Flood Preparedness and Early Warning Project

Nile Basin Initiative Eastern Nile Technical Regional Office (ENTRO) Flood Preparedness and Early Warning Project

Flood of 2006

A Documentation and Analysis Report

Mohamed Abdel Aty Sayed (Dr.) Regional Coordinator Eastern Nile Technical Regional Office (ENTRO) Addis Ababa July 2004

June 2007

Table of content 1. Introduction...... 7 2. The Eastern Nile basin...... 8 2.1. Geography...... 10 2.2. Climate...... 10 2.3. Hydrology ...... 11 3. Floods in Eastern Nile Basin...... 12 4. Description of Flood Prone Areas...... 13 4.1. Flood Prone Areas in Ethiopia...... 13 4.2. Flood Prone Areas in Sudan ...... 14 4.3. Flood Prone Areas in Egypt...... 15 5. Flood of Year 2006 ...... 17 5.1. Rainfall Analysis...... 17 5.1.1. Rainfall Analysis at Key Stations ...... 17 5.1.2. The Nile Forecast System Analysis ...... 25 5.1.3. Rainfall Analysis Summary ...... 34 5.1.4. Rainfall Forecast for 2007 from GCM...... 42 5.2. Hydrologic Analysis...... 46 5.2.1. The Blue Nile sub-basin...... 47 5.2.2. Baro-Akobo-Sobat and white Nile Basin ...... 54 5.2.3. Tekeze-Atbara-Setit Sub-basin...... 58 5.2.4. Main Nile Sub-basin ...... 60 5.2.5. Hydrologic analysis summary...... 62 5.3. Flood Affected Sites and Flood Damage in 2006...... 63 5.3.1. Sectors affected by the flood...... 70 5.3.2. Estimated Loss of Life and Property Damage ...... 73 5.4. Differences between Current Flood and Previous Floods ...... 77 5.5. Reservoir Operation Strategies during the Flood...... 80 6. Measures Taken for Flood Mitigation and Flood Response...... 85 6.1. Flood Mitigation Measures Taken...... 85 6.1.1. Structural Measures...... 85 6.1.2. Non-Structural Measures...... 86 6.2. Flood Response...... 88 6.2.1. Flood Response in Ethiopia ...... 88 6.2.2. Flood Response in Sudan...... 89 6.3. Cost Incurred for flood mitigation and response ...... 90 7. Preparedness for the Coming Floods ...... 91

List of Tables Table 5-1: Annual Rainfall & Runoff for the area...... 19 Table 5-2: Maximum Daily Rainfall for Different Return Periods ...... 20 Table 5-3: Annual Rainfall According to Probability Percentage...... 20 Using exponential distribution daily rainfall for different return period was computed and given in Table 5-4...... 20 Table 5-5: Daily Rainfall for Different Return Periods...... 21 The rainfall characteristic is uni-modal with extended rainy season from May to October; however June-September is the actual rainy season; July and August have high rainfall concentrations. Results have indicated that mean annual rainfall of 1440 mm is recorded in this station. Table 5-6 summarizes the rainfall statistic results at Bahirdar...... 21 Table 5-7: Mean Rainfall Statistics at BahirDar...... 21 Table 5-8: Average Rainfall Estimates of 2006 vs. Long Term Mean Monthly Rainfall for Blue Nile Basin from Monthly Anomalies Maps ...... 34 Table 5-9: Average Rainfall Record Of 2006 And Long Term Mean Monthly Rainfall For Lake Tana Basin From Rainfall Stations ...... 34 Table 5-10: Monthly Analysis of Rainfall for Stations In Lake Tana Basin...... 36 Table 5-11: Average Rainfall Estimates Of 2006 Vs. Long Term Mean Monthly Rainfall For Baro-Akobo-Sobat Basin From Monthly Anomalies Maps...... 36 Table 5-12: Average Rainfall Record of 2006 and Long Term Mean Monthly Rainfall for Stations in Baro Basin...... 36 Table 5-13: Monthly Analysis of Rainfall For Stations In Baro Basin ...... 37 Table 5-14 :Average Rainfall Estimates of 2006 Vs. Long Term Mean Monthly Rainfall For Tekeze-Atbara-Setit Basin From Monthly Anomalies Maps...... 38 Table 5-15: Average Rainfall Record of 2006 and Long Term Mean Monthly Rainfall for Stations in Tekeze Basin...... 38 Table 5-16: Monthly Analysis of Rainfall For Stations in Tekeze Basin...... 39 Table 5-17: Average Rainfall Estimates of 2006 Vs. Long Term Mean Monthly Rainfall for Sudd Swamps From Monthly Anomalies Maps ...... 40 Table 5-18: Average Rainfall Estimates Of 2006 Vs. Long Term Mean Monthly Rainfall For Equatorial Plateau From Monthly Anomalies Maps...... 40 Table 5-19: Water Levels and Discharges during the Flood Months for El Deim Station49 Table 5-20: Discharge record at El Deim Station...... 50 Table 5-21: Comparison of Accumulated Flow Volumes at Diem with Past Year...... 50 Table 5-22: Exceedance probability for July at Diem station, Blue Nile ...... 51 Table 5-24 Water Levels and Discharges during the Flood Months for Khartoum Station ...... 51 Table 5-25: Comparison of Accumulated Flow Volumes at Khartoum, Blue Nile with Past Years...... 52 Table 5-26 shows water levels and discharges of Dinder River at El Gewiasi station:.... 53 Table 5-27: Water levels and Discharges during the flood months for El Gewaisi Station ...... 53 The Table 5-28 shows water levels and discharges of Rahad river at El Hawata station.53 Table 5-29: Water Levels and Discharges during The Flood Months For El Hawata Station ...... 53 Table 5-30: Water Levels and Discharges Of White Nile At Malakal Station...... 56

Table 5-32: Comparison of Accumulated Flow Volumes at Malakal, White Nile with Past Year...... 57 Table 5-33: Water Levels and Discharges during the Flood Months, Khashm El Girba Dam Station ...... 59 Table 5-34: Nile Discharges During the Flood of 2006 Compared To Average at Dongola Station ...... 61 Table 5-35: Comparison of Accumulated Flow Volumes at Dongola, Wmain Nile with Past Years...... 61 Table 5-36: Lake Nasser and HAD Situation In Comparison With Past Years ...... 62 Table 5-37 Population Affected/under Threat by Flood Disaster (DPPA, 2006)...... 73 Table 5-38: Areas Affected/under Threat by Flood Disaster (DPPA, 2006)...... 74 Table 5-39: Number of Flood Affected Residential Areas in Singa Locality ...... 75 Table 5-40: Number of Flood Affected Residential Areas in Dindir Locality...... 76 Table 5-41: Number of Flood Affected Residential Areas in Sinnar Locality...... 76 Table 5-42: Number Of Persons Affected Due To Flood And Received Relief Support By DPPC In Lake Tana Area Comparing 5 Years...... 77

Table 5-44: Flood Damages to the Gambella Area ...... 78 Table 5-45: Summary of Crops Damaged by Floods in Gambella...... 79 Table 5-46: Comparison of 2006 And 1988 Flood For Period of July – Sept and the Average...... 80 Table 5-47 Rosaries Dam Reservoir Operation Strategies ...... 82 Table 5-48 Sennar Dam Reservoirs Operation Strategies ...... 82 Table 5-49 Khashm El Griba Dam Reservoirs Operation Strategies ...... 83 Table 5-50 Jebel Aulia Dam Reservoirs operation strategies...... 83 Table 6-1 River Regulation in Ethiopia (source: SMEC, 2006)...... 85 Table 6-2: Irrigation Storages Being Investigated (source: SMEC, 2006)...... 86 Table 6-3: Food Requirement for flood affected areas in Metric Tone (MT) ...... 88 A Total of 470,000 UDS is estimated for Water supply rehabilitation works alone to provide potable water to flood affected areas in Ethiopia, Table 6-4...... 90 Table 6-5 Requirement for Potable Water Supply Rehabilitation (DPPA, 2006) ...... 90 Table 6-7 Cost Incurred For Mitigation Measures (USD)...... 90

List of Figures Figure 2-1: Major Sub-Basins within the Eastern Nile Basin...... 9 Figure 4-1 Flood prone area in Eastern Nile Region...... 16 Figure 5-1 Selected Rainfall Stations for Analysis...... 18 Figure 5-2: Intensity – Duration – Frequency relationships for Damazin Station...... 19 Figure 5-3 Annual and 5-year moving average rainfall and Monthly Rainfall at Bahir Dar...... 22 Figure 5-4 Comparison of Mean and 2006 Rainfall in lake Tan basin Stations...... 23 Figure 5-5: Comparison of Mean and 2006 Rainfall for stations in Gambella plain...... 24 Figure 5-6: Comparison of Mean and 2006 Rainfall for stations in Tekeze Basin...... 25 Figure 5-7: May Rainfall Anomalies (as percentages of long-term Average)...... 26 Figure 5-8: June Rainfall Anomalies (as percentages of long-term Average)...... 27 Figure 5-9: July Rainfall Anomalies (as percentages of long-term Average) ...... 28 Figure 5-10: August Rainfall Anomalies (as percentages of long-term Average)...... 29 Figure 5-11: September Rainfall Anomalies (as percentages of long-term Average) ...... 30 Figure 5-12: October Rainfall Anomalies (as percentages of long-term Average) ...... 31 Figure 5-13: November Rainfall Anomalies (as percentages of long-term Average) ...... 32 Figure 5-14 Rainfall Anomaly Map for the Ethiopian Rainy Season (Apr-Nov 2006)...... 33 Figure 5-15: Spatial Distribution of rainfall and comparison of long-term and 2006 monthly rainfall for major sub-basins of Eastern Nile Basin...... 41 Figure 5-16: Selected Key Nodes For Hydrologic Analysis ...... 46 Figure 5-17: Lake Tana Annual Maximum Daily Water Level...... 47 Figure 5-18: Lake Tana water level (August – December, 2006) ...... 48 Figure 5-19: Abbay at Bahir Dar Annual Maximum Daily Discharge...... 48 Figure 5-20: Abbay at Bahir Dar Daily Discharges in 2006 ...... 48 Figure 5-21: Level Regime at Diem, Blue Nile...... 49 Figure 5-22: Accumulated Flow Volumes at Diem, Blue Nile ...... 50 Figure 5-23: Level Regime at Khartoum, Blue Nile ...... 52 Figure 5-24: Accumulated Flow Volumes at Khartoum, Blue Nile ...... 53 Figure 5-25: Baro at Gambella Mean Annual Discharges...... 54 Figure 5-26: Comparison of 2006 and Mean Monthly Discharges ...... 54 Figure 5-27: Daily Discharges of Baro River from August-October 2006...... 55 Figure 5-28: Baro at Gambella Annual Maximum Daily Discharges fitted to Gumbel Distribution ...... 55 Figure 5-29: Gilo near Pungido Mean Monthly Discharges...... 56 Figure 5-30: Level Regime at Malakal, White Nile ...... 57 Figure 5-31: Accumulated Flow Volumes at Malakal, White Nile ...... 58 Figure 5-32: Tekeze near Embamadre Annual Maximum Daily Water Level...... 58 Figure 5-33: Tekeze near Embamadre Daily Water Levels in Augut 2006...... 59 Figure 5-34: Level Regime at Dongola, Main Nile...... 60 Figure 5-35: Accumulated Flow Volumes at Dongola, Main Nile...... 61 Figure 5-36: Flood Affected sites in 2006 flood...... 64 Figure 5-37: Flood Affected sites in 2006 flood Around Lake Tana...... 65 Figure 5-38: Flood Vulnerable Areas in Ethiopia ...... 66 Figure 5-39: Flood Vulnerable Areas in Ethiopia, in 2006 Flood ...... 66

Acknowledgements

The author would like to appreciate the assistance accorded by many people in the EN countries. Special thanks to the national flood coordinators (Dr. Mamdouh Ahmed Antar from Egypt, Mr. Hayder Bakhiet Yousef from Sudan and Mrs Semunesh Golla from Ethiopia) for their sincere support and help. Thanks are due to all ENTRO staff, which helped in one way or another, specially Eng. Yohanas Daniel; ENSAPT members in the three EN countries, staff at the various ministries and authorities in the EN countries.

Mohamed Abdel Aty (Dr.) Regional Flood Coordinator Eastern Nile Technical Regional Office Addis Ababa, Ethiopia

1. Introduction Eastern Nile Technical Regional Office (ENTRO) was established in June 2002, in Addis Ababa, Ethiopia. Establishment of ENTRO was given at the 7th and 8th Eastern Nile Council of Ministers of Water Resources of Egypt, Ethiopia and Sudan. ENTRO’s role is to support Eastern Nile Council of Ministers and Eastern Nile Subsidiary Action Program Team in Preparing the Eastern Nile Subsidiary Action Program (ENSAP). Flood Preparedness and Early warning is one of the Eastern Nile Program to reduce human suffering and damages. Establishing a comprehensive regional approach to flood management that integrates watershed, river and floodplain management, and incorpor- ates a suite of structural and non-structural flood mitigation measures within a broad multipurpose framework is one of the objectives of ENTRO. The 2006 was one of the highest floods that happened in the Nile basin over the past 20 years, which resulted in increasing the runoff of the Nile as well as loss of properties and people. Over the past ten years or so, the Eastern Nile Region has been subjected to a number of damaging floods: 1994, 1996, 1998, 1999, 2001 and 2006. These floods impacted a large number of communities causing significant human and agricultural losses (crops, seeds, fodder, pumps, stock, etc). Historically, the region has experienced severe floods in 1878, 1946, and 1988. The 1988 flood is still vivid in the memories of many people to the extent that it has become the bench mark for comparing flood levels and severity. Ethiopia's topography, both mountainous and flat, induces two types of floods: flash floods and river floods. Both occur from time to time at varying locations with varying, but often, tolerable magnitudes. Owing to its topographical characteristics, floods are not new to Ethiopia. However, this year the' rainy season has overwhelmed the country with flooding of an unprecedented magnitude, breadth frequency and devastation. Water level at which flooding and related damages start along the Blue and Main Nile Rivers in Sudan is not a consistent height above river bed level. This means that in some areas flooding frequently causes some damage while in other reaches (eg. at Khartoum) flood related damage is less common. The Nile floodplains in Sudan are wide and generally flat. Once river levels exceed bank top level, any small rise in water level generally causes a considerable increase in the area inundated and consequential increase in flood related damages. As part of the Flood preparedness and early warning project’s activities, ENTRO has started a process of documenting remarkable floods within the Nile basin. This report, therefore, is a synthesis work of the flood compilations and it is aimed at providing one comprehensive view of the flood within the region from regional perspective. At the end of 2007 flood, a regional meeting will be organized among flood experts and researchers from the region to analyze the performance and also look forward for means of improving the flood preparedness and forecasting activities within the Eastern Nile basins.

2. The Eastern Nile basin The Nile is one of the most remarkable and the second longest river in the world. The length of its course from the most remote source near Lake Tanganyika to the Mediterranean Sea is about 4000 miles. The main tributaries for the Nile river are streams from Ethiopia high lands from which the Blue Nile (Abbay in Ethiopia) , Atbara (Tekeze in Ethiopia), Sobat (Baro-Akobo in Ethiopia), Dinder , and Rahad rivers are descending as well as from the equatorial lakes. The Nile waters then passes on to Egypt through the main Nile. The total Nile basin area is around 3,038,100 km2 in ten riparian countries. Majority of The Nile basin area lies within Sudan, which is about 1,935,700 km2 amounts to 77% of the total basin. This area represents 64% of the total area of the country. On the other hand, Uganda, although 99 % of it lies in the basin, it represents 8% of the basin area. The table below shows the Nile basin area in each of the riparian countries.

Country Country area Basin area % of the basin % of the country Sudan 2.506.000 1.933.300 63.66 77.15 Ethiopia 1.104.000 356.900 11.75 32.33 Egypt 1.001.000 277.500 9.14 27.72 Uganda 241.000 238.900 7.87 99.13 Tanzania 945.000 120.300 3.96 12.73 Kenya 580.000 50.900 1.68 8.78 Congo 2.345.000 21.700 0.71 0.93 Rwanda 26.000 20.800 0.68 80.00 Burundi 28.000 13.000 0.43 46.43 Eriteia 118.000 3.500 0.12 2.97 Total area 8.894.000 3,036,800 100 - Table 2-1: Nile Basin Area in Riparian Countries The Eastern Nile Basin as part of the Nile Basin constitutes four countries, Ethiopia, Egypt, Sudan and Eritrea. The total area of the Eastern Nile Basin is estimated at 1,657,845 km2. This Eastern Nile basin is mainly composed of the four major sub-basins namely Baro-Akobo-Sobat and White Nile sub-basin, the Blue Nile sub-basin, Tekeze- Setit-Atbara sub-basin and the main Nile Sub-basin [4], Figure 2-1.

Figure 2-1: Major Sub-Basins within the Eastern Nile Basin

2.1. Geography The countries of the Eastern Nile Region are Egypt, the Sudan and Ethiopia. Main rivers of the Eastern Nile region rise in the Ethiopian Highlands in the western half of Ethiopia and drain generally westerly or north-westerly into the Sudan where the White Nile and the Main Nile drain generally north, and then the Nile flows further north through Egypt to the Mediterranean Sea. The Eastern Nile Basin lies between latitudes 7º N and 31º N.

2.2. Climate Ethiopia and Sudan experience tropical or sub-tropical climates, with rainfall seasonally biased and most rain falling in the summer months (June to August). Temperatures and annual rainfall depths vary widely however, depending on elevation and orographic influences. Parts of the Ethiopian highlands receive average annual rainfall exceeding 2000 mm, while in far northern Sudan and Upper Egypt there is very little rain at all. The elevated plateaus in Ethiopia experience cool to mild temperatures year round, whereas in central and northern Sudan the climate is hot year-round and very hot in the late spring and early summer (May to July).The seasonal rainfall is a consequence of the shifts in the Inter-Tropical Convergence Zone (ITCZ), the boundary of which demarcates unstable tropical disturbances from more stable sub-tropical weather. In the winter months the ITCZ lies to the south of Ethiopia and Sudan, but as the path of the sun moves north in the spring and early summer the ITCZ follows, and in a typical year the band of unstable tropical air masses will lie directly over southern Sudan and the Ethiopian highlands, drawing moist air from the Atlantic Ocean to the west or the Indian Ocean to the east. High rainfalls occur over western Ethiopia which is the uplands of the Eastern Nile basin, particularly in July and August, due to the orographic effects on the moist air masses. The rainfalls are variable, however, depending largely on the extent of northerly movement of the ITCZ which varies from year to year. In the extreme south of the Eastern Nile river basin (e.g. in the Baro-Akobo sub-basin) rainfall exhibits a diatonic seasonal trend, with “small rains” also occurring in the months of February and March. During the remainder of the year as the ITCZ recedes southwards, the country is open to prevailing dry northeasterly winds generated by the Eurasian landmass.

The far northern part of the Eastern Nile river basin in Lower Egypt experiences a Mediterranean climate, with cool winters and hot summers. Rainfall is very low throughout the year, with a low peak in winter months (December to February)

Figure 2-2: Rainfall Distribution in Ethiopia Figure 2-3: Rainfall Distribution in Sudan

2.3. Hydrology The Nile is one of the most remarkable and the second longest river in the world. The length of its course from the most remote source near Lake Tanganyika to the sea is about 4000 miles. Its rival in length is the Mississjppi – Misouri River, which is about 4200, miles long. The Nile has an average annual flow of 84 milliard cubic meters measured at Aswan. This flow constitutes only 6 percent of the total amount of rain falling on the Nile Basin. The phenomenon of unpredictability in discharge is of special importance in the Nile valley. This is because of the total absence of rain in most of its basin and the exclusive reliance of its inhabitants upon the river waters for their survival. All of the waters of the Nile are drived from rainfall upon the Ethiopian plateau and upon the hinterlands of the equatorial lakes. The contribution of rainfall further downstream, for instance, in the Sudd area. is negligible. The second fluctuation of rainfall in the Lake Tana region (the headwaters of the Blue Nile), are much more marked than those prevailing at the source of the White Nile. River Percentage Contribution On the average During flood time Blue Nile 59 68 Atbara 14 22 Sobat 13 5 Bahr el Jebel 11 5

Table 2-2: Percentage Contributions of Main Tributaries

The variation in discharge of the Nile is illustrated by the fact that more than 80% of its annual flow occurs from August to October and only 20% occurs during the remaining nine months. It is also interesting to note that the annual discharge of the Nile for the year 1913/1914 was 41 milliard cubic metres as compared to 151.1 milliard cubic meters in 1978/1979. The percentage contributions of the main tributaries of the Nile on the average and during flood time a shown in table (2-2). This shows that on the average 85% of the flow of the Nile comes from the Ethiopian plateau and only 15% comes from East Africa. During flood time 95% of the water originates from Ethiopian highlands and only 5 % originate from East Africa. During the low flow period 60% of the water comes from Ethiopia and 40% comes from East Africa. The low contribution of the White Nile to the Main Nile is attributed to the great amount of water which is lost by evaporation in the swamps while the Ethio pian plateau acts efficiently for draining the water to the Nile. The White Nile is characterized by its relatively uniform flow as compared to the Blue Nile and Atbara River. Its average seasonal variation at Malakal for the period 1912-1962 ranges from 525 cubic meters per second to 121 cubic metres per second as compared to the average variation of the Blue Nile at Roseires for the same period which ranges from 123 cubic meters per second to 6200 cubic metres per second.

3. Floods in Eastern Nile Basin The impact of 2006 flood in Ethiopia was particularly severe, partly due to limited preparedness and response capacity for quick-onset emergencies. Since late July 2006 heavy rains and storms resulted in flash floods and overflow of rivers in many parts of Ethiopia. The floods claimed considerable human life especially in Dire-Dawa, South Omo zone of SNNPRS and Gode zone of Somali Region (DPPA, 2006). The flooding caused mass displacement and sizeable damage to property and infrastructure in all the affected areas In this regard, over 700 people were reported to have died and about 240,000 were displaced out of the over 670,000 people affected. Although much of the above casualties particularly deaths are outside Eastern Nile Region (Dire Dawa and South Omo) flood incidence and damage including life losses has occurred in Lake Tana area, Gambella plain (Baro Akobo Basin), and Humera area of Tekeze basin.in the Eastern Nile Region (Figure 1 & 2). In fact the majority of the displaced people about 38% of the total are in Amhara Region most of them in Lake Tana area (DPPA, 2006). Flooding from the River Nile is also a serious hazard in Sudan. The 1999 flood in Sudan has caused more than ten-thousand people to be homes, destruction of schools, public buildings and mosques and hundreds of livestock drowned. Khartoum, capital city of Sudan have frequently been threatened of flooding and been affected by flood in significant times. The vast agricultural lands in Gezira and Sennar state have been often flooded from the Nile River causing damage to the irrigation infrastructure and to the crops affecting Sudan economically. The 2003 flood in Sudan, when the Qash River burst its banks in Kassala, at least nine people reported to die and tens of thousands were left homeless. Particular states that lay following the banks of the river have been victims of flood frequently causing sever property damage as well as losses of life.

Egypt is the most downstream country of the 10 countries that share the Nile basin and thus it has been prone to floods and droughts for centuries. However, since the completion of the High Aswan Dam (HAD) in 1968, Egypt has become much less prone to the consequences of floods and droughts. The reservoir that formed behind the HAD (named Lake Nasser) has provided large storage capacity that can accommodate above average annual floods in most cases allowing the provision of a very high supply reliability. But in cases of consecutive high floods or consecutive low floods (e.g. 1978- 1987) that Egypt remain prone to flood and drought risks which can still be mitigated to a large extent through the operation and management of the HAD and Lake Nasser. These previous flood events in different parts of the region have made flood hazard a serious issue and calls for a joint action to the prevention and preparedness of further disaster that may be caused by flood.

4. Description of Flood Prone Areas

4.1. Flood Prone Areas in Ethiopia In Eastern Nile Part of Ethiopia the well known flood prone areas are the flood plains abutting Lake Tana, Gambella plain, and Humera area (near Ethio-Sudan Boarder) of Tekeze basin and flash floods in different locations. • Lake Tana: The fertile flat lands around Lake Tana support dense rural populations, however large tract of land is subject to flooding, either from the lake or from flows of tributary rivers (Ribb, Gumera, Megech Rivers) virtually every year. Fogera and Libo Kemkem woredas, Dembiya woreda and Bahir Dar special zone, all adjoining Lake Tana are the flood risk areas. In the urban areas of Bahir Dar, flood impacts have largely been the consequence of poor drainage systems in the city and local catchment runoff (SMEC, 2006). The large flat land between the Gumera and Ribb rivers is annually flooded and in extreme rainfall years the effect on humans, livestock, and infrastructure will be significant. • Gambella Plain: The plain area, belonging to the lowlands of Baro-Akobo Basin, is partially inundated by floodwaters every year. While most of the agrarian land use has adapted to the seasonal flux of floodwaters, there are several towns affected by larger floods including the city of Gambella, and larger floods also cause hardship in rural areas. The Gambella plain lies in south-western Ethiopia and is part of the Baro-Akobo river basin (Sobat River in Sudan). Gambella city is the regional capital, about 800 km from Addis Ababa. Almost every year, over 35% of the Gambella plain is subject to flooding (SMEC, 2006). Major rivers in the areas are Baro, Akobo, and Gilo their origin is the highland high rainfall area around Gore and Masha. The ground surface elevation in along the watershed divide in the east, south-east and north-east varies from about 1700 m to values in the range of 2500–3000 m amsl. As one approaches the foot of the mountainous part of the catchment, one observes the steep decent down to the Gambella plain, where the elevation is of the order of 400-500 m amsl (Seid, 2004).

• Tekeze near Humera (Ethio-Sudan Boarder): The flat area at Humera (near Ethio-Sudan boarder) is flooded from overflow of Tekeze River over its banks. This will occur during extreme rainfall conditions in the upper catchment of Tekeze basin as in the case of August 2006. • Flash floods: Flash floods are more commonly associated with isolated and localized intense convective rainfalls. They occur both in highland and lowland areas and their occurrence is very random. They cause life loss as well as property damage. They can better be mitigated through watershed management instead of flood protection works.

4.2. Flood Prone Areas in Sudan In Sudan a large area along the banks of the river Nile and tributaries in different states in Sudan are primarily identified as flood prone zones. The states in which flooded area and encountered include, Khartoum state, Gezira state, Sennar state, Nile state, Northern state, Kassala. The flooded areas included residential areas in towns, agricultural lands, industrial areas and villages. • Khartoum State: The flood areas in Khartoum State included the following localities: Khartoum, Khartoum North, East of the Nile, Umdurman, Karari, Um Badda, Jebel Awlia. Many residential areas in these localities lie in the flood plain of level for below the flood maximum level. Residential areas are also found along the courses of the big natural Khors which are low lands usually affected by natural Khors waters together with Nile flood waters. • Gezira state: This state lies in central Sudan and many of is inhabitants live on the Blue Nile river banks. The state capital Wad Medani and many villages lie on the river flood plain and they are usually affected by the river high floods. Gezira State is famous for its irrigated agriculture. The cultivated lands are more than two million acres .Vast areas are cultivated in the Blue Nile flood plain .During high floods part of this agricultural area is inundated which results in considerable damage to the crops. Consequently, the agricultural production is affected due to the flood. • Sennar State Sinnar state is located in Central East Sudan, Sinja city in the capital of the state, bordering Gezira state to the north, Blue Nile and Upper Nile states to the south, White Nile state to the west and Gedaref state and Ethiopia to the East.Due to heavy rainfall rate within the area and Ethiopia, the state is vulnerable to annual floods and flash floods. The latest two devastating floods were the 2000 flood by the Blue Nile river and 2003 flood by Dinder seasonal river where the state received assistance from different components of the International Movement.This flood has been known to cause damages for many sites in the different localities. The main localities affected as observed during the 2006 flood are Singa Locality in which about 17 small towns and villages are were affected during the flood , Dinder Locality in which about 35 vilages and towns were affected and Sinnar Locality where Kartekaila village was reported to be affected during the flood.

• The Nile river state: is always under presume during the flood time. The main Nile river passes through the state and the full discharge of the river Nile is completed within the state. The flood plains are usually very much affected by high floods. 2006 flood is one of the highest. Many sectors were affected by the flood and it could be said that it was disastrous in many locations

4.3. Flood Prone Areas in Egypt Flood protection in Egypt is mainly carried out through the management of HAD. However, when consecutive high floods occur, Lake Nasser may not have enough storage capacity to accommodate the coming flood and therefore water has to be released either via the Toshka spillway or to the river downstream in excess of demand to make room for the coming flood, especially if forecasts show high probability for an above-normal flood. Currently, the maximum discharge allowed downstream the HAD is set to 240 MCM/day, however excess release from HAD results possible flooding to Nile river valley and delta. • Nile Valley: The whole stretch of Nile Valley extends from HAD up to Delta barrages. It is divided into four sections (reaches) between the main control structure on the river: Reach 1 extends from the HAD to Esna Barrage; Reach 2 extends from Esna to Naga Hammadi Barrage; Reach 3 from Naga Hammadi to Asyut; Reach 4 from Asyut to the Delta Barrages. The possible effects of flooding in the Nile valley when larger volumes of water than the maximum are released from the HAD have been assessed during the Lake Nasser Flood and Drought Control project, hosted by the NFC, using the flood extend mapper. The approach estimates flood extent by the combination of a one dimensional flow model that estimates water levels and compares them with levels of surrounding land areas using GIS based flood extent mapping using a 1-D flow model (SOBEK). The study produced flood maps of the Nile valley for releases from the HAD between 240 MCM and 605 MCM. • Nile Delta: This area includes the lower parts of Nile downstream of Delta barrages starting from Nile branches into the floodplains. Food risk zone covers relatively over a much wider area. A possible effect of flooding in the Nile deta has also been assessed in the Lake Nasser Flood and Drought Control project. This study has produced maps and the amount of inundated area as a result of different releases from HAD. The study has indicated that for the considerable flooding could start if the releases at Aswan exceed 350 MCM/day. In this case an area about 250 km2 are inundated.

Figure 4-1: Flood prone area in Eastern Nile Region

5. Flood of Year 2006

5.1. Rainfall Analysis Rainfall within the eastern Nile basin is highly variable with time and space. In Space it varies from annual 2270mm in Baro-Akobo-Sobat sub-basin to less than a mm at some spots in Main Nile Sub-basin [4], Figure 5-15. In its southern portion mean annual rainfall exceeds 2000mm (at Masha, station located in the upper course of the Baro-Akobo-Sobat-WN sub basin) and reduces to 675 mm in its northern portion (at Mekelle, station located in the upper course of the Tekeze-Setite- Atbara sub basin).Spatial variation observed along the course of the river flow is closely correlated with altitude. In high altitude areas of Baro-Akobo-Sobat, Blue Nile and Tekeze-Atbara-Setit, mean annual rainfall is in the range of 2270 mm to 675 mm. In the middle course, at Khartoum and Atbara for instance where the altitude is below 500 masl mean annual rainfall is in the range of 90mm to 180mm. Close to the Ethiopian border, in stations such as Gambella, El Damazin and Humera for instance, mean annual rainfall ranges from 700 mm to 1000 mm. In the Lower course at Aswan dam mean annual rainfall is nearly zero [4]. Nile flood in Sudan and in Egypt is mainly caused by river flows coming from Ethiopia high lands namely, Blue Nile , Atabra, Dinder and Rahad rivers. And hence, flood occurrences are directly related to the rainfall in Ethiopia. Generally, in many parts of Ethiopia, there are three seasons: the first is the dry season, which prevails from October to January; the second is the short rainy season that runs from February to May and the third is the main rainy season, which prevails from June to September. However, in Eastern Nile Region the short rainy season is combined with the main wet season to form uni-modal rainfall pattern with peaks in July and August

5.1.1. Rainfall Analysis at Key Stations In the following section rainfall analysis is presented from three rainfall stations in Sudan and twelve rainfall stations in Ethiopia that lie within the extent of the Eastern Nile basin. The selected stations for analysis in Sudan include Damazin Station, Um Seenat - Doka station and Khartoum Station. Rainfall analysis for these stations is carried out for different periods. The analysis for each station is done according to the available data and selected suitable probability distributions. The rational method is used to estimate the annual runoff. For time of concentration kirpich / Ramsar formula is used in some cases. Similarly, twelve rainfall stations, four in each of the flood affected sub basins in Ethiopia, are selected for analysis. Again here the stations are selected due to their representative ness of the catchments of the flood prone areas in Ethiopia. Figure 5-1 shows location of the selected rainfall stations for analysis in the pending section of this report.

Figure 5-1: Selected Rainfall Stations for Analysis

A) Damazin Station, Sudan

Damazin station in found in the middle reaches of the Blue Nile River in Sudan. Annual rainfall for Damazin for a period of 30 years (1970 – 2000) has been analyzed. As indicated in the Sudan report [2], Kirpich/Ramser formula was employed to calculate the time of concentration and annual flows have been estimated by the rational formula. For estimating the peak flow, intensity – Duration – Frequency relationships were established. For this station the mean Annual rainfall was calculated to be 699 mm with standard deviation of 85%.The annual rainfall with 90% reliability is 597.6 mm. This rainfall was used for estimating the water resources of streams. For estimating the peak flow,

intensity– Duration – Frequency relationships for Damazin have been obtained and the resulting curves are shown in Figure 5-2 Time of concentration for the area was found to be more than the maximum duration of rainfall (120 min), hence, the time of concentration was taken as 120 minutes.

IDF Curves for Damazin

180

160

T=100 years 140

120

100 T= 20 years

80 Intensity mm/hr

60 T=50 years

0 0 10203040506070 Duration Minutes

Figure 5-2: Intensity – Duration – Frequency relationships for Damazin Station

B) Um Seenat Station and Doka Station

The area lies between latitudes 13oN and 15oN, and longitudes 36oE and 36.5oE in eastern Sudan. The annual rainfall is about 653 mm. Being a mountainous area, numerous ephemeral streams are present in all parts of the project area. Annual rainfall for different probabilities of exceedance was computed for these stations using normal probability distribution. And in order to calculate the maximum daily rainfall for different return periods the extreme value type 1 was reported to have been employed in the analysis. Rational Method was then used to estimate the annual runoff. Results indicated that the mean annual rainfall at Um Seenat is 657.1 mm with a standard deviation of 87.3 mm, while the mean annual rainfall at Doaka is 649.0 mm with a standard deviation of 116.3 mm. Consequently, the average annual rainfall for the area represented by these two stations is 653.1 mm with a standard deviation of 92.5 mm. It was also found that the normal probability distribution is suitable for the region. Hence using this, the annual rainfall was calculated for different probabilities of exceedance as shown in Error! Reference source not found..

Prob. of Exceedance Annual Rainfall (mm) 80% 576.3 90% 534.3 95% 500.7 98% 463.0 99% 437.6 Table 5-1: Annual Rainfall & Runoff for the area

In a gauged catchment (Wadi Abu Fargha), which is in the eastern region, the average runoff coefficient was calculated as 13% for a catchment area of 65 km2. Hence, for the

streams in the area runoff coefficient between 8% and 15 % was assumed depending on the catchment area. Furthermore, it was found that suitable distribution for maximum daily rainfall is the extreme value type I. Hence, for estimation of the maximum daily discharge series, maximum daily rainfall was selected for the area (El-Gadarif), for the period (1960- 1989). As a result, represented by Gadarif, the area maximum daily rainfall for different return periods were calculated and are given in Table 5-2.

Return Period Max. Rainfall (Years) Gadarif (mm) 10 87 20 97 50 110 100 120

Table 5-2: Maximum Daily Rainfall for Different Return Periods

C) Khartoum Station Khartoum station is found in the capital of Sudan close to the confluence of the Blue Nile and White Nile rivers .The average, maximum and minimum annual rainfall for this region and the highlands in the vicinity is calculated to be about 100mm, 350mm and 20mm respectively. The coefficient of variation for Khartoum area is 0.33 and therefore the standard deviation for the area is 33mm and the probable reasonable distribution for the annual rainfall is observed to be the natural distribution. Error! Reference source not found. shows the annual rainfall according to probability percentage. For example for 80% of the years the annual rainfall in the Wadi catchment area is equal or greater than 73mm.

Probability Annual rainfall mm 50% 100 80% 73 90% 59 95% 46 Table 5-3: Annual Rainfall According to Probability Percentage

It was also possible to calculate the annual discharges for the area using the rational equation. Because of lack of recorded discharges, the runoff coefficient for the area may not be so accurate. Nevertheless, the runoff coefficient usually ranges between 6% - 30% depending on the catchment area size. . Using exponential distribution daily rainfall for different return period was computed and given in Table 5-4.

Return period (year) Daily Rainfall mm. 10 42 25 61 50 72 100 86 Table 5-5: Daily Rainfall for Different Return Periods Lake Tana Basin Stations Bahirdar station, found near mouth of the Blue Nile River in Bahirdar city, is one of the stations with longest rainfall recording in the Lake Tana area. 44 years of rainfall record (1961-2004).Gondar Station is located in the northern Part of Lake Tana Sub-Basin. Addis Zemen and Debretabor Stations represent eastern watersheds of the Lake Tana representing rainfall which causes runoff to Ribb and Gumara catchments. These four stations have been analyzed using statistical techniques.

A) Bahirdar Station The rainfall characteristic is uni-modal with extended rainy season from May to October; however June-September is the actual rainy season; July and August have high rainfall concentrations. Results have indicated that mean annual rainfall of 1440 mm is recorded in this station. Table 5-6 summarizes the rainfall statistic results at Bahirdar.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Mean 2.8 2.2 7.5 24.4 80.5 189.7 430.7 391.3 193.7 93.8 20.2 3.6 1440 St Dev 5.0 5.6 10.6 28.0 74.6 79.3 112.0 107.4 59.4 58.1 27.3 6.9 235.9 CV % 181 260 142 115 93 42 26 27 31 62 135 192 16 80% low 0 0 0 1 12.8 121.7 314.2 273.2 145.6 32 0.9 0 1207 RC 0.02 0.02 0.06 0.20 0.67 1.58 3.59 3.26 1.61 0.78 0.17 0.03 Table 5-7: Mean Rainfall Statistics at BahirDar

A comparison of the mean vs 2006 rainfall and the Annual and 5 year moving average rainfall is shown in Figure 5-3. The maximum annual rainfall occurred in 1973 is 2037 mm and the minimum in 1982 amounting 895 mm. In 2006 the June to September Rainfall at Bahir Dar is higher than the Normal (Mean) by 163 mm about 14%. The high rainfall in July particularly is considerable in contributing for flooding around Bahirdar City. The 563 mm July rainfall at Bahirdar is the 5th highest from the 45 year record series. This is equivalent to about 11 Year return period.

July monthly rainfall at Bahir Dar 2500 700 600 2000 500 1500 400 300 200 1000 (mm)Rainfall 100 500 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 0 0 0 0 0 6 6 6 6 6 7 7 7 7 7 8 8 8 8 8 9 9 9 9 9 0 0 0 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 Years Annual 5 year Moving Average July rainfall series 5-yr moving average Mean Figure 5-3 Annual and 5-year moving average rainfall and Monthly Rainfall at Bahir Dar

B) Debre Tabor Debre Tabor is a key rainfall station because the major rivers contributing for flooding of the area Gumara and Ribb Rivers originate around it. It can be considered representative of the upper catchments of the two watersheds. In 2006 Debre Tabor registered above normal rainfall condition from July upto the second decade of September (only the 2nd decade of August shows below normal rainfall). Generally the station recorded about 20% higher rainfall than the normal in the period. Because the land is already saturated and knowing that the area is normally flooded the excess rainfall (above normal) of 189 mm in the three months will have a tremendous impact on flooding.

C) Gondar The 2006 August and September rainfall at Gondar is above normal by 134 mm about 33%. The Gondar rainfall data shows that the 20 days period, the last decade of July and the first decade of August, were very critical in producing flood in Megech River, the overflow of which affected large area. The total rainfall during this period is about 73% above normal.

D) Addis Zemen The 2006 rainfall in the whole month of July and first decade of August is about 24% higher than normal. Generally, the 2006 rainy season (June-September) rainfall in the Lake Tana sub basin is above normal (mean) this exacerbate the already flood prone areas around the lake. Figure 5-4 shows graphical comparison of Mean and 2006 Rainfall in Lake Tan basin stations discussed above. Detailed decadal rainfall summary for Lake Tana Basin stations is provided in the Ethiopian flood report [1] .

June - September Rainfall at Bahir Dar July - September Rainfall (Debre Tabor) 600 600 500 500 400 400

300 Mean Mean 300 2006 2006

Rainfall (m m200 ) Rainfall (m200 m )

100 100

0 0 Jun Jul Aug Sep July August September Month Month

July-September Rainfall at Gondar June-September Rainfall (Addis Zemen) 400.0 600 350.0 500 300.0

) 400 250.0 mm ( 200.0 Mean 300 Mean 150.0 2006 2006 Rainfall Rainfall Rainfall (mm) Rainfall 200 100.0 100 50.0

0.0 0 July August September June July August September Month Month

Figure 5-4: Comparison of Mean and 2006 Rainfall in lake Tan basin Stations Gambella Plain Stations The Gambella plain is found in Baro Sub-basin four stations Namely Gore,Metu, Masha and Tepi were selected for analysis, Figure 5-1. For Gore Station the 2006 rainfall is higher than normal in the last decade of July and first decade of August and in September generally. Similarly, for Masha Stations rainy season (June-September) rainfall is about 10% higher than normal. Particularly, the July rainfall is about 25% higher than normal.Metu Station Also has resulted 56% higher records than the normal in the second and third decades of June. However, the rainfall is below normal in July-September period. Tepi rainfall records showed high above normal by about 26% starting from the second decade of June to end of second decade of July in 2006. Since the Baro-Akobo basin start rainy season earlier rainfall in April and May will saturate the land runoff in the rivers will be high in June and July. Generally the 2006 rainfall in Tepi is above normal in June-August but below normal in September. As the four rainfall stations indicates the upper Baro Akobo basin where most of the the tributary rivers of Baro, Akobo, and Gilo are originating the rainfall was above normal mainly in June and July which contributes for the above normal flooding in the Gambella plain. Figure 5-5 shows graphical comparison of Mean and 2006 Rainfall for stations in Gambella plain Ethiopia. Detailed decadal rainfall summary for stations is provided in the Ethiopian flood report [1].

July-September Rainfall (Gore) June-September Rainfall (Metu) 310 400 300 350 290 300 250 280 Mean 200 Mean 270 2006 150 2006 Rainfall (mm) 260 Rainfall (m m100 )

250 50 0 240 June July August September Jul Aug Sep Month Month

June - September Rainfall (Masha) June-September Rainfall (Tepi) 450 250 400 350 200 300 250 150 Mean 200 Mean 2006 100 2006 Rainfall (mm) Rainfall 150 Rainfall (mm) Rainfall 100 50 50

0 0 Jun Jul Aug Sep Jun Jul Aug Sep Month Month

Figure 5-5: Comparison of Mean and 2006 Rainfall for stations in Gambella plain

Rainfall Stations in Tekeze Basin The Tekeze basin belonging to the north Ethiopia receive less rainfall as compared to Abbay and Baro-Akobo basins in the eastern Nile Region. As ITCZ enters late in north Ethiopia and exit fast the main rainy season concentrates in July and August. Four key stations have been analyzed within the Tekeze basin in Ethiopia, namely Lalibela, Mekele, Shire and Debarek Stations. Results have indicated that in these selected four stations the recorded rainfall was observed to be generally higher than the normal values in rainy seasons. Tekeze River originates near Lalibela. The Lalibela rainfall is, therefore, representative of the upper catchment of Tekeze. The 2006 records at Lalibela and Shire-Endaselasie stations have rainfall above normal in the main rainy season of July and August. The 2006 July-August rainfalls are about 26% and 34% higher than normal for these two stations respectively. In particular, the whole month of August and the first decade of September received above normal rainfall for Lalibela station. Similarly, the 2006 June to September (rainy season) rainfall for Mekele was higher than normal by about 17%. In August the rainfall was higher from the normal by 33%. The flood in Humera is from the high rainfall in August. It was also observed that The August 2006 rainfall for Debarek station was about 55% higher than normal. In summary, Tekeze basin in August 2006 received high rainfall. As all of the four key rainfall stations indicates that the highest rainfall is mainly in the third decade of August; where the flood in the river overflows at Humera and displace people and cause damage. During the third decade of August Lalibela, Mekele, and Shire got high rainfalls

indicating the flood at Humera is caused by the main Tekeze above the gauging at Embamadre. Debark belonging to near Zarema catchment which is a tributary down stream of the gauge at Embamadre and up stream of Humera received high rainfall during the first decade not the third of August which indicates the flood was caused by the rainfall from up stream catchments above the gauging station. As the catchment of Tekeze basin is largely degraded the river exhibits a fast hydrograph rise and relatively quick recession.

June-September Rainfall (Lalibela) June-September Rainfall (Mekele) 350 350 300 300 250 250 200 Mean 200 Mean 150 2006 150 2006 Rainfall (mm) 100 Rainfall (m m100 ) 50 50 0 0 Jun Jul Aug Sep Jun Jul Aug Sep Month Month

June - September Rainfall (Shire) June-August Rainfall (Debark) 450.0 600 400.0 500 350.0

300.0 400 250.0 Mean 300 200.0 Mean 2006 2006 Rainfall (mm) Rainfall 150.0 Rainfall (mm) Rainfall 200 100.0 100 50.0 0.0 0 Jun Jul Aug Sep Jun Jul Aug Month Month

Figure 5-6: Comparison of Mean and 2006 Rainfall for stations in Tekeze Basin

5.1.2. The Nile Forecast System Analysis The NFS is a real-time distributed hydro-meteorological forecasting system designed for forecasting Nile flows at designated key points within the Nile; of major interest is the inflow of the Nile into the High Aswan Dam, Egypt. The Nile Basin Hydro-Meteorological Information System (NBHIS) presents one of the most important modules of the NFS. It contains on line hydrological and meteorological database consisting of: (1) daily and monthly river stages and discharges, reservoir elevations and releases for many profiles along the Nile river for the longest possible long historical record; (2) daily meteorological data (temperature, dew point, wind, visibility and precipitation) for about 100 observational stations inside of Nile catchment since 1992, and historical monthly precipitation grids for the period since 1940. These data are used as inputs to the meteorological and climatological analyses, and to the hydrological simulation and forecasting system, for the calibration, and to allow the user to perform and evaluate simulation runs for historical periods.

Two main types of rainfall data are collected by the NFC: satellite data, and gauge data. Each type is used to generate a separate estimate of rainfall on a grid covering the Nile basin before the satellite and gauge estimates are merged (using a set of monthly weights) to obtain what is referred to as the “best estimate” of rainfall for the Nile window. Infrared cloud top temperature data are obtained from the European Space Agency (ESA) geostationary METEOSAT 5 satellite positioned over Africa is the primary data utilized in preparation of the precipitation estimates. These data are received using the Primary Data User System (PDUS), a hardware/software system for real-time acquisition, processing, quality control, display, storage and automatic transfer of the METEOSAT Satellite infrared (IR), visible (VIS), and water vapour (WV) raw images.

I. Monthly Analysis Figure 5-7 shows the rainfall situation of May 2006 over the Nile Basin. Over the Ethiopian plateau, MAP over the Blue Nile Basin amounted to 133.5 mm which is 60% above the long term average (83.5mm). Similarly over the Sobat Basin, MAP was estimated as 158 mm while the normal amount is only 125 mm, i.e. recorded May rainfall is 26% above normal. The MAP over the Atbara Basin (67 mm) is more than double the long-term mean for this month (only 29 mm). MAP over the SUDD swamps amounted to about 123 mm which is also higher than the long-term average (105.5 mm) for May by about 16%. Meanwhile, MAP over the Equatorial plateau was about 168.5 mm, and it is also over the rate by approximately (145.5 mm) that is representing 15% over the rate mostly due to heavy rainfall over the western part of the basin.

Figure 5-7: May Rainfall Anomalies (as percentages of long-term Average)

During June, average rainfall over the Ethiopian plateau became around or below normal except for the Atbara sub-basin where rainfall remained slightly above normal (Figure 5-8). MAP over the Blue Nile Basin during June amounted to 133.5 mm which is around the normal rainfall value given as 138mm. For the Sobat, recorded MAP was estimated as 105.8mm which is about 16% below the normal amount of precipitation (126.5 mm). Over Atbara basin river amounted to 58.5 mm, which is slightly (10%) higher than normal (53 mm). It is important to indicate the large anomalies around and north (especially to the northwest) of Khartoum which caused flash floods in the Khartoum area from areas that normally do not contribute to the Nile flow. Over the SUDD swamps and the Equatorial Lakes, the estimated MAP was also below normal during June 2006. The long term average MAP over the Sudd and the Equatorial Lakes are 143 and 74 mm respectively, while the estimated values for June 2006 amounted to 120 and 53 mm respectively. These indicate normal precipitation falling on the swamp area was about 120 mm, while the normal rate is 143 mm. These values are 16% and 28% below normal for the Sudd and the Equatorial Lakes respectively.

Figure 5-8: June Rainfall Anomalies (as percentages of long-term Average) During July 2006, rainfall over the Ethiopian highlands was generally around or slightly higher than normal (Figure 5-9). MAP for the Blue Nile, Sobat, and Atbara were estimated as 263.5, 190, and 158.5 mm respectively. These figures are within 9% of the

normal for these sub-basins which amount to 255, 174.5, 154 mm for the three sub-basins respectively. The situation was similar over the Sudd swamps and the Equatorial Lakes as the estimated MAP was within 10% of the normal (on the positive side). MAP over the Sudd swamps was estimated as 191.5 mm and over the Equatorial Lakes was 76 mm while the long-term normals for those two areas are 172 and 76 mm respectively.

Figure 5-9: July Rainfall Anomalies (as percentages of long-term Average)

The situation changed August with much higher than normal rainfall rates over the Ethiopian Plateau. Figure 5- 10 shows that August rainfall over the Blue Nile Basin amount to 285 mm which is 23% higher than normal (285 mm). For the Sobat, MAP was much higher than normal with estimated value for August 2006 as 273 mm compared to 174 mm for the normal value (57% higher). Total average precipitation over the Atbara Basin amounted to about 185.5mm which is 13% higher than the long-term average (164 mm).

A similar situation prevailed over the Sudd swamps and the Equatorial Lakes with large and very large anomalies over the whole area. MAP over the Sudd was estimated as 246mm, 30% higher than normal 190.5 mm. Anomalies for Lake Victoria reached as high as 200% over the southwestern part of the basin (the Kagera basin). Aggregating over the whole basin, the recorded MAP amounted to 145 mm which is 48% higher than normal (98 mm)

Figure 5-10: August Rainfall Anomalies (as percentages of long-term Average) Rainfall over both the Ethiopian and Equatorial Plateaus returned to near normal values (despite being still on the positive side for most areas) in September (Figure 5-11). Estimated MAP for the Blue Nile, Sobat, and Atbara sub-basins were 152.5, 141, 60.5 mm respectively, which are all within 9% of the long-term average precipitation (139, 135, 59 mm respectively). MAP over the Sudd swamps amounted to 164mm, 13% above normal (145.5 mm) while the MAP over the Equatorial lakes was almost normal (estimated 95.5 mm is comparable to the long-term mean of 97 mm).

Figure 5-11: September Rainfall Anomalies (as percentages of long-term Average) Figure 5-12 shows that rainfall anomalies rose again in October especially for the northern parts of the Basin. Anomalies reached 200% again for areas to the west and south of Khartoum that normally do not contribute to Nile flows. Some these large anomalies occurred over the Blue Nile, Sobat and Atbara sub-basins as reflected in MAP values. MAP over the Blue Nile Basin during October reached 93 mm, about 52% higher than normal. MAP was recorded as 133 and 31 mm over the Sobat and Atbara sub-basins respectively. These values are 37% and 63% higher than normal respectively (96.5, 19 mm for the Sobat and the Atbara sub-basins respectively). Meanwhile, recorded rainfall over the Sudd swamps and the Equatorial Lakes remained considerably higher than normal. MAP over the Sudd recorded 106 mm, which is 22% higher than normal (87 mm) and recorded 149 mm over the Equatorial plateau, which is 30% higher than normal (115 mm).

Figure 5-12: October Rainfall Anomalies (as percentages of long-term Average) By November (Figure 5-13), most of the rainfall over the Ethiopian plateau has already fallen. Thus, even if large anomalies (percentage terms) are observed in some sub-basins, they may be small in absolute terms. For example, MAP over the Blue Nile and Atbara (12 and 3.5 mm respectively) is 25% and 50% lower than normal respectively (12 and 7 mm respectively) but noting the small value of the normal in this month, these large anomalies should not get much attention. MAP remained higher than normal over the Sobat basin (51.5 mm estimated vs. 43.5 mm normal). Meanwhile, MAP over the Sudd swamps was around the normal value (recorded 16 mm compared to 17 mm for the normal). Average rainfall over the Equatorial lakes for November was estimated as 205.5 mm which is 66% above the normal value (123.5 mm). In fact, large anomalies reaching 200% have been observed over the Eastern parts of the catchment which is responsible for flooding in Tanzaia and Kenyia

Figure 5-13: November Rainfall Anomalies (as percentages of long-term Average) II. Annual Analysis As pointed earlier, the rainfall season over the Ethiopia plateau, which is responsible for peak Nile flows that reach Egypt, starts in spring (April/May) and extends over the summer till autumn when the region is generally dry. Throughout the year, rainfall over the Equatorial Plateau also occurs but the Equatorial Lakes system combined with the large plains of the Sudd regulate the flow to contribute a nearly steady discharge to the main Nile flow. Thus, from a flood analysis point of view, the most important rainfall season to focus on is the wet season of the Ethiopian plateau extending from April to November. The rainfall season started with above average anomalies over all sub-basins in May and then returned to around normal conditions in June in the Ethiopian highlands and to less than normal in the Equatorial Lakes and Sudd areas. In July, rainfall rates were normal or slightly above normal for all sub-basins. August recorded high rainfall anomalies for all sub-basins but rates returned to near normal in September. The high August anomalies especially around Khartoum caused devastating flooding. The highest recorded anomalies occurred in areas west of Khartoum that do not normally contribute to Nile flows. Similar events occurred in 1988 as documented by Sutcliffe et al. (1989). High anomalies were

recorded again for October on both the Ethiopian and Equatorial plateaus. By the end of the rainy season of the Ethiopian highlands in November, rates were still high in the Sobat sub-basin but were lower than normal for the Blue Nile and Atbara sub-basins. However, high anomalies were recorded in November for the eastern parts of the Equatorial Lakes which caused floods in Kenya and Tanzania. Figure 5-14 shows that 2006 rainfall over the Ethiopia plateau to be above normal. Mean Areal Precipitation (MAP) over the Blue Nile basin is estimated as 1150mm compared to the long-term average of 970mm, i.e. 18% higher. Similarly, MAP average rainfall over the Sobat basin was about 1140 mm, while the normal (i.e. long-term average) precipitation is 999 mm (i.e. 14% higher). Then total average precipitation over the Atbara basin river was 628mm, also 14% higher than the long-term average of 548 mm. For the While Nile sub-basins, rainfall was also higher than average. Average rainfall over the Sudd swamps during this period was about 1052 mm, which is also higher than normal (946 mm) by about 11%. In addition, average rainfall over the Equatorial lakes is estimated as 1150 mm, which is 17% higher than long-term rate (about 981 mm).

Figure 5-14 Rainfall Anomaly Map for the Ethiopian Rainy Season (Apr-Nov 2006)

5.1.3. Rainfall Analysis Summary In the Blue Nile basin the 2006 estimated rainfall by NFS has indicated higher rainfall in all the wet months except for June in which the estimated rainfall is a bit less than the normal recorded. The maximum variation between the predicted and the normal reaches about 60% in May. Maximum absolute difference noted for same month is 50 mm in excess of the long-term mean. Table 5-8 summarizes and compares the Long-term mean rainfall and the 2006 estimated rainfall as extracted from the monthly anomalies maps. The rainfall analysis from the Ethiopian report [1] is mainly done for Lake Tana basin which is found in most upstream part of the Blue Nile sub-basin. The analysis is carried out for four rainfall station within the sub-basin and the result of the analysis is summarized in Table 5-9 for the four months June to September. Percentage of deviation from the normal, estimated from NFS for June, closely relates with the recoded rainfall depths for Lake Tana basin. And the remaining months the deviation is higher as indicated by the NFS however the estimated values can not directly be compared since lake Tana basin only comprises small part of the blue Nile basin by area.

Month Long term 2006 estimated Deviation Mean rainfall(mm) from rainfall Normal (mm) May 83.50 133.50 60% June 138.00 133.50 -3% July 255.00 263.50 3% August 231.00 285.00 23% September 139.00 152.50 10% October 61.00 93.00 52% November 12.00 12.00 0% Annual Rainfall 970 1150 19% Table 5-8: Average Rainfall Estimates of 2006 vs. Long Term Mean Monthly Rainfall for Blue Nile Basin from Monthly Anomalies Maps

Month Long term 2006 Recorded Deviation from Mean rainfall rainfall(mm) Normal (mm) June 176.90 175.88 -2% July 385.63 463.08 19% August 348.03 368.82 6% September 163.96 200.48 25% Table 5-9: Average Rainfall Record Of 2006 And Long Term Mean Monthly Rainfall For Lake Tana Basin From Rainfall Stations Monthly analysis of rainfall from each station in Lake Tana basin is presented in Table 5-10.Maximum value of rainfall is recorded in Bahirdar station in July, 563.4 mm. Similarly Addis Zemen Station has also recorded about 513 mm. This station represents the catchment of Fogera plains where flooding frequently occurs in Tana basin.

According to NFS analysis the annual rainfall for the entire Blue Nile basin was estimated to be 1150 mm using anomalies maps. This is higher than the long tem normal rainfall by 19% which was 970 mm, Table 5-8. NFS analysis has also obtained rainfall estimates for the Baro-Akobo-Sobat basin. This part of the basin comprises the catchment that drains the Ethiopian highlands through the Baro and the Pibor river and the lowland part that is found in Sudan area that is drained by the Sobat that starts at the confluence of Baro and Pibor rivers, Figure 2-1.The Long tem mean and the estimated rainfall for 2006 is shown in Table 5-11. Higher rainfall than the Long term mean has been estimated for May and July to October however lesser rainfall values have been obtained for June and November. Rainfall records in November are relatively small than the rest of the wet months therefore, on the whole, higher rainfall was observed in the sub-basin for instance, for august about 57% deviation from the normal was estimated. Total annual rainfall depth for 2006 has shown 14% increase than the normal.

Station Long term 2006 Recorded Deviation Mean June June from rainfall (mm) rainfall(mm) Normal Debre Tabor 171.5 160 -7% Bahir Dar 191.5 225.5 18% Gondar 166.2 96.7 -42% Addis Zemen 178.4 221.3 24% Average Tana 176.9 175.875 -2% Basin

Station Long term 2006 Recorded Deviation Mean July July from rainfall (mm) rainfall(mm) Normal Debre Tabor 416.5 482.2 16% Bahir Dar 413 563.4 36% Gondar 299.8 293.5 -2% Addis Zemen 413.2 513.2 24% Average Tana 385.625 463.075 19% Basin

Station Long term 2006 Recorded Deviation Mean August August from rainfall (mm) rainfall(mm) Normal Debre Tabor 398.3 452.3 14% Bahir Dar 360.7 372.89 3% Gondar 291.9 349.1 20% Addis Zemen 341.2 301 -12% Average Tana 348.025 368.8225 6% Basin

Station Long term 2006 September Deviation Mean rainfall rainfall(mm) from (mm) Normal Debre Tabor 198.35 255 29% Bahir Dar 186.7 210.7 13% Gondar 117.2 192.5 64% Addis Zemen 153.6 143.7 -6% Average Tana 163.9625 200.475 25% Basin Table 5-10: Monthly Analysis of Rainfall for Stations In Lake Tana Basin

Like wise, four Station have been analyzed in the Ethiopian Flood report [1] from the upstream portion of the basin, As the four rainfall stations indicates the upper Baro Akobo basin where most of the tributary rivers of Baro, Akobo, and Gilo are originating the rainfall was above normal mainly in June and July which contributes for the above normal flooding in the Gambella plain, Table 5-12.

Month Long term 2006 Predicted Deviation from Mean rainfall rainfall(mm) Normal (mm) May 125.00 158.00 26% June 126.50 105.80 -16% July 174.50 190.00 9% August 174.00 273.00 57% September 135.00 141.00 4% October 96.50 133.00 38% November 7.00 3.50 -50% Annual 999 1140 14% Rainfall Table 5-11: Average Rainfall Estimates Of 2006 Vs. Long Term Mean Monthly Rainfall For Baro-Akobo-Sobat Basin From Monthly Anomalies Maps.

Month Long term Mean 2006 Recorded Deviation from rainfall (mm) rainfall(mm) Normal June 250.23 289.33 16% July 265.80 280.98 5% August 271.23 233.03 -14% September 258.43 258.15 0% Table 5-12: Average Rainfall Record of 2006 and Long Term Mean Monthly Rainfall for Stations in Baro Basin In August much higher rainfall than the normal is reported by the NFS 57%, while smaller rainfall than the normal is recorded by the station in Ethiopia. However, again the station from Ethiopian highland only represent portion of the total Baro-Akobo-Sobat sub-basin by area. But majority of the rainfall still happens in this portion of the sub-

basin as shown in the anomalies maps of rainfall distribution. The annual rainfall reported by the NFC has 14% increases than the long tem normal. Detailed monthly analysis is presented for station in Ethiopia below in Table 5-13.

Station Long term Mean 2006 June Deviation June rainfall (mm) rainfall(mm) from Normal Gore Masha 307.7 326 6% Metu 256.4 335.2 31% Tepi 186.6 206.8 11% Average Baro Basin 250.23 289.33 16%

Station Long term Mean 2006 July Deviation July rainfall (mm) rainfall(mm) from Normal Gore 289.9 294.9 2% Masha 321.9 402.6 25% Metu 257.7 220.7 -14% Tepi 193.7 205.7 6% Average Baro Basin 265.8 280.975 5%

Station Long term Mean 2006 August Deviation August rainfall rainfall(mm) from Normal (mm) Gore 297.7 264.9 -11% Masha 324.7 271.9 -16% Metu 258.3 200.1 -23% Tepi 204.2 195.2 -4% Average Baro Basin 271.23 233.03 -14%

Station Long term Mean 2006 Deviation September rainfall September from Normal (mm) rainfall(mm) Gore 279.9 300.4 7% Masha 296.1 370 25% Metu 275.2 217.7 -21% Tepi 182.5 144.5 -21% Average Baro Basin 258.43 258.15 -2% Table 5-13: Monthly Analysis of Rainfall For Stations In Baro Basin Monthly analysis tables indicate that rainfall was above normal mainly in June and July which resulted in flooding in the Gambella plain. Rainfall in the Tekeze-Setite-Atbara sub basin is substantially reduced a compared to the Baro-Akobo and Blue Nile sub basins. Mean annual rainfall varies from above 200mm in the upper courses of the Baro-Akobo-Sobat sub basin to above 1500mm in the upper course of Blue Nile and further reduced to 1000mm in the northern highlands of the

Tekeze watershed, which further reduces to 675mm at Mekelle station, located in the upper course of the Tekeze-Setite-Atbara sub basin. In the middle course as in Humera station (at the Ethio-Sudan border) mean annual rainfall is reduced to less than 700mm and further in the lower course (in Sudan) it is reduced to less than 400mm at El-Girba station and to 20mm at Atbara station, the mouth of the sub basin [4]. The NFC has reported higher rainfall records in all months of the wet season ranging from 31mm in October up 185.5mm in August. The difference from the Long-term normal values ranges from 3% in July up to 131% in May. A total annual rainfall estimate has also shown 15% increase when compared to the long tern normal rainfall in the basin. The differences between monthly estimated rainfall for 2006 and Long term mean monthly rainfall is shown in Table 5-14.

Month Long term 2006 Deviation Mean rainfall Estimated from Normal (mm) rainfall(mm) May 29 67 131% June 53 58.5 10% July 154 158.5 3% August 164 185.5 13% September 59 60.5 3% October 19 31 63% November 43.5 51.5 18% Annual 548 628 15% Rainfall Table 5-14 :Average Rainfall Estimates of 2006 Vs. Long Term Mean Monthly Rainfall For Tekeze-Atbara-Setit Basin From Monthly Anomalies Maps.

Month Long term 2006 Recorded Deviation from Mean rainfall(mm) Normal rainfall (mm) June 95.18 81.53 -11% July 268.20 269.33 1% August 263.35 376.79 42% September 57.25 38.33 -13% Table 5-15: Average Rainfall Record of 2006 and Long Term Mean Monthly Rainfall for Stations in Tekeze Basin The Tekeze basin belonging to the Tekeze-Atbara-Setit basin and is found in the central north highland plateaus of Ethiopia. Tekeze basin in August 2006 received high rainfall. As all of the four key rainfall stations indicate that the highest rainfall is mainly in the third decade of August a 42% increase than the normal rainfall is recorded, Table 5-15. This highest rainfall also corresponds to the analysis report from NFC. Similarly higher rainfall records than the normal have also been obtained as reported by the NFC. 21 mm difference have been reported in the total Tekeze-Atbara-Setit basin as per NFC while

113 mm difference in depth is indicated by the Ethiopia flood report in Tekeze basin alone. Station Long term 2006 Deviation Mean rainfall Recorded from (mm) rainfall(mm) Normal Lalibela 40.6 23.9 -41% Mekele 34 44.1 30% Shire 146.6 136 -7% Debark 159.5 122.1 -23% Average Tekeze Basin 95.175 81.525 -11%

Station Long term 2006 Deviation Mean rainfall Recorded from (mm) rainfall(mm) Normal Lalibela 256.1 300.9 17% Mekele 201.3 194.1 -4% Shire 285.9 307.3 7% Debark 329.5 275 -17% Average Tekeze Basin 268.2 269.325 1%

Station Long term 2006 Deviation Mean rainfall Recorded from (mm) rainfall(mm) Normal Lalibela 240.5 324.35 35% Mekele 230 306.9 33% Shire 265.8 393.3 48% Debark 317.1 482.6 52% Average Tekeze Basin 263.35 376.7875 42%

Station Long term 2006 Deviation Mean rainfall Recorded from (mm) rainfall(mm) Normal Lalibela 44.2 43.6 -1% Mekele 28.7 32.6 14% Shire 156.1 77.1 -51% Debark Average Tekeze Basin 76.33 51.1 -13% Table 5-16: Monthly Analysis of Rainfall For Stations in Tekeze Basin Rainfall in Sud Swamps and in the areas of Equatorial plateau as obtained by the NFC is showin the Table 5-17 and Table 5-18 . In both cases mostly high rainfall estimates than the normal is obtained. Annual deviation of rainfall from the normal was calculated to be 11% and 17% for Sud Swamps and Equatorial plateau respectively.

Month Long term Mean 2006 estimates Deviation from rainfall (mm) rainfall(mm) Normal May 105.5 123 17% June 143 120 -16% July 172 191.5 11% August 190.5 246 29% September 145.5 164 13% October 87 106 22% November 17 16 -6% Annual 946 1052 11% Rainfall Table 5-17: Average Rainfall Estimates of 2006 Vs. Long Term Mean Monthly Rainfall for Sudd Swamps From Monthly Anomalies Maps

Month Long term Mean 2006 estimated Deviation from rainfall (mm) rainfall(mm) Normal May 76 76 0% June 74 53 -28% July 145.5 168.5 16% August 98 145 48% September 97 95.5 -2% October 115 149 30% November 123.5 205.5 66% Annual 981 1150 17% Rainfall Table 5-18: Average Rainfall Estimates Of 2006 Vs. Long Term Mean Monthly Rainfall For Equatorial Plateau From Monthly Anomalies Maps

In conclusion, higher rainfall than the long term rainfall records have been observed in the Eastern Nile Basin .The flooding occurred at different parts of the region could be attributed to unusually high rainfall in the basin.

Figure 5-15: Spatial Distribution of rainfall and comparison of long-term and 2006 monthly rainfall for major sub-basins of Eastern Nile Basin

5.1.4. Rainfall Forecast for 2007 from GCM Cairo University carried out rainfall analysis for the Nile basin using global climate models and outputs indicate that there will be a general increase of rainfall compared to the normal average monthly rainfall. Figure 5-16 shows rainfall spatial maps forecast for the month of June in 2007. On Average about 50% rise above the long term normal rainfall is expected for Lake Tana area. In the central part of the blue basin in Ethiopia, however, the rainfall rise could reach up to 150% higher than the long term normal which is considerably high when compared to the previous year 2006.Similarly rainfall depths of 5-10mm are expected in the lower part of the blue Nile basin in Sudan. In the Gezira state the rainfall forecast indicates rainfall depths in the orders of 15-20 mm.

Figure 5-16 rainfall forecast for the month of June from GCM for the year 2007(Units cm )

For July the rainfall forecast showed relatively lower rainfall in the central part of the Blue Nile basin, the expected rainfall depths being in the orders of 50-200 mm. When this is compared to the long term normal rainfall the expected deviation from the normal is less than 20%.however in the lower reaches of the Blue Nile basin the expected rainfall is still higher than June rainfall and the long term normal. In the Sud-marsh areas the rainfall is much within the orders of 5-15mm which is normal compared to the long term mean rainfall. In Tekeze-Atbara-Setit sub-basin the monthly rainfall forecasted is in the orders of 10-20 mm this is within the long term normal range.

Figure 5-17 rainfall forecast for the month of July from GCM for the year 2007 (Units cm )

In the lower part of Lake Tana basin a stronger rainfall is predicated for August. The spatial maps indicated rainfall around 300 mm, this is much higher than the long term normal rainfall which is within 100 to 120 mm. Similarly, in the central part of the Blue Nile basin rainfall estimates for August is in the range of 120 to 160 mm which is about 20% higher than the long term average. In the upper part of the White Nile basin close to Sud-marshes also the rainfall is predicted to be in the ranges of 270 to 300 mm. This could be up to 30% higher than the long term mean rainfall. In tekeze-atbara-setit basin the rainfall is however expected to continue as normal, Figure 5-18.

Figure 5-18 rainfall forecast for the month of August from GCM for the year 2007 (Units cm )

Rainfall forecasts for September, Figure 5-22, showed normal rainfall for Lake Tana area and for lower and central areas of the Blue Nile basin, which is within the ranges of 100 to 150 mm. Similarly In Tekeze-Atbara-Settit basin the total area average the rainfall is expected to remain within normal ranges 50-70 mm. However, as the rainfall maps in dictate, high spatial variability is indicated. In some patches the rainfall could reach up to 120 mm. In most upper part of the Baro basin the rainfall forecast indicated less rainfall than the long term normal.

Figure 5-19 rainfall forecast for the month of August from GCM for the year 2007 (Units cm ) Generally the rainfall forecast for the year 2007 has indicated an expected rainfall much higher than the long term mean in the Blue Nile basin, especially for the months of June and July. This could result in potential flood incident in most downstream part of the Blue Nile River; therefore, potentially areas of Gezira and Khartoum state could be exposed to flooding.

5.2. Hydrologic Analysis Hydrologic Analysis has been carried out at key locations from each country it is being presented here in sub-basin level. This section of this synthesis report presents analysis for the four major sub-basins of the Eastern Nile basin, Figure 2-1.Mainly focusing on the recorded water levels and discharges.

Figure 5-20: Selected Key Nodes for Hydrologic Analysis

5.2.1. The Blue Nile sub-basin The Blue Nile sub basin, located in the middle east of the Eastern Nile Basin, is the largest contributor (56bcm/year, including Dindir & Rahad) of the Eastern Nile Basin system accounting 67% of the inflow at Aswan. The Blue Nile River starts at the outlet of Lake Tana and extends up to Khartoum, its mouth, with a total of estimated drainage area of 313,547km2 [4], Figure 2-1. Here Bahirdar , Khartoum ,El Deim stations on the Blue Nile river; El Gewaisi station on Dinder river and El hawata Station on Rahad river have been selected for analysis,Figure 5-20. These stations represent major nodes on the Blue Nile sub-basin.

I. Bahirdar Station Bahirdar station measures the outflow from Lake Tana sub-basin which is about 15,320 km2 of area .This sub-basin comprises Lake Tana and the surrounding watersheds which contains the flood plain area, Fogera , Libo Kemkem woredas, Dembiya woreda and Bahir Dar special zone and where flooding mostly occurs. Water levels: The average Annual Daily maximum Water Level Recorded by Hydrology Department of Ethiopian MoWR is 3.48 m the 2006 water level reached 3.64 m in September and remained high in October before it started to decrease in November. Figure 5-21 and Figure 5-22 show Lake Tana annual maximum daily water level (1959- 2006) and 2006 Lake Tana water level from August to December respectively.

Lake Tana at Bahir Dar Annual Daily Maximum Water Level

5 4.5 4 ) 3.5 3 2.5 2 ater Level (m 1.5 W 1 0.5 0 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 Year

Figure 5-21: Lake Tana Annual Maximum Daily Water Level

Lake Tana water level (August-December, 2006)

3.5

2.5

1.5 Water Level (m) 1

0.5

0 1-Aug-06 21-Aug-06 10-Sep-06 30-Sep-06 20-Oct-06 9-Nov-06 29-Nov-06 19-Dec-06 Date

Figure 5-22: Lake Tana water level (August – December, 2006) Discharges: Hydrological records at Bahirdar on Abbay River as it outflows from Lake Tana shows large discharge as compared to previous years. Since outflow from the lake is regulated by Chara Chara Weir it is not natural outflow but for fear of large flooding in the surrounding high discharges are released in September.

Abbay at Bahir Dar (Outflow from Lake Tana) 800

e 700

i scharg 600

500 aily D aily

D 400 3/sec) um

(m 300 axi m 200

100 Annual M 0 1971 1976 1981 1986 1991 1996 2001 2006 Year

Figure 5-23: Abbay at Bahir Dar Annual Maximum Daily Discharge

Abbay at Bahir Dar (Lake Tana outflow)

800 700 600

3/sec) 500 400 300 200 Discharge (m 100 0 1-Aug- 16-Aug- 31-Aug- 15-Sep- 30-Sep- 15-Oct- 30-Oct- 14-Nov- 29-Nov- 06 06 06 06 06 06 06 06 06 Date

Figure 5-24: Abbay at Bahir Dar Daily Discharges in 2006

II. El Deim station

Water levels: The water level at El Deim station was the highest ever recorded reaching 14.03 m on 25/8/2006. The following table, Error! Reference source not found., shows the average water levels during the flood months.

Month Level Average level Discharge Average discharge July 10.24 10.93 8787mm3 6837 Aug. 12.75 12.45 22082 15287 Sept. 12.19 11.53 14054 12091 Total - - 44923 34215 Table 5-19: Water Levels and Discharges during the Flood Months for El Deim Station Figure 5-25 shows that the recorded level at Diem was fluctuating above the long-term mean (normal) values over the months of May and June 2006. During the first decade of July, the level dropped to normal values but this was short-lived as it rose again by July 10th and remained higher than normal till October 10th. During this period, the level fluctuated around the maximum year values. By the second decade of October, the level dropped again to normal values until the end of October. The level rose again, fluctuating around the maximum year values the first of November until the end of March, the end of available observations at the time of preparation of this report.

LEVEL REGIME AT DIEM 15 BLUE NILE 31 March. 14

10 LEVEL (m) 9

6 JUL. SEP. JUN JUN JAN. FEB. DEC. APR. AUG. OCT. NOV. MAR. MAY.

Long Term Mean (1945-2005) Obs. Year (2006-2007) Abs.Daily Max(1945-2005) abs.Daily Min (1945-2005) Min. Year (1984-1985) Max. Year (1998-1999) Figure 5-25: Level Regime at Diem, Blue Nile Discharges: Figure 5-26 show the discharges trough the station in comparison with different years and the average. The Total flow volume accumulated from the 1st May 2006 until the 31st of March 2007 amounts to 62.05 BCM, which is about 35% higher than the long-term mean volume for the same time period (46.11 BCM). Table 5-19

compares the total flow volume accumulated at Diem with values for the same period (May – March) for the last five years.

Period July - Sept Average 1984 1988 1946 2005 2006 Percentage Remarks of the average (1965 – 1996) 32.5 22.4 47.4 49.9 32.92 44.9 138% less than 1946 and 1988 floods (1912-2004) 34.21 131% Table 5-20: Discharge record at El Deim Station

Total Flow Period (BCM) 1/5/2006 – 31/3/2007 62.05 1/5/2005 – 31/3/2006 47.12 1/5/2004 – 31/3/2005 41.47 1/5/2003 – 31/3/2004 45.72 1/5/2002 – 31/3/2003 37.65 Long-Term Mean (1945-2005) 46.11 Table 5-21: Comparison of Accumulated Flow Volumes at Diem with Past Year

FLOW VOLUME AT DIEM BLUE NILE 140.00

120.00 62.05

100.00 ) 3

80.00

60.00 THOUSANDS VOLUME (MILLIONm 40.00

20.00

0.00 MAY. JUN JUL. AUG. SEP. OCT. NOV. DEC. JAN. FEB. MAR. APR.

Abs. Daily Max. (1945-2005) Abs. Daily Min. (1945-2005) Long Term Mean (1945-2005) Max. Year (1998-1999) Min. Year (1984-1985) Obs. Year (2006-2007) Figure 5-27: Accumulated Flow Volumes at Diem, Blue Nile

Period Average Mm3 discharge Index Excedence prob July 6775 8787 14 %14.6 Aug. 145.21 220.82 2 %2.1 Sept. 10872 140.54 19 %19.8 July Sept. 32168 44923 Table 5-22: Exceedance probability for July at Diem station, Blue Nile

III. Khartoum station :

Water levels: The highest water level recorded during the flood of 2006 is 17.08 m on 31/8/2006 while the highest ever recorded level was 17.4 m on 2/9/1946. The following table (Table 5-23) Shows the water levels and discharges recorded during the flood period.

Period Level M Average level Mm3 discharge Average discharge July 12.95 12.27 3403 3592 Aug. 16.36 14.95 19808 13967 Sept. 16.34 14.70 18567 11167 Total - - 41778 28726 Table 5-24 Water Levels and Discharges during the Flood Months for Khartoum Station

Figure 5-28 shows the water level hydrograph at Khartoum on the Blue Nile. The water level at Khartoum was higher than normal at the beginning of May. The difference between the observed levels and the normal values started to decrease until the end of first decade of July when it reached the normal values. The level rose again above the normal values and then dropped again to near normal values by the end of July. By the beginning of August, the level started to increase rapidly exceeding the maximum year values and the maximum absolute values occasionally until the end of September. The recorded level at Khartoum (17.08m) on the 1st September 2006 was the maximum of all times. During the entire month of October the level decreased to be lower than normal. The level started to increase again at the beginning of November and remained above the normal until the end of March.

LEVEL REGIME AT KHARTOUM 19 BLUE NILE

18 31 March.

LEVEL (m) 13

9 MAY. JUN JUL. AUG. SEP. OCT. NOV. DEC. JAN. FEB. MAR. APR.

Abs. Daily Max. (1945-2005) Abs. Daily Min. (1945-2005) Long Term Mean (1945-2005) Max. Year (1998-1999) Min. Year (1984-1985) Obs. Year (2006-2007) Figure 5-28: Level Regime at Khartoum, Blue Nile Discharges: The total flow volume accumulated from the 1st May 2006 until 31st March 2007 amounts to 58.24 BCM which is about 42% above the long-term mean volume for the same time period. This is 17.60 BCM larger than higher than last year at the same time. It is worth noting that the accumulated volume was slightly higher than the maximum year till the end of September when it started to go below it but still above normal. From Figure 5-29, the maximum year (1998/99) was unusual as the level had a second peak in October which was not repeated this year.

Table 5-25 compares the total flow volume accumulated at Khartoum with the long-term mean and corresponding values for the last five years.

Period Total Flow (BCM) 1/5/2006 – 31/3/2007 58.24 1/5/2005 – 31/3/2006 40.64 1/5/2004 – 31/3/2005 32.67 1/5/2003 – 31/3/2004 41.29 1/5/2002 – 31/3/2003 28.29 Long-Term Mean (1945- 41.14 2005) Table 5-25: Comparison of Accumulated Flow Volumes at Khartoum, Blue Nile with Past Years

FLOW VOLUME AT KHARTOUM 140 BLUE NILE

120 58.24

100 ) 3

60 THOUSANDS VOLUME (MILLION m 40

0 MAY. JUN JUL. AUG. SEP. OCT. NOV. DEC. JAN. FEB. MAR. APR.

Abs. Daily Max. (1945-2005) Abs. Daily Min. (1945-2005) Long Term Mean (1945-2005) Max. Year (1998-1999) Min. Year (1984-1985) Obs. Year (2006-2007) Figure 5-29: Accumulated Flow Volumes at Khartoum, Blue Nile

IV. El Gewaisi station ( Dinder river ) Table 5-26 shows water levels and discharges of Dinder River at El Gewiasi station:

Period Level M Average level Mm3 discharge Average discharge July 8.49 4.79 106 203 Aug. 10.30 9.08 537 770 Sept. 11.58 9.28 802 807 Total - - 1445 1779 Table 5-27: Water levels and Discharges during the flood months for El Gewaisi Station

V. El hawata Station ( Rahad river ) The Table 5-28 shows water levels and discharges of Rahad river at El Hawata station.

Period Level M Average level Mm3 discharge Average discharge July 4.95 3.31 171 143 Aug. 10.64 5.68 422 341 Sept. 7.30 6.09 441 355 Total - - 1034 840 Table 5-29: Water Levels and Discharges during The Flood Months For El Hawata Station

5.2.2. Baro-Akobo-Sobat and white Nile Basin I. Baro at Gambella

Discharges: As depicted in Figure 5-30 the mean annual discharge of Baro River in 2006 is a little above average, however, the main reason for the flooding can be observed from Figure 5-31. The monthly flow in the Baro River was a little above average in the normally peak month of September but continues increasing abnormally in October which causes overflow of the banks of the river and inundate large areas.

Baro at Gambella 500.0

450.0 e 400.0 350.0 300.0 250.0 200.0 (m3/sec) 150.0 100.0

Mean Annual DischargMean 50.0 0.0

8 0 2 4 6 8 0 2 4 6 8 0 4 6 7 7 7 7 7 8 82 84 90 9 9 9 9 0 02 0 06 Years

Figure 5-30: Baro at Gambella Mean Annual Discharges

Baro at Gambella 1200

1000

800

600 Mean 2006 400

Discharge (m3/sec) Discharge 200

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

Figure 5-31: Comparison of 2006 and Mean Monthly Discharges

Baro at Gambella 1400

1200

1000

800

600

400 Discharge (m3/sec) 200

0 08/01/06 08/21/06 09/10/06 09/30/06 10/20/06 11/09/06 11/29/06 Date

Figure 5-32: Daily Discharges of Baro River from August-October 2006 Discharges in the Baro River were high from mid August to end of October. The maximum daily discharge was reached 1186 m3/sec in October 12, 2006. The discharge is equivalent to a return period of 1.88 years. The annual daily maximum discharge is less than the mean annual daily maximum. This will indicate that normally every year the Gambella plain will be flooded; the 2006 flood is different in that after the bank full discharge is exceeded water stage remains high for extended period of time. Baro

GENERALISED EXTREME VALUE DISTRIBUTION (TYPE 1)

RETURN PERIOD (YEARS) at

1600 Gam ) bella

1500

Annual Discharge (m3/sec Discharge

1400 M axim um

1300 a ly Dai

Discharge

1200

(m 1100 3/sec)

1000 FITTED DISTRIBUTION

95% CONFIDENCE LIMITS

900 -2 1 5 10 20 30 40 50 60 70 80 90 95 96 97 98 99 99.5 99.7 99.8 99.9 PROBABILITY (%)

Figure 5-33: Baro at Gambella Annual Maximum Daily Discharges fitted to Gumbel Distribution The Akobo River defines the border with Sudan, access is very difficult, and there are no river gauges on the Akobo River in Ethiopia. The Akobo from the south-east joins the Pibor flowing from the south out of Sudan, and the Pibor then defines the Ethiopian- Sudan border until where it is joined by the Baro flowing from the east out of Ethiopia. The river then becomes the Sobat, and flows west through southern Sudan to its confluence with the White Nile about 800 km south of Khartoum. Regular widespread flooding occurs seasonally in the flat plain areas upstream of the Sudan border. Gilo River, a large tributary of Akobo/Pibor, River is gauged near Pungido with a catchment area of 10,137 km2. The gauging station was started in 1977 and was operational upto 1990 since then the station has been out of operation and no data is available. The mean annual discharge at the station is about 96 m3/sec. Gilo River has

large flows from June-Ocober which contributes a lot to the flood inundation of the low lands of the Baro-Akobo Basin.

Gilo near Pungido 200.0

e 180.0 160.0 140.0 120.0 100.0 80.0 (m3/sec) 60.0 40.0

Meam Monthly Discharg 20.0 0.0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

Figure 5-34: Gilo near Pungido Mean Monthly Discharges

II. Malakal station ( White Nile )

Water levels: The water level, Figure 5-35, stated from near normal levels at the beginning of May and remained close to the normal until the end of second decade of May. Then, it started to rise gradually and stayed above normal until the middle of September when it decreased gradually to reach the normal again at the beginning of November. The level remained close to the long-term mean during November and then rose again in December and remained above the normal values till the end of March when it started to decrease again to reach the normal. In summary, the water level was above normal except for short periods when it was normal but it was n. The gradual transitions reflect the regulating effect of the Lakes and Swamps.

Period Level M Average level m discharge Mm3 Average discharge Mm3 July 12.12 11.56 2942 2550 Aug. 12.46 11.97 3234 2908 Sept. 12.68 12.29 3322 3094 Total - - 9498 8552 Table 5-30: Water Levels and Discharges Of White Nile At Malakal Station

LEVEL REGIME AT MALAKAL

15 WHITE NILE

31 March. 14

13 )

12 LEVEL (mLEVEL 11

9 MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR

Abs. Daily Max. (1945-2005) Abs. Daily Min. (1945-2005) Long Term Mean (1945-2005) Max. Year (1964-1965) Min. Year (1951-1952) Obs. Year (2006-2007)

Figure 5-35: Level Regime at Malakal, White Nile Discharges: The accumulated volume was slightly above normal for the whole year Figure 5-36.The total flow volume accumulated from 1st May 2006 until 31st March 2007 amounts to 32.75 BCM which is about 8% above the long-term mean volume for the same time period and 2.73 BCM higher than last year at the same time. Table 5-31compares the total flow volume accumulated at the profile Diem during the last five years. Tekeze River flows from near Lalibela first north, then west and north-west to the Sudan border at Humera where the catchment area is 63,375 km2. The Tekeze becomes the Atbara River in Sudan, which is the only major tributary that joins the Nile downstream of Khartoum.

Total Flow Period (BCM) 1/5/2006 – 31/3/2007 32.75 1/5/2005 – 31/3/2006 30.02 1/5/2004 – 31/3/2005 29.25 1/5/2003 – 31/3/2004 28.23 1/5/2002 – 31/3/2003 27.39 Long-Term Mean (1945-2005) 30.44 Table 5-32: Comparison of Accumulated Flow Volumes at Malakal, White Nile with Past Year

FLOW VOLUME AT MALAKAL 140 WHITE NILE

120

100 3

32.75 80 ILLION m

E (M 60 THOUSANDS VOLUM 40

0 MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR

Abs. Daily Max. (1945-2005) Abs. Daily Min. (1945-2005) Long Term Mean (1945-2005) Max. Year (1964-1965) Min. Year (1984-1985) Obs. Year (2006-2007) Figure 5-36: Accumulated Flow Volumes at Malakal, White Nile

5.2.3. Tekeze-Atbara-Setit Sub-basin

I. Tekeze near Embamadre

At the gauging station near Embamadre Tekeze covers a catchment area of 45,529 km2. There are two periods of flow data at this site 1969-1976 and 1994-2002 discharges are not calculated since 2002, however, water level measurement still continued and data is available upto 2006. Water levels:The water level record reveals that a maximum stage of 11.5 m is recorded in the River on August 9, 2006.

Tekeze near Embamadre 14 er

at 12 W 10 um ) 8 axim 6 Level (m 4

2 Annual Daily M 0 1966 1971 1976 1981 1986 1991 1996 2001 2006 Years

Figure 5-37: Tekeze near Embamadre Annual Maximum Daily Water Level

Tekeze near Embamadre 14.00

12.00

) 10.00

8.00

6.00 ater Level(m

W 4.00

2.00

0.00 6 6 6 6 6 6 6 6 6 6 6 06 0 0 006 006 0 006 00 00 00 00 00 /2 /2 /2 /2 /2 /2 /20 /2 /2 /20 /2 /7/2006 7 5 8/1 8/3 8/5 8 8/9 /11 13 /15/200 /19 /21 /23/200 /27 8 8/ 8 8/1 8 8 8 8/2 8 8/29/2008/31/200 Date

Figure 5-38: Tekeze near Embamadre Daily Water Levels in Augut 2006

Discharge: The maximum daily discharge calculated at the station is 1479.6 m3/sec for a stage of 5.45 m in August 5, 1976. Since the gauging station is re-instated in 1994 discharges are calculated upto a water level of 5.8 m but water level records much higher than 5.8 m are observed. The flood of 2006 at Humera was caused by two high flows in August on the dates of 9th and 26th of August 2006 which record water stages of 11.5 and 8 m respectively. Most of the flow is coming from catchments up stream of the gauging station. Zarema is the only major tributary between Embamadre and Humera. There were no dams in the Tekeze sub-basin; however a large dam, the Tekeze Dam, is currently under construction, primarily for hydropower generation. It will command an upstream catchment of 30 390 km2, and will have an active storage capacity of 9 293 MCM. Even though the primary purpose of the dam is hydropower generation, it will be useful in regulating peak flows. II. - Downstream Khashm el Girba dam station (Atbara river ) :

Discharge: Atbara and setit tributaries are the confluents of Atbara River. The confluence of the two tributaries is just upstream kashm el Girba dam. The following table shows the water levels and discharges downstream the dam.

Period Level M Average level m discharge Mm3 Average discharge Mm3 July 436.93 435.01 1903 2507 Aug. 437.66 436.15 7776 5795 Sept. 433.72 434.35 4520 2413 Total - - 14199 10715 Table 5-33: Water Levels and Discharges during the Flood Months, Khashm El Girba Dam Station

5.2.4. Main Nile Sub-basin

I. Dongola station

Water levels : The highest water level recorded during the flood of 2006 in the main Nile at Dongola station is 15.57 m on 10/9/2006 and corresponding is 1005 million m3 .This has been the highest ever recorded with level of 15.93 m. in 2001 by 36cm . The water level regime for 2006/07 at Dongola (Figure 5-39) is very similar to that of the Blue Nile at Khartoum, because the contribution of the White Nile is nearly steady over the year. At the beginning of May 2006, the water level was lower than normal and then it started to rise till it reached normal values by mid May. The level fluctuated around the normal values over the entire time period from 15 May – 15 July, then it fluctuated above the long-term mean to record the maximum value (15.90m) in this flood year at the end of second decade of August. The level then started to drop gradually at the beginning of the second decade of September but remained above the normal values until the middle of October when it dropped below the normal until the middle of November. The level started to increase and remained above the normal until the end of March.

LEVEL REGIME AT DONGOLA 18 MAIN NILE

) 14 31 March.

LEVEL (m 12

8 MAY. JUN JUL. AUG. SEP. OCT. NOV. DEC. JAN. FEB. MAR. APR.

Abs. Daily Max. (1945-2005) Abs. Daily Min. (1945-2005) Long Term Mean (1945-2005) Max. Year (1998-1999) Min. Year (1984-1985) Obs. Year (2006-2007)

Figure 5-39: Level Regime at Dongola, Main Nile

Discharge: The accumulated flow volumes for this year (Figure 5-40) nearly coincided with those of the maximum year (1998/99) till the end of September when the level started to go below the normal (see above) and thus the flow volumes became lower and remained lower than the maximum year, despite remaining above average. As noted earlier, the maximum year was somehow unusual as it had a secondary peak for Blue Nile flows in October, which did not occur this year. The total accumulated flow volume for this year (1st May 2006 – 31st March 2007) amounts to 87.22 BCM, which is around 25% above the long-term mean volume for the same period and about 19.46 BCM higher than the corresponding volume of last year. Figure 5-33 shows that the total river yield at Dongola is higher than the past five years.

Period Average ( 1965 – 2004 ) Mm3 discharge ( 2006 ) Mm3 July 5371 5735 Aug. 17056 21584 Sept. 16571 25117 July Sept. 38998 52436 Table 5-34: Nile Discharges During the Flood of 2006 Compared To Average at Dongola Station

FLOW VOLUME AT DONGOLA MAIN NILE 140 87.22

120

100 ) 3

60 THOUSANDS VOLUME (MILLION m 40

0 MAY. JUN JUL. AUG. SEP. OCT. NOV. DEC. JAN. FEB. MAR. APR.

Abs. Daily Max. (1945-2005) Abs. Daily Min. (1945-2005) Long Term Mean (1945-2005) Max. Year (1998-1999) Min. Year (1984-1985) Obs. Year (2006-2007) Figure 5-40: Accumulated Flow Volumes at Dongola, Main Nile

Total Flow Period (BCM) 1/5/2006 – 31/3/2007 87.22 1/5/2005 – 31/3/2006 67.76 1/5/2004 – 31/3/2005 59.96 1/5/2003 – 31/3/2004 72.57 1/5/2002 – 31/3/2003 55.87 Long-Term Mean (1945-2005) 69.71 Table 5-35: Comparison of Accumulated Flow Volumes at Dongola, Wmain Nile with Past Years

II. Lake Nasser At the first of August, the U.S level of the HAD was 168.69 m, then it rose to 175.19 m on 31/3/2007 with change in volume equal to 30.26 BCM. The HAD release during the entire time period from 1st August 2006 – 31st March 2007 was 48.51 BCM. To follow up the Lake Nasser status, comparisons has been done between the flood seasons in years

1984/ 1985, 1998/1999, 2005/2006, 2006/2007 these comparisons show several items: levels, contents, releases downstream HAD, evaporation losses and the total natural flow. To complete the estimates till the end of the water year, forecasting is used for the period 1st April – 31st July 2007 using the ESP method. Table 5-36 summarizes the situation of Lake Nasser for this year in comparison with past years.

Items 1984/1985 1998/1999 2005/2006 2006/2007 (Min (Max (Last Year) Year) Year) U.S. Level at the beginning of the 164.86 174.80 169.61 168.69 year (m) Contents at the beginning of the year 77.00 120.84 95.92 92.03 (BCM) U.S. Level at the end of the year (m) 156.37 175.82 168.65 173.12+ Contents at the end of the year (BCM) 51.03 126.16 91.87 112.42+ Max. U.S. Level (m) 164.86 181.30 174.72 176.53 Max. Surface Area (m2) 3567.09 6387.90 5124.26 5453.94 Evaporation Losses (BCM) 8.62 15.86 12.8 12.78+ Release D.S HAD (BCM) 55.50 71.22 57.5 55.50+ Release to Toshka (BCM) 0.00 8.25 0.00 0.00 Natural Flow (BCM) 56.06 121.56 82.91 108.8+ Table 5-36: Lake Nasser and HAD Situation In Comparison With Past Years

5.2.5. Hydrologic analysis summary Hydrological records at Bahirdar on Blue Nile River as it outflows from Lake Tana shows that high discharge than the long term mean values. This is reflected in the water level measured which reached 3.64 m while the long term recorded average annual daily maximum water Level is only about 3.48 m. The discharge of the Blue Nile at El Deim station was 44.923 million m3 in 2006, higher than the average by 45%. This flow was marked to be second highest measured next to the 1988. Similarly, this high flood is also reflected in Kharoum station the water level reaching 17.4 m which is highest ever recorded and it accumulated volume from 1st May 2006 until the 31st of March 2007 reached 58.24 BCM, 42% higher than the long term average volume This indicated that the Bule Nile has recorded the highest level ever in the last 90 years. But on the other hand, the discharges of the Dinder and Rahad rivers remained similar to the average, flows from these two rivers is relatively very small compared to the main blue Nile stream . Therefore, Blue Nile basin in general was subjected to high flood during the wet season which caused severe flood damages in Lake Tana basin flood plains and different states in Sudan along the banks of river. The monthly flow in the Baro River was a little above average in the normally peak month of September but continues increasing abnormally in October which causes overflow of the banks of the river and inundate large areas. Correspondingly, Gilo River was also distinguished to have large flows from June-October which contributed

extensively to the flood inundation of the low lands of the Baro-Akobo Basin. The White Nile River discharges at Malakal station is above the average by 9%. This is a combination of the flow from Sobat River and from the Sud-Swamps. This high flow is as the result of above normal rainfalls both in Sudd-Swamps and Baro-Akobo-Sobat basin as indicated in the rainfall analysis section of this report. The maximum stage recorded in Tekeze River at station Embamadre was 5.8 since re- instated in 1994. However, corresponding to the flood events of 2006 at Humera high flows above normal were observed specially two high flows, 9th and 26th of August 2006, which record water stages of 11.5 and 8 m respectively.In Atbara river , water levels remained around the average during the whole of July . In the second period of August water levels rose above average by 30% and continued as such until the end of September. Furthermore, annual discharge of Atbara was 14.2 BMC which is above the normal by 32.5%. The total accumulated flow volume of the main Nile discharges at Dongola station for this year (1st May 2006 – 31st March 2007) amounts to 87.22 BCM, which is around 25% above the long-term mean volume for the same period and about 19.46 BCM higher than the corresponding volume of last year. This High flow in the main Nile river is also reflected in the storage content of Lake Nasser at the end of the year it was 112.42 BCM which was higher than the long-term normal but less than the 1998/99 storage by 10%.

5.3. Flood Affected Sites and Flood Damage in 2006 As a result of 2006 flood extensive plain fields surrounding Lake Tana and Gumara and Rib Rivers in Amhara Regional State; low-lying areas falling along Baro, Gilo and Akobo Rivers in Gambella Regional State; and the Humera area of Tekeze basin near Sudan boarder are the flooded areas in Ethiopia. Likewise, this flood has also affected a wide area along the banks of the river Nile and tributaries mainly in four states of Sudan namely Khartoum state, Gezira state , Sennar state and Nile state, Figure. However, there has not been any reported flood damage or flood affected area downstream of HAD, in Egypt on 2006.

Figure 5-41: Flood Affected sites in 2006 flood

5.3.1 Inundated Areas in 2006 Flood i. Around Lake Tana

Lake Tana (Ethiopia): Due to overflow of Ribb and Gumara rivers and Lake Tana water levels, In Amhara region, 23 administrative units of 7 woredas surrounding Lake Tana have been affected with more than 10,000 people displaced and staying in temporary shelters. Some 12,769 individuals had been displaced due to the floods that hit three woredas of South Gondar zone since August 7. 13 kebeles of the Fogera, Kemkem and Dera woredas were flooded as Ribb and Gumara Rivers overflowed. As a result one person was killed and 45 houses demolished, adding that 2,478 domestic animals were also swept away and crops destroyed. 4,518 individuals were resettled and 5,371 hectares of land was washed away. Floods in September in Amhara Region affected about

100,000 people, displacing more than 37,000 people, and inundated more than 15,000 Ha of crop land (ENTRO, 2007). In the Fogera plains, found in the neighborhood of Lake Tana, floods killed three people, made 35,889 people homeless, inundated over 6,673 ha of cropland, destroyed more than 320 beehives, damaged a school and several water points, spoiled stored seeds, and deposited large volume of gravel and sand on farmlands (ENTRO, 2007).

Figure 5-42: Flood Affected sites in 2006 flood Around Lake Tana ii.Gambella Plain (Ethiopia):

Overflow of Baro River has caused flooding in the Region. Areas affected by the flood are Gambella Zuria, Jikawo, Itang, Lare and Gillo woredas. A total of 26,100 people are affected and 2 persons died 335 households about 1,675 people are displaced in Lare area (DPPA, 2006). Flooding in Gambella is normal but its magnitude in 2006 is above normal as a result high rainfall in the upper Baro Akobo basin. An area of about 300,000 to 350,000 ha is prone to flooding during the wet season.

iii.Humera (Ethiopia):

Overflow of Tekeze River affected 706 households (450 in Humera and 256 in Adi Goshu) Western Tigray Zone destroyed houses and damaged crop fields. A total of 3,530 people (2600 in Humera) are affected in this area. 406 ha of farmland belonging to 256 house holds in Adi Goshu damaged by rainfall related causes (DPPA, 2006).

Figure 5-43: Flood Vulnerable Areas in Ethiopia

Figure 5-44: Flood Vulnerable Areas in Ethiopia, in 2006 Flood

iv.Flash floods (Ethiopia):

Flash floods in several pocket areas of Central Tigrai (Tekeze basin) and Amhara Region (Abbay basin) have affected people and killed 2 persons. Flash flooding is as a result of short and intensive rainfall is a serious issue across Ethiopia affecting humans, livestock, infrastructure, and environment (creating undesirable wide gully erosion). However, the mitigation measures can be different from riverine flooding. The riverine floods are more of permanent type and their areas can be delineated and mapped. The flash floods are random and limited near their water courses. Their effect can be mitigated through watershed management, better urban planning to address the poor housing condition of the poor, and expanding the road network and bridges in the rural area.

v.Khartoum State (Sudan):

In Khartoum state there are many locations where property damage is experienced. Property damage includes residential areas, industrial areas, and public services infrastructures like schools health centers, roads and other. Umdurman city and Khartoum city were seriously affected during the 2006 flood. In Jebel Auila locality many villages along the White Nile were affected and many houses collapsed due to the fact that the flood waters surrounded these houses within Khartoum city there are many depressions and low lands filled with rain water or from the flood waters. The stay of the water in these depressions for many days without being drained caused environmental hazards .Some life losses also has occurred.

vi.Gezira State (Sudan):

Gezira state lies in central Sudan and many of is inhabitants live on the Blue Nile river banks. The state capital Wad Medani and many villages lie on the river flood plain and they are usually affected by the river high floods. Many residential houses, schools and hospitals collapsed in Wad Medani. Furthermore, vast area was inundated in the Gezira irrigated agricultural lands. Flood waters stayed for weeks in the flood plain and consequently the crops were damaged. vii.Sennar State (Sudan):

In Many villages, that lie on the banks of the Blue Nile, sever damage has happened to most of the residential houses and the inhabitants were displaced. Centers that used to give health service have become out of use due to the flood. Schools were destroyed. Moreover, irrigated agricultural areas were inundated which resulted in considerable damage in crops affecting the farmers economically.

Figure 5-40: Flood Affected Areas in Gezera, in 2006 Sudan

Figure 5-41: Flood Affected Areas in South Sudan, in 2006 Sudan

Nile River State (Sudan): The Nile river state is always under presume during the flood time. The main Nile River passes through the state and the full discharge of the river Nile is completed within the state. The flood plains are usually very much affected by high floods. 2006 flood is one of the highest. Many sectors were affected by the flood and it could be said that it was disastrous in many locations. Flood downstream of HAD (Egypt): The total natural flow is estimated as 108.8 BCM which is about 30% higher than the long term mean (84 BCM). However, because the last few years were all below average, Lake Nasser water level at the beginning of the year was adequate to accommodate the coming flood without taking any actions to spill water downstream or to the Toshka depression. The maximum recorded water level (176.53 m) during the 2006/07 water year did not reach the 178 m critical level to operate Toshka spillway. Therefore, there are no consequences for the current flood for Egypt. There are no flooded areas, damaged sites, or loss of life/property although these occurred in July and August in Ethiopia and Sudan due to intense rainfall and in November and December in Kenya and Tanzania for the same reason.

5.3.1. Sectors affected by the flood Many sectors were affected in the Sudan as well as in Ethiopia as a result of 2006 flood including residential houses, agricultural lands, Health Services, Educational centers, road Infrastructures, Water Supply and Water schemes and Inhabited Islands.

• Residential:

Fogera and Libo woredas: thatched roof houses whose walls are made of mud and wood are the ones most affected by flood. Many residential houses were destroyed partially and completely.

Khartoum State: Many houses lying in the flood plain were affected. Many are totally damaged while others are partially damaged.

Sennar State: There are many villages in Sennar state which lie on the Blue Nile banks .A great number of these villages lies in the river flood plain .During the high floods many residential areas are affected by the flood waters . The affect is rather severe because most of the houses are constructed from local material i.e mud . these houses can not resist the flood waters staying for some days . People are moved during the flood to higher lands and are supplied with tents for temporary stay.

Gezira State: Wad Medani, the capital of the state, and many villages are affected by 2006 flood. Many residential areas are affected by the flood and houses collapsed. Affected residents were supplied with tents for temporary stay in relatively higher locations.

River Nile State: Almost all villages and towns of the state lie on the main Nile river banks. This is because the river is running through a desert. Many of the towns and villages residential areas were affected by 2006 flood. Many houses collapsed and affected residents were accommodated in tents for temporary stay.

• Agriculture

Fogera and Libo woredas: The agricultural sector is the most affected as a result of flood inundation of large areas and crop failure.

Khartoum State :In the flood plain farmers use to cultivate the land with many short duration crops like vegetables , orchards are also grown in these low lands . Because of the long stay of the water in these low lands these crops are affected very mush the farmers since they lost their crops.

Sennar State: Sennar state is an agricultural state with a big area of irrigated sector withdrawing water from Blue Nile . The irrigated area in the state is almost 400000 acres. An appreciable area is in the flood plain. In this area farmers grow vegetables, banana orchards and fodder crops. The high flood of 2006 has very much affected these areas. Almost all the crops within the flood plain were damaged. The farmers became poor in just few days. The recovery is rather difficult especially regarding crops like fruits or banana since it takes a long time to get back into production.

Gezira State: Gezira State is famous for its irrigated agriculture . The cultivated lands are more than two million acres. Vast areas are cultivated in the Blue Nile flood plain. The flood of 2006 was a high flood and was able to cover a vast area under different crops. Flood waters stayed for weeks in the flood plain and consequently the crops were damaged. This has very much affected the farmers’ income and consequently their lives since the recovery is rather difficult.

River nile State: The Nile River State is famous for its high value crops irrigated from the Nile river. A big area lies in the flood plain. 2006 flood was disasterous in the agricultural sector. Many crops were lost and this very much affected the farmers in their income and consequently their lives.

• Health Services

The type and scale of occurrence of health and nutrition emergencies (HNEs) and the onsequence arising thereof following the current flooding has surpassed the capacity of he existing regular services (DPPA, 2006).

Khartoum State: Many health centers within the flood plain of the while Nile are damaged and they went out of service. This had affected very much the health services in the area knowing that health services need to be increased because of the many diseases which arose during the flood time.

Sennar State: The health services are also very poor in their structure. In most cases they are built from same local material ie red bricks with mud mortar. It is evident that these services centers either fall down or can fall down any time. Therefore they are not in use any more. This increases the suffering of the people bearing in mind that spreading of water born diseases is eminent.

Gezira State: In the affected villages health services centers were surrounded by the flood waters and they either collapse or about to do so. Consequently they are out of use. This affected very the health services which is faced with more diseases and more ill people due to the water born diseases. This added more to the suffering of the people in the area.

River nile State: The health sector services structures are poor . Water stayed within the buildings for weeks and this affected very much their capability to with stand the flood situation and consequently many of them collapsed . The health services are very much reduced , dispite the efforts made to compact the water born diseases .

• Educational Sectors:

Education sector will also be affected as beginning of school will be delayed until flood recedes and damaged class rooms need rehabilitation.

Khartoum State : Many schools collapsed because of the high water levels during the flood . Students are compelled to continue their education lectures out side their schools or lectures were stopped all together.

Sennar State: Most of the schools are built of local material ie red bricks with mud mortar .When these buildings are surrounded by the flood water for more than tow days they usually collapse. Therefore students are evacuated from these buildings .This affect very much the education sector and interrupt the study year. Because it is not easy to find rooms for these students so that they can continue their and if they find space it will be uncomfortable and not suitable for study.

Gezira State: Many schools were affected with the flood waters and some of them collapsed. It was difficult for the students to continue their study. Some temporary solutions were made to accommodate the students but they did not make the study as smooth as it was lack of concentration was always there.

River nile State: The education sector was very much affected by 2006 flood. The collapse of many schools in the villages is made it difficult for the students to continue their studies in a smooth manner although many solutions were offered.

Infrastructures: Rural roads have been damaged by flood making access difficult both for emergency requirements and isolating societies hampering market activities in both Ethiopia and Sudan.

Water Supply and Water schemes: Critical water supply interventions that include water tankering, provision of water bladders and tanks, and reinforcement of flood protection dykes are envisaged for three months (DPPA, 2006).

Inhabited Islands: In main Nile reach through the Nile river state there are many inhabited islands where people live and cultivate many crops .2006 flood was high and many islands were flooded and therefore their residents were evacuated to the banks . Here the loss is total and people lost everything they own.

5.3.2. Estimated Loss of Life and Property Damage

Due to the 2006 flood total of 75,800 people were affected in which 7 causalities were reported. Table 5-31 Summaries estimates loss of life and number of population affected as a result of 2006 flood in the three regions in Ethiopia.

No Region Vulnerable Affected* Died

1 Amhara 47,100 47,100 5 2 Tigray 122,300 2,600 - 3 Gambella 62,000 26,100 2 Total 231,400 75,800 7 Table 5-37 Population Affected/under Threat by Flood Disaster (DPPA, 2006)

The main health impacts are deaths, injuries, and mental health illnesses during the flood event itself, during the restoration process, or from knock-on effects brought about by damage to major infrastructure including displacement of populations. The risk of communicable disease outbreaks and malnutrition following flooding are greatly increased. Of the communicable diseases, diarrhea, malaria, acute respiratory illnesses, measles, and relapsing fever are the outstanding ones the occurrences of which are enhanced following floods (DPPA, 2006).

Khartoum state In Khartoum state there are many locations where property damage is experienced. Property damage includes residential areas, industrial areas, and public services infrastructures like schools health centers, roads and other. It can be listed according to location as follows: In Umdurman city many houses collapsed in Al Amirya locality when heavy rains fall in the area and no good drainage was there. The new constructed road system in the area

leads to the disaster because of lack of proper drainage system. Some of infrastructures in public services like schools and health centers also collapsed. Similarly in Khartoum city in Jebel Auila locality many villages along the White Nile were affected and many houses collapsed due to the fact that the flood waters surrounded these houses within Khartoum city there are many depressions and low lands filled with rain water or from the flood waters. The stay of the water in these depressions for many days without being drained caused environmental hazards .It to be mentioned that some life losses was there.

Region Zone Woreda Type of Consequences of Remarks disaster the disaster Amhara West Bahirdar River 941ha of different Livestock Gojam Zuria flood crops have been disease damaged outbreaks are anticipated 122 beehives damaged South Fogera River 6319 ha of different 70-100% crop Gondar flood crops have been damage and affected Livestock disease outbreaks are anticipated Libokemekem River 6,319 ha of 70-100% crop flood different crops have damage and been affected Livestock disease outbreaks are anticipated North Dembia River 444 ha of different 70-100% crop Gondar flood crops have been damage and affected Livestock disease outbreaks are anticipated Tigray Western Kafta Humera River 500 ha of different Flood crops have been damaged Table 5-38: Areas Affected/under Threat by Flood Disaster (DPPA, 2006)

Sennar States Many areas were flooded during the flood duration time causing damages for many sites in the different localities. About a total of 1406 residential plots were affected in Singa locality alone in which 1201 suffered total damage while the remaining were damages partially. In Dinder Locality 1239 houses were reported to be affected during the flood

leaving 865 with total damage. The number of residential places affected totally in Sennar State amount to 2656 from the three localities. The damaged sites can be listed as follows with the number of residential plots affected:

№ Village or Town Type of damage Total Total Partial 1 Um Benain 310 24 334 2 Sabonabi 133 93 226 3 Hai el Ingaz 194 - 194 4 El Azaza 382 - 382 5 Sairo elGaayeen 59 18 77 6 Tangaro 1 4 5 7 Kareema - 3 3 8 Barankwa - 3 3 9 Abu hugar - 2 2 10 El Daira 1 2 3 11 El Sidrat - 11 11 12 Singa wasat - 2 2 13 Wad el Gezoli 38 22 60 14 El Dbkara 23 9 32 15 El Rayat 11 8 19 16 El Ramash 41 - 41 17 El Shalal 8 6 14 Total 1201 206 1406 Table 5-39: Number of Flood Affected Residential Areas in Singa Locality

№ Village or Town Type of damage Total 1 Al Lakandi 17 23 40 2 Abu Teiga 62 44 106 3 Bunzuga 8 12 20 4 Al Gaziar (a) 183 - 183 5 Al Gaziar (b) 205 - 205 6 Shashina 21 23 44 7 Andarba 8 3 11 8 Ronga 10 9 19 9 El Suki el Turraa 4 2 6 10 El Suki el Aftah 22 16 38 11 Hillat Said 41 19 60 12 Abu Garaa 36 16 52 13 Maina el Mak 1 8 9 14 Bagi 8 4 12 15 Wad el Aies 9 11 20 16 Muna 34 - 34 17 Allah Maana 5 5 10 18 Abu el Banat - 2 2 19 Galadeema 16 14 30 20 Um el Gora 7 9 16 21 El higair 3 5 8 22 Gindeel - 2 2 23 Farahna 18 32 50 24 Um Sunut 60 8 68 25 El Azaza el rawaj 2 8 8 26 Karkoaj 3 17 20 27 Rumrukka 6 9 15 28 Mabrooka 72 28 100 29 El Debaiba - 7 7 30 Dontai 2 20 22 31 El khajolab - 22 22 Total 865 374 1239 Table 5-40: Number of Flood Affected Residential Areas in Dindir Locality

№ Village or Town Type of damage Total Total Partial 1 Kartekaila 9 2 11 Total 9 2 11 Table 5-41: Number of Flood Affected Residential Areas in Sinnar Locality

5.4. Differences between Current Flood and Previous Floods Flood in Lake Tana area Flooding in Lake Tana area has been noted since 1960, though no systematic data collection has been made. The three Weredas (Districts) most affected by flooding are Fogera, Libo Kemkem and Dembia (Seid, 2004).Difference of previous flood damages for five years are presented below in Table 5-42 in terms of number of people affected within different districts in Lake Tana area. Woreda Kebele Year 1996 1997 1998 1999 2001 Fogera Nabega 1 603 6 022 5 544 4 000 3 575 Abuwana Kokit 875 - - 2 580 2 074 Shina 635 - - - 160 Shaga 1 784 - - 2 657 2 200 Wagie Tera 5 548 5 000 5 567 5 238 1 717 Kidist Hana - - - 2 695 1 800 Libo Shina 160 Kemkem Gambiko 994 Genda Wuha 357 918 Teza Amba 1 270 1 716 Kabo 816 1 188 Tabega 1 072 Bura 1 000 Agdina Kirigna 1 450 Dembia Gura Amba Michael 3 886 Gura Amba Bahita 2 139 Debre Zuria 2 553 2 333 Achera 1 515 Adisge 3 237 Tana Woyine 3 738 Chanqua 1 505 Serbana Jeblo 3 591 Kesige 1 125 Janqua Abraham 587 Awuha Abo 1 128 Chenker 596 Table 5-42: Number Of Persons Affected Due To Flood And Received Relief Support By DPPC In Lake Tana Area Comparing 5 Years. Source: Woreda Agriculture and Rural Development Office and FSDPO in (SMEC, 2006).

Flood in Gambela area

The two most important causes of flooding in the Gambella area are flooding resulting from rivers overflowing their banks and flooding due to inadequate drainage. Riverine flooding is further aggravated by backwater effects from the Pibor and Sobat rivers. The city of Gambella is subject to occasional flooding caused by overflow of the Baro River and some of its tributaries. There are also other cities located on the north of the Baro river that are occasionally flooded (Seid, 2004). Table 5-44 compares flood damage of previous three years and is presented in terms of number of population affected due to flood in Gambella area. Similarly, Table 5-43 compares flood damage of four consecutive years in terms of damaged crops area.

Woreda Year Population Damaged property affected Gambella 1993 6 157 No systematic collection of data 1995 27 207 1996 10 000 following have been reported as Abobo 1993 500 Major types of property damages... 1995 33 906 - residential houses; 1996 - - house furniture Gog & Jor 1993 9 000 - crops 1995 8 510 1996 22 500 No data on human and livestock Itang 1993 28 431 casualties 1995 33 906 1996 24 267 Jikao 1993 27 236 1995 19 910 1996 10 000 Akobo 1993 12 921 1995 17 641 1996 18 000 Table 5-44: Flood Damages to the Gambella Area Severe flooding, estimated to be of annual exceedance probability 2%, occurred in 1988, with the following consequences (SMEC, 2006):

• The city of Itang and a considerable part of Gambella city were under water. • Several houses, public buildings, hotels, etc. were inundated in Gambella city. • The electric power station was inundated and was out of operation for one month. • Grain was lost with an estimated value of about 4.0 – 4.5 million Birr. • Loss of cattle, sheep and goats.

Year Type Of Crop And Land Size 2001 Gambella 100 ha. Maize Itang 340 ha. Maize 2002 Gambella 320 ha. Maize 2.2 ha. Sorghum Jori (Gilo) 50.8 ha. Maize 36 ha. Sorghum Jikao 35 ha. Maize 10 ha. Sorghum 5 ha. Cowpea 3 ha. Lweze Itang 149.26 ha. Maize 4.8 ha. Cowpea 2 ha. Seleit 2003 Gambella 0.5 ha. Maize 2004 Gog (Gilo) 104 ha. Maize Jikao 300 ha. Maize 2005 No report Source: DPPFSO (2004) in Teshome, 2005 Table 5-45: Summary of Crops Damaged by Floods in Gambella Flood in Sudan

The 2006 flood is one of the highest during the last 90 years. The total discharge of the flood during July, August, and September about 71.100 million meter cube measured at the upper reaches. The flood is above the average which is 56.043 million meter cube. It is ranks third in the recorded flood after 1988 and 1946 floods with 78000 million meter cube and 75000 million meter cube respectively. The 2006 flood started in early second week of July which is little late than the start of previous floods which usually starting in the first week of July. The flood recorded a level of 14.03 m on 25/8/2006 at El Diem station which is the highest in the history of the station records. The discharge at El Diem station reached 1022 million m3 on the same day which is above the average by 40% .It is to be understood that the Blue Nile at El Diem station had recorded the highest level and largest discharge for the last 90 years. The highest recorded level ever is 13.96 m on 3/9/1985 . This had lead to forced storage in Roseires reservoir. For Atbara river the flood levels continued to be around average during July and then moved above the average in the second half of August and kept level above average by 30 % until the end of September.

It was found from the beginning of the flood that it resembles the flood of 1988.Table 5-46 shows the water levels and discharges of the main rivers during the 2006 flood period (July – Sept) in comparison with 1988 flood and the average. July August September Water Discharge Water Discharge Water Discharge River Level Level Level Blue Nile ( El Diem station ) 10.24 8787 112.75 22082 12.19 14054 2006 flood 10.98 10.194 12.44 19903 11.74 15133 1988 flood 9.63 6837 11.48 15287 10.82 12091 Average Rahad river (El Hawata station ) 4.95 171 10.64 422 7.3 289.5 2006 flood 5.36 234 7.60 461 7.53 438 1988 flood 3.31 143 5.68 225.3 6.09 241 Average Dinder river (El gewaise station) 8.49 80 10.30 396 11.58 576 2006 flood 9.65 326 12.03 1575 12.54 1753 1988 flood 4.79 203 9.08 770 9.28 807 Average WhiteNile (Malakal station ) 12.12 2942 12.46 2324 12.68 3322 2006 flood 11.74 2675 12.15 3051 12.42 3301 1988 flood 11.56 2550 1197 2908 12.29 30.94 Average Atbara river Griba d/s 436.93 4522.2 437.66 4529.7 436.72 4520 2006 flood 436.15 4145 437.73 9789 435.95 3275 1988 flood 4502.3 2595 436.15 4514 434.53 4497.3 Average Main Nile ( Dongola station ) 11.01 2735 14.50 21584 15.7 25117 2006 flood 11.25 7328 14.94 24965 15.2 24363 1988 flood 10.33 5371 13.02 17056 13.04 16571 Average Blue Nile ( Khartoum station ) 12.95 3403 16.36 19808 16.34 185567 2006 flood 12.66 4821 16.25 22345 16.38 22135 1988 flood 12.27 3224 14.95 13967 14.70 11167 Average Table 5-46: Comparison of 2006 And 1988 Flood For Period of July – Sept and the Average

5.5. Reservoir Operation Strategies during the Flood In Ethiopia the Blue Nile River is regulated at the outlet of Lake Tana by Chara-Chara weir. The primary function of this weir is to regulate water for hydropower purpose. This weir can server to regulate water levels of Lake Tana

The Nile river system in Sudan is regulated mainly for irrigation and power by four reservoirs namely, Roseries , Sennar . KhasmelGirba and jebl Auila . The main purpose of these dam reservoirs is for agriculture and power generation. Flood control is rather impossible because of the small capacities of the reservoirs and the high silting in these reservoirs which affected the reservoirs capacities. The High Aswan Dam plays a key role in securing Egypt during floods and droughts. Impacts of historical high and low flood years were tremendously mitigated through operating the HAD in such a way that accommodates the surplus annual inflows to be used in low flood years Below is discussed the reservoir operation strategies for the reservoirs in the Nile system

Reservoirs in Sudan

The strategy of reservoirs operation during the flood time in mainly to pass the flood water which is highly silted. Filling of the reservoirs starts at the beginning of the recession period when the silt content is relatively small. Jebel Auila reservoir and because of the low silt content in its waters is used to control floods in the main Nile North of Khartoum when the high floods of the Blue Nile and Atbara river coincide . This is usually done by controlling the releases downstream the reservoir, which very much affects the water levels in the Main Nile. This is clearly noticed in the 2006 flood .

Rosaries Dam Month Per Water level m Release mm3 Evaporation rate mm3 Estimated Measured Estimated Measured Estimated Measured 1st per. 469.45 1697 4 July 2nd per 467.25 3194 3 3rd per 467.60 4026 3 1st per. 472.02 6050 2 Aug. 2nd per 469.99 7241 2 3rd per 469.98 7047 2 1st per. 471.55 5325 3 Sept. 2nd per 469.95 50.78 3 3rd per 472.45 3712 4 Table 5-47 Rosaries Dam Reservoir Operation Strategies

Sennar Dam Month Per Water level m Release mm3 Evaporation rate mm3 Estimated Measured Estimated Measured Estimated Measured 1st per. 417.65 1198 4 July 2nd per 417.75 2691 4 3rd per 417.75 3280 4 1st per. 417.11 5620 2 Aug. 2nd per 417.24 7193 3 3rd per 417.30 8347 3 1st per. 417.36 5923 4 Sept. 2nd per 417.65 5300 5 3rd per 418.68 3743 5 Table 5-48 Sennar Dam Reservoirs Operation Strategies

Khashm el Griba Dam Month Per Water level m Release mm3 Evaporation rate mm3 Estimated Measured Estimated Measured Estimated Measured 1st per. 467.73 46.03 3 July 2nd per 464.73 67.87 3 3rd per 464.2 63.40 2 1st per. 464.63 180.8 5 Aug. 2nd per 464.14 306.20 6 3rd per 464.66 250.80 5 1st per. 464.66 244.19 5 Sept. 2nd per 472.18 116.9 5 3rd per 773.79 42.5 6 Table 5-49 Khashm El Griba Dam Reservoirs Operation Strategies

Jebel Aulia Dam Month Per Water level m Release mm3 Evaporation rate mm3 Estimated Measured Estimated Measured Estimated Measured 1st per. 374.44 374.64 36.16 1.8 July 2nd per 375.18 375.74 9.05 1.8 3rd per 376.18 376.43 29.82 .9 1st per. 376.49 376.64 44.7 3.0 Aug. 2nd per 376.80 377.23 48.06 3.6 3rd per 377.29 377.50 46.06 3.0 1st per. 377.48 377.55 68.19 3.3 Sept. 2nd per 377.45 377.37 102.15 3.3 3rd per 377.30 11.9 3.6 Table 5-50 Jebel Aulia Dam Reservoirs operation strategies

High Aswan Dam Reservoirs Operation Strategies

The operating rules of the High Dam for over year storage include the release of Egyptian share of water only, which is fixed at an annual amount of 55.5 billion cubic meters. During high flood years, when levels exceed 175.0 m, the operation programs would be

prepared in the light of forecasts; and water in excess of the quota would be released so that the level upstream of the High Dam does not exceed 175.0 m on 1st August in order to allow for the reception of the new flood. As from 1st August, the water requirement are to be released and the levels to be observed. Then, the forecast of the natural river yield is carried out to make possible adjustments to HAD releases according to the expected levels upstream the Dam. In implementing these rules, the possibility of having to increase the releases from the reservoir has been taken into account. If the reservoir level exceeds the critical value of 178 m, water from the reservoir is spilled to Toshka depression. As mentioned earlier, it is possible that there will be a succession of low yield years that the reservoir levels continue to decrease to the degree of preventing Egypt and the Sudan from withdrawing their complete requirements, it was essential to put a sliding scale for the water requirements of the two countries to guarantee that live storage in the reservoir would not be exhausted. Recently, the HAD control model was developed with the aim to quantify the operational tradeoffs of the HAD and to identify the release sequences that realize the selection of the decision maker. The advantage of HAD control model is that it makes use of the forecasted inflows in producing the tradeoffs for both cases of high and low floods. During high floods, tradeoff is between potential Toshka spills and energy generation. On the other side, as future conditions are unknown and a decision which minimizes Toshka spillage may lead to unexpected reservoir drawdown and a potential loss of energy in the longer term. It would, thus, be interesting to also quantify the tradeoff between short-term and long-term energy generation. During low floods, the management authorities must decide whether it is preferable to continue to release the water requirements and risk facing sever water shortages in the near future, or start scaling back the releases to maintain reduced water supplies longer. Again, this choice is complicated by the uncertainty of coming inflows necessitating that this tradeoff be cast in a probabilistic form. Thus if we continue to release the water requirements, the probability that sever shortages will actually occur is high. If however we implement some strategy of release reduction, we can trade-off the high likelihood of sever shortages for the certainty of low to moderate deficits. For this particular flood year 2006, the levels of the HAD were in the moderate range (not extremely high or low) and the forecasted flows was also higher than average but not extremely high to trigger extra spillage. For that reason, the operation of the dam was driven by the water requirement with the total amount of 55.5 BCM. The simulation model of HAD with scenarios used for Lake Nasser simulation, and the results of the simulation of HAD for the flood year of 2006 is described in the Egypt flood report [3].

6. Measures Taken for Flood Mitigation and Flood Response

6.1.Flood Mitigation Measures Taken This section discusses the structural as well as the non-structural measures taken in the region for flood protection. Structural measures include structural interventions such as dams, dikes, flood control reservoirs, i.e. constructing reservoirs where the excess flood waters can be stored, and then released as a controlled flow to help alleviate the flood problem by attenuating flood peaks, dikes, etc… Non-structural measures include early warning, spatial planning, zoning, ‘living with water’, insurance, capacity building and other measures that don’t not involve structural interventions.

6.1.1. Structural Measures There are no significant flood protection structures in the Ethiopian part of the Eastern Nile Region. In the plains surrounding Lake Tana some farmers have attempted to reduce the hazard to their crops by crude low embankments made from readily available local materials such as mud and sticks, but these are poorly effective and are easily overtopped and damaged or collapse under prolonged immersion. However, on going dam construction and studies will have impact in mitigating flood damage by absorbing peak floods, nevertheless, high spillway discharge releases may affect downstream settlements. Early warnings before high spillway discharge releases can be given to communities to minimize hazards. The following are dams commissioned, under construction or studied in the Eastern Nile Region.

Name River Capacity Catchment’s Year (m3x106) Area (km2) Commissioned Abobo Alwero (Baro-Akobo 74 1 043 c. 1995 basin) Chara-Chara Weir (L. Abbay 9 000 1 15 300 1999 Tana) Finchaa Finchaa (Abbay 900 2 500 1973 tributary) Koga Koga (tributary to L 77 164 Under Tana) construction Tekeze Tekeze 9 293 30 390 Under construction 1. Capacity of Lake Tana

Table 6-1 River Regulation in Ethiopia (source: SMEC, 2006)

Dam Stream Lat. Long Catchment Nominal (º N) (ºE) Area Capacity (km2) (MCM) Gumara B Amora 37.79 11.74 401 340 Mawanya Ribb Ribb 40.00 12.04 677 173 Megech Megech 37.47 12.53 416 203 NOTE: A dam is also being investigated on the Gilgel Abbay River. Table 6-2: Irrigation Storages Being Investigated (source: SMEC, 2006) A tunnel is currently being under construction between Lake Tana and the Beles River tributary to tap the hydropower potential of Lake Tana. The implementation of this project will definitely reduce flood damage due to lake level rise. Small-scale structural intervention such as elevated all-weather roads, raised earth platforms, drains, levees, gabions, etc, is under way. Local structural measures to stabilize the river banks and to increase the discharge capacity of the river are seen as one solution to protect agricultural lands from regular damage (SMEC, 2006). The Major structural measures taken for flood mitigation in Sudan consist of the following:

• Supply people with tents, water supply and sanitation services. Supply pumping units to withdraw water from depressions at permanent locations. • Strengthening of existing earth embankments and rehabilitation of the surface drainage system in the cities. • Construction of new structures such as drains at location of low lands, flood protection retaining walls at known locations and earth embankments.

6.1.2. Non-Structural Measures Non-Structural measure taken in Ethiopia involves coordination of various stake holders working in water and meteorology mainly they are: MoWR who operates all hydrological gauging stations in the country, NMSA who operates almost all meteorological stations, EEPCO who operates dams of hydropower projects, and DPPA who is responsible for early warning systems and disaster management need to work closely to establish early warning system. If well organized system is setup involving the above agencies and communication with local authorities in flood prone areas flood disaster could be reduced to manageable size. Except some attempts to forecast flood up stream of Koka dam in Awash basin, by Hydrology Department (HD) of Ministry of Water Resources, no practical flood forecasting capability currently exists in Ethiopia. The HD uses Danish Hydraulic Institute’s (DHI) MIKE 11 model for flood forecasting. NMSA has few weather stations that can report in real time. Both NMSA and HD need considerable institutional upgrading to acquire genuine capability in flood forecasting. The FPEW study (SMEC, 2006) gave the following key recommendations to establish Flood Forecasting Center (FFC).

• establishment and support of a Flood Forecasting Center in Addis Ababa; • Installation and operation of a real-time reporting network of rainfall and river gauges in Ethiopia. The FFC in Addis Ababa would greatly improve the capacity of Ethiopia to plan for and manage floods. The initial focus in Project implementation should be first on provision of flood forecasting services for the Fogera plain and Dembiya woreda on the shores of Lake Tana, second on forecasting for Gambella and district and for dam operations of existing reservoirs in the Eastern Nile basin, and third on forecasting flows in the Abbay and Tekeze rivers. For effective outcomes to be achieved, the flood forecasting must be linked to a flood warning system and a flood emergency response system capable of rapid response remote from Addis Ababa (SMEC, 2006). Some non –Structural measures are taken in Sudan these include

• Training and public awareness: Perform training for technicians involved in the flood protection activities for good and efficient performance. Alleviation of community awareness regarding surface drainage system • Studies such as morphological effects for the Nile and tributaries and effects at location of pumps, Restudy of the river routing reaches, Study of the NILE and tributaries relief projects have also been carried out. • Identification of the flood plain zones and the low lands and preparation of their contour maps using modern technologies, carry out of bathymetric surveys for all dams reservoirs to monitor the silt deposition and know about reservoir capacity. Execution of the surface drains already studied and designed. Introduction of automatic gauging systems especially at import out gauge station. • Emphasizing importance of continuous inspection for the flood protection works • Rehabilitation of the early warning system • Coordinator with the states authorities for inspection of the protection works. • Prevention of unplanned housing especially in khors flood plains • Preparation of local act based on general heath law which deals with wrong acts during flood time • Early preparation for the flood season In Egypt, the High Aswan Dam plays a key role in securing Egypt during floods and droughts. Impacts of historical high and low flood years were tremendously mitigated through operating the HAD in such a way that accommodates the surplus annual inflows to be used in low flood years. In additional to that, Egypt does consider research studies for long term mitigation plans against high downstream releases in flood prone areas. Past experiences have proved noticeable positive effects of implementing outcomes of such research studies in actual operation. Indeed the flood of year 2006 is considered high flood (108BCM). However, Egypt was not affected because the initial level of the lake at 1st August was considered relatively low (168.69 m). Therefore, no mitigation measures were taken during the current flood year 2006/07.

6.2. Flood Response

6.2.1. Flood Response in Ethiopia For understandable reason, unlike drought-induced food shortage crises, there is less experience and poor preparedness in Ethiopia against fast-onset disasters, including flooding. In some areas of the Amhara floodplains, peasants will build levees around their land before the rainy season, but these are seldom effective to withstand high floods. Therefore, efforts to alleviate the consequences of flood damage are concentrated on relief items such as evacuating people from the flooded area establishing temporary camping sites and supplying food and non-food items. Rehabilitation of flood affected sectors. The Regional Health Bureaus and NGOs such as UNICEF, WHO, MSF, etc. were currently working on treatment, prevention and control including IEC materials in the affected areas (DPPA, 2006). The Government and its partners made concerted efforts to respond to the flood and drought crises and to minimize the adverse effects of the disasters. Relief food, shelter materials and essential household items, potable water tankering and health care were provided to the victims as well as veterinary services to their livestock in a timely manner (DPPA, 2006). The nationwide flooding increased incidences of waterborne diseases including Acute Watery Diarrhoea (AWD). AWD first appeared in Gambella Region in April on the heels of a similar epidemic in neighbouring Sudan. The nationwide flood crisis and the AWD epidemic reinforced the need for better preparedness for all emergencies, particularly those of fast on-set such as flood and health epidemics. There is a need for an enhanced sectoral early warning mechanisms and contingency planning to facilitate early response and support for early recovery (DPPA, 2006). The most basic nonfood relief items sought include, among others: plastic sheets and tents for sheltering, lifesaving jackets, plastic boats, blankets, and household utensils, such as cooking pots, ladles, jerry cans, jogs, plastic plates, cups, bowels, etc. Training to community members to protect against malaria and other flood-related water-borne diseases (DPPA, 2006), is needed.

S.No Region Beneficiary Cereal Edible Blended Biscuits Pulse Total Number Oil Food 1 Amhara 47,100 2,119.5 63.6 222.5 35.3 212.0 2,652.9 2 Tigray 2,600 117.0 3.5 12.3 2.0 11.7 146.5 3 Gambella 26,100 1,174.5 35.2 123.3 19.6 117.5 1,470.1 Total 75,800 3,411 102.3 358.1 56.9 341.2 4,269.5 Table 6-3: Food Requirement for flood affected areas in Metric Tone (MT)

Emergency seed intervention: The intervention focuses on the provision of short season varieties of different crops for replanting of damaged fields during the remainder rainy season as well as on residual moisture following cessation of rainfall and also when the floods recede. Vegetable seeds and seedlings of different fruits will also be distributed for planting during the Bega season using available irrigation schemes (DPPA, 2006).

Emergency animal support: Livestock are the main means of crop production and livelihood in the affected areas. The high occurrence of high flooding and eventually bringing and concentrating the livestock from different areas in one place so as to get them away from otherwise imminent risk, often induce stress and aggravate livestock diseases (anthrax, pasturellosis, CBPP, CCPP), parasitic infestations and also favor the outbreak of Tran boundary and vector-born animal diseases. Therefore, it is very important to prevent these risks through vaccination and treatment. To this effect, emergency animal health intervention is envisaged to save the livestock assets in the disaster affected areas (DPPA 2006).

6.2.2. Flood Response in Sudan Flood response measures have been taken in Sudan for flood affected states these response measures have been outlined below for the two flood affected states, Khartoum and Sennar State. Khartoum State: In Khartoum state the following food response measures were taken:

• Construction of new drains to drain water from depressions within the cities • Transfer of people from low lands ( flood plain ) to relatively higher lands • Pumping of flood and rainwaters from low land within the cities in the streets. • Transfer of drains clearance material away from the drains so as to open the way for water to find its way into the drains. • Pumping of water from the big drains which use to bring flood water into the low areas when flood level is high • Clearance of the drains from trashes which used to be thrown into drains by people misbehaving. • Supply of people with tents for temporary loading

Sennar state: In Sennar state the flood high committee had responded as follows:

• supply of sags to the affected reaches to be filled with soil for flood protection • make available earthmoving machinery to places of need • supply of earth material using tippers ( 2441 times ) this mainly in Singa town to extent the old embankment and strengthen it . • construction of protection embankments at different villages e.g.Umbenain , El Sabonabi , Sairo , wad El Gizoli , El Dabkara , Wad el Aies , El Gazair , Maina , Hillat Saed , El Suki and the Hai El Genaina. • Call for all the Ministry of physical planning and public utilities works to be alert. • Supply of tents, pumping units, mosquito nets etc. to help people who lost their houses • Preparation of camps which includes tents, health services, water supply, sanitation services and some food supply a period of time. • People living in the flood plain are offered new locations for their new homes including necessary services. • The limit of the flood was identified so that people will not be allowed to reside with the flood plain.

• A model design for health centre, water yard m rural house, two class and office, a complete preliminary school is to be prepared.

6.3. Cost Incurred for flood mitigation and response A Total of 470,000 UDS is estimated for Water supply rehabilitation works alone to provide potable water to flood affected areas in Ethiopia, Table 6-4 . Furthermore, rehabilitation requirements including housing, water supply, agricultural, educational, health services, and infrastructural rehabilitations needs were included in the Joint Flood Flash Appeals. The two Appeals sought a total of US$ 8.7 million to meet the emerging rehabilitation requirements. In addition, further assessments were conducted raising the total rehabilitation requirement to US$ 22 million, out of which over US$ 7 million, constituting 32 percent was contributed (DPPA, 2007). The flood appeal includes rehabilitation requirements out side East Nile Region.

S. Region No of Activities Unit Qty Total No Benefi- Cost ciaries (Birr) 4 Amhara 33,000 Drilling of three motorized deep No. 7 3,651,340 and four shallow wells 6 Tigray 4,000 Drilling of one deep motorized No 2 500,000 and one shallow wells Total 37,000 4,151,340 Table 6-5 Requirement for Potable Water Supply Rehabilitation (DPPA, 2006)

In Sudan, a total cost of 595,000 USD is roughly estimated for flood mitigation measures. The estimated amount includes the cost of earthmoving machinery for emergency works, pumps systems construction of earth embankments, retaining walls and other small protection works. Table 6-6 Summarizes the cost incurred for mitigation measures for the four flood affected states in Sudan.

State Machinery Pumps Earth Total embankment Khartoum 60.000 10.000 180.000 250.000 Sennar 40.000 10.000 90.000 140.000 Nile river 50.000 15.000 40.000 105.000 Northern - 20.000 80.000 100.000 Table 6-7 Cost Incurred For Mitigation Measures (USD)

7. Preparedness for the Coming Floods Though local people in flood affected areas in Ethiopia have some adaptive capacity to low level flooding they are highly vulnerable to large floods. Increased population concentrations in flood prone areas, as well as land use and river channel changes are the main contributors to this enhanced vulnerability. While Ethiopia’s humanitarian structure is better prepared for slow onset emergencies, the various hazards experienced in 2006 have emphasized the need for comprehensive disaster risks management and mitigation. The nationwide flood crisis and the AWD epidemic reinforced the need for better preparedness for all emergencies, particularly those of fast on-set such as flood and health epidemics. There is a need for an enhanced sectoral early warning mechanisms and contingency planning to facilitate early response and support for early recovery (DPPA, 2006). DPPA deals with response to flood by coordinating with other Ministries with which they work directly during the flood season (June-October). The Natural Disaster Prevention and Preparedness Committee (NDPPC), comprised of Departmental Heads is the peak body for the coordination of flood disaster response and the authority that is empowered to “declare a natural disaster”, which it does on the advice received from the National Early Warning Committee (NEWC). The NEWC comprises senior officers from several Ministries with a role in natural disaster issues (SMEC, 2006).

The following needs have been identified as most relevant to communities located within these flood-risk areas of Ethiopia (SMEC, 2006): a. Early warning systems: greater access to information about imminent serious flooding. b. Reliable communication systems (mobile phone networks, radio, television) to facilitate information sharing and post-flood relief. c. Training and education to raise awareness, dealing with a broad range of issues pertaining to flood preparedness, management and relief. d. Health (human and animal): this is a critical area focusing on preventative care with a specific focus on malaria prevention/treatment/eradication and the prevention/treatment of other water-borne diseases. e. Water and sanitation: public education on water treatment to counter periods when latrines and water sources are flooded or contaminated by stagnant water. f. Institutional strengthening at community/Kebele level using local knowledge, strategies and capacities to increase self-reliance. g. Improved resources to manage post-flood conditions: e.g. pumps, better drainage systems, boats for emergency evacuation, etc. h. Increased access to government or public flood management and emergency relief services, particularly in remote rural areas.

i. Training in sustainable house design and construction based on more effective use of local resources and capacities. j. Development of more effective water harvesting/irrigation systems to exploit floods. k. Expansion of flood-based crop cultivation such as rice (particularly in Dembiya Woreda). Lessons have been learned from many high floods experience in the Sudan. These have enabled the states officials, involved in the flood relief and protection works, to device ways to prevent damage due to further floods events. Following points have mainly been mentioned in flood reports of officials regarding preparedness for incoming flood.

l. Making available earthmoving machinery eg excavators, bulldozers , motor graders , loaders , compactors , tippers etc. m. Making available pumps of different sizes fixed and mobile ones with all necessary accessories. n. Making avail a responsible number of tents for temporary use during the flood period o. Making alert the health sector for quick movements during the flood period and immediately after the flood to contain water borne diseases. Preparedness for the next flood in Egypt is routinely done through maintaining the operating rules of the High Dam. During high flood years, when level exceeds 175.0 m, an operation program would be prepared in the light of forecasts; and water in excess would be released so that the level upstream of the High Dam does not exceed 175.0 m on 1st August in order to allow for enough room to accommodate the new flood. As from 1st August, the water requirement are to be released and the levels to be observed. Then, the forecast of the natural river yield is carried out to make possible adjustments to HAD releases according to the expected levels upstream the Dam. In implementing these rules, the possibility of having to increase the releases from the reservoir is taken into account. On the other hand, if the reservoir level exceeds the critical value of 178 m, water from the reservoir is spilled to Toshka depression. As mentioned earlier, it is possible that there will be a succession of low yield years that the reservoir levels continue to decrease to the degree of preventing Egypt and the Sudan from withdrawing their complete requirements, it was essential to put a sliding scale for the water requirements of the two countries to guarantee that live storage in the reservoir would not be exhausted.

References [1] Flood Analysis report ,Ethiopia [2] Flood Analysis Report ,Sudan [3] Documentation and Analysis of Nile Hydro-meteorological Conditions during the 2006/07 Hydrological Year,Egypt [4] ENSAP Joint Multipurpose Program, One System Inventory Synthesis Report,2007 [5] Sayed, M.A.A. (2006), Flood Preparedness and Early Warning System, Arab Water, Cairo, 2006. [6] Hartfield (2006), Rapid Assessment of 2006 floods