Natural Dam Research Articles

Experimental study of the impact factors of natural dam failure introduced by a landslide surge

A large amount of loose deposit between the sides of a landslide lake may slide into a reservoir at any time because of influences such as earthquakes, heavy rainfall or other triggering factors. These factors can cause the formation of a huge surge and result in the instantaneous failure of a landslide dam. The failure of a landslide dam can threaten people's lives and property downstream. This paper analyzes the destruction mechanism of landslide dams because of a surge and the impact of the contact area, the landslide height, and the distance between the entry point and the dam site for a dam break through physical experiment and compares the experimental results with the calculated values. Experimental results show that the contact area and the landslide height have a significant impact on the dam-break surge. A measure based on the previously mentioned factors can be made to reduce the dam failure risk caused by a landslide surge. Two empirical methods (Pan's method and Miller's method) are used to predict the landslide surge wave and compared with the experimental results; the simulated results show that the Miller's method used for predicting the landslide surge wave is more reasonable.

The Kambarata 2 blast-fill dam, Kyrgyz Republic:blast event, geophysical monitoring and dam structure modelling

The blast- and earth-fill dam of the Kambarata 2 hydropower station is situated in the seismically active Central Tien Shan region of the Kyrgyz Republic. More than 70% of the dam volume was produced during a blast event on December 22, 2009. In 2010–2011, dam construction was completed after earth filling on top of the blasted material and installing concrete and clay screens together with bentonite grouts. A geophysical survey had been completed in 2012–2013, mainly to monitor the resistivities inside the dam. The geophysical survey completed on the Kambarata 2 dam site showed lower resistivity zones in the earth fill and relatively higher resistivities in the blast-fill material. Topographic, geophysical and piezometric inputs had been compiled within a 3D geomodel constructed with GOCAD software. This model was compared with the design structure of the dam in order to define the upper limits of the underlying alluvium, the deposited blast fill, earth fill and top gravel materials (represented by the dam surface). The central cross-section of this model was extrapolated over the full length of the main dam profile. On the basis of a calibrated hydrogeological model and known geomechanical properties of the materials, dam stability calculations were completed for different scenarios considering different reservoir levels and varying seismic conditions. Some of these scenarios indicated a critical vulnerability of the dam, e.g., if impacted by a horizontal seismic acceleration of Ah = 0.3 g and a vertical seismic acceleration Av = 0.15 g, with an estimated return period of 475 years. As a general conclusion, it was noted that this case study can be used as an example for surveys on much larger natural – landslide or moraine – dams. A series of geophysical methods (e.g., electrical and electro-magnetic techniques, seismic and microseismic measurements) can be applied to investigate even very deep dam structures. These methods have the advantage over classical direct prospecting techniques, such as drilling, of using equipment that is much lighter and thus more easily transportable and applicable in difficult terrain. Furthermore, they can provide continuous information over wider areas. This specific application to a blast-fill dam allows us to better outline the strengths and weaknesses of the exploration types and geomodels as a series of investigated parameters can be verified more easily than for natural dams.

Post-rock-avalanche dam outburst flood sedimentation in Ram Creek, Southern Alps, New Zealand

Rock avalanches are common in mountainous regions that are tectonically active. They are capable of forming natural dams of uncertain persistence that have significant impacts on the river system over wide spatial scales and possibly over geological time scales. Here we combine field data and digital elevation model (DEM) analysis to show the response of Ram Creek, New Zealand, to 28years of sediment dispersion following the 1968 emplacement of a co-seismic, rock-avalanche dam that breached catastrophically in 1981. The results show a system that has not attained equilibrium, being unable to move the quantity of dam-derived sediments, and will likely not attain equilibrium before the next major sediment input; it is in a state of persistent disturbance where localised reworking dominates. Erosion in Ram Creek is focussed on lateral bevelling and bedrock gorge widening rather than vertical incision to keep pace with tectonic uplift. Importantly for studies of tectonic geomorphology, this widening — which if sustained will form a strath terrace — does not represent a period of reduced uplift. Stream metrics (concavity and steepness) are unable to differentiate the identified rock-avalanche-induced knickpoint from tectonic and lithological knickpoints.

Jure landslide and a subsequent natural damming due to long term gravitational deforamtion of valley slope along Sun Kosi river, central Nepal, occurred in August 2014

Jure landslide and a subsequent natural damming due to long term gravitational deforamtion of valley slope along Sun Kosi river, central Nepal, occurred in August 2014

Geotechnical Distinction of Landslides Induced by Near-Field Earthquakes in Niigata, Japan

Landslides triggered by near-field earthquakes with epicentres directly beneath towns have attracted intense attention since the 2004 Mid-Niigata (Niigata-ken Chuetsu) Earthquake. Hilly and mountainous areas sustained heavy damage. Social problems developed when many towns became isolated because landslides cut off traffic and public service lifelines. Soil from landslides closed river channels and formed natural dams. The natural dams submerged some towns. Emergency measures were undertaken promptly to prevent debris flows caused by natural dam breaks. Subsequently, the 2007 Mid-Niigata Offshore (Niigata-ken Chuetsu-oki) Earthquake and the 2011 Northern Nagano Earthquake struck the Niigata region. Landslides triggered by those earthquakes differed in terms of their number, scale, and location. Therefore, characteristics of the landslide sites of the respective earthquakes were examined to ascertain their topographical and geological features. Furthermore, differences in groundwater level and damage related to compound disasters were explained for discussion of the stability progress of damaged slopes.

Evaluation of landslide dams hazard and risk: an application in Upper Tiber Valley (central Italy)

The note presents the results of a project, carried out by the Engineering Geology Group of Department of Physics and Geology of University of Perugia and funded by the Umbria Region, aimed at evaluating the hazard of occlusion of riverbeds by landslide (landslide dams) in the Upper Tiber Valley. The authors explain the used methodology that, starting from the data available in the catalogs of IFFI (Inventario dei Fenomeni Franosi in Italia, i.e. Italian Landslides Inventory) and PAI (Piano di Assetto Idrogeologico, i.e. Hydrogeological Assessment Plan), concerning the active and quiescent landslides, selects, through different steps (preliminary identification of landslides for which it is assumed the interference with riverbeds; photointerpretation; geomorphological survey; simulation of the total occlusion of riverbed; simulation of the collapse of the natural dam) the landslides for which is considered realistically possible the occlusion of riverbed due to a reactivation or persistence of the mass movement. The methodology also provides for a first evaluation of conditions of risk related to the complex phenomenon of interference between landslide and dynamics of riverbeds, for both areas located upstream of the dam, at risk of drowning due to the formation of the dam lake, both for those located downstream, where it is possible the transit of an abnormal flood wave, resulting from the eventual collapse of the natural dam and the rapid emptying of the lake.

The Tienchi Pond on Lanyu Island (Western Pacific): Lake formation and potential as environmental archive

The formation, evolution, and potential as a climate archive of Tienchi Pond was evaluated using geomorphology, sedimentology, geochemistry, and AMS radiocarbon measurements of tree ring cores. Tienchi Pond is a small ephemeral lake situated on the subtropical Lanyu Island in the Western Pacific Ocean about 90km east of southern Taiwan. The lake is situated on a mountain ridge and is today characterized by numerous dead trees and stumps. The position at the boundary between the two main components of the SE Asian monsoon system, the Asian landmass and the Western Pacific, makes this lake particularly interesting as a potential natural climate archive.Since previous studies have shown that the bedrock underlying the lake formed over 2my ago, a volcanic crater origin was ruled out. Rather, element ratios of K/Ti and Ca/Fe together with 210Pb dating suggest a recent origin for the lake, probably as the result of a natural damming event in the southern, narrower, part of the lake basin, or as a result of increased precipitation at the end of the Little Ice Age (or a combination of both). Radiocarbon measurements on a dead tree near the lake perimeter show 14C levels of more than 1.7% modern radiocarbon near the bark, suggesting that the tree died in the early 1970s. In contrast, by correlating a large number of radiocarbon measurements to a northern hemisphere reference curve, it was shown that trees closer to the center of the lake died in the early 20th century. This agrees with a scenario where a small lake formed by initial damming, and gradually grew larger through erosion of the surrounding shore lines caused by rapid lake level oscillations.

Modeling of natural dam failure modes and downstream riverbed morphological changes with different dam materials in a flume test

Landslide dam failure modes are influenced by dam geometry, material characteristics, and riverbed conditions. The different characteristics of earthquake- and rainfall-induced natural dams and the effects of riverbed conditions on dam failure have not attracted much attention from researchers in the past. This study used flume tests to simulate earthquake- and rainfall-induced landslide dam failures for various combinations of dam geometry, materials, and riverbed conditions. The 64 flume test combinations thus included two discharge rates, two dam shapes (triangular and trapezoidal) with two heights, two types of riverbed conditions, and two types of dam material with two different water contents. The experimental results show that dam geometry, the amount of inflow, hydraulic conductivity of the dam material, and riverbed conditions have considerable effect on dams' lifespan and their corresponding failure mode. The hydraulic conductivity of the dam material affected the dam lifespan and its corresponding failure mode. The four observed failure modes of dam breaks in rigid and mobile riverbeds constitute progressive erosion, overtopping erosion, slope slide, and complex failure. The complex failure mode, which involves headward erosion, slope slide, and overtopping, can occur in highly hydraulically conductive dams with high discharge. Progressive erosion occurs in highly hydraulically conductive dams with low discharge. Dam material with low hydraulic conductivity tends to fail by pure overtopping. Regardless of the dam shape and material, dams in a mobile riverbed had a longer lifespan than those in a rigid riverbed. The composition of the dam material affected the peak outflow discharge after dam break. Compared with rigid riverbeds, dams in mobile riverbeds delay the arrival time of peak sediment discharge. Failure modes triggering flash floods and sediment transport after a dam break involved a series of sandbars and an armoring layer in the downstream riverbed. Earthquake-induced dry material forming highly hydraulically conductive dams generally fail through complex when failure was subjected to a high discharge. Dams composed of wet materials tend to fail by overtopping. In flume tests, dam failure mode and inflow changed downstream mobile riverbed morphology in ways similar to those seen in full-scale model tests conducted in the field.

Research of Devdoraki Glacier Based on Satellite Remote Sensing Data and Devdoraki Glacier Falls in Historical Context

The problem of the transportation safety for Mtskheta-Stepantsminda-Larsi road is overviewed. The scientific study of glaciers in the Caucasus started in the first half of the 19th century. From that time the terrestrial observations on glaciers were carried out. The outputs of terrestrial observations resulted in different series of various temporal duration characteristics of glaciers due to the difficulties of field works organization. The data received contain uncertainties and have no sufficient resolution in time and space. With the invention of the Earth’s satellites it was determined that satellite remote sensing is the best technology allowing to receive the data with needed regularity both in terms of time and space resolution. The results of various researches show that sometimes the satellite remote sensing data is difficult to interpret and determine needed glacier characteristics. In such cases the data of the terrestrial observations are used for validation of glacier characteristics along with the expert knowledge of corresponding glaciers. This complex approach gives the possibility to adjust glaciers contours and calculate more accurately various characteristics of a glacier. At present the main problem for the safety of the Georgian Military Road in the territory of Georgia is the glacial and hydrological disasters such as ice blocks falls from the Kazbegi glaciations accompanied with the debris, followed by the river bed blockage and natural dam formation, with a consequent break and pass of catastrophic mudflows. The glacial catastrophes of Kazbegi glaciers: Devdoraki, Mna, Gergeti, Abano and Chachi have great impact on Mtskheta-Stepantsminda-Larsi road safety on the territory of Georgia. The biggest catastrophes on the Georgian territory took place due to Devdoraki glacier fell in 1776, 1778, 1785, 1808, 1817, 1832. The Devdoraki glacier listed falls during those years were connected with the pulsation of the glaciers and their increase. In Kazbegi glaciation the environmental disasters occurred in 2002, 2007 and 2014 (twice). It was the result of ice layers movement. Based on the analysis, it was concluded that the creation of the May 17 and August 20, 2014 catastrophic mudflows was not connected with the glacier pulsation.

Types and Forms of Relief on Gherasim Torrential Valley, Târgu Ocna

Abstract The present study brings new data regarding the landforms occurring on gypsum rocks through the action of denudation processes. The landforms signaled complement the domain literature with natural dams, vertical shafts and reappearing springs, developed at the contact between the Subcarpathians and Berzunţi Mts. The presence of the gypsum dam has slowed down the intensity of erosion processes upstream, in comparison to the neighboring valleys. The analyzed area has also an educational importance, offering sufficient objectives for the knowledge of the local characteristics or for field applications. The perimeter presents sufficient objectives also to be included on the list of protected areas of national interest.

Late Quaternary valley infill and dissection in the Indus River, western Tibetan Plateau margin

The Indus, one of Earth's major rivers, drains large parts of the NW Himalaya and the Transhimalayan ranges that form part of the western Tibetan Plateau margin. In the western Himalayan syntaxis, where local topographic relief exceeds 7 km, the Indus has incised a steep bedrock gorge at rates of several mm yr−1. Upstream, however, the upper Indus and its tributaries alternate between bedrock gorges and broad alluvial flats flanked by the Ladakh and Zanskar ranges. We review the late Quaternary valley history in this region with a focus on the confluence of the Indus and Zanskar Rivers, where vast alluvial terrace staircases and lake sediments record major episodes of aggradation and incision. New absolute dating of high-level fluvial terrace remnants using cosmogenic 10Be, optically and infrared stimulated luminescence (OSL, IRSL) indicates at least two phases of late Quaternary valley infilling. These phases commenced before ∼200 ka and ∼50–20 ka, judging from terrace treads stranded >150 m and ∼30–40 m above modern river levels, respectively. Numerous stacks of lacustrine sediments that straddle the Indus River >200 km between the city of Leh and the confluence with the Shyok River share a distinct horizontal alignment. Constraints from IRSL samples of lacustrine sequences from the Leh-Spituk area reveal a protracted lake phase from >177 ka to 72 ka, locally accumulating >50-m thick deposits. In the absence of tectonic faulting, major lithological differences, and stream capture, we attribute the formation of this and other large lakes in the region to natural damming by large landslides, glaciers, and alluvial fans. The overall patchy landform age constraints from earlier studies can be reconciled by postulating a major deglacial control on sediment flux, valley infilling, and subsequent incision that has been modulated locally by backwater effects of natural damming. While comparison with Pleistocene monsoon proxies reveals no obvious correlation, a late- or post-glacial sediment pulse seems a more likely source of this widespread sedimentation that has partly buried the dissected bedrock topography. Overall, the long residence times of fluvial, alluvial and lacustrine deposits in the region (>500 ka) support previous studies, but remain striking given the dominantly steep slopes and deeply carved valleys that characterise this high-altitude mountain desert. Recalculated late Quaternary rates of fluvial bedrock incision in the Indus and Zanskar of 1.5 ± 0.2 mm yr−1 are at odds with the longevity of juxtaposed valley-fill deposits, unless a lack of decisive lateral fluvial erosion helps to preserve these late Pleistocene sedimentary archives. We conclude that alternating, ∼104-yr long, phases of massive infilling and incision have dominated the late Quaternary history of the Indus valley below the western Tibetan Plateau margin.

Analysis of Debris Flow Kuranji River in Padang City Using Rainfall Data, Remote Sensing and Geographic Information System

Flash flood is the most common environmental hazard worldwide. This phenomenon is usually occurs due to intense and prolonged rainfall spells on saturated ground. When there is a rapid rise in water levels and high flow-velocities of the stream occur, the channel overflows and the result is a flash flood. Flash floods normally cause a dangerous wall of roaring water carrying rocks, mud and other debris. On Tuesday, July 24, 2012 at 18:00 pm, a flash flood (debris flow) struck Kuranji River whereby 19 urban villages in seven (7) sub-districts in the city of Padang were affected by this flood disaster. The temporary loss estimated is 40 Billion US Dollar reported by the West Sumatra Provincial Government due to many damages of the built environment infrastructures. This include damaged houses of 878 units, mosque 15 units, irrigation damaged 12 units, bridges 6 units, schools 2 units and health posts 1 unit. Generally, widely used methods for making a landslide study are Geographic Information System (GIS) and Remote Sensing techniques. The landslide information extracted from remotely sensed products is mainly related to morphology, vegetation and hydrologic conditions of a slope. While GIS is used to create a database, data management, data display and to analyze data such as thematic maps of land use/land cover, normalized difference vegetation index (NDVI), rainfall data and soil texture. This paper highlights the analysis of the condition of the Watershed Kuranji River experiencing flash floods, using remote sensing satellite image of Landsat ETM 7 in 2009 and 2012 and Geographic Information System (GIS). Furthermore, the data was analyzed to determine whether this flash flood occurred due to extreme rain or collapse of existing natural dams in the upstream of the Kuranji River.

The effect of seepage on prediction of water level in a natural dam

The effect of seepage on prediction of water level in a natural dam

Using real-time abnormal hydrology observations to identify a river blockage event resulted from a natural dam

This study proposes an automatic identification approach for landslide dam formation using a real-time abnormal hydrology record and artificial neural network (ANN). In Taiwan, natural dams occur frequently and have the potential to cause significant disasters, especially in the presence of fragile geological conditions such as steep mountains, earthquakes, intense typhoon, and storm events. During a river blockage event, obtaining immediate real-time information can be difficult or even impossible due to extreme weather conditions, remote locations, and the mountainous terrain of the area. As a result of these issues, there is a strong need for a practical tool that can not only detect the occurrence of this type of natural dam but also estimate the potential real-time risk of dam failure. In order to develop the appropriate safety response, a rapid preliminary assessment of the failure type must be identified, followed by a thorough investigation into the failure process after the event has occurred. In this study, a new method is developed that applies an ANN model (1) to evaluate, in real time, the occurrence of a natural dam and the storage changes behind that dam; (2) to rapidly assess the natural dam failure type and failure process; and (3) to reconstruct the dam height variation during the dam failure process after the event. The proposed methodology is applied to Chi-Shan River Basin located in Kaohsiung, Taiwan, during Typhoon Morakot in 2009. In 3 days, Typhoon Morakot produced 1,911 mm of precipitation. The typhoon event produced a landslide dam and a debris flow that inundated Hsiaolin Village, causing 398 deaths. The tragic results of this case study demonstrate the need for an applicable, accurate, and efficient method to evaluate dam formation and its failure rate.

Threat of glacial lake outburst flood to Tehsil Gupis from Khukush Lake, District Ghizer, Gilgit Baltistan, Pakistan

Glacial lake outburst flood (GLOF) is a powerful natural phenomenon that is very active in the Karakoram and Himalayas. This paper presents a case study from Gupis Tehsil in northern areas of Pakistan that is exposed to GLOFs from nine different glacial lakes in its upper catchment areas. Khukush Lake being the largest of all the glacial lakes has been studied and a flood attenuation model has been created for the whole Gupis Tehsil. This lake covers almost 2.2 km2 of surface area, and its calculated volume is 2.6 × 104 m3. In case of its outburst, the peak flow discharge is calculated to be 7,642 m3/s. The catchment area which contributes water and debris to the lake is 170 km2. This lake is dammed by a glacial moraine, which is not strong enough to sustain the pressure for a longer period of time. Other factors that are reducing the reliability of the dam are the secondary hazards which are in direct contact with the lake, and in case of their reactivation, they can put severe impacts on the dam. There are eight potential sites of the snow avalanche activity where debris along with snow may fall directly into the lake producing a strong wave. This strong wave of water will increase the pressure on the dam and ultimately will increase the probability for its outburst. The presense of water springs towards the downstream side of the natural dam also indicate the presence of hidden channels passing through the dam which may weaken the shear strength of the dam. Almost 24 villages settled along either sides of the Gupis River are critically studied for the expected flood from Khukush Lake. With few exceptions, almost 20–25 % area of all the villages will be affected from this flood.

A ninth century earthquake-induced landslide and flood in the Kashmir Valley, and earthquake damage to Kashmir’s Medieval temples

An entry in the Tarikh-i-Hassan records that in 883 AD during the reign of King Avantivarman (855–883) an earthquake in Kashmir triggered a landslide that impounded the River Jhelum and flooded the Kashmir Valley. Kalhana’s Rajatarangini provides abundant details about how the ninth century engineer Suyya both cleared the natural dam, drained the valley and instituted numerous irrigation works. We identify the landslide(s) responsible for this Medieval flood and from twentieth century discharge statistics of the Jhelum calculate that it would have taken at least 2 years to flood the Kashmir Valley to near Anantnag. This presents a chronological difficulty, for the causal earthquake could not have occurred in the last 4 months of Avantivarman’s rule, and we conclude that it must have occurred much earlier, perhaps before the start of his reign. The flood occurred during a period of widespread temple building using massive uncemented limestone megablocks, capped by monolithic multi-ton roofs. Many of these magnificent temples, now in ruinous condition, are located close to the shores of the inferred Medieval flood level, suggesting that the transport of construction materials for these temples may have been ferried by barge from distant quarries. Historians and archaeologists have attributed the partial collapse of these temples to malicious damage by subsequent occupants of the valley, but the misalignment of blocks at lower levels within each edifice in recent earthquakes suggests that their lateral offsets are the result of jostling during prolonged shaking in historical earthquakes. From the serendipitous entrapment of datable materials beneath fallen blocks from Kashmir’s ninth century temples we can, in principle, identify the times of historical earthquakes. We chose the ruined Sugandhesa temple near Patan to test this hypothesis. Preliminary results indicate collapse in the tenth or eleventh century, and significant damage in 1885, with at least one intervening earthquake possibly in the seventieth century.

Quaternary gravitational morpho-genesis of Central Apennines (Italy): Insights from the Mt. Genzana case history

Abstract This paper focuses on a study aimed at defining the role of geological-structural setting and Quaternary morpho-structural evolution on the onset and development of a deep-seated gravitational slope deformation which affects the western slope of Mt. Genzana ridge (Central Apennines, Italy). This case history is particularly significant as it comprises several aspects of such gravitational processes both in general terms and with particular reference to the Apennines. In fact: i) the morpho-structural setting is representative of widespread conditions in Central Apennines; ii) the deforming slope partially evolved in a large rockslide-avalanche; iii) the deformational process provides evidence of an ongoing state of activity; iv) the rockslide-avalanche debris formed a stable natural dam, thus implying significant variations in the morphologic, hydraulic and hydrogeological setting; v) the gravitational deformation as well as the rockslide-avalanche reveal a strong structural control. The main study activities were addressed to define a detailed geological model of the gravity-driven process, by means of geological, structural, geomorphological and geomechanical surveys. As a result, a robust hypothesis about the kinematics of the process was possible, with particular reference to the identification of geological-structural constraints. The process, in fact, involves a specific section of the slope exactly where a dextral transtensional structure is present, thus implying local structural conditions that favor sliding processes: the rock mass is intensively jointed by high angle discontinuity sets and the bedding attitude is quite parallel to the slope angle. Within this frame the gravitational process can be classified as a structurally constrained translational slide, locally evolved into a rockslide-avalanche. The activation of such a deformation can be in its turn related to the Quaternary morphological evolution of the area, which was affected by a significant topographic stress increase, testified by stratigraphic and morphologic evidence.

Review Article: Lake and breach hazard assessment for moraine-dammed lakes: an example from the Cordillera Blanca (Peru)

Abstract. Glacial lake outburst floods (GLOFs) and related debris flows represent a significant threat in high mountainous areas across the globe. It is necessary to quantify this threat so as to mitigate their catastrophic effects. Complete GLOF hazard assessment incorporates two phases: the probability of water release from a given glacial lake is estimated through lake and breach hazard assessment while the endangered areas are identified during downstream hazard assessment. This paper outlines a number of methods of lake and breach hazard assessment, which can be grouped into three categories: qualitative, of which we outline eight; semi-quantitative, of which we outline two; and quantitative, of which we outline three. It is considered that five groups of critical parameters are essential for an accurate regionally focused hazard assessment method for moraine-dammed lakes in the Cordillera Blanca. These comprise the possibility of dynamic slope movements into the lake, the possibility of a flood wave from a lake situated upstream, the possibility of dam rupture following a large earthquake, the size of the dam freeboard (or ratio of dam freeboard), and a distinction between natural dams and those with remedial work. It is shown that none of the summarised methods uses all these criteria with, at most, three of the five considered by the outlined methods. A number of these methods were used on six selected moraine-dammed lakes in the Cordillera Blanca: lakes Quitacocha, Checquiacocha, Palcacocha, Llaca, Rajucolta, and Tararhua. The results have been compared and show that each method has certain advantages and disadvantages when used in this region. These methods demonstrate that the most hazardous lake is Lake Palcacocha.

Diversity and community analysis of ammonia oxidizing bacteria in a streambed surrounding an artificial dam

The degree to which small natural dams affect the native bacterial nitrogen cycling community was explored by molecular methods. The identities and relative abundances of ammonia oxidizing bacteria in the sediment surrounding an artificial dam both at the surface and in the hyporheic zone were characterized. Analyses were performed using tRFLP of the conserved amoA gene using a semi-nested degenerate PCR approach. Additionally, an amoA gene library was constructed to characterize the most dominant sediment genotypes. The results of the tRFLP analyses showed clear differences between the upstream and downstream communities at different depths in the sediment column. Non-metric multidimensional scaling ordination of the tRFLP data set produced a stable one-dimensional solution with significant correlations to oxygen, pH, nitrate, and dissolved organic nitrogen levels. The sample corresponding to the hyporheic zone downstream of the dam showed 28–50% higher amoA richness and higher diversity than the other samples. All gene fragments sequenced from the samples grouped with sequences of the Nitrosospira type. Ordination of 16S rDNA tRFLP data revealed a two dimensional data structure, one axis of which had similar chemical correlation characteristics as the amoA model axis. Taken together, the results from this study suggest that the presence of the dam creates physical and chemical heterogeneity that may foster genetic diversity and community changes amongst ammonia oxidizing bacteria.

Concept for Eritrea’s Sustainable Economic Development Red Sea, the Natural Dam of Eritrea

The Danakil Depression is located in Eritrea, a few kilometers inland from the Red Sea coast and sinks 120 meters below sea level. This concept paper attempts to explore Eritrea's ability to develop a hydroelectric and potable water generation capacity from the Red Sea. Unlike many countries with access to seas and oceans, Eritrea is endowed with a natural hydro dam because of its geographical location and topography. The Red Sea can be used as a resource for the production of energy as hydro dam and potable water source through desalination. The availability of cheap, clean and environmentally safe energy and water sources will enable the country to eliminate poverty and stop environmental degradation, thus contributing to reduce or minimize the global warming problem. Index Terms—Danakil-depression, economics, Eritrea, hydroelectric-power, red sea I. I NTRODUCTION Eritrea is a young nation, only 20 years old since it achieved its independence in 1993. It is located in the Horn of Africa, bordered in the north and west by Sudan, in the south by Ethiopia and Djibouti, and in the east by the Red Sea Fig. 1. It has an estimated population of about 5.9 million and a total land area of some 12.2 million hectares. Its annual population growth is estimated at 2.9 percent (1). Eritrea is a poor country and faces economical and environmental challenges. Both challenges lead to wide spread poverty for the population. The economic challenges relate to resource constraints to meet the national demand for commercial energy production and inadequate water resources needed for agriculture, mining manufacturing, or service industries (2). The environmental challenges stem from the global warming phenomenon, due to the expansion of the Sahara desert which causes frequent drought across the Sub-Saharan Sahel region. The economic challenge also contributes to wide spread deforestation and overgrazing for subsistence, exposing the barren land to water and wind erosions (3). Subsistence crop production and cattle keeping are the two most important economic activities in Eritrea (4). However, these traditional production methods and livestock populations used in much of the country contribute heavily to land degradation and soil erosion. Desertification due to overgrazing and soil erosion is common in many parts of the country. Energy requirements also put a lot of pressure on the