Check Dams Research Articles

Risk analysis for clustered check dams due to heavy rainfall

Check dams are commonly constructed around the world for alleviating soil erosion and preventing sedimentation of downstream rivers and reservoirs. Check dams are more vulnerable to failure due to their less stringent flood control standards compared to other dams. Determining the critical precipitation that will result in overtopping of a dam is a useful approach to assessing the risk of failure on a probabilistic basis and for providing early warning in case of an emergency. However, many check dams are built in groups, spreading in several tributaries in cascade forms, comprising a complex network. Determining the critical precipitation for dam overtopping requires a knowledge of its upstream dams on whether they survived or were overtopped during the same storm, while these upstream dams in turn need the information for their upstream dams. The current paper presents an approach of decomposing the dam cluster into (1) the heading dam, (2) border dams, and (3) intermediate dams. The algorithm begins with the border dams that have no upstream dams and proceeds with upgraded maps without the previous border dams until all the dams have been checked. It is believed that this approach is applicable for small-scale check dam systems where the time lag of flood routing can be neglected. As a pilot study, the current paper presents the analytical results for the Wangmaogou Check Dam System that has 22 dams connected in series and parallel. The algorithm clearly identified 7 surviving dams, with the remaining ones being overtopped for a storm of 179.6 mm in 12 h, which is associated with a return period of one in 200 years.

Assessing, mapping, and optimizing the locations of sediment control check dams construction

Check dams are considered to be one of the most effective measures for conservation of the soil and water resources. However, identifying the most suitable sites for the installation of check dams remain quite demanding. This research investigates and compares five machine learning algorithms (MLAs) – boosted regression trees (BRT), multivariate adaptive regression spline (MARS), mixture discriminant analysis (MDA), random forest (RF), and support vector machine (SVM) – for generating check-dam site-suitability maps (CDSSMs) and assessing them in Firuzkuh County, Iran. First, the locations of 475 existing check dams were monitored, registered, and divided into calibration (70%) and testing datasets (30%) for training and validation of the models. Fourteen check-dam conditioning factors (CDCFs) were selected and checked for multicollinearity. The relative importance of the CDCFs assessed using the elastic net (ENET) algorithm. Results demonstrated that distance from river (DFR) and drainage density (DD) to be the most significant factors for mapping the suitable sites for the erection of check dams. This research revealed that all of five MLAs had excellent accuracy for predicting the check-dam site-suitability with high AUC values: RF (0.966), SVM (0.878), MARS (0.878), MDA (0.844), and BRT (0.843). The most accurate model (RF) showed that 16.95%, 35.55%, 31.08%, and 16.42% of study area comes under low, moderate, high, and very high suitability classes. The outcome achieved by this research will be helpful to sustainability planners and managers in constructing check dams at suitable sites for better conservation of soil and water resources.

Quantitative assessment of the influence of terrace and check dam construction on watershed topography

Terrace and check dam construction has substantially changed land surface morphology, which in turn affects modern surface processes. Digital elevation models (DEMs) provide an effective way to quantitatively analyze surface morphology and processes. However, existing DEMs lack sufficient ability to express artificial terrain. Based on 1:10000 topographic maps of the Zhifanggou watershed, a series of artificial terrain DEMs for the study site were constructed by both field investigation and remote sensing images from 1938 to 2010. Digital terrain analysis was used to quantitatively assess the influence of terrace and check dam construction on the watershed terrain. The results showed that the artificial terrain DEM could capture the spatial distribution patterns of terraces and dam lands and improved the ability of DEM to express terrain. The construction of terraces and check dams clearly changed the surface elevation. The average elevation change of each terrace mainly ranged between —1.5 and 1.5 m, while the annual average deposition height of the dam lands was 9.16 cm. The average slope, slope length, and slope length and steepness factor of the watershed decreased with the effect of the artificial terrain on the surface, and their averages decreased by 0.65°, 6.75 m, and 0.83, respectively, from 1938 to 2010. Although the construction of terraces reduced their surface slope to nearly 0°, the slope of terrace embankments rapidly increased, to more than 45°, which may lead to gravitational erosion and potential terrace damage. Terracing reduced the slope length in both the terrace distribution area and downslope of the terraces. Check dam deposition reduced the slope and slope length of the channel. This study contributes to a better understanding of the topographic change rules after terrace and check dam construction, and aids in elucidating the mechanisms of soil erosion process influenced by artificial topography.

Optimizing Height and Spacing of Check Dam Systems for Better Grassed Channel Infiltration Capacity

The check dams in grassed stormwater channels enhance infiltration capacity by temporarily blocking water flow. However, the design properties of check dams, such as their height and spacing, have a significant influence on the flow regime in grassed stormwater channels and thus channel infiltration capacity. In this study, a mass-balance method was applied to a grassed channel model to investigate the effects of height and spacing of check dams on channel infiltration capacity. Moreover, an empirical infiltration model was derived by improving the modified Kostiakov model for reliable estimation of infiltration capacity of a grassed stormwater channel due to check dams from four hydraulic parameters of channels, namely, the water level, channel base width, channel side slope, and flow velocity. The result revealed that channel infiltration was increased from 12% to 20% with the increase of check dam height from 10 to 20 cm. However, the infiltration was found to decrease from 20% to 19% when a 20 cm height check dam spacing was increased from 10 to 30 m. These results indicate the effectiveness of increasing height of check dams for maximizing the infiltration capacity of grassed stormwater channels and reduction of runoff volume.

Impacts of Filled Check Dams with Different Deployment Strategies on the Flood and Sediment Transport Processes in a Loess Plateau Catchment

As one of the most widespread engineering structures for conserving water and soil, check dams have significantly modified the local landform and hydrologic responses. However, the influences of sedimentary lands caused by filled up check dams on the runoff and sediment transport processes were seldom studied. Employing an integrated hydrologic-response and sediment transport model, this study investigated the influences of filled check dams with different deployment strategies in a Loess Plateau catchment. Six hypothetical deployment strategies of check dams were compared with no-dam scenario and the reality scenario. Results showed that filled check dams were still able to reduce Flood peak (Qp) by 31% to 93% under different deployment strategies. Considerable delays of peak time and decreases were also found in scenarios, which were characterized as having larger and more connective sedimentary lands on the main channel. Reduction rates of Sediment yield (SY) and the total mass of Eroded sediment (ES) ranged from 4% to 52% and 2% to 16%, respectively, indicating that proper distributions of check dams can promote sediment deposition in the channel and reduce soil erosion. The results of this study indicate that (1) check dam systems could still be useful in flood attenuation and sediment control even when they were filled, and (2) optimizing the deployment strategies of check dams can help reduce erosion.

The Changing Relationship Between Rainfall and Surface Runoff on the Loess Plateau, China

AbstractLack of hydrological data of high spatiotemporal resolution has been a major challenge for understanding the rainfall‐runoff relationship on the Loess Plateau of China. In this study, we examined this relationship across 82 watersheds on the plateau for two time periods: P1 (1971–1987) and P2 (2008–2016). We found linear relationships between the annual rainfall series and annual surface runoff series in P1 that were stronger in the southeast and that declined toward the northwest, but this spatial pattern was slightly disrupted during P2. The mean annual runoff coefficient ranged from 0.056 to 0.126 for the 25th and 75th percentiles, respectively, during the P1 period, but the corresponding values were smaller in P2 (0.035 and 0.088, respectively). In total, the runoff coefficient decreased for 87% of the watersheds, with an average reduction of 0.033. For most watersheds of the plateau, we found a stable threshold value for the monthly runoff coefficient when monthly rainfall reached a certain value (i.e., a critical point). Between P1 and P2, the threshold value of the runoff coefficient decreased for 57 watersheds as a result of soil conservation measures. The rainfall critical point represents the minimum monthly rainfall to maintain the stable relationship between monthly infiltration and monthly rainfall in the process of runoff production. This value became greater on the middle regions of the plateau during P2 (increasing by 28% on average). Check dams, vegetation, and land use all have profoundly influenced the relationship between rainfall and surface runoff in this region.

Identification of suitable sites and structures for artificial groundwater recharge for sustainable groundwater resource development and management

Artificial recharge is the process of augmentation of the natural infiltration of precipitation or surface water into aquifers by some methods of construction, spreading of water or by artificially changing natural conditions. Upper Betwa watershed, has been taken under study is a semi-arid region, part of Obedullahganj block, Raisen district, M.P., India. The area is hard rock terrain with rugged topography and varying geology. Long term analysis of groundwater level conducted by CGWB, Bhopal has shown sharp decline in groundwater level from past one decade. To increase the groundwater potential of the area, action plan for artificial groundwater recharge has been developed using remote sensing and GIS techniques. Survey of India toposheet no's 55 E/8, 55 E/12, 55 F/5 & 55 F/9, GSI, 2002 resource map, LANDSAT 8, and SRTM (DEM) satellite data and NBSS&LUP soil map were processed in ArcGIS to prepare the various thematic layers viz. Geology, geomorphology, topography, soil, land use/land cover, slope, lineament, drainage and drainage density. Sub-watershed wise action plan of the area has been developed for the area using these thematic layers following the criteria given by NRSA, 1995. In the action plan, development of water harvesting structures (Check dam, Nala bund, Contour bund, Gully plug etc.) were proposed. These structures will provide a measure of artificial recharge in this hard rock terrain by collecting of the surface runoff and increasing the surface area of infiltration. Further, the developed action plan addresses identification of sites for groundwater recharge, through the anticipated artificial recharge structures. Thus, it is suggested that execution of the proposed sub-watershed wise action plan will help in development and management of groundwater resources of the area. Excavation of the proposed structures at their suitable sites identified will enhance the groundwater recharge potential of the area.

Water Storage Assessment of Khapri Watershed through Geospatial Techniques

Khapri watershed is mountainous region having average 2255 mm rainfall every year. In the last few months of hydrological year i.e. April & May, there is an acute shortage of drinking water. To overcome this short fall, it is necessary to manage natural watersheds available in the region. water harvesting is a system that collects rainwater from where it falls around its periphery rather than allowing it to go as runoff. The strategy of “Think Globally, Act Locally” should be used in this area for management of water. Local water that is rainwater stored using Rainwater Harvesting Structure and Conservation used optimally before it goes in drain or river.The subsurface reservoirs are very attractive and technically feasible alternatives for storing surplus monsoon runoff. But in the study region, this is not possible as there is a basalt rock. Recharging is not advisable as water table in post monsoon just touches ground level. So, Rainwater harvesting structures for direct use of water may be the possibly best solution.For community requirement rainwater may be stored in checkdams or depressed area naturally available. Construction of small barriers across small streams to check and store the running water also can be considered as water harvesting structure. This may fulfil the drinking water requirement of their cattles. Check dams in the watershed has been ascertain using Geospatial techniques and few of them verified by visiting the sites. In site visit it is found that open wells near the stream has water level above stream water level. At few places farming is done in check dam reservoir or in stream itself.

Soil conservation practices contribution in trapping sediment and soil organic carbon, Minizr watershed, northwest highlands of Ethiopia

Globally, land degradation and climate change are priority problems. Therefore, this study was conducted in Minizr catchment in the northwest highlands of Ethiopia to investigate the sediment and sediment organic carbon (SOC) trapping role of soil and water conservation practices (SWCPs) constructed inside fields, check dams (CDs) constructed inside gullies and micro-trenches constructed on degraded grazing lands, which would help to reduce land degradation and climate change. Our three research questions were: How much sediment was trapped by SWCPs? How much SOC was trapped by SWCPs? What was the role of SWCPs in mitigating climate change? Google Earth Imagery was used to map the SWCPs constructed inside fields; a Digital Elevation Model (ASTER DEM 20 m) was used to delineate the boundary of the study watershed and to evaluate elevation and slope characteristics, and GPS was used to collect watershed outlet coordinate points, CD locations and to accurately digitize SWCPs. Three different SWCPs, five different CDs and 30 micro-trenches were evaluated for their sediment and SOC trapping efficiency. The experiment was designed in three treatments with three replications, except for the CD studies. The volume of sediment trapped was quantified using field measurements of the deposited sediment and SOC was determined in a soil laboratory. The investigated SWCPs, CDs and micro-trenches trapped ~584,745 kg SOC together with 32,105 t of sediment. The percentage SOC was higher in the CD sediments (1.98%) than SWCPs (1.38%) and micro-trenches (1.49%). A large amount of SOC was deposited in vegetative-supported CDs than CDs constructed from structures alone, i.e. CDs supported with vegetative practices trapped more SOC. In general, SWCPs, CDs and micro-trenches were found to reduce soil erosion or land degradation by enhancing sediment deposition. They also trapped large amounts of SOC together with the sediment, which can reduce the greenhouse gases emission to the atmosphere. Therefore, governmental and non-governmental organizations and professionals should also consider SWCPs as climate change mitigation measures, like that of afforestation/plantation.

Sediment Trap in the Downstream of Check Dam: The Effect of Changes in Channel Depth on Sediment Deposition

Reservoir sedimentation is a major problem experienced by reservoirs in Indonesia. Reservoir sedimentation can be overcome by reducing the amount of sediment that enters the reservoir, among others, by building a Check dam. Check dam deposits more sediment loads with coarse grains, while sediment loads with fine grains will escape and enter the reservoir. So it is necessary to have construction to hold and settle fine sediment loads downstream of the Check dam. Construction is planned like a sediment trap in an irrigation system with variations in the cross-sectional area. In this study, the cross-section was expanded by changing its depth. The purpose of this research is to determine the effect of changes in the channel depth with discharge and grain size distribution variation on sediment deposition that occurs. The calculation is done using the HEC-RAS software. Simulation results show the deeper the sediment trap, the smaller the amount of sediment deposit. The large discharge, the smaller of deposit percentage. The greater of fine sediment percentage, the less the deposit.

Damage of check dams by extreme rainstorms on the Chinese Loess Plateau: A case study in the Chabagou watershed

Check dams are widely distributed and abundant on the Chinese Loess Plateau and play an important role both in reducing damage from flash floods and in retaining sediment. Some check dams are destroyed either partially or fully during rainstorms. The investigation of the actual damage caused to check dams as a result of specific rainstorm floods is of great value for analyzing their effects and failure modes, and is also helpful for proposing a reasonable approach for their improvement. The “7.26” extreme rainstorm event on July 25 and 26, 2017, in Yulin in northern Shaanxi Province, China, resulted in serious infrastructural damage and economic losses. This study reports on a detailed investigation undertaken between August 27 and October 28, 2017, of the causes and severity of the damage to the check dams in the Chabagou watershed. The results showed that out of a total of 572 check dams surveyed, 63.6% were destroyed and 9.3% were damaged. The mean dam opening was 4.8 m wide and 3.4 m deep, while the mean water culvert was 1.7 m wide and 2 m deep. The main causes of the damage were as follows: (1) the flood return period exceeded the dam design standards, (2) 94.1% of the check dams lacked a spillway, and (3) the main land use types on the check dams were farmland and bare soil. Based on the findings of this study, the following recommendations are made: (1) improve the existing design standards for check dams, (2) build additional spillways and maintain existing spillways in a timely fashion, and (3) encourage the development of natural grass and shrub land as the best land use type on check dams.

Identification of groundwater recharge-based potential rainwater harvesting sites for sustainable development of a semiarid region of southern India using geospatial, AHP, and SCS-CN approach

Groundwater recharge-based rainwater harvesting (RWH) is a standout among the most capable structures to reduce water deficit issues and to build the accessibility of water for sustainable development in the semiarid regions because of absence of precipitation and flighty precipitation patterns. The delineation of potential recharge zone (PRZ) with RWH and selection of sites cause a greater dispute for the water stakeholders because of deficient framework. The essential thematic layer such as land use/land cover, soil, geology, vadose zone, drainage density, slope, and runoff were used for delineation of PRZ and RWH sites. Analytical hierarchical process (AHP) was carried out by assigning different weights to different thematic layers to determining the PRZ and RWH sites. The present study endeavours to decide the suitable areas for RWH using Soil Conservation Service curve number (SCS-CN) based on surface runoff with geospatial techniques. The enlargement of water asset is proposed by the development of RWH structures such as farm pond (FP), percolation tank (PT), check dam (CD), and gully plug (GP) having 73.53% (358.08 km2) appropriate for FP, 8.62% (42 km2) reasonable for PT, 17.48% (85.16 km2) reasonable for CD, and 0.35% (1.71 km2) for GP of the present study region. Based on integrated mission of sustainable development specification, 20 PT, 11 FP, and 4 CD were identified having 85%, 90%, and 100% accuracy in agreement between existing structures and predicted potential site. The present study approach demonstrates the higher accuracy for identification of RWH at any scale with sustainable water resources development.

Identification of potential sites for water harvesting structures in Gadela watershed using remote sensing and GIS

In this study the suitable sites for water harvesting structures in Gadela watershed has been identified using remote sensing and GIS. The satellite imagery of 30 m resolution data downloaded from bhuvan was used to prepare Elevation and slope map for the study area. The other thematic maps such as Land use land cover, Geomorphology, Soil, Transmissibility and Runoff maps were prepared to suggest suitable water harvesting structures. The weighted overlay approach has been applied for the prepared thematic maps based on their importance in water harvesting and converted to normalized maps. These maps were overlaid using Arc GIS tool to get the final suitability map. The suitability of the study area divided in to low, medium and high priority zones and found 31% of area is highly suitable and 45% as medium and 24% less suitable. 62 places Suitable for various harvesting structures. Twenty four Check dams, twenty five farm ponds, four nala bunds, contour trench in 187 ha for barren land and a Gully plug were proposed for the study area as per Integrated Mission For Sustainable Development (IMSD) guidelines.

The Effect of Check Dam Installation and Gabion with Distance Variation at River Turn using a Laboratory Test Model

Scour or avalanche is a problem that often occurs in river turn. One of the cliff guard buildings are check dam and gabion. This research aims to determine the effect of the distance variation of check dam and gabion installation at the river turn. This test is hydraulic model test using river flume with turn length of 5 m, width of 0.8 m, and height of 0.5 m with trapezoidal channel. Observation’s held with a constant discharge of 7.07 liters / second for 3 hours, the angle for check dam was 90° with 3 distance variations were 68 cm, 85 cm and 102 cm, while the gabion angle was 30° with distance variation of 17 cm, 34 cm, and 51 cm. The scour occurred in the river model without protection was 4.70 cm, while the scour occurred in the river model with check dam was -4.32 cm (3.08%), -3, respectively. 69 cm (1.21%), -3.72 cm (1.25%). The results of gabion tests were 3.01 cm (7.9%), -1.07cm (0.22%), -2.07 cm (0.27%). The results of the tests showed the check dam reinforcement effectively used at the beginning and the center of the turn, while at the end of the gabion.

GIS-Based Site Selection for Check Dams in Watersheds: Considering Geomorphometric and Topo-Hydrological Factors

Check dams are widely used watershed management measures for reducing flood peak discharge and sediment transport, and increasing lag time and groundwater recharge throughout the world. However, identifying the best suitable sites for check dams within the stream networks of various watersheds remains challenging. This study aimed to develop an open-source software with user-friendly interface for screening the stream network possibilities and identifying and guiding the selection of suitable sites for check dams within watersheds. In this developed site selection software (SSS), multi-criteria decision analysis (MCDA) was integrated into geographic information systems (GIS), which allowed for numerous spatial data of the multiple criteria to be relatively simply and visually processed. Different geomorphometric and topo-hydrological factors were considered and accounted for to enhance the SSS identification of the best locations for check dams. The factors included topographic wetness index (TWI), terrain ruggedness index (TRI), topographic position index (TPI), sediment transport index (STI), stream power index (SPI), slope, drainage density (DD), and stream order (SO). The site identification performance of the SSS was assessed using the receiver operating characteristic (ROC) curve method, with results for the case study example of the Poldokhtar watershed in Iran showing excellent performance and identifying 327 potential sites for efficient check dam construction in this watershed. The SSS tool is not site-specific but is rather general, adaptive, and comprehensive, such that it can and should be further applied and tested across different watersheds and parts of the world.

Multi-temporal analysis of the role of check dams in a debris-flow channel: Linking structural and functional connectivity

Check dams represent one of the most common hydraulic engineering solution to manage debris-flow risk. However, the design of these structures only rarely considers their impact on sediment connectivity and sediment fluxes, both at the channel reach and catchment scale. In the last two decades, High-Resolution Topography (HRT) provided fundamental data to analyse the morphology evolution of landscapes through the realization of sequential DTMs (Digital Terrain Models) and DTMs of Difference (DoDs). In the context of mountain catchments, HRT offers essential information on the evolution of erosion and deposition patterns and allows the application of multi-temporal geomorphometric indexes that can enrich the DoDs analysis with important data as the assessment of sediment connectivity. In this research, multi-temporal LiDAR-derived DTMs were used to derive DoDs and to perform a multi-temporal analysis of an index of sediment connectivity (IC) in three reaches of a debris-flow channel (Moscardo torrent, eastern Italian Alps) where several check dams have been built over time. The research aims at outlining the effects of torrent control works on sediment dynamics in steep channels affected by frequent debris flows. The integration of the difference of IC with DoD maps allowed quantifying the impact of newly built check dams on changes in sediment pathways and related erosion processes, highlighting a close relationship between structural and functional connectivity: in areas where erosive processes prevailed, there were increases in connectivity, while deposition areas showed a decrease of IC. The geomorphometric analyses show that the new check dams have affected the sediment transfer along the main channel but also the hillslope-to-channel connectivity by altering sediment pathways. In the Moscardo torrent, however, the strong impact of these structures on sediment transfer is not matched by long-term effectiveness in debris-flow control.

Mitigation and Bioengineering Measures for Prevention of the Surbhi Resort Landslide, Mussoorie Hills, Uttarakhand Lesser Himalaya, India

Recent cloud bursts and Glacial Lake Outburst Flood ( GLOF ) in the Uttarakhand Himalaya have triggered catastrophic landslides. Heavy monsoon precipitation lashed Uttarakhand causing devastation and series of new landslides in the region. The Surbhi Resort Landslide is located near the hill station of Mussoorie in Garhwal Himalaya, India, in the Upper Krol Limestone. After intense rain in August 1998, the Krol sedimentary deposits suddenly gave way as a deep-seated landslide, blocking the main Mussoorie-Kemptyartery for 15 days. In 2005, the velocity of the slide was determined to be 4–14 mm/year by previous workers, thus it was still active with a modest intensity. Recently in 2018, during monsoon there was heavy rainfall in the Mussoorie and mud flow in the Kemty Fall area. Huge amounts of quaternary debris are still lying on the slope, another high intensity rainfall or cloud burst in future could trigger another large-scale failure. Based on our recent detailed investigations, following mitigation and bioengineering measures are suggested. To lower the ground water table, a series of horizontal drains should be installed at the base of the crown portion of the slide. This would generate an additional discharge which has to be channeled down Rangaon-ka-Khala, the natural channel, down the slope to the Aglar River flowing in the valley below. To prevent further surface erosion, it is suggested that the Rangaon-ka-Khalamust be bioengineered with shrubs and grasses such as Eriophorum comosum, Saccharum spontanum, Pogonatherum spp. And Wood fordia fruticosa while the surrounding slope must be reforested with Quercus leucotrichophora, Alnus napelensis , Pinus spp.and Cedrus spp. Check dams must be constructed on the entire 3.5 km stretch of the Rangaon-ka-khala to lower the velocity of thewater. This could be done either as gabions or in the form of live fascines of Salix tetrasperma or Dalbergia sissoo. The catchmentarea above the Mussoorie-Kempty road can be expected to collect 60,000 m3 in 24 hours in a 25-years reoccurrence cloud burst. Thus proper drains (0.40 m in dia.) on the inside of the road must be installed. The flow velocity at these extreme events would be 4.8 m/switch is slightly above the recommended value. If this water is allowed to flow down the Rangaon-ka-Khala it will most certainly lead to a major debris slide with a vertical velocity of almost 100 m/s with huge erosive power. For this reason, this discharge should be channeled down in plastic or cement lined pipes, preferably to the west of the Siyagaon Village which is reported as stable rather than in the landslide zone itself. It is concluded that these mitigation measures and bioengineering plantation would certainly help stabilize the Surbhi landslide area to prevent further disaster in future that destroyed the water mills, fields of the surrounding villages and mud flow in popular Kempty Fall area. These measures may also be applicable for the other active landslide zones in the NW(Jammu and Kashmir) and NE ( Darjiling-Sikkim ) Himalaya.

Physics-Based Simulation of Hydrologic Response and Sediment Transport in a Hilly-Gully Catchment with a Check Dam System on the Loess Plateau, China

Check dams are among of the most widespread and effective engineering structures for conserving water and soil in the Loess Plateau since the 1950s, and have significantly modified the local hydrologic responses and landforms. A representative small catchment was chosen as an example to study the influences of check dams. A physics-based distributed model, the Integrated Hydrology Model (InHM), was employed to simulate the impacts of check dam systems considering four scenarios (pre-dam, single-dam, early dam-system, current dam-system). The results showed that check dams significantly alter the water redistribution in the catchment and influence the groundwater table in different periods. It was also shown that gully erosion can be alleviated indirectly due to the formation of the expanding sedimentary areas. The simulated residual deposition heights (Δh) matched reasonably well with the observed values, demonstrating that physics-based simulation can help to better understand the hydrologic impacts as well as predicting changes in sediment transport caused by check dams in the Loess Plateau.

English

Physical soil and water conservation measures with ultimate intention of reducing sever soil erosion and its associated impact had been implemented for the last four decades in southern Ethiopia. Yet, so far the technical viability of the implemented structures weren't studied. Therefore, the objective of this study was to evaluate the technical viability of the implemented physical soil and water conservation measures and its management, maintenance and appropriateness in communal and private lands of the upper catchments of Lake Hawassa watershed. The data was collected by field observation and direct measurement of the implemented structures. Moreover, focused group discussion and key informant interview was done. Descriptive statistics was used for data analysis. The results were compared with standards.  The collected data were presented in Table and Figures. The study result showed that Level soil bund and Check dam were implemented in communal land by public participation, while Level soil bunds and Fanya- juu were found in private land. The implemented structures were appropriate for the catchment, while the layouts of most implemented structures were not as the standard. The regular maintenance and management practices were also minimal. As the result, technically deficient SWC measures were found as cause of soil erosion and witnessed that construction of SWC structure in field is not an end means by itself for effective controlling of soil erosion. To be effective the implemented SWC structures has to be appropriate for the area and technically be sound. Regular maintenance and management of the structure after implementation is also vital to achieve its very inception objective. Key words: Check dam, Level Fanya- juu, soil bund, standards. &nbsp

A numerical framework for the multi-objective optimal design of check dam systems in erosion-prone areas

Check dams are one of the most popular measures for soil erosion control. Despite the availability of various process-based modelling tools, their design is often carried out in an uncoordinated manner, potentially leading to check dam systems with limited life expectancy or unreliable sediment retention capacity. In this study, we consider the problem of determining the optimal location and size (i.e., initial storage capacity) of a given number of check dams, and tackle this problem by contributing a numerical framework that builds on geo-processing, two process-based models (WaTEM/SEDEM and StoDyM), and multi-objective evolutionary computation. The application of our framework to two catchments in the Chinese Loess Plateau, characterized by similar erosion processes but different extensions (4.26 and 13.97 km2), reveals a strong trade-off between three criteria of system's performance, namely life expectancy, sediment retention capacity, and storage dynamics. Results also show that there are opportunities for improving the performance of existing check dam systems through a coordinated, optimization-based, planning exercise.