment. The study deals with Digital Elevation Model (DEM) to generate

basin, flow accumulation, flow direction, flow length, streams, and watershed of the study area.

CHAPTER 2

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Use of DEM for Hydrological Analysis

According to Forkuo, “A digital elevation model (DEM) is a digital representation of the Earth’s

relief that consists of an ordered array of elevations relative to a datum, and referenced to a

geographic coordinate system”.

DEMs are the major basis to generate land topography. It gives elevation information that is

useful for various environmental purposes including hydrologic modeling and flood management

planning. The use of DEM has extensive applications in geomorphologic and hydrological

purposes. It allows the extraction of topographic features of the earth surface and displays all

natural features for both the vertical and horizontal resolutions [6]. Isma’il created flow

accumulation model from DEM using ArcGIS software to find out flood prone areas. Using the

elevation of the area, flow accumulation analysis was carried out to discover the natural drainage

pattern of the area and DEM was reclassified into high risk, moderate risk and low risk. Konadu

used a vector based GIS and DEM in order to distinguish watershed margins and forecast

potential flood areas during a flood incident in the city of Accra. The terrain representation and

flow direction of water that enters into an area can be obtained from DEM. DEM was used to

create data on flow direction, stream definition, flow accumulation, stream segmentation and

watershed delineation in ArcGIS. Important elements for drainage analysis can be evaluated

using DEM. Flood depth is considered essential for flood hazard mapping and DEM is the most

effective means to estimate flood depth from remotely sensed or hydrological data. Resolution of

the DEM is an important factor for accurate flood estimation in flat terrain. Al-Saud used DEM

with 30 meters precision to analyze drainage system in flood occurrence of Jeddah city in

Western Saudi Coast. DEM can be used to extract flow directions, and locating low-lands. The

DEM is vital to perform the modeling of flooded areas in the simulated case of a flood incident.

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Physical factors of the sub-basins were extracted from DEM. A DEM can be used with

hydrodynamic model to calculate depth, local velocity, scour, and habitat characteristics.

Accuracy of flood estimation primarily depends on resolution of DEM in flat terrain area. 25 m

cell size DEM with GIS analyses can be used for extraction of total streams power, channel

gradient and small and high relief in Australia. The high-resolution DEM is used to estimate

slope, aspect, topographic wetness index, stream power index, and flow direction. Drainage

network is extracted by using DEM. DEM was used to create flood inundation map.

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CHAPTER 3MATERIALS AND METHODS

This study formulates a GIS based methodology for flood hazard zoning. This method has been

used by Ajinfor Vamanapuram River basin in Kerala State, India that faces challenge in terms of

repeated flash flood hazard. The present study aims to prepare flood hazard risk zone maps of

District Charsadda using GIS tools. Al-Saud used DEM with 30 meters precision to analyze

drainage system in flood occurrence of Jeddah city in Western Saudi Coast. Riaz also used 30

meters DEM for district Charsadda flood risk assessment of monsoon 2010 floods. This study

also processed 30 meters DEM to make flood hazard map using ArcGIS 10.1.

3.1 DATASETS USED

The following datasets were used for carrying out the present research project:

3.2 Reference Map of the Study Area

The shape file of the boundary of district Charsadda was obtained from Population Censes

Organization. The reference map of Charsadda was created from the shape file using ArcGIS

10.1 software.

3.3 DEM

The DEM of 30 meters resolution was taken from ASTER GDEM in order to extract aspect

classification, slope classification, flow length, flow accumulation, flow direction, basin

classification, drainage points, drainage lines, catchments classification, water bodies (streams)

and watersheds of the study area.

3.4 SOFTWARE USED

The following software was used in the present study:

Arc GIS 10.1

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Arc Hydro Toolbar

Microsoft Word

3.5 METHODOLOGY

DEM is the key factor for conducting this project. Aspect, slope, flow direction, stream network,

flow accumulation, catchment, basin classification, watershed area, are extracted from DEM.

Buffering of streams are performed for flood hazard zoning The methodology adopted in the

research is explained in the flow chart given in the figure 3.1

Figure 3.1: Flow chart of hydrological analysis

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CHAPTER 4

RESULTS AND DISCUSSION

This chapter includes the data analysis and discussion of the results. The processes applied have

been discussed along with the generated graphs and maps from the data using hydrological

analysis techniques. Analysis was done by using Arc Toolbox in ArcGIS 10.1 software.

4.1DEM

Freely available ASTER GDEM of 30 meter resolution is download and extract by mask tool is

used for the extraction of DEM according to district Charsadda boundary shown in figure 4.

Figure 4: Extraction of DEM according to study area

4.2 Hydrologic Modeling Tool in ArcGIS

The hydrologic modeling tools in the ArcGIS Spatial Analyst extension toolbox provide methods

for describing the physical components of a surface. The hydrologic tools allow you to identify

sinks, determine flow direction, calculate flow accumulation, delineate watersheds, and create

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stream networks. Using an elevation raster or digital elevation model (DEM) as input, it is

possible to automatically delineate a drainage system and quantify the characteristics of the

system. 

4.3 Fill DEM

The elevated cells encircle a cell; the water cannot flow because the water is trapped in that cell.

Filling of sinks is done by using fill tool, a part of hydrology tool in Spatial Analyst Tools. This

task modifies the elevation value to reduce these problems. The prepared map is shown in the

Figure 4.1. Light color in the map shows the high values (i.e. 285) while dark color in the map

represents the low values (i.e. 951).

Figure 4.1: Fill DEM of the Study Area4.4 Basin Classification Map

A drainage basin is an area of the land occupied by the surface water bodies. Size of drainage

basin will help to determine the amount of water reaching the river. If the size of drainage basin

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is larger, there is greater potential for flooding. For extraction of basins Hydrology Tool in

Spatial Analyst Tools was used. The input raster was flow direction and output raster was

Basins. There are three basins in the study area and are labeled as A, B, and C in the prepared

map shown in Figure 4.2.

Figure 4.2: Map showing the weighted Basins

4.5 Flow Accumulation Map

Flow accumulation has a great role in floods. These are the main source of flood in an area. More

the flow accumulation means more chances of flood. The flow accumulation distribution layer

has been generated using the Flow Accumulation Tool; a part of Terrain Preprocessing in Arc

Hydro Toolbar. The input raster was flow direction and got major flow accumulations of the

study area. The map shown in Figure 4.6 indicates four major flow accumulation points in the

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study area i.e. River Kabul, River Swat, Kalpani River, and Jindai Khwar. The study reveals that

these are the main sources of floods in the study area shown in figure 4.3.

Figure 4.3: Map showing the Flow Accumulation of the Study Area

4.6 Flow Direction

Flow direction is very important for flood probability mapping. Flow direction also tells about

the direction of flooding mostly in flash floods. As the study area is facing both flash floods and

riverine floods; therefore. Flow direction map is prepared by using DEM. Using the DEM as

input to the Flow Direction tool, the direction in which water would flow out of each cell is

determined. By using Flow Direction Tool in Terrain Preprocessing flow direction was

generated. Input for flow direction was Fill DEM. The water bodies were overlaid above the

flow direction map. The prepared map of flow direction is shown in Figure 4.4.

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Figure 4.4: Map showing the Flow Direction of the Study Area

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4.7 Flow Length

Input raster flow direction. Using the Flow Length tool, the length of the flow path, either

upslope or downslope, from each cell within a given watershed can be determined. This is useful

for calculating the travel time of water through a watershed shown in figure 4.5.

Figure 4.5: Flow length of the study area

4.8 Sink

Input raster flow direction. With the Sink tool, any sinks in the original DEM are identified. A

sink is usually an incorrect value lower than the values of its surroundings. Lower area of the

Charsadda is high sink area shown by red color and have high stagnant water capacity. Shown in

figure 4.6.

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Figure 4.6: Sinks Identification

4.9 Stream Network Map

Stream definition and stream segmentation was done by using “Stream Definition” and “Stream

Segmentation” Tools in the Terrain Preprocessing Tool. The input grid was Flow Accumulation

and Stream Definition respectively. For creating stream network “Raster Calculator” in “Map

Algebra”; a part of “Spatial Analyst Tool” was used. Raster was created by calculating “flow

Accumulation” greater than 1110 and converting it into polyline by conversion tool present in

the Arc Toolbox. The prepared Map is shown in Figure 4.7 that reflects the major water bodies

of the study area. Swat River (Kayali), Kabul River (Sardaryab), Kalpani River, Jindai Khwar,

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Aisi Khwar, and Nawe Dand Khwar are the rivers in the study area. Small streams are also

shown in the given map.

Figure 4.7: Map showing the Major Stream Network in the Study Area

4.10 Catchments Classification Map

Catchment grid is produced on the basis of streams segmentations that drain the area. Tool in

Terrain Preprocessing catchments are generated by using “Catchment Grid Delineation”. The

input raster for catchment grid are the “Flow Direction” and “Streams Segmentation”. There are

total 17 catchments in the study area. 17 catchments are then reclassified into 8 catchments. The

prepared map is shown in Figure 4.8.

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Figure 4.8: Map showing the Catchments Classification of the Study Area

4.11 Delineation of Watershed Map

Watershed is an important parameter for creating flood risk map of an area. Size of watershed

affects the frequency and intensity of flood. If the size of watershed is large, there will be higher

intensity of floods. There is one large size watershed in the study area. Batch point was generated

for locating outlet of the watershed. By using Batch Watershed Delineation Tool in Watershed

Processing, Batch Watershed was delineated. Input raster was Batch Point, Flow Direction,

Streams, Catchments, and Adjoint Catchments. The map is shown in Figure 4.9.

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Figure 4.9: Map showing the Weighted Watershed

4.12 Buffer Analysis of Stream Network

A buffer map of the stream network was generated in ArcGIS 10.1 and four different classes

were created, based on distance from the streams, ranging from within 20 meters (m) to 150 m.

Buffering is done by using “Buffer” Tool present in the Analysis Tool. Four Buffers were made

and then merged together by using “Merge” Tool in “Data Management Tools”. The buffer map

identified area nearest to the streams as the most prone to flooding. The prepared map is shown

in Figure 4.10. The results explained four types of zones, very high risk zone (20 m), high risk

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zone (20-50 m), moderate risk zone (50-100 m) and low risk zone (100-150 m) to flooding.

Figure 4.10: Map of Potential Flood Risk Zones along Stream Network in District Charsadda

4.13 Flood Hazard Zones (Multiple Ring Buffer Analysis)

Creates multiple buffers at specified distances around the input features. These buffers can

optionally be merged and dissolved using the buffer distance values to create non-overlapping

buffers. Hazard zones have been calculated using the digital elevation model and historical

floods experienced by the district. Flood 2010 has been mapped and three categories have been

drawn based on distance from flood inundation. The elevation of the district has been extracted

from DEM and categorized accordingly. Figure 4.11 shows that low lying areas overlapping with

the areas near to the historical flood inundations has been considered as potentially high hazard

zone, others areas are categorized as high, medium, low and very low potential hazard zones.

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Figure 4.11: Flood Hazard Zoning of District Charsadda

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CHAPTER 5

CONCLUSION AND RECOMENDATIONS

In this research DEM is used for flood hazard zoning which suggests that GIS techniques can be

effectively used to monitor and measure flood risk. GIS hydrology techniques have been

efficiently used for flood risk assessment. DEM can be effectively used to extract flood risk

assessment parameters such as stream network, flow direction, watershed, catchments etc.

Intense rainfall in the monsoon season is the major cause of flooding. GIS techniques in the

study are helpful for all stakeholders of disaster management in rapid risk assessment, flood

damage assessment, hazard zonation and evacuation planning. The research indicates that there

is very high flood risk in the large catchment area and along the banks of stream network.

RECOMMENDATIONS

For further research, the following recommendations are made:

Better results can be obtained by having high resolution DEM.

Rainfall map can give better results but there is no meteorological station in the study

area.

There should be at least 3 meteorological stations at different locations in the study area

for flood fore-casting, reporting and measuring rainfall, and discharge data.

RS and GIS data should be made easily available for researchers.

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References

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(SMEDA), Government of Pakistan, (2009). available at:

http://www.smeda.org/index.php?

option=com_content&view=article&id=105:charsadda&catid=47&Itemid=258,

[2] Adeoye, N. O., Ayanlade, A., & Babatimehin, O. (2009). Climate change and menace of

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[3] Ajin, R. S.1., Krishnamurthy, R. R., Jayaprakash, M., & Vinod. P. G.1. (2013). Flood

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ISSN: 0976-8610

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[5] ASTER GDEM available at: http://gdem.ersdac.jspacesystems.or.jp/

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[8] Population Census Organization available at:

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[9] Reinfelds, I., Cohen, T., Batten, P ., & Brierley, G (2004). Assessment of downstream

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