CRWR Online Report 05-04  
 
Arc Hydro Data Model for Ethiopian Watersheds 
 
by  
Seyoum Ayele Asamenaw, B.S. 
Graduate Research Assistant  
 
and  
Daene C. McKinney, PhD.  
Principal Investigator  
December 2005 
 
CENTER FOR RESEARCH IN WATER RESOURCES  
Bureau of Engineering Research • The University of Texas at Austin  
J.J. Pickle Research Campus • Austin, TX 78712-4497  
 
This document is available online via World Wide Web at  
http://www.ce.utexas.edu/centers/crwr/reports/online.html 
 
 
 
 
 
 
 
 
 
Copyright 
by 
Seyoum Ayele Asamenaw 
2005 
 
 
 
Arc Hydro Data Model for Ethiopian Watersheds 
 
by 
Seyoum Ayele Asamenaw, B.S. 
 
 
Thesis 
Presented to the Faculty of the Graduate School of 
The University of Texas at Austin 
in Partial Fulfillment 
of the Requirements 
for the Degree of 
 
Master of Science in Engineering 
 
 
The University of Texas at Austin 
December 2005 
 
 
Arc Hydro Data Model for Ethiopian Watersheds 
 
 
 
 
 
 
 
Approved by 
Supervising Committee: 
 
 
 
Daene McKinney 
David R. Maidment 
 v
 
Acknowledgments 
I would like to express my best gratitude to Dr. Daene McKinney of the Center 
for Research in Water Resources for his guidance and enthusiasm.  I would also like to 
thank Dr. David Maidment for motivation and support for the project. My Thanks go to 
Dr. Gabriel Senay and Dr. Kwbana Asante of United States Geological Survey EROS 
data center for providing valuable assistance in data acquisition.  I would like to express 
my appreciation for my Dad, my two brothers and my recently deceased Mom for their 
patience and support. Finally, my thanks go to Fulbright foundation for financially 
supporting this research.  
 
 
  
 
 
 
 
 
 
December 2005 
 vi
Abstract 
 
Arc Hydro Data Model for Ethiopian Watersheds 
 
Seyoum Ayele Asamenaw, M.S.E. 
The University of Texas at Austin, 2005 
 
Supervisor:  Daene McKinney 
Abstract 
 
Ethiopia is endowed with a substantial amount of water resources. The country’s 
renewable surface and ground water amounts 123 and 2.6 billion cubic meters per 
annum, respectively, but its distribution shows high temporal and spatial variation. The 
Ministry of Water Resources of Ethiopia (MoWR) planned to develop a digital 
hydrologic data model that supports management of the country’s water resources. The 
purpose of this project is to use the Arc Hydro data model organize and manage water 
resource data in Ethiopia. To accomplish this, raw Shuttle Radar Topographic Mission 
(SRTM) data was processed and a 90m*90m Digital Elevation Model (DEM) was 
created. Second, drainage lines and watersheds were created using the Arc Hydro tools. 
Third, six hydro administrative regions were identified based on the flow direction of the 
streams. This project has shown that Arc Hydro is an effective tool for storing and 
analyzing hydrologic information for very large areas. 
 vii
Table of Contents 
List of Tables ...........................................................................................................x 
List of Figures........................................................................................................ xi 
CHAPTER 1:  INTRODUCTION 1 
1.1 Background........................................................................................................1 
1.2 Study Objectives ................................................................................................2 
1.3Thesis outline......................................................................................................3 
CHAPTER 2:  LITERATURE REVIEW 4 
2.1 The study area....................................................................................................4 
2.2 Water Resources of Ethiopia .............................................................................6 
2.3 Transboundary Waters and the Nile Basin Initiatives .......................................9 
CHAPTER 3:  METHODOLOGY 12 
3.1Geographic Information Systems (GIS) Data...................................................12 
3.1.1 Major Africa’s Streams........................................................................12 
3.1.2 Major Drainage Basins ........................................................................15 
3.1.3 Inland water Bodies of Africa..............................................................17 
3.1.4 Creating and adding Ethiopia’s Outline shapefile ...............................19 
3.1.5 Summary of GIS Data and shape files.................................................20 
 viii
CHAPTER 4: GETTING DIGITAL ELEVATION DATA 22 
4.1 Shuttle Radar Topography Mission (SRTM)...................................................22 
4.2 Obtain SRTM data ...........................................................................................23 
4.3 Convert ASCII to Raster Grids........................................................................28 
4.4 Mosaic Multiple Grids .....................................................................................30 
4.5 Remove “NoData” Values from DEM ............................................................32 
4.6 Define the Spatial Reference for the Grids......................................................35 
4.7 Project Grids ....................................................................................................40 
4.8 Make Buffer for Area of Interest .....................................................................44 
CHAPTER 5: WATERSHED AND STREAM NETWORK DELINEATION 50 
5.1 Introduction......................................................................................................50 
5.2 Hydro Administrative regions of Ethiopia.......................................................50 
5.3 Setting up the Arc Hydro tools ........................................................................51 
5.4 Terrain Processing ...........................................................................................52 
5.4.1 DEM Reconditioning...........................................................................53 
5.4.2 Fill Sinks ..............................................................................................53 
5.4.3 Flow direction ......................................................................................55 
5.4.4 Flow Accumulation..............................................................................56 
5.4.5 Stream Definition.................................................................................57 
5.4.6 Stream Segmentation ...........................................................................58 
5.4.7 Catchment Grid Delineation ................................................................59 
5.4.8 Catchment Polygon Processing............................................................61 
5. 4.9 Drainage Line Processing ...................................................................62 
5.4.10 Drainage point Delineation................................................................64 
 ix
CHAPTER 6: ARC HYDRO DATA MODEL AND FRAMEWORK 67 
6.1ArcGIS Hydro Data Model...............................................................................67 
6.2Geodatabase design...........................................................................................68 
6.2.1 Creating Geodatabase ..........................................................................69 
6.2.2 Creating Feature Dataset......................................................................71 
6.3.3 Importing feature classes into the Geodatabase...................................75 
6.4 Building an Arc Hydro Geodatabase and Geometric Network .......................76 
CHAPTER 7: CONCLUSION AND RECOMMENDATION 82 
7.1 Project Summary..............................................................................................82 
7.2 Project Conclusion...........................................................................................82 
7.3 Future Work.....................................................................................................83 
APPENDIX A 84 
APPENDIX B 100 
BIBLOGRAPHY 113 
VITA 115 
 x
List of Tables 
Table 2.1 Area and runoff by river basin for Ethiopian water system.. 7 
                 Table 2.2 water sources and use in Ethiopia ......................................... 8 
 
 
 xi
List of Figures 
Figure 2 .1 Location of Ethiopia........................................................... 5 
Figure 2.2  Nile basin riparian countries ............................................ 11 
Figure  3.1 Rivers in Africa ............................................................... 14 
Figure  3.2 Hydrological Basins in Africa .......................................... 16 
Figure 3.3 Inland water bodies in Africa ............................................ 18 
Figure 3.4 Shape of Ethiopia and its neighboring countries............... 20 
Figure 3.5 Ethiopia Country’s boundary, Streams, Water Bodies and 
Basins from Hydro1K................................................................ 21 
Figure 4.1 Illustration of interferometry on the Endeavour................ 22 
Figure 4.2 Processed SRTM 90m Digital Elevation Data (DEM) for entire 
globe........................................................................................... 24 
Figure 4.3 SRTM data search page in Microsoft Internet explorer .... 25 
Figure  4.4 SRTM search results in GeoTiff format........................... 26 
Figure 4.5 SRTM Data zip files in ASCII format............................... 27 
Figure  4.6 Converting files from ASCII to raster format. ................. 29 
Figure 4.7 Tiles of rasters for SRTM 90m.......................................... 30 
Figure 4.8 Mosiac to raster dialog box ............................................... 31 
Figure 4.9 Mosaiced DEM of Ethiopia and its surroundings ............. 32 
Figure 4.10 Seams at the boundary of quadrangle.............................. 35 
Figure  4.11 Raster dataset properties................................................. 36 
Figure 4.12 Define projection wizard ................................................. 37 
 xii
Figures 4.13 Define projection wizard dialog boxes .......................... 38 
 Figure 4.14 Raster dataset properties dialog box............................... 39 
Figure 4.15 Project Raster dialog box................................................. 42 
Figure 4.16Regional DEM after projection ........................................ 43 
Figure 4.17 Regional DEM and Ethiopia country boundary .............. 44 
Figure 4.18 Buffer wizards dialog box ............................................... 46 
Figure 4.19 Attribute table of Buffer of Ethiopia with field one........ 47 
Figure 4.20 Field Calculator dialog box ............................................. 48 
Figure 5.1 the outline of Blue Nile DEM and hydro 1k streams ........ 52 
Figure 5.2 Blue Nile DEM after sinks have been filled...................... 54 
Figure 5.3 Flow direction grids for Blue Nile Basin .......................... 55 
Figure 5.4 Flow direction and Flow accumulation models (Source Arch 
Hydro help)................................................................................ 56 
Figure 5.5 Flow accumulation grids for Blue Nile Basin ................... 57 
Figure 5.6 Stream definition grids for Blue Nile basin....................... 58 
Figure 5.7 Stream segmentation grids for Blue Nile Basin ................ 59 
Figure 5.8 Catchment grid delineation grids for Blue Nile Basin ...... 60 
Figure 5.9 Catchment polygon processing grids for Blue Nile Basin 62 
Figure 5.10 Drainage line processing grid for Blue Nile basin .......... 63 
Figure 5.11  Drainage point processing grid for Blue Nile Basin ...... 65 
Figure 5.12 The six hydro administrative regions of Ethiopia and the 
associated streams...................................................................... 66 
Figure 6.1 ArcGIS Hydro Data Model ............................................... 68 
Figure 6.2 Creation of personal geodatabase...................................... 70 
 xiii
Figure 6.3 Personal geodatabases for each Hydro Administrative regions 
of Ethiopia.................................................................................. 70 
Figure 6.4 Creating a Feature Dataset................................................. 71 
Figure 6.5 Geographic coordinate generation for new feature dataset72 
Figure 6.6 Geographic coordinates from Hydro 1K ........................... 73 
Figure 6.7 Albers Geographic coordinates from Hydro 1K. .............. 73 
Figure 6.8 a and b. Importing feature Class to geodatabase ............... 76 
Figure 6.10 Importing XML workspace document ............................ 77 
Figure6.11 Importing XML workspace Document ............................ 77 
Figure 6.12 HydroEdge feature class for Blue Nile Basin.................. 79 
Figure 6.13 HydroJunction feature class for Blue Nile Basin ............ 79 
Figure 6.14 HydroNetwork feature class for Blue Nile Basin............ 80 
Figure 6.15 Waterbody feature class for Blue Nile Basin .................. 80 
Figure 6.16 Arc Hydro Framework with Hydro Network for Blue Nile 
basin........................................................................................... 84 
 
 1
CHAPTER 1:  INTRODUCTION 
1.1 Background 
           Ethiopia, with a total area of 1.13 million square kilometers,
 
has a total population 
of 63.5 million (CIA, 2004). The economy of the country is highly dependent on 
agriculture, which in turn is dependent on the availability of seasonal rainfall.  The 
country’s renewable surface and ground water amounts to 123 and 2.6 billion cubic 
meters per annum respectively but its distribution shows high temporal and spatial 
variation. Furthermore, rainfall is highly variable across the country, from season to 
season, and from year to year. This temporal variation of rainfall subjects the country to 
frequent droughts and famine. Ethiopia is also the source of nearly 85% of the Nile River. 
             The Ministry of Water Resources (MoWR) of Ethiopia is the sole responsible 
agency for the distribution and conservation of water resources in the country. The 
MoWR signs international agreements related to Transboundary Rivers in accordance 
with the law. The department of Transboundary Rivers in the MoWR provides a policy 
advisory on strategies and legal matters pertaining to negotiation with the riparian states, 
particularly with Sudan and Egypt. The departments of Basin Study and Hydrology have 
a huge amount of basin resource potential and hydrological data respectively. The 
hydrology department also possesses large amounts of datasets related to river flow, 
sediments, and other hydrological characteristic of the major Rivers in the country.  Most 
of the study output is in the form of classical paper report format that is difficult to 
manage. Thus, the Ministry of Water Resources (MoWR) planes to develop a digital 
hydrologic data model that supports management of the countries water resources. The 
 2
Arc Hydro data model can be used to support the MoWR plan to develop a digital 
hydrologic data set. 
 Arc Hydro, which is developed by the Center for Water Resources (CRWR) at 
the University of Texas at Austin, is a geospatial and temporal data model for water 
resources designed to operate within ArcGIS. Arc Hydro opens the way to building 
hydrologic information systems that synthesize geo-spatial and temporal water resource 
data to support hydrologic analysis and modeling (Maidment 2002). The purpose of a 
geographic information system (GIS) is to provide a spatial framework to support 
decisions for the intelligent use of earth’s resources and manage the manmade 
environment.  
1.2 Study Objectives 
This project is aimed at developing a geodatabase to build hydrologic information 
systems for Ethiopian watersheds and modeling of the rivers. The geodatabase will 
consist of an Arc Hydro-based geographic information system and relational database 
containing hydrologic, hydraulic and related data for Ethiopian watersheds. Generally 
this project will have the following outputs: - 
0. Generate a 90*90 m cell Digital Elevation Model (DEM) of Ethiopia from SRTM 
data. 
0. Develop a prototype Arc Hydro data model for Ethiopia water sheds 
0. Represent the drainage system into appropriate Basins, Watersheds, and 
Catchments  
0. Represent stream flows using time series attribute tools 
 3
 1.3Thesis outline 
 
Chapter 2 is literature review about the Arc Hydro data model, the Ethiopia Water 
system and the Hydro-politics in East Africa. Chapter 3 discusses the different data 
archives collected and used for this project. Chapter 4 discusses how 90m digital 
elevation data was obtained and processed. Chapter 5 how the Blue Nile watershed was 
delineated using the terrain analysis tool in Arc Hydro. Chapter 6 describes the 
Geodatabase design and Arc Hydro framework for Blue Nile Basin. The last chapter 
describes the project summary and conclusions. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 4
CHAPTER 2:  LITERATURE REVIEW 
 
 Previous chapters provided background information about the importance of this 
study and the primary objectives of this project. This chapter provides a review of 
geographic location of Ethiopia and previous water resource studies conducted in 
Ethiopia.  
2.1 The study area 
 
Ethiopia is located in the Horn of Africa and is bordered on the north and 
northeast by Eritrea, on the east by Djibouti and Somalia, on the south by Kenya, and on 
the west and southwest by Sudan (Figure 2.1). The country has a high central plateau that 
varies from 1,800 to 3,000 meters (6,000 ft.-10,000 ft.) above sea level, with some 
mountains reaching 4,620 meters (15,158 ft.). Elevation is generally highest just before 
the point of descent to the Great Rift Valley, which splits the plateau diagonally. A 
number of rivers cross the plateau-most notably the Blue Nile flows from Lake Tana. The 
plateau gradually slopes to the lowlands of Sudan on the west and Somali-inhabited 
plains to the southeast.  
The climate is temperate on the plateau and hot in the lowlands. At Addis Ababa, 
where the elevation ranges from 2,200 to 2,600 meters (7,000 ft.-8,500 ft.), maximum 
temperature is 26
o
 C (80
o
 F) and minimum temperature is 4
o
 C (40
o
 F). The weather is 
usually sunny and dry with the short rains occurring February to April and the heavy rain 
begin in mid-June and ending in mid-September (US Department of State, 1998). 
 5
 
 
 
Figure 2.1 Location of Ethiopia (PCL 2000) 
 
 6
2.2 Water Resources of Ethiopia 
  Ethiopia is endowed with a substantial amount of water resources. The surface 
water resource potential is impressive but little developed. The country possesses twelve 
major river basins (FAO, 2005), which form four major drainage basins (table 2.1): 
� The Nile Basin (including Abbay or Blue Nile, Baro-Akobo, Setit-Tekeze/Atbara and 
Mereb) covers 33% of the country and drains the northern and central parts westward. 
� The Rift Valley (including Awash, Denakil, Omo-Gibe and central lakes) covers 28% 
of the country. 
� The Shebelle-Juba basin (including Wabi-Shebelle and Genale-Dawa) covers 33% of 
the country and drains the southeast mountains towards Somalia and the Indian 
Ocean. 
� The North East Coast (including the Ogaden and Gulf Aden basins) covers 6%of the 
country.       
Integrated development master plan studies and related basin surveys, undertaken 
at the end of the 1990s, indicate that the aggregate annual runoff from Ethiopian river 
basins is about 122 x 10
9
km
3 
(table 2.2). Abay, Baro-Akobo and Omo-Gibe basins 
account for about 76% of the total runoff from an area of only 32% of the total area of the 
country. Most of the rivers in Ethiopia are seasonal and about 70% of the total runoff 
takes place during the months of July-August. Dry season flow originates from springs, 
which provide base flows for small-scale irrigation. The ground water potential of the 
country is estimated to be 2.6 billion cubic meters. Intense rainfall sometimes causes 
flooding particularly along the Awash River and in the lower Baro-Akobo and Wabe-
Shebelle river basins, causing damages on standing crops and infrastructure (FAO, 2005). 
 7
Table 2.1 Area and runoff by river basin for Ethiopian water system (MoWR 2002) 
Major  River Area % of total 
Annual 
Runoff % of Total 
Drainage Basin (10
4
 m
2
) Area (%) (km
3
/yr) Runoff (%) 
system    (10
4
 m
2
) (%) (km
3
/yr) (%) 
Nile Basin   36,881,200 32.4 84.55 69 
  Blue Nile 19,981,200 17.6 52.6 42.9 
  Baro-Akobo 7,410,000 6.5 23.6 19.3 
  SetitTekeze/Atbara8,900,000 7.8 7.63 6.2 
  Mereb 590,000 0.5 0.72 0.6 
Rift    31,764,000 27.9 29.02 23.7 
Valley Awash 11,270,000 9.9 4.6 3.7 
  Denakil 7,400,000 6.5 0.86 0.7 
  Omo-Gibe 7,820,000 6.9 17.96 14.7 
  Central Lake 5,274,000 4.6 5.6 4.6 
Shebelli-Juba   37,126,400 32.7 8.95 7.3 
  Wabi-Shebelli 20,021,400 17.6 3.15 2.6 
  Genale-Dawa 17,105,000 15.1 5.8 4.7 
North East    7,930,000 7 0 0 
Coast Ogaden 7,710,000 6.8 0 0 
  Gulf of Aden 220,000 0.2 0 0 
Total    113,701,600 100 122.5 100 
 
Ethiopia has several lakes (about 7,000 km
2
), a number of saline and crater lakes 
as well as several wetlands. All lakes, except Lake Tana, which is the source of Abbay 
River in the Nile Basin, are found in the Rift Valley and among these lakes only Zway 
has freshwater while others are saline. Rising of Lake Tana and Lake Awassa after 
intense rainfall is creating concerns to the city of Bahir Dar and Awassa respectively. 
 8
Large wetlands serve as source of water for large rivers, flood retention and groundwater 
recharge (FAO, 2005). 
Table 2.2 water sources and use in Ethiopia (FAO, 2005) 
 
Renewable water resources  Year  Value  Unit 
Average precipitation  848 mm/yr 
Total actual renewable water resources  122 10
9
 m
3
/yr 
Total actual renewable water resources 
per inhabitant 2004 1,685  m
3
/yr 
Total dam capacity 2002 2,458 10
6
m
3
 
Water withdrawal    
Total Water withdrawal 2002 5,558 10
6
m
3
/yr 
             -irrigation +livestock 2002 5,204 10
6
m
3
/yr 
             -domestic 2002 333 10
6
m
3
/yr 
             - industry 2002 21 10
6
m
3
/yr 
         -per inhabitant 2002 86 m
3
 
         -as % of total actual renewable 
water resources 2002 4.6 % 
 
 
 
 
 9
          Ethiopia has many small, medium and large reservoir dams constructed for 
hydropower generation, irrigation and drinking water supply. Small dams are less than 15 
m high and have a capacity of less than 3 million m
3
. The height of the medium and large 
dams in Ethiopia is 15 -30 m and their capacity ranges from 4 to 1,900 million m
3
. 
Totally, there are nine medium and large dams, with a total capacity of almost 3.5 km
3
. 
Two large dams are used for hydropower generation only, one dam is used for irrigation 
and supply and hydropower generation, two dams are used for irrigation supply only and 
the remaining four supply to the Addis Ababa city and Gonder town. 
2.3 Transboundary Waters and the Nile Basin Initiatives  
 
(Gulilat, 2002) described that 75% of the rivers, which originates in highlands of 
Ethiopia, cross the borders and feed neighboring countries. These Transboundary Rivers, 
particularly the Nile Tributaries (Abbay, Tekeze, and Baro-Akobo) are also source of 
conflict with the down stream riparian countries like Sudan and Egypt. Ethiopia also 
contributes 86% of the Nile water. 
There are ten countries that make up the Nile River Basin.  Some of the countries 
have only a small part of their area within the basin, whilst others are virtually entirely 
within the Basin (Figure 2.2).  All the countries contribute differently to the basin and 
have different needs for the water and other resources of the basin (NBI, 2005). 
International efforts and policy direction have brought together the partners in the Nile 
basin under the umbrella of the Nile Basin Initiative (NBI) (Gulilat, 2002). The Nile 
Basin Initiative created and prepared a Strategic Action Program, which consists of two 
 10
sub-programs: the Shared Vision Program (SVP) and the Subsidiary Action Program 
(SAP). SVP is to help create an enabling environment for action on the ground through 
building trust and skill, while SAP is aimed at the delivery of actual development projects 
involving two or more countries. Projects are selected by individual riparian countries for 
implementation and submitted to the Council of Ministers of the Nile Basin Initiative for 
the approval (FAO, 2005). 
  
 
 11
 
Figure 2.2 Nile basin riparian countries (NBI 2005) 
 12
CHAPTER 3:  METHODOLOGY 
The previous chapters gave background information about the objective of the 
research and discussed previous water resource studies done in Ethiopia. This chapter 
discusses details of data used for applying Arc Hydro tools for Ethiopian Watersheds. 
 3.1Geographic Information Systems (GIS) Data 
 GIS is a system of computer software, hardware, data and personnel to help 
manipulate, analyze and present information that is tied to a spatial location 
(ESRI,2005):- 
• Spatial location –a geographic location 
• Information – visualization of analysis of data 
• System – linking software, hardware and data 
• Personnel- a thinking explorer who is key to the power of GIS 
 
GIS data about major streams, major basins and waterbodies of Africa were 
obtained from the Food and Agricultural Organization (FAO) GeoNetwork. GeoNetwork 
allows for easily sharing geographically referenced thematic information between 
different FAO Units, other United Nations (UN) Agencies, Non-Governmental 
Organizations (NGO's) and other institutions.  
3.1.1 MAJOR AFRICA’S STREAMS 
Stream data of Ethiopian watersheds were obtained from FAO GeoNetwork 
(FAO, 1998). This digital data layer is a 1: 5, 000, 000 shapefile with the rivers of Africa 
 13
that was digitized in 1994 for the United Nations Environmental Program (UNEP) and 
Food and Agricultural Organization (FAO) Desertification Assessment and Mapping 
Project. 
The dataset consists of the following information:  
• GIS generated codes (FNODE_, TONODE_, AFRIVLL_) 
•  a code to describe the hydrological rank of the river starting with rank 1 for the 
most upstream contributories and counting downstream according to Strahler's 
stream order method (RNK) 
• a code to show the hydrological regime (1 = perennial, 2 = intermittent) 
• a code that combines the two codes in one value (CODE, first digit RNK, second 
digit REGIME) 
 14
 
Figure 3.1 Rivers in Africa (FAOa, 2000) 
 
 
 
 
 
 
 
 15
3.1.2 MAJOR DRAINAGE BASINS 
 
 GIS data on major drainage basins were obtained from FAO GeoNetwork (FAO, 
1998). The dataset divides the African continent according to its hydrological 
characteristics (Figure 3.2) and consist of the following information: 
•  numerical code and name of the major basin (MAJ_BAS and MAJ_NAME) 
• area of the major basin in square km (MAJ_AREA) 
•  numerical code and name of the sub-basin (SUB_BAS and SUB_NAME) 
•  area of the sub-basin in square km (SUB_AREA) 
•  numerical code of the sub-basin towards which the sub-basin flows 
(TO_SUBBAS)  
 16
 
 
Figure 3.2 Hydrological Basins in Africa (FAOb, 2000) 
 
 
 17
3.1.3 INLAND WATER BODIES OF AFRICA 
 
The Shape file of inland water bodies in Africa was obtained from FAO 
GeoNetwork (FAO, 1998). This dataset originates from the Digital Chart of the World 
1:1000000. The water bodies for Africa have been characterized as lake, lagoon, 
reservoir etc.) . The data layer presented contains all the water bodies that had a name and 
were not characterized as river. The dataset consists of the following information:  
• GIS generated codes (FID, AF_WTR_ID) 
•  Area of waterbody (SQKM) 
•  Name of  waterbody (NAME_OF_WA) 
•  Type of waterbody (TYP_OF_WA) 
 18
 
Figure 3.3 Inland water bodies in Africa (FAOc, 2002) 
 
 
 
 
 
 
 
 
 
 19
3.1.4 CREATING AND ADDING ETHIOPIA’S OUTLINE SHAPEFILE 
 
The shapefile of Ethiopia’s outline was created from Environmental System 
Research Institute (ESRI’s) World Basemap Data. Basemap data are used to create maps 
of geographic features such as country boundaries, city points, rivers, roads, railroads, 
and airports. The World Basemap Data includes data layers from a variety of ESRI 
products, including Arc Atlas, Arc World, and digital map of the World. ESRI assembled 
selected data layers from these sources into a Spatial Database Engine (SDE) database to 
provide a continuous display of basemap data from a small-scale global display to a 
medium-scale regional display. 
The Data Downloader opens the ESRI World Basemap; Ethiopia’s shapefile was 
selected by entering Ethiopia in the search box and using the Zoom and Pan Tools to 
adjust the area. This action displays the Select windows layer. The default is all available 
layers. All layers include: Countries and Regions (Data and Maps), Major Rivers (Arc 
Atlas), Water Bodies (Arc Atlas), Major Highways (Arc Atlas), and Major Cities (Arc 
World). Then the Major Rivers, Water Bodies and Countries layers were checked and the 
other two layers were unchecked. Then the Download file was clicked to retrieve the 
shape file for Ethiopia and Ethiopia’s shape file was retrieved as shown in figure 3.4. 
 20
 
 
Figure 3.4 Shape of Ethiopia and its neighboring countries (ESRI, 2005). 
 
3.1.5 SUMMARY OF GIS DATA AND SHAPE FILES 
 
All the GIS data for Ethiopia was clipped out from Figures 3.1, 3.2, 3.3 and 3.4 in 
ArcGIS desk top and layered as shown in Figure 3.5. The basins shape file protruded out 
side of Ethiopia’s political boundary since some of the basins are shared between 
 21
Ethiopia and its neighboring countries. The streams shape files showed all the streams 
from Hydro1k. HYDRO1k, developed at the U.S. Geological Survey's (USGS) Earth 
Resource and Observation System (EROS) Data Center, is a geographic database 
providing comprehensive and consistent global coverage of topographically derived data 
sets with a spatial resolution of 1 km (USGS,2003). The water bodies shape file showed 
all the lakes in Ethiopia that lies in the rift valley system except Lake Tana. 
 
Figure 3.5 Ethiopia Country’s boundary, Streams, Water Bodies and Basins from Hydro1K. 
 
 
 
 22
CHAPTER 4: GETTING DIGITAL ELEVATION DATA 
4.1 Shuttle Radar Topography Mission (SRTM) 
 
The Shuttle Radar Topography Mission (SRTM) obtained elevation data on a 
near-global scale to generate the most complete high-resolution digital topographic 
database of Earth. SRTM consisted of a specially modified radar system that flew 
onboard the Space Shuttle Endeavour during an 11-day mission in February of 2000.  
The data are published in 1-arc second (30 m resolution) grids for the US and 3 arc 
second (90 m resolution) grids for the rest of the globe from 56
o
 S - 60
 o
 N latitude. 
 
 
Figure 4.1 Illustration of interferometry on the Endeavour (JCP, 2005) 
  
Two radar data sets were collected at the same time separated by 60 m, the 
distance between the main antenna and the outboard antenna (Figure 4.1).  Knowing the 
distance between the two antennas and the differences in the reflected radar wave signals, 
accurate elevation of the Earth's surface was calculated.  
 23
4.2 Obtain SRTM data 
There are several sources available from which SRTM data can be obtained, 
including: 
 
NASA (raw data): ftp://e0mss21u.ecs.nasa.gov/srtm/ 
USGS (somewhat corrected data): http://seamless.usgs.gov/ 
CGIAR (No Data holes filled): http://srtm.csi.cgiar.org/ 
 
The Consortium for Spatial Information (CIS), an initiative of the many 
geospatial scientists with in the Consultative Group for International Agriculture 
Research (CGIAR), site is the best data source since Data holes are filled and the data are 
ready for use. The CGIAR-CSI GeoPortal provided SRTM 90m Digital Elevation Data 
for the entire world as shown in Figure 4.2.  However, they are not provided in a 
“seamless” data format and several tiles must be mosaiced together. The DEM files are 
available for down load as 5 degree * 5 degree tiles in geographic coordinate system - 
WGS84 datum. 
 These files are available for download in both Arc-Info ASCII format, and as 
GeoTiff, for easy use in most GIS and Remote Sensing software applications. 
 24
 
 
Figure 4.2 Processed SRTM 90m Digital Elevation Data (DEM) for entire globe (CGIAR, 2005) 
 
From Figure 4.2 selecting SRTM Data Search and Download and then entering 
the Latitude and Longitude of choice will allow choose SRTM data of interest. This 
 25
yields the world map divided in to 60 rows and 72 columns as shown in Figure 4.3. 
 
Figure 4.3 SRTM data search page in Microsoft Internet explorer (CGIAR,2005) 
 
To select SRTM data for Ethiopia, enter the coordinates: 30-48
o
 Longitude and 3-
15
o
 Latitude.  Then select Search. This will select 12 tiles that can be readily downloaded 
as shown in Figure 4.4. The SRTM data from this option is in GeoTiff format. 
 
 26
 
Figure 4.4 SRTM search results in GeoTiff format (CGIAR, 2005) 
 
Alternatively, it is possible to select Direct Link to FTP Download and select 
and download all the tiles at once. In this case, Arc info ASCII option is checked instead 
of GeoTiff. This option is relatively time consuming and used to down load SRTM data 
for Ethiopia.  
 
 27
 
Figure 4.5 SRTM Data zip files in ASCII format (CGIAR, 2005) 
 
Right clicking and selecting Copy to Folder, will select the folder where the 
SRTM zip files for selected coordinates to be downloaded.  For instance, to download all 
the data for Ethiopia, the following zip files were selected: 
srtm_43_12.zip,srtm_44_12.zip,srtm_45_12.zip,srtm_46_12.zip, srtm_43_11.zip, 
srtm_44_11.zip,srtm_45_11.zip,srtm_46_11.zip,srtm_43_10.zip, srtm_44_10.zip, 
srtm_45_10.zip and srtm_46_10.zip as shown in Figure 4.5.  
 28
4.3 Convert ASCII to Raster Grids  
The zip files from Figure 4.5 were unziped and the tiles from the downloaded 
files were saved in separate directories. In order to display the raster grids in ArcMap the 
following tool was used to convert ArcASCII format: 
ArcMap: ArcToolbox: Conversion Tools: To Raster: ASCII to Raster 
 
 
 29
 
Figure 4.6 Converting files from ASCII to raster format. 
 
After processing each of the four downloaded tiles, we have the result shown in Figure 
4.7. 
 30
 
Figure 4.7 Tiles of rasters for SRTM 90m. 
 
4.4 Mosaic Multiple Grids  
Since there are 12 tiles Ethiopia, all the tiles were mosaiced together into a larger 
grid using ArcToolBox (in ArcCatalog or ArcMap).  The following command will 
mosaic all the grids from N3E030 to N15E048 into a single grid : 
             ArcMap: ArcToolbox: Data Management Tools: Raster:        
Mosaic_to_New_Raster 
 31
 
Figure 4.8 Mosiac to raster dialog box 
 
Finally, the resulting DEM was added to the display. A single tile for the whole region as 
shown in Figure 4.8. 
 32
 
Figure 4.9 Mosaiced DEM of Ethiopia and its surroundings 
 
4.5 Remove “NoData” Values from DEM 
One of the problems that arises during mosaicing multiple grids together is that 
you can receive no-data values at the seams between the grids as shown in Figure 4.7. 
Cells with NoData value are those cells for which a valid value is not known such as a 
cell past the edge of a quadrangle. NoData and “0” (zero) are not the same- 0 is a valid 
cell value. These NoData areas will cause significant problems later during the terrain 
processing procedures and they must be patched.   
 33
This problem can be fixed by resetting the NoData values for the DEM grid in ArcView 
GIS using the following three methods: 
0. For small holes, the NoData value can be set to zero using the following 
command to fill the holes: 
ArcMap: Spatial Analyst: Raster Calculator:  
Con (isnull ([raster]), 0, [raster]) 
     2.  For medium sized holes of NoData, the following command averages the values   
surrounding NoData and fills the holes:  
ArcMap: Spatial Analyst: Raster Calculator:  
Con( isnull( [raster] ), focalmean( [raster] , rectangle, 5, 5 ), 
[raster] ) 
This procedure had to be repeated several times to fill all of the holes. The resulting raster 
is in the floating-point format and it needs to be converted back to integer using the 
following command: 
ArcMap: Spatial Analyst: Raster Calculator: Int( [raster] ) 
Then, the resulting grid is made permanent as follows: 
ArcMap: Right Click on Grid: Make Permanent 
 
3.  Finally, larger holes, like in Denakil depression, can be filled by resampling from the 
old 1 km data from the following site: 
 http://edcdaac.usgs.gov/gtopo30/hydro/readme.asp#RasterDataFormats 
 
 34
The 1 km grid had to be transformed from “*.bil” form to a regular ARC/INFO grid with 
the command IMAGEGRID. IMAGEGRID does not support conversion of signed image 
data, therefore the negative 16-bit image values will not be interpreted correctly.  
ARC: imagegrid [input bil file name] [in grid] 
After running IMAGEGRID, an easy fix was accomplished using the following formula 
in GRID:  
GTOPO30 Raster = con (in_grid >= 32768, in_grid - 65536, in_grid)  
Clipping your basin DEM [Basin DEM Raster], and the 1 km DEM [GTOPO30 Raster], 
using the mask (see below) and the larger DEM 
[Clipped_Basin_DEM_Raster] = Mask * [Basin_DEM_Raster] 
[Clipped_GTOPO30_Raster] = Mask * [GTOPO30_Raster] 
 
Resample the 1 km DEM [Clipped GTOPO30 Raster] to 90 m DEM using the 
following command: 
 
Arc Toolbox: Raster: Resample ([Clipped_GTOPO30_Raster],  
use cell size of your DEM) 
Make it permanent with the name [resample GTOPO30 Raster] 
Finally, fill the NoData in your DEM [GTOPO30 Basin DEM Raster] with the 1 Km 
DEM 90m data [resample GTOPO30 Raster]  
ArcMap: Spatial Analyst: Raster Calculator:  
 Con( isnull( [Clipped_Basin_DEM_Raster] ),  
  [Resample_GTOPO30_Raster],  
 35
                   [Clipped_Basin_DEM_Raster] 
Figure 4.8 final result of resampling  
 
Figure 4.10 Seams at the boundary of quadrangle. 
4.6 Define the Spatial Reference for the Grids 
Spatial Reference provides the description of the reference frame for, and the 
means to encode, coordinates in a data set. Since the Spatial Reference of the 
gridsdiscussed in the previous section has yet been defined, it should be defined as 
follows : 
ArcCatalog: Right Click on Grid: Properties Scroll down to “Spatial 
Reference” 
 
 36
 
Figure 4.11 Raster dataset properties 
 
Make sure the Define the “coordinate system interactively” option is selected.  
Click Next.  
 37
 
Figure 4.12 Define projection wizard 
 
Select the Geographic projection with decimal degrees (DD) and a WGS-1984 
datum. This is not a map projection. The Geographic Reference System maps locations 
on a globe using latitude and longitude. This system treats the globe as if it were a sphere 
or spheroid. 
 38
 
 
 
Figures 4.13 Define projection wizard dialog boxes 
 
Review the summary of the coordinate system that will be assigned to the grid. If 
you want to change an entry, go back through the wizard by clicking the Back button. 
Click Finish if you want to use this coordinate system. The coordinate system and its 
parameters appear in the Raster Properties dialog box. Click OK in the Raster Dataset 
 39
Properties dialog. This procedure defined the spatial reference of the Raster Dataset as 
shown in the following diagram. 
  
 
Figure 1.14 Raster dataset properties dialog box 
 
 
 
 
 
 
 40
4.7 Project Grids 
Project the grids into your working projection with the appropriate cell size (e.g., 
90m at the equator) as follows: 
ArcMap or ArcCatalog: ArcToolbox: Data Management: Projections and 
Transformations: Raster: Project Raster 
For this research, the Albers system was chosen as the Coordinate system in order that 
areas and distances are computed correctly later. The Albers System has the following 
properties 
The Cell size:  92.076753327191767 m 
Projection: Albers 
Parameters: 
False_Easting: 0.000000 
False_Northing: 0.000000 
Central_Meridian: 25.000000 
Standard_Parallel_1: 20.000000 
Standard_Parallel_2: -23.000000 
Latitude_Of_Origin: 0.000000 
Linear Unit: Meter (1.000000) 
Geographic Coordinate System:  
Name: GCS_WGS_1984 
Angular Unit: Degree (0.017453292519943299) 
Prime Meridian: Greenwich (0.000000000000000000) 
 41
Datum: D_WGS_1984 
 Spheroid: WGS_1984 
 Semimajor Axis: 6378137.000000000000000000 
 Semiminor Axis: 6356752.314245179300000000 
Inverse Flattening: 298.257223563000030000 
 
 
 42
 
 
 
Figure 4.15 Project Raster dialog box 
 
Click OK and the result is calculated  
Open ArcMap. Find and display the new grid as shown in Figure 4.15. 
 43
 
 
Figure 4.16 Regional DEM after projection 
 
 
 
 
 
 
 
 
 
 44
4.8 Make Buffer for Area of Interest 
Create a new Geodatabase for the project: Ethiopia_GDB.mdb. Also, 
create a new FeatureDataset named Base in the new Geodatabase, with the same 
coordinate system as the Projected DEM from the previous section. 
Export the Ethiopia country boundary polygon from the NEW_DEM Coverage into the 
Base FeatureDataSet, name it Ethiopia _Boundary. 
Display the Ethiopia_Boundary polygon on the map. 
 
 
Figure 4.17 Regional DEM and Ethiopia country boundary 
 45
 
Create a 50-km buffer polygon [Buffer_of_Ethiopia_Boundary] around the 
boundary using buffer wizard as follows: 
 
ArcMap: Tools: Buffer Wizard 
 Distance: 50 km 
 Dissolve: yes 
 Outside and include inside 
   Location and name: eg., “[Buffer_of_Ethiopia_Boundary]” 
 
 46
 
 
Figure 4.18 Buffer wizards dialog box 
 47
 
Add a field of “One” to [Buffer_of_Ethiopia_Boundary] 
ArcMap: Select [Buffer_of_Ethiopia_Boundary]: Right Click: Open 
Attribute Table 
Attribute Table: Options: Add Field: Name [One]: Short Integer 
 
Figure 4.19 Attribute table of Buffer of Ethiopia with field one 
 
Attribute Table: Select Field [One]: Right Click: Calculate Values 
Calculate Values: Value of One = 1 
 
 48
 
Figure 4.20 Field Calculator dialog box 
 
Create a raster [Buff_Raster] from [Buffer_of_Ethiopia_Boundary] using the 
following commands: 
ArcMap: Spatial Analyst: Convert: Features-to-Raster 
Input Feature: [Buffer_of_Ethiopia_Boundary] 
Attribute to Use:  [One] 
Cell size = 92.076753327191767 
   Location and name: eg., “[Buff_Raster]” 
 
Clip your basin DEM raster [Dem] to the area of the [Buff_Raster] by multiplying the 
rasters: 
 
 49
 ArcMap: Spatial Analyst: Raster Calculator 
  [Buff_Raster]  * [Dem] 
Make the temporary raster permanet. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 50
CHAPTER 5: WATERSHED AND STREAM NETWORK 
DELINEATION 
5.1 Introduction 
 
The previous chapter discussed how elevation data could be obtained from SRTM 
data for Ethiopia. This chapter illustrates how to use the major functionality available in 
the Arc Hydro tools for Raster analysis and perform drainage analysis on a terrain model 
using the Digital Elevation Model of Ethiopia and Hydro 1 K streams.  The Arc Hydro 
tools are used to derive several data sets that collectively describe the drainage patterns of 
the catchment.  Raster analysis is performed to generate data on flow direction, flow 
accumulation, stream definition, stream segmentation, and watershed delineation.  These 
data will then be used to develop a vector representation of catchments and drainage lines 
from selected points.  
5.2 Hydro Administrative regions of Ethiopia 
 Based on the flow direction of the streams, the country is divided into six hydro 
administrative regions: 
• The Blue Nile region (BN) 
• The South West region (SW) 
• The South Central region (SC) 
• The South East region (SE) 
• The Rift Valley region (RV) 
• The North East-West region  (NEW) 
 51
Since the Blue Nile region is the source of nearly 85 % of the Nile water and 
vigorously erodes the country’s fertile soil, water shed and stream network delineation is 
shown for this region. But, a similar procedure was followed for the rest of five hydro 
administrative regions to develop the stream network delineation for the whole country. 
5.3 Setting up the Arc Hydro tools  
The Arc Hydro Toolset is a suite of tools that facilitate the creation, manipulation, 
and display of Arc Hydro features and objects within the ArcMap environment.  The 
tools provide raster, vector, and time series functionality, and many of them populate the 
attributes of Arc Hydro features. The Arc Hydro tools were installed from Center for 
Research in Water Resources (CRWR) web site 
(http://www.crwr.utexas.edu/gis/gishydro04/index.htm). 
The existing data for the Blue Nile (BN) basin, including bn_dem1 and BN hydro 
1k streams, were added into ArcMap document and saved before the analysis of the 
dataset using Arc Hydro tools as shown in Figure 5.1. The procedure of getting the blue 
Nile Basin DEM is explained in Appendix A. Similar procedure was used to obtain the 
DEM for the rest of the Hydro Administrative regions. 
 
 52
 
Figure 5.1 the outline of Blue Nile DEM and hydro 1k streams 
 
5.4 Terrain Processing  
 
The purpose of terrain preprocessing is to perform an initial analysis of the terrain 
and to prepare the dataset for further processing. Once preprocessed, the DEM and its 
derivatives can be used for efficient watershed delineation and stream network 
generation.  
 53
All the steps in the Terrain Preprocessing menu were performed in sequential 
order, from top to bottom. All of the preprocessing had to be completed before Watershed 
Processing functions could be used (Maidment, 2004). 
5.4.1 DEM RECONDITIONING 
 
The DEM Reconditioning function (Terrain Preprocessing menu) modifies Digital 
Elevation Models (DEMs) by imposing linear features onto them (burning/fencing). This 
function is an implementation of the AGREE method developed by Ferdi Hellweger at 
the University of Texas at Austin in 1997.   
5.4.2 FILL SINKS 
 
The Fill Sinks function (Terrain Preprocessing menu) fills sinks in a grid.  If a 
cell is surrounded by higher elevation cells, the water is trapped in that cell and cannot 
flow. The Fill Sinks function modifies the elevation value to eliminate these problems. 
This function produced a Hydro DEM where sinks didn’t exist (Figure 5.2). 
 54
 
 
Figure 5.2 Blue Nile DEM after sinks have been filled 
 
 
 
 
 
 
 55
5.4.3 FLOW DIRECTION  
 
            This function computes the flow direction in a given grid by using “Fil_bn” hydro 
DEM as an input (Figure 5.3). The values in the cells of the flow direction grid indicate 
the direction of the steepest descent from that cell. 
 
 
Figure 5.3 Flow direction grids for Blue Nile Basin 
 56
 
4.3.3 FLOW ACCUMULATION 
 
This function takes the flow accumulation grid as an input. It computes the 
associated flow accumulation grid that contains the accumulated number of cells 
upstream of a cell, for each cell in the input grid as shown in Figure 5.4. 
 
Figure 5.4 Flow direction and Flow accumulation models (Source Arc Hydro help) 
 
The output of flow accumulation grid is shown in Figure 5.5. 
 57
 
Figure 5.5 Flow accumulation grids for Blue Nile Basin 
 
4.3.3 STREAM DEFINITION 
This function takes the flow accumulation grid as an input and generates a Stream 
Grid for a user- defined threshold (Figure 5.6). The resulting stream grid contains a value 
 58
of "1" for all the cells in the input grid that have a value greater than the given threshold.  
All other cells in the Stream Grid contain no data. 
 
Figure  
5.6 Stream definition grids for Blue Nile basin 
5.4.6 STREAM SEGMENTATION 
The Stream Segmentation function creates a grid of stream segments that have a 
unique identification (Figure 5.7).  Either a segment may be a head segment, or it may be 
 59
defined as a segment between two segment junctions.   All the cells in a particular 
segment have the same grid code that is specific to that segment. 
 
Figure 5.7 Stream segmentation grids for Blue Nile Basin 
5.4.7 CATCHMENT GRID DELINEATION 
 
The Catchment Grid Delineation function creates a grid in which each cell carries 
a value (grid code) indicating to which catchment the cell belongs.  The value 
 60
corresponds to the value carried by the stream segment that drains that area, defined in 
the stream segment link grid. The output from catchment grid delineation is shown in 
Figure 5.8. 
 
 
Figure 5.8 Catchment grid delineation grids for Blue Nile Basin 
 
 
 
 
 
 61
5.4.8 CATCHMENT POLYGON PROCESSING 
 
The Catchment Polygon Processing function takes as input a catchment grid and 
converts it into a catchment polygon feature class.  The adjacent cells in the grid that 
have the same grid code are combined into a single area, whose boundary is vectorized. 
The output from catchment polygon processing is shown in Figure 5.9. 
 
 
 62
 
Figure 5.9 Catchment polygon processing grids for Blue Nile Basin 
5. 4.9 DRAINAGE LINE PROCESSING 
 
The Drainage Line Processing function converts the input Stream Link grid into a 
Drainage Line feature class.  Each line in the feature class carries the identifier of the 
 63
catchment in which it resides. The output from Drainage line processing command is 
shown in Figure 5.11. 
 
 
 
Figure 5.10 Drainage line processing grid for Blue Nile basin 
 64
5.4.10 DRAINAGE POINT DELINEATION   
 
This function generates the drainage points associated with the catchments.  
The fields created by this function are: 
1. HydroID: Unique identifier of the drainage point in the Hydro database. System 
generated. 
2. GridID: GridID of the catchment draining to the drainage point. 
3. DrainID: HydroID of the catchment draining to this drainage point 
 
 65
 
 
Figure 5.11 Drainage point processing grid for Blue Nile Basin 
  
Similar procedures were followed to generate the catchments and streams lines 
for the other five Hydro Administrative regions of Ethiopia. The final output is shown in 
Figure 5.13. 
 66
 
 
 
 
 
 
Figure 5.12 The six hydro administrative regions of Ethiopia and the associated streams. 
 The red lines show the Hydro 1k streams. 
 
 67
CHAPTER 6: ARC HYDRO DATA MODEL AND FRAMEWORK 
6.1ArcGIS Hydro Data Model 
 
The Arc Hydro framework provides a simple, compact data structure for storing 
the important geospatial data describing the water resource system (Maidment,2002). A 
geodatabase model is generated in a series of steps, beginning with the definition of 
classes and attributes in a Unified Modeling Language (UML) diagram created in Visio 
2000. The second step is to export the diagram to a Microsoft repository format, which is 
an equivalent tabular structure, or schema, for loading into Microsoft Access (personal 
geodatabase) or other relational data servers (enterprise geodatabase). Finally, the data 
are imported into the Arc Hydro format by applying the schema to an ArcGIS 
geodatabase. 
The ArcGIS Hydro Data Model (Arc Hydro) stores data in four feature datasets, 
each corresponding to one of the main domains of the UML analysis diagram:  
• Hydrography (map hydrography and associated data inventories), 
•  Drainage (drainage areas derived from digital elevation models or 
manually digitized), 
•  Channel (3-D profile and cross-section representation of stream 
channels), and 
•  Network (a geometric network representation of the connectivity of the 
surface water features of the landscape). 
 68
 Associated with these four feature datasets are a set of object tables for additional 
information, such as events defined on the river network, and time series of monitoring 
data (Figure 6.1). 
 
Figure 6.1 ArcGIS Hydro Data Model (Maidment, 2002) 
6.2Geodatabase design 
 
 A Geographic Information System (GIS) database design is founded on 
geographic representations. For instance, entities can be represented as features (such as 
 69
points, lines, and polygons); and continuous surfaces and imagery using raster. Arc 
Hydro features for this research were organized in a series of thematic layers. A thematic 
layer is a collection of common geographic elements, such as a road network, a collection 
of parcel boundaries, soil types, an elevation surface, satellite imagery for a certain data, 
or well locations (Arctur et al 2004). Before creating the Geodatabase for the Blue Nile 
Basin and for the rest of the Ethiopian basins a study was performed regarding the 
structure of the Geodatabase, the data that will be included in the Geodatabase and the 
different types of relationships among the features and attributes. 
6.2.1 CREATING GEODATABASE 
 
 A simple personal geodatabase was created in Arc Catalog for each Ethiopian 
Hydro Administrative region after identifying the relation between the features classes 
and attributes. Once created, the geodatabase is a Microsoft Access file called an ArcGIS 
personal geodatabase.    
Procedures: 
• In the ArcCatalog tree (left window) navigate to the folder in which you will save 
your geodatabase (for example, Ethio-Geodatabase).  Right click on the Ethio-
Geodatabase folder and choose New -- Personal Geodatabase as shown in Figure 6.2. 
 70
 
 
Figure 6.2 Creation of personal geodatabase 
 
• Change the name of the new personal geodatabase.  The default is "New Personal 
Geodatabase.mdb" so make it BlueNile to make it consistent with the Hydro 
Administrative region name. Similarly, generate a personal geodatabase for each 
hydro administrative region as shown in Figure 6.3. Be sure to leave the .mdb 
extension. 
 
Figure 6.3 Personal geodatabases for each Hydro Administrative regions of Ethiopia 
 71
6.2.2 CREATING FEATURE DATASET 
 
A “Feature Dataset” is a collection of related feature classes. Feature classes are 
organized in an integrated feature dataset for many purposes- primarily to manage spatial 
relationships among related feature classes (Arctur et al, 2004). The feature datasets 
created for each hydro-administrative area geodatabase are shown in Figure 3.3. 
Procedures 
• Right click on the newly created file in the ArcCatalog tree.  Choose New -- Feature 
data set as shown in Figure 6.4. 
 
 
Figure 6.4 Creating a Feature Dataset 
 
 72
• Name the new feature dataset Arc Hydro, and select Edit to set the projection and 
map extent as shown in Figure 6.5. 
 
Figure 6.5 Geographic coordinate generation for new feature dataset 
 
• Import the coordinate system of existing data, such as data from Hydro1K documents 
that were explained in chapter three (Figure 6.6). 
 
 73
 
Figure 6.6 Geographic coordinates from Hydro 1K 
 
• Finally, you will see that the coordinate system is specified. Then, Click OK 
 
Figure 6.7 Albers Geographic coordinates from Hydro 1K. 
 
 The spatial properties dialog box has the following components: 
 74
• Coordinate system 
 The coordinate system of a dataset identifies its projection and datum. The coordinate 
system and datum should be set to be the same as any data intended to be loaded into the 
dataset. This information allows ArcMap and other applications to represent your data in 
the correct place relative to other data. Unlike the rest of the Spatial References, the 
coordinate system information can actually be changes after it has been established; this 
doesn’t reproject the data. 
• XY domain 
 The XY Domain, or Extent, of a dataset is the range of X and Y coordinates values that 
it will store. This permanently defines the area in the dataset that can contain features; in 
a sense it defines the edge of the world with respect to the dataset. No features can have 
coordinate values that are greater or less than these values. Features that exceed these 
limits can’t be loaded or digitized in to the dataset. 
• Precision  
The precision is the number of internal geodatabase storage units allocated to each 
Coordinate System unit.  
 
 
 
 
 
 
 75
6.3.3 IMPORTING FEATURE CLASSES INTO THE GEODATABASE 
 
A feature class is a collection of feature representing the same geographic 
elements, such as rivers, water bodies, or catchment areas. All the features in a feature 
class have the same spatial representation (for example, point, line, or polygon) and share 
a common set of descriptive attributes (Arctur et al, 2004). Individual features in a feature 
class can also share spatial relationship with other features. For Examples, adjacent 
polygons share boundaries according to well -defined integrity rules (such as that Hydro 
Administrative region can’t overlap one another). 
The feature classes created in chapter five and those obtained from other sources, 
such as those explained in chapter three were imported to the geodatabase as follows: 
• Right-click on your feature dataset and press Import � Feature Class (single)… as 
shown in Figure 6.8 and name is Hydro Edge. 
 
 
a 
 76
 
b 
Figure 6.8 a and b. Importing feature Class to geodatabase 
 
Similarly, other feature classes, such as monitoring points, watershed, and water 
body were imported to the feature dataset for each Hydro Administrative regions. 
6.4 Building an Arc Hydro Geodatabase and Geometric Network 
To apply the schema to the empty geodatabase created in section 6.2, right-click 
on the geodatabase and select Import/XML Workspace Document as shown in 
Figure 6.10. 
 77
 
Figure 6.10 Importing XML workspace document 
 
• Click Schema only option and import hydro framework schema from CRWR website 
(figure 6.11). 
 
Figure 6.11 Importing XML workspace Document 
 78
Press Next and then Finish. Refresh Arc Catalog and you will see the result shown in 
Figure 6.17. 
 
Arc Hydro Framework for the Blue Nile basin consists of one feature dataset 
called ArcHydro. The feature dataset contains only five feature classes: 
MonitoringPoint, Waterbody, Watershed, HydroEdge, and HydroJunction. 
• HydroEdge and HydroJunction (Figure 6.12 and 6.13 respectively) form a 
geometric network called HydroNetwork (Figure 6.14). 
• MonitoringPoint represents point features from map hydrography and inventory 
sources used to collect water resources data. 
•  Waterbody represents area features from map hydrography (Figure 6.15) and 
contains water bodies obtained from Hydro 1K. 
•  Watershed is a polygon feature class, which contains any subdivision of the 
landscape into drainage areas  
 79
 
Figure 6.12 HydroEdge feature class for Blue Nile Basin 
 
Figure 6.13 HydroJunction feature class for Blue Nile Basin 
 80
 
Figure 6.14 HydroNetwork feature class for Blue Nile Basin 
 
Figure 6.15 Waterbody feature class for Blue Nile Basin 
 81
 
Finally, a hydro geometric network was created for Blue Nile basin and the rest of 
Ethio-Hydro Administrative regions following the same procedure explained in 
Appendix A. The output of the hydro geometric network is added in Blue Nile basin 
geodatabase and is shown in Figure 6.16.   
 
 
Figure 6.16 Arc Hydro Framework with Hydro Geometric Network for Blue Nile basin 
 
 
 
 
 
 
 
 
 
 82
CHAPTER 7: CONCLUSION AND RECOMMENDATION 
7.1 Project Summary 
This project examined the possibility of using the Arc Hydro data model for 
Ethiopian Watersheds. Initially, existing Geographic Information data on Ethiopian were 
collected from Food and Agricultural organization (FAO) and Environmental System 
Research Institute (ESRI) Web achieves. Then, the Shuttle Radar Topographic Mission 
(SRTM) data was obtained from the Consultative Group for International Agriculture 
Research (CGIAR) web achieves and those data were processed to get 90 m Digital 
Elevation Data (DEM) for Ethiopia. Once those data were collected and processed, the 
country was divided into six Hydro-Administrative namely:  Blue Nile, Rift valley, South 
East, South Central, South West and North East-West region by tracing upstream of 
streams crossing the country. Then, a Geodatabase containing five feature dataset was 
created for each of the Hydro-Administrative regions in the country. Finally, a geometric 
network was created and an Arc Hydro Schema was applied for each Geodatabase.  
7.2 Project Conclusion  
  A number of conclusions were drawn from this project. Some of them are: 
1. The Arc Hydro data model is a very useful tool for organizing hydrologic information 
data for a very large area like Ethiopia (national scale). Thus, this project serves as a 
springboard for using the Arc Hydro data model for managing Ethiopia’s water 
resources. 
 
 83
2.  This project has shown that the Arc Hydro Framework is a very useful tool for 
managing GIS hydrological data for Ethiopian watersheds. It could also enable the 
Ministry of Water Resources of Ethiopia (MoWR) the ability of addressing streams, 
tracing upstream and downstream on the streams network. 
 
3. The Arc Hydro Time Series Component provides a means for storing spatially and 
temporally irregular measurements including stream flow and monitoring point 
measurements. Unfortunately, it was difficult to acquire stream flow and monitoring 
point data for Ethiopia and those components of the Arc Hydro were not included in this 
project.  
 
7.3 Future Work 
The ability to query by time and location is important to studying hydrologic data. 
It is of interest, for example, to be able access all stream gauges, rainfall gauges, and 
water quality data in Ethiopia and incorporate with Arc Hydro Framework developed in 
this project. The time series object class in Arc Hydro data model could also help store 
hydrological temporal event data for Ethiopian watersheds. 
 
 
 
 
 
 
 84
APPENDIX A 
Steps for preparing the Regional Data and Data preparation for building a 
geometric network 
 
The following procedures explain how the regional data were obtained for the Blue Nile 
Basin. A similar procedure was pursued to acquire the regional data for the other Hydro 
Administrative regions in Ethiopia. 
• Display EthioHydro1K Streams accessed from  USGS server 
< http://lpdaac.usgs.gov/gtopo30/hydro/> 
 
 85
 
• Display EthioHydro1KBasins accessed from USGS server  
http://lpdaac.usgs.gov/gtopo30/hydro/ 
 
 
Create a Geometric Network 
• Open ArcCatalog and navigate to EthioGeodatabase data folder  
• In the Blue Nile Geodatabase and ArcHydro feature dataset right click select New and 
Geometric Network...   
 
 86
 
 
Click Next on the Geometric Network Wizard options until you get to Selecting the 
feature classes and network name.  Select HydroEdge and HydroJunction as your 
network feature classes.  Change the network name to HydroNetwork. 
 
 
 87
Continue through the wizard and accept all the defaults EXCEPT say yes when it 
asks if you want complex edges in the network.  When you finish you’ll see that you’ve 
created a new geometric network, HydroNetwork, which includes a set of generic 
network junctions called HydroNetwork_Junctions whose function is to provide 
geometric connectivity between the HydroEdge features. 
 
 
Generating Flow on the Network 
• In Arc Hydro toolbar in Arc Map document click Network tools and set flow 
direction. 
 
 
 
 88
 
• You will see the Set Flow Direction dialog box. This will enable to set the flow 
with the following criteria: 
esriFDUninitialized  0 Uninitialized 
esriFDWithFlow             1 In the direction of digitization of the edge 
esriFDAgainstFlow 2 Opposite to the direction of digitization of the edge 
esriFDIndeterminate 3 Indeterminate flow direction 
 
The default option is initialized and agrees with that condition and click OK. 
 
 
 89
• To view the flow set on the network click on the Flow dropdown menu and go to Display 
Arrows.  The arrows may not all appear and only some black circles may appear.  The 
software is still not foolproof when displaying the arrows.  If you have a problem, try turning 
on and off display arrows, and that may work.     
 
The picture below shows how the arrows should appear. Turn on your 
HydroNetwork_Junctions feature class.  
 
 90
 
Set the Trace Task to Trace Upstream.   
 
To delineate the Blue Nile streams at the western side of the country and use 
 
the Solve tool  also on the Utility Network Analyst to run the trace upstream process. 
This procedure will turn Blue Nile streams red indicating that all reaches are upstream of 
the outlet junction as shown in the following figures. 
 
 
 
 91
• Next open the Options window Analysis/Options.  Under the Results tab, 
change the results format the Selection 
 
• Select streams from EthioHydro1K. Place a flag on an edge in the network and 
press the Solve button. Thus, you will see the result shown in the following 
figure. 
 92
 
•  Export  the selected them to a feature class as NB_af_Streams 
 93
 
 
•  Click Selection from the menu bar and Click →Select by Location. 
•  Select basins from EthioHydro1K , using NB_Af_Streams  with a 15 km buffer. 
 94
 
• Click Apply 
 This will select Ethiopia Hydro 1K basins that will intersect the streams within the Blue 
Nile Basin as shown in the flowing figure. 
• Export the selected feature class as BN_Af_Basins 
 95
 
• Dissolve basins into a single polygon BN_af_Dissolve 
• Right Click BN_af_Dissolve feature class and open the attribute table. 
• Add field named “One” to BN_Basins_Dissolve and give it the value 1 
 
 
 
 
 
 
 
 
  
 
 96
 
• Spatial Analyst – Convert Feature to Raster (BN_Basins_Dissolve, field One, 
Cell size from DEM) 
 
 
 97
 
 
• Multiply new raster of 1’s times DEM to get buffer DEM 
 
 98
 
 
• Clip Ethiopia_DEM to basin: Ethiopia_DEM * Raster_of_1 
The out put is shown in the following Figure. 
 99
 
 
• Make permanent the resulting grid from the above procedure 
 Similarly, the DEM for the rest of five Hydro Administrative regions was obtained for 
terrain analysis. 
 
 
 
 
 
 100
 
APPENDIX B 
The following procedure shows how terrain analysis was performed in Arc Hydro tools 
to obtain stream lines and catchments for each Hydro Administrative regions.  The Blue 
Nile basin was used as demonstration. 
 
The function needs inputs of bn_dem1 and bn_af_streams and the default output will be 
AgreeDEM. 
     Input                   Output 
"bn_DEM1" Grid    "Agree DEM" Grid 
"bn_af_Streams" Featuredataset 
 101
 
 
After initiating the function accept the default reconditioning parameters shown 
below.  
 
Click OK the flowing warning. 
 
 
Finally, the reconditioned AGREE DEM was processed with the Fill Sinks function 
to make sure that the potential sinks in the stream were removed. 
 102
•   Select Terrain Preprocessing | Fill Sinks.  
 
 
• Confirm that the input for DEM is bn_dem1.  The default Hydro DEM is “Fil” 
but for this project Fil_bn is selected. 
 
The “Fil_bn” Hydro DEM layer is shown below. 
 
• Select Terrain Preprocessing | Flow Direction. 
 
 103
 
• Confirm that the input for Hydro DEM is “fil_bn”.  The output is the Flow Direction 
named by “Fdr_bn”.   
 
 
 
• Press OK. Upon successful completion of the process, the flow direction grid “Fdr” is 
added to the map.  
 104
 
• Select Terrain Preprocessing | Flow Accumulation 
 
• Confirm that the input of the Flow Direction Grid is “Fdr”.  The output is the 
Flow Accumulation Grid having a default name of “Fac” that can be 
overwritten 
 
 
 
 105
• Press OK. Upon successful completion of the process, the flow accumulation grid 
“Fac” is added to the map. 
 
• Select Terrain Preprocessing | Stream Definition. 
 
 
 
• Confirm that the input for the Flow Accumulation Grid is “Fac”.  The output is the 
Stream Grid.  “Str” is its default name that can be overwritten. 
 
 106
 
A default value is displayed for the river threshold.  This value represents 1% of the 
maximum flow accumulation: it is the recommended threshold for stream determination.  
However, any other value of threshold can be selected. Smaller threshold will result in 
denser stream network and usually in a greater number of delineated catchments. For the 
project a threshold value of 50 square kilometers of area was defined. 
 
• Press OK. Upon successful completion of the process, the stream grid “Str” is added 
to the map. 
• Select Terrain Preprocessing | Stream Segmentation 
 107
 
 
• Confirm that “Fdr” and “Str” are the inputs for the Flow Direction Grid and the 
Stream Grid respectively.  The output is the Link Grid, with the default name “Lnk” 
that can be overwritten. 
 
• Press OK. Upon successful completion of the process, the link grid “Lnk” is added to the 
map. 
 108
 
• Select Terrain Preprocessing | Catchment Grid Delineation 
 
 
• Confirm that the input to the Flow Direction Grid and Link Grid are “Fdr” and “Lnk” 
respectively. The output is the Catchment Grid layer. “Cat” is its default name that 
can be overwritten. 
 
 
 109
 
• Press OK. Upon successful completion of the process, the Catchment grid “Cat” is 
added to the map. 
• Select Terrain Preprocessing | Catchment Polygon Processing. 
 
 
• Confirm that the input to the CatchmentGrid is “Cat”.  The output is the Catchment 
polygon feature class, having the default name “Catchment” that can be overwritten. 
 
 110
 
• Press OK. Upon successful completion of the process, the polygon feature class 
“Catchment” is added to the map. 
• Select Terrain Preprocessing | Drainage Line Processing 
 
• Confirm that the input to Link Grid is “Lnk” and to Flow Direction Grid “Fdr”.  The 
output Drainage Line has the default name “DrainageLine” that can be overwritten. 
 
 111
 
• Press OK. Upon successful completion of the process, the linear feature class 
“DrainageLine” is added to the map. 
• Select Terrain Preprocessing | Drainage Point Processing. 
 
 
• Confirm that the input flow accumulation grid is “fac”, the catchment grid is “cat” 
and the input to Catchment is “Catchment”. The output is Drainage Point, having the 
default name “DrainagePoint” that can be overwritten. 
 112
 
 
• Press OK.  Upon successful completion of the process, the point feature class 
“DrainagePoint” is added to the map. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 113
BIBLOGRAPHY 
 
CGIAR, Consortium for Spatial Information (CGIAR-CSI), March 20, 2005 
<http://srtm.csi.cgiar.org> 
 
CIA, the World Fact Book, July 2005  
http://www.cia.gov/cia/publications/factbook/geos/et.html 
 
David Arctur and Micheal Zeiler, Designing Geodatabases, ESRI, 2004 
 
ESRI, World Base Map, April 19, 2005 
< http://www.esri.com/data/download/basemap/index.html> 
 
Food and Agricultural Organization, Land and water development division, 2005 
< http://www.fao.org/ag/agl/default.stm> 
 
FAOa , Land and water development division, May 10 2005. 
<http://www.fao.org/geonetwork/srv/en/metadata.show?id=12&currTab=summary>, 
 
FAOb, Land and water development division, May 10 2005. 
< http://www.fao.org/geonetwork/srv/en/metadata.show> 
 
FAO c, Land and water development division, May 10 2005, 
<http://www.fao.org/geonetwork/srv/en/metadata.show?id=281&currTab=summary> 
 
Gulilat  Berehane, Present and future water resources development in Ethiopia related to 
research and capacity building, June 13, 2005 
<http://www.ilri.org/publications/cdrom/integratedwater/iwmi/Documents/Papers/Gu
lilat.htm> 
 
Jet Propulsion Laboratory, Shuttle Radar Topographic Mission the Mission to the World 
map. 
<http://www2.jpl.nasa.gov/srtm/instrumentinterferometry.html> 
Maidment, Arc Hydro GIS for Water Resources, August 2002 
 
Maidment, GIS in Water Resources Fall 2004 
< http://www.ce.utexas.edu/prof/maidment/giswr2004/ex3/ex32004.htm> 
 
 
Perry- Castaneda Library Map Collection, 2000 
< http://www.lib.utexas.edu/maps/africa.html> 
 
 114
Nile Basin Initiative (NBI), July 12 2005 
http://www.nilebasin.org/_borders/theNileRiver.htm 
 
Nile Basin Initiative (NBI), May 10 2005  
< http://www.thewaterpage.com/images/nilebasin.gif 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 115
 
VITA 
 
 
Seyoum Ayele Asamenaw was born in Dessie, Ethiopia on March 30, 1976, the 
son of LeteMicheal G/Medhin and Ayele Asamenaw.  After completing his work at W/o 
Siheen Vocational and Academic high school, Dessie, Ethiopia, in 1994, he entered 
Dessie Nursing College and got his diploma in 1996. Then, he entered Mekelle 
University and received his Bachelor of Science in Applied Geology in July, 2001. After 
teaching in the same alma mater for two years he entered the Graduate School at The 
University of Texas at Austin. 
 
 
 
Permanent address: P.O.Box 1412  
                                    Dessie, S. Wollo, Ethiopia    
This thesis was typed by the author.