Dam Breach Analysis of Wadi Al Arab Dam Using GIS and HEC-RAS

Jordan University of Science and Technology Civil Engineering Department Graduation Project II

2105

Huda Ahmad Hajjaj

20100023113

Yazan Rafiq Al Haddad

20102023117

Supervised by:

Dr. Samer tallouzi 1

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Table of Contents:

1.0 Introduction 1.1 1.2 1.3

………………………………………………………..5

Abstract…………………………………………………………………...5 Wadi Al Arab Dam………………………………………………...….5 Choosing Wadi Al Arab Dam……………………..………………6

2.0 Dam Breach Analysis……...……………………..8 2.1 2.2 2.3 2.4

Dam Breach Definition…………………………………..8 Objectives………………………………………………...8 Dam Breach Modeling Scenarios…………………...……9 Choosing a Dam Breach Modeling Scenario……………13

3.0 GIS and HEC-RAS Approach......................15 3.1 3.2

GIS and HEC-GEORAS……………………….......……15 Analysis using GIS and HEC-GEORAS…………….....16

3.3 3.4

Dam Breach Parameters and Calculations……..………18 Flood Analysis Using HEC-RAS……………………….20

4.0 Results and Discussion……………………...….23 4.1 4.2

Results……………………………………………….......23 Damage Assessment………………………….…………28 3

4.3 4.4

Conclusion………………………………………..……..28 Recommendations………………………………………28

References…………………………………………………..29

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1.0 Introduction 1.1 Abstract This work describes the analysis of a dam break in the aspects of simulation and various parameters. The parameters and outflow predictions are mainly for the understanding of dam break mechanics, which is essential for the dam break analysis, and eventually determine the flood in each river station for a specific interval. In this work we use GIS model tightly coupled with the HEC-GEORAS extension based on available geometry data by considering Wadi Al Arab dam as study area. It was modeled using GIS and analyzed using these. HEC-RAS is a steady flow hydraulic model designed to aid hydraulic engineers in channel flow analysis and flood plain determination. Here, parameters associated to specific spatial features having coordinates are located on object classes and connected its corresponding features like by means of database relationships.

1.2 Wadi Al-Arab Dam This project is a part of a study conducted to analyze the dam breach of Wadi Al-Arab Dam and provide a scenario for the breaching of the dam.

Wadi Al-Arab Reservoir is located in the northern part of Jordan Valley, about 25 km from Irbid City. The reservoir water comes mainly from the King Abdallah Canal and partially from precipitation. This reservoir is mainly used for irrigation. However, it supplies drinking water during the water shortage periods for the Northern Jordan Rift Valley, Salt and Amman.

The catchment area of Wadi Al-Arab measures 267 km². The average amount of precipitation ranges from 500 mm over the highlands west of the city of Irbid, to 350 5

mm in the town of North Shuna in the Jordan Valley. The potential evaporation ranges from 2,000 mm/year in the northwest, to 2,400mm/year in the southwest of the catchment. The average discharge of the wadi is around 28 MCM/year equally distributed between flood and base flows.

1.3 Choosing Wadi Al Arab Dam Wadi Al Arab Dam is one of the largest and most important dams in north of Jordan.

We chose this dam for our study after considering so many factors.

Based on our researches we didn’t find any study about breaching of the dam though it’s very important to consider it to estimate the magnitude of potential floods due to dam breach, hydraulic models can be developed to simulate downstream floods, which can provide insights regarding the potential downstream hazards to life and property, the population affected by the flood scenario about 8000 capita.

Another factor we took it in consideration is that the area of the dam is a seismic action area. Because the dam lies along the tectonic plate boundary between the African Plate and the Arabian Plate.

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Figure 1.1 Study Area within the region

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2.0 Dam Breach Analysis 2.1 Dam Breach Definition Dams are built for water supply, hydro-power, flood control, etc. However, dams may cause catastrophic damage to human life and property if they collapse. In order to be able to assess the consequences of a dam failure, simulation of the flood caused by a dam break is required.

The purpose of the dam break analyses has been to illustrate how the flood wave propagates and attenuates along the North Shuna in the Jordan valley. In the present analyses the Hec-RAS model is used for simulation of the flood wave caused by dam failure. This model is one of the most widely accepted models of its kind.

2.2 Objectives The two primary tasks in the analysis of a potential dam failure are the prediction of the reservoir outflow and the routing through the downstream valley to determine dam failure consequences. The routing of large floods is a well developed science, although some areas of uncertainty do remain . Great progress is also being made in this field, as geographic information technology and computing resources continue to improve, making more sophisticated flow modeling possible, and making it easier to integrate flow information with geographic information to simulate dam failure consequences. The greater source of uncertainty in most situations is the prediction of the reservoir outflow, especially for embankment dams in which dam failure is usually the end result of a progressive erosion process that is itself very complex and difficult to accurately model. Prediction of the reservoir outflows especially important

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when the population at risk is located close to the dam, where peak attenuation and other flood routing effects have not yet taken place. As our nation’s population continues to grow and urban areas expand into formerly rural areas, this situation is becoming ever more commonplace.

2.3 Dam Breach Modeling Scenarios To determine the scenario that will we use for our modeling, we viewed a various number of studies. Mechanisms that cause dams to fail include overtopping of an unprotected portion of the dam during a significant hydrologic event, piping, liquefaction of foundation from seismic activity, slope/stability issues, uncontrolled seepage, and other deficiencies. The resulting flood waves, including those from domino-type or cascading dam failures, should be evaluated for each site as applicable. Acceptable models and methods used to evaluate the dam failure and the resulting effects should be appropriate to the type of failure mechanism.

From our reading to these different studies, we choose some of these scenarios that might be applicable for Wadi Al-Arab Dam region. These scenarios are: 1. Seismic action dam failure 2.

Overtopping dam failure

3.

Piping dam failure

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Figure 2.1 Types of Dam Failures

Table 2.1 Causes of Dam Failure 1975-2011

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The primary criterion for assessing dam failures scenario is due to Seismic Action.

We can define the seismic action by the dam failure induced by an earthquake that causes weakening of the dam’s structural components, embankment, foundation, and/or abutments. The size of seismically induced floods and water waves that could affect a site from either locally or distantly generated seismic activity must be determined In regions where two or more dams are located close together, a single seismic event shall be evaluated to determine if multiple dam failures could occur.

Earthquake hazard assessment is an integral part of dam safety assessment, especially for dams located in seismic zones like Wadi Al Arab Dam. Extreme and rare earthquakes may occur randomly in time and space. These events could cause partial damage or collapse of dams. The losses associated with the partial damage and collapse may be small or large depending on the geographic condition, environment, infrastructure, and number of people exposed to the damage or collapse of the dam. The losses may increase as the earthquake intensity increases.

The seismic evaluation requirements should consider both the expected losses of given earthquake intensities and the probabilities of those intensities occurring or being exceeded during specified time intervals.

The breach caused by earthquake can lead to other types of breaching like overtopping and piping.

Overtopping is defined as the point at which an unprotected portion of the dam, or portion of the dam structure not designed to convey floodwater, is subject to an extreme discharge/runoff combined with clogging of the spillway or insufficient spillway capacity caused by a flood larger than the design flood or malfunction of spillway gates.

Overtopping occurs when the water surface elevation in the reservoir exceeds the height of the dam; water can then flow over the top crest of the dam, an abutment, or a low point in the reservoir rim (Overtopping usually results from a design inadequacy of the dam/spillway system and reservoir storage capacity to handle the resulting 11

flooding event. A failure may also occur when a reservoir’s outlet system is not functioning properly, thereby raising the water surface elevation of the dam.

Figure 2.2 Overtopping Failure

Another important type of failure is Piping . This could occur when concentrated seepage develops within an embankment dam. The seepage slowly erodes the dam embankment or foundation leaving large voids in the soil. Typically, piping begins near the downstream toe of the dam and works its way toward the upper reservoir.

As the voids become larger, erosion becomes more rapid. Once the erosion reaches the reservoir, it can enlarge and cause catastrophic dam failure.

Piping failures typically occur only in earthen dams. The failure begins when water, naturally seeping through the dam core, increases in velocity and quantity to begin eroding fine sediments out of the soil matrix. If enough material erodes, a direct piping connection may be established from the reservoir water to the dam face. Once such a piping connect is formed, it is almost impossible to stop the dam from failing.

Piping failures begin at a point in the dam face and expand as a circular opening.

When the circular opening reaches the top of the dam, it continues expanding.

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Figure 2.3 Piping Failure

2.4 Choosing a Dam Breach Failure Scenario

After studying the three expected scenarios we figured out that choosing any of the scenarios won’t affect the methodology in the HEC-GeoRAS modeling.

We decided to choose a Seismic action dam failure scenario due to the fact that the Jordan valley, which constitutes a major part of the Dead Sea Transform (DST), is the most seismically active region in the Middle East, having a history of four thousand years of documented destructive earthquakes. Regional cooperation is a basic requirement for a better assessment and, consequently, mitigation of the possible effects of earthquakes that will most definitely occur in this region. The occurrence of strong earthquakes along the Dead Sea transform fault system becomes a major threat to the safety, social integrity and economics forth peoples of the Middle East. Extensive damage to the dam and appurtenant structures is possible under severe seismic shaking. However, there is no known method of measuring and 13

collecting data that would alert operations staff to the danger. Earthquakes are not predictable and therefore do not lend themselves to a monitoring program.

Failure mechanisms due to seismic activities include: -

Slope instability

-

Permanent deformations

-

Fissures or cracking

-

Differential settling

Figure 2.4 Earthquake Failure

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3.0 GIS and HEC-RAS Approach

3.1 GIS and Hec-GeoRAS An analysis of dam failure models provides a scenario generating tool for identifying the resulting hazards. Floodplain managers and emergency management personnel may then utilize the resulting contingencies to protect against the loss of life and property damage. The Hydrologic Engineering Center’s River Analysis System (HECRAS) can be used in concert with HEC GeoRAS to develop a dam failure model.

HEC-GeoRAS is used to extract geometric information from a digital terrain model and then imported into HEC-RAS. The use of geographic information systems (GIS) and has become more mainstream and data have become more readily available. In particular, the availability of terrain data has improved the proficiency with which skilled engineers can develop hydraulic models capable of simulating a dam breach scenario and evaluating the resultant flood wave. The use of HEC-RAS in modeling dam failure scenarios and HECGeoRAS in model development and analysis of the flooded area using a GIS is discussed.

Steady flow simulation of the dam break is performed using HEC-RAS and results are mapped using the GIS. Inundation mapping of water surface profile results from dam failure models provides a preliminary assessment of the flood hazard and provides insight for emergency preparedness. The process for gathering and preparing data, creating an unsteady-flow model in HEC-RAS, entry of dam breach parameters, performing a dam failure analysis, and mapping of the flood progression is discussed.

HEC-GeoRAS is a set of tools specifically designed to process geospatial data to support hydraulic model development and analysis of water surface profile results 15

GeoRAS assists engineers in creating datasets (referred to collectively as RAS Layers) in ArcGIS to extract information essential for hydraulic modeling.

Table 3.1 Description of RAS layers

3.2 Analysis using GIS and HEC-GEORAS Extension GIS and HEC-GEORAS consist of a set of tools and procedures for extracting primarily topographic data within the GIS platform and importing directly into a HECRAS geometric file. HEC-GeoRAS allows for a quick and seamless conversion of electronic contour data into a cross section format used by HEC-RAS to facilitate the calculation of water surface elevations.

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After completing the analysis using GIS we exported the file into HEC-RAS

Figure 3.1 a map shows the cross sections, the flow bath and the banks 17

Figure 3.2 A map shows the cross section, flow path and banks with the main roads

3.3 Dam Breach Parameters and Calculations

Breach shape is assigned or pre-determined depending on the model used. Usually, this shape is assumed to be triangular or trapezoidal. The HEC-RAS model uses a trapezoidal section to simulate the final stages of the dam breach.

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Empirical relations for peak breach outflow estimation have been developed through simple regression analysis of compiled case study data from real dam failure events.

Wahl (2004) presents a compilation and a thorough evaluation of several of the derived equations. Three of the equations presented by Wahl were used to estimate the maximum breach outflow for the three scenarios modeled in this study to verify the peak breach discharges generated by the simulations.

The three relationships are based on studies performed by the U.S. Bureau of Reclamation (1988), MacDonald and Langridge-Monopolis (1984), and the Soil Conservation Service (1981).

The Bureau of Reclamation (1988) presents an empirical equation for peak discharge estimation using water depth above the breach invert through the following equation.

The Soil Conservation Service (1981) proposes a similar relationship using the same parameters with only a small variation in the coefficient. The suggested equation is presented below.

MacDonald and Langridge-Monopolis (1984) incorporate the volume of water stored above the breach invert (�� ) into the equation. The resulting relationship is similar to the previous two and has the form:

The table below summarizes the dam parameters and the dam failure peak discharge estimations made using the previous equations. The peak discharges computed by the HEC-RAS model are also presented for comparison.

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ℎ�

60 đ?‘š

��

18 Ă— 106 đ?‘š3

Table 3.2 Parameters of the Dam

The Bureau of Reclamation

đ?‘„đ?‘?

37206 đ?‘š3 /đ?‘

The Soil Conservation Service 32336 đ?‘š3 /đ?‘

MacDonald and LangridgeMonopolis 19870 đ?‘š3 /đ?‘

Table 3.3 Peak Breach Outflow

3.4 Flood analysis using HEC-RAS The HEC-GeoRAS extension was developed through a Cooperative Research and Development Agreement between the Hydrologic Engineering Center (HEC) and the Environmental Systems Research Institute, Inc. (ESRI).

GeoRAS extracts terrain information stored in TINs and generates a HEC-RAS import file. TINs are created from points, polygons, and lines stored in different formats. Since the focus of this exercise is on the development of a river model and its spatial import/export features within GIS. The goal of this section is to develop the spatial data required to generate a HECRAS import file with a 3-D stream network and 3-D cross sections defined. After importing the GIS file into HEC-RAS using the geometric data

Areas inundated by flooding occur wherever the elevation of the floodwater exceeds that of the land. Floodplain mapping is accomplished in the GIS using HEC-GeoRAS. GIS information is exported from HEC-RAS and read into the GIS with GeoRAS. The geo-referenced cross sections are imported and water surface elevations attached to the cross sections are used to create a continuous water surface. The water surface is then compared with the terrain model and the floodplain is identified where the 20

water surface is higher than the terrain. HEC-GeoRAS produces inundation maps for flood extent and depth, when displayed with aerial photographs can be used to identify the area impacted during a dam failure scenario. For our study we mapped two floodplain. One shows the flood using đ?‘„đ?‘? from The Bureau of Reclamation equation, and the other from MacDonald and Langridge-Monopolis.

Figure 3.3 Geometric Data for Profile 1

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Figure 3.4 Geometric Data for Profile 2

Figure 3.5 HEC-RAS Flood Model

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Figure 3.6 HEC-RAS Flood Model

4.0 Results and Discussion 4.1 Results After post processing both of the flood inundation maps can be generated, these maps show the areas that will be flooded with water. These areas classified into two main categories, residential areas and agriculture areas. Depth of water is distributed from a few centimeters to 54 meter in the first flood. For the other scenario the maximum flood the water depth reached 44. The velocities of water is variable from station to another station, this depends on the depth of water in each station, the velocity increase while the depth of water is increasing, by using these results a damage analysis can be done.

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Table 4.1 velocity and Area of water in each station for Profile 1 24

Figure 4.1 Flood inundation map for Profile 1 25

Table 4.2 velocity and Area of water in each station for Profile 2

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Figure 4.2 Flood Inundation Map for Profile 2 27

4.2 Damage assessment

A risk-based approach to dam design and dam safety evaluations has been developed to account for the downstream consequences of a potential dam failure.

The consequences evaluation is not based on the probability of failure, but instead on the potential loss of life or increase in economic losses caused by a potential dam failure.

It is important that consistent approaches for consequence estimation be adopted across the dam-safety sector. Estimating Loss of Life for Dam Failure Scenarios discusses the strengths and limitations of several methods for estimating loss of life.

This section further describes the procedure described in USBR’s publication A Procedure for Estimating Loss of Life Caused by Dam and companion document Guidelines to Decision Analysis (1986), as it is the most currently and widely used procedure for estimating loss of life resulting from dam failure.

4.3 Conclusion GIS and HEC-RAS together can be strong tools to simulate dam failure flood inundation and determined the velocities and discharge of water in each station on the stream. By using the best available topographic data and included all major topographic features and hydraulic structures. The maximum depth was in non residential areas.

4.4 Recommendations

Due to the serious compensation of dam break on human life and facilities, dam breach should be included in the dam design. It is not enough to consider safety factor to build up a dam design. The engineers should keep in what will happen if the dam collapsed by an earthquake and take a preventive actions and early warning and plans to evacuate.

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References 1. Hazard Classifications & Dam Break Analysis – MDE 2. Federal Guidelines for Inundation Mapping of Flood risk Associated with Dam Incidents and Failures – FEMA 3. Technical Guidelines and Requirements for Approval Under The Lakes & Rivers Improvement Act - Ministry of Natural Resources (France) 4. Reduction of the Storage Capacity of two Small Reservoirs in Jordan - Nadhir A. Al-Ansari and S. Knutsson 5. Floodplain Mapping and Terrain Modeling Using HEC-RAS and ArcView GIS Eric Tate (Center for Research in Water Resources)

6. Flood Plain Determination using ArcView and HEC-RAS Richard A. Kraus, P.E. Dodson & Associates, Inc.

7. Dam Break Analysis using GIS Applications - Rasif Razack (Institute of Engineering and Technology Kalady, India)

8. Dam Breach Analysis For Urbanizing Basins - Charles D. Absher, John K. McWhorter, Robert Vicevich

9. Landslide dam and subsequent dam-break flood estimation using HEC-RAS model in Northern Pakistan - Mohsin Jamil Butt, Muhammad Umar & Raheel Qamar

10. Fundamentals of Hydraulic Engineering System – Houghtalen, Akan, Hwang, Fourth edition

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