Levees Research Articles

Analyzing the adoption of nutrition-sensitive carp-SIS polyculture technology: evidence from a case study in Bangladesh

IntroductionSmall indigenous species (SIS) of fish are rich in micronutrients that are essential to combat the existing malnutrition in Bangladesh. However, their availability is constantly decreasing due to gradual environmental degradation making their availability irregular and hence expensive in the market. Integrating SIS with carps in homestead ponds is being promoted as a form of nutrition-sensitive aquaculture to enhance both production and consumption of these nutrient-rich species. Various improved pond management techniques (IPMTs) are suggested to boost the nutrition-sensitive carp-SIS polyculture.ObjectivesThis study examines the trends and factors influencing the adoption of IPMTs using the sustainable livelihood framework (SLF) approach. We address the following three key questions: (i) What are the trends in production and consumption of fish, in particular SIS from homestead ponds? (ii) Have farm households adopted or disadopted IPMTs over time? (iii) What are the determinants of adoption and disadoption of IPMTs?MethodsBased on primary data of 234 households from Barishal district from 2014 and 2022, we perform significance tests to compare project and non-project households in 2014 versus 2022 and apply fixed effects Poisson regression and fixed effects negative binomial regression models to identify household decisions to adopt the IPMTs.Results and conclusionQuantitative survey results indicate a significant increase in the production and consumption of SIS over time. In 2014, the project households exhibited adoption rates of 60% or more for various IPMTs such as stocking of fast-growing species, pre-stocking liming, pond dike construction, fertilizer application, stocking of high quality fish seeds, aquatic weed control, and turbidity management. However, by 2022, some of these IPMTs were disadopted by project households and only a few techniques, including providing sunlight exposure to ponds, pre-stocking liming, and supplementary feeding, were more widely used. Additionally, many non-project households also increased their adoption rates of IPMTs significantly. The fixed effects regression model shows that adoption is positively influenced by the number of household members participating in aquaculture, size of the pond, sole ownership of the pond and the number of years household has been involved in aquaculture. Follow-up activities such as monitoring and training of the project beneficiaries and government support are recommended to support long-term adoption of the IPMTs.

Rainfall Variability, Flood Hazards and Adaptation Strategies in Douala IV and V Municipalities, Littoral Region of Cameroon

Excessive rainfall resulting to floods remain a thorny problem in developing countries including Cameroon. This follows the negative impacts of floods on the population, infrastructure and public services. This study examines rainfall variability, population vulnerability to floods and measures put in place by the population and other stakeholders to adapt to the situation in the Douala IV and V municipalities in Littoral Cameroon. The study exploits both primary and secondary sources data for its realization. Heads of households, quarter’s heads, municipal authorities and its personnel, and public administrative officials were contacted for data collection. The data focused on floods manifestation, their effects on the city, and adaptation strategies put in place to mitigate the negative outcomes. Data from semi structured interview conducted were analyzed using content analysis methods. Sociological and spatial data also collected were analyzed using remotely sensed techniques and statistical tools such as SPSS and Microsoft excel. Climatic data were collected from the urban council, the meteorological units in the town and the National Observatory on Climate Change of Cameroon. Sequential analyses (linear trend curves, standard deviations, and cumulative balances) were used to evaluate the evolution of rainfall and correlation to floods events. The result revealed that floods in Douala IV and V result from rainfall variability, characterized by deficit and excessive rains in the months of June, July, August and September. These heavy rains accompanied by human induced factors such as uncontrolled urbanization, anarchy in construction and occupation of wetlands, poor waste management, pollution of water ways and lack of drains for stagnant water evacuation leads to floods. Also, natural drivers such as the low relief of the area, a dense hydrographic network and contact with the Atlantic Ocean via the Wouri estuary result to floods. These floods are a problem to the health of the population, public services and infrastructure and sustainability of the city. Faced with the numerous damages caused by floods, remediation strategies such as: the construction of traditional dikes, solid house foundations, water embankments, and periodic weather forecasting by the National Observatory on Climate Change of Cameroon to reduce the negative outcomes of flooding has been ineffective in reduction of floods outcomes. Consequently, floods still remains a concern in Douala town. Good environmental practices such as civil education on hygiene and sanitation, periodic cleaning of drains, combats on deforestation of mangroves and afforestation campaigns, government investment on decentralization of waste collection and management will be productive in reducing the effects of floods in Douala. The implementation of all these remedial measures will not only ensure the safety of vulnerable civilian populations but the protection of their activities.

The impact of extension delivery through private local service providers on production outcomes of small-scale aquaculture farmers in Bangladesh

ABSTRACT Purpose This study delves into the effectiveness of local service providers (LSP) in improving production outcomes of small-scale aquaculture farmers in Bangladesh. Design/methodology/approach To gauge the effectiveness of LSPs, the research employs a performance-based assessment approach, focusing on 1653 fish farming households distributed across four different participation levels. Essentially, it compared quantifiable variables like the number of species cultured, productivity, proportion of fish sold and revenue metrics of the LSP-trained farmers against a control group that has not received training from LSPs. Data analysis was conducted with Multivalued Treatment Effects (MTE) estimated using an augmented inverse-probability weighting method that allows for heterogeneous treatment effects. Findings Findings revealed that farmers who received the LSP extension training exhibited a significant increase in all outcomes compared to their counterparts. The LSP extension participating farmers are more likely to adopt better management practices like improved feeding routines, dike constructions, pond cleanliness, and fish growth monitoring. Practical implications LSP extension model with enhanced capacity can be a catalyst for improved production of small-scale aquaculture farmers. Theoretical implications This study contributes to a research agenda related to the efficiency of emerging pluralistic extension service systems that favors decentralization, privatization, and outsourcing of extension service, and their capability to enhance the production outcomes of small-scale farmers. Originality/value This study addresses an important research gap in the agricultural extension literature, which is the value-for-money of Local Service Providers, and their capability to enhance the production outcomes of small-scale farmers.

PHYSICOCHIMICAL,MINERALOGICALAND GEOTECHNICALCHARACTERIZATION OF THE EARTH OF THE 9TH DISTRICT OF THE CITY OF NDJAMENA IN CHAD WITH A VIEW TO THE CONSTRUCTION OF HYDRAULIC STRUCTURES

The work carried out in this paper aims at the physicochimical, mineralogical and geotechnical characterization of the soils used in the construction of dikes in the 9th district of the city of NDjamena in Chad in order to guide those responsible for the construction of structures related to this soil.Physicochimical,mineralogical and geotechnical analyses were conducted. The results obtained show that the soils used for the construction of the dikes (existing structure is a dam made of earth without a coating at the time) are fine soils with a percentage of the fines that varies between 38.7% and 73.1% at the 80μm screen. According to the GTR classification, these floors belong to classes A2 and A3.The plasticity index of the soils studied ranges from 18 to 35. These values confirm that the soils used are plastic soils. The porosity is in the range of 34.23% to 40% and the void index is between 0.36 and 0.59. These soils are very sensitive to water, compaction and deformation.Chemical analysis shows us that Silicon oxide is the most dominant constituent (63.29% to 80.22%) followed by Aluminum oxide (10.49% to 18.15%) and iron oxide (3.22% to 5.87%).Mineralogical analysis confirms that Quartz is dominant (56.24% to 46.5%) followed by Kaolinite (27.41% to 12.07%), illite (12.38% to 9.43%), k-feldspar, plagioclase and other minerals. The presence of smectite shows that the soils are made up of clays that have a high swelling capacity. Thus, the use of these soils in hydraulic structures such as dikes and dams requires special treatment so that it can effectively perform their roles.

A Model Of Wave Attenuation In Vegetated Environments

Mangrove degradation and rapid coastline erosion have been widely observed at many locations along the Mekong Delta Coast. These locales frequently display narrow mangrove forests, occasionally spanning as few as 100 meters. This phenomenon of the narrower mangrove forests is supposed to be due to the construction of sea dikes in a search to establish room for agricultural purposes and to hinder the salinity intrusion, referred to as "mangrove squeeze". Within the context of monitoring mangrove forest evolution alongside the shoreline's dynamic processes of erosion and accretion, the hypothesis of a "squeeze mangrove forest" was advanced by Phan (2015) and Truong (2017). This conceptual construct underscores the fundamental importance of "mangrove width" as a critical length scale influencing the sustainable growth of a mangrove forest. The physical interpretation of this length scale is intricately tied to the extent of the mixing layer's intrusion into the vegetative domain (Truong et al., 2019). It is important to note that while the mixing dynamics of estuarine mangroves are primarily regulated by lateral flow events induced by large vortex structures moving along the vegetation edge, the characteristics of incoming waves primarily determine the length to which the mixing layer penetrates within coastal mangroves. The latter is the primary focus of this study.

Impact of Structural and Non-Structural Measures on the Risk of Flash Floods in Arid and Semi-Arid Regions: A Case Study of the Gash River, Kassala, Eastern Sudan

Sediment precipitation in riverbeds influences the effectiveness of structural and non-structural measures for flash flood mitigation and increases the potential for flooding. This study aimed to disclose the effectiveness of the implemented measures for flood risk mitigation in Kassala town, eastern Sudan. We employed remote sensing (RS) and GIS techniques to determine the change in the Gash River riverbed, the morphology, and the leveling of both the eastern and western sides of the river. Flood model simulation and a 3D path profile were generated using the digital elevation model (DEM) with a data resolution of 12.5 m from the ALOS BILSAR satellite. The main purpose of this study is to extract the layer of elevation of the riverbed on both the western and eastern banks and to determine the variations and their relationship to flood occurrence and mitigation. The construction of dikes and spurs near Kassala town has led to sediment precipitation, causing the riverbed to rise. The results show that it is now 1.5 m above the eastern Kassala town level, with a steep slope of 2 m/km, and the cross-section area at Kassala bridge has shrunk, which indicates that the bridge body will partially impede the river’s high discharge and increase the potential for flood risk in the study area. The eastern part of Kassala town has a higher likelihood of flooding than the western side. This study suggests redesigning structural measures like widening the Gash River, extending Kassala bridge for normal water flow, strengthening early warning systems, and implementing soil conservation activities for normal water flow.

Facies analysis, architectural elements, and paleoenvironmental reconstruction of alluvial deposits of the low terraces and floodplains in the Middle Sebou river (Eastern Saïss foreland basin, Morocco)

This paper focuses on the study of the floodplain and low terrace deposits of the Middle Sebou Valley, which crosses the south-rif corridor and constitutes the eastern limit of the Saïss Basin. The study includes the identification of facies, the determination of architectural elements, the reconstruction of paleoenvironments, and the proposal of a model for deposit formation. The work is based on detailed sedimentological analysis of the deposits, focusing on lithology, grain size, primary sedimentary structures, and the types of contact between facies. Facies analysis identified 21 facies grouped into three associations corresponding to nine architectural elements whose identification was based on the study of their lateral and vertical profiles. The architectural elements identified include the channel (CH), gravel bars and bedforms (GB), sandy bedforms (SB), downstream accretion (DA), lateral accretion (LA), sediment gravity flows (SG), natural levee (LV), floodplain (FF), and abandoned channels and meanders (FF (CH)). The alluvium is organized into rhythmic and fining-up elementary sequences reflecting its deposition in different fluvial environments: alluvial fan, straight to slightly sinuous and braiding-tending fluvial environment, and meandering fluvial environment. Alluvial deposition is controlled by lithology, climate, and tectonics. Lithology and tectonics controlled the slope, the degree of valley confinement, the accommodation space, and the alluvial fan development. Climate controlled the flow regime, sediment dynamics, and the formation of paleosol and calcrete.

Macroscale impact assessment of flood damage reduction from climate change adaptation policies

AbstractAdaptation policies are being increasingly implemented to cope with the increased frequency of natural disasters due to climate change. However, it is crucial to quantitatively evaluate the mitigating effects of these policies, as this allows for their assessment and prioritization. Therefore, this study sought to develop a nonlinear flood damage function for each administrative region of South Korea to quantify the potential damage caused by extreme rainfall events. Afterward, a power function was nested to model the coefficient of the flood damage function with regional factors characterizing each region's flood mitigation capacity. Here, regional factors were selected based on their linkage to two potential adaptation policies: enhancing retention reservoir and pumping capacity and enhancing river dike construction. The proposed evaluation framework was tested in 15 administrative districts in South Korea and the flood damage reduction effects of the two policy scenarios were estimated. The enhancement of retention reservoir and pumping capacity showed a 6.7% reduction effect, whereas enhancing river dike construction showed a 29.2% reduction effect. The implementation of both policies yielded a 34.3% reduction effect. Despite the limitations of this study, our findings still provide a quantitative comparison of the long‐term effects of national climate change adaptation measures. Additionally, accumulating more damage records would allow for the development of damage functions at a finer scale.

Spatial Design Thinking in Coastal Defence Systems: Overtopping Dikes in Southend-On-Sea

Coastal dikes have been built for millennia to protect inhabited lands from exceptional high tides and storm events. Currently, many European countries are developing specific programs to integrate the construction of new dikes (or the raising of existing ones) into the built environment to face sea level rising. Technical difficulties in succeeding in this operation are questioning the paradigm of protection for the long term, pointing out the need for alternative strategies of adaptation that are not yet fully explored. This paper elaborates on innovative models to deal with coastal flooding, presenting the results of an interdisciplinary research and design process for the case-study of Southend-on-Sea (UK). Detailed numerical simulations are used to develop a spatial strategy to accommodate water during extreme events, introducing different prototypes of dike designs that include seawalls, enhanced roughness through rock and stepped revetments, as well as vegetation. The overall goal is to push forward the traditional approach of planning water protection infrastructure within the solely field of civil engineering. It elaborates on the integration of the disciplines of spatial design and engineering and presents novel advances in terms of spatial design for the revetment of overtopping dikes.

Risk assessment of flood disasters in the Poyang lake area

Floods are one type of common and catastrophic disaster and cause extensive destruction areas, enormous casualties, and huge economic and environmental losses worldwide. Flood risk assessment is crucial to disaster mitigation and prevention, social stability and prosperity, and economic and environmental sustainability. This work establishes comprehensive risk indices of geoenvironmental, disaster-triggering, disaster-vulnerable, and disaster-preventive factors to improve the rationality of risk assessment. Moreover, a novel combined method of context-perception long short-term memory (LSTM), analytic hierarchy process, and entropy weight is suggested to perform relative accurate risk assessment in the Poyang lake region, one of the worst-hit areas in China. The new context-perception LSTM algorithm can adequately learn comprehensive and significant context characteristics and outperforms the context-based convolutional neural network and conventional LSTM algorithms. The test precision reaches 95.7%, 99.1%, 0.958, and 0.981 in Accuracy, TPR, F1-score, and AUC, respectively. Some significant insights into flood risk are suggested as follows. (1) High flood risk mainly occurs in the densely populated regions with gentle topography close to main streams. The concentrated population and intensive town construction have destroyed surface permeability and soil consolidation and caused high flood risk. (2) In the high-risk urban regions, the operational condition of old soil dikes should be continuously monitored, and the construction of high rock dikes are necessary to effective flood prevention in the future. In the densely-populated and high-risk urban regions, more emergency rescue infrastructures, for example hospitals and emergency shelters, are required to arrange or build. Rational planning of emergency shelters can not only protect people against floods but also reduce government investment. (3) Significant hydrological infrastructures require high-frequency or even near real-time monitoring to timely discover engineering diseases and to avoid huge losses caused by unstable prevention infrastructures during flash floods.

A Study of Abrasion Identification for Coastal Areas at Sidangoli Gam Village

An abrasion of the coastal areas has occurred at Sidangoli Gam Village, West Halmahera of North Maluku. The original condition was planted mangroves for coastal areas protection. However, it has recently been abraded due to big waves from the Pacific Ocean. Local people and the government constructed a conventional dike using coral stone and wooden piles. Nonetheless, this dike construction is designed without physical meaning. On the other hand, local people cannot be moved to another location because they have fishermen, and this place is very familiar to them. This research aimed to study the identification factor of coastal abrasion area in the field, such as observation in length, abrasion in width, the measured elevation of land, taken coordinates by using GPS (Global Positioning System) for two points and measuring the slope of the land, lithology of the soil layer, land use, and also enquire about how long people have lived in the nearby coastline area. Therefore, the index of susceptibility to abrasion, called IKP, will be presented. The index of susceptibility of abrasion (CVI) results are obtained at 48,99, a moderate vulnerability condition. This value is considered as shoreline change of 4.0, visually observed of 5.0, abrasion in the length of 1.0, abrasion in width of 4.0, green belt width of 4.0, soil lithology of 4.0, land use of 4.0 and slope on land of 5.0. These results may be conducted using coastal dikes to avoid big and high waves from the Pacific Ocean.

The Multi-Channel System of the Vietnamese Mekong Delta: Impacts on the Flow Dynamics under Relative Sea-Level Rise Scenarios

The Mekong Delta has the world’s third-largest surface area. It plays an indisputable role in the economy and livelihoods of Vietnam and Cambodia, with repercussions at regional and global scales. During recent decades, the Vietnamese part of the Mekong Delta underwent profound human interventions (construction of dykes and multi-channel networks), which modified the hydrodynamic regime, especially cycles of field submersion. In this study, we first applied a full 2D numerical hydraulic model, TELEMAC-2D, to examine the effects of the complex channel and river networks on the spatial and temporal distribution of the flow in the 40,000 km2 of the Vietnamese Mekong Delta. Then, two scenarios of relative sea-level rise in 2050 and 2100 were implemented to simulate the future patterns of water fluxes in the delta. The results show that dykes and multi-channel networks would reduce the inundation area by 36% and lessen the peak water level by 15% and the discharge over the floodplains by 24%. Despite this protection, under a relative sea-level rise of 30 cm and 100 cm, the maximum flooded area could occupy about 69% and 85% of the whole delta in 2050 and 2100, respectively.

Dike risk evaluation incorporating the contribution of coastal wetlands: A case study on Chongming Island, China

Due to the increasing risk of coastal disasters and climate change, the traditional gray sea dikes may become unsustainable. Coastal wetlands provide natural protection for shoreline areas and have wave attenuation capacities as green dikes. In this study, we developed a new assessment approach to evaluate comprehensive dike risk for coastal gray-green defense systems, based on the dike characters and the wave attenuation capacity of coastal wetlands for the Chongming Island. The risk assessment system consists of nine indicators of dike constructure standards, dike-top height, land subsidence, wetland vegetation width, wave attenuation capacity of vegetation, mean high water level, storm frequency, rain intensity, and annual rainfall, to determine the dike risk index (RI). The information of dike and meteorological conditions were obtained by carrying out a field survey and referring to construction bulletins and domestic statistical yearbooks. The wave attenuation effect of wetland vegetation was characterized by plant morphology and seasonality. The results indicated that, without the coastal wetland indicators, the RI values of most parts of the dike ring of the island were high. The high-risk regions were mainly located in the south and north shores, consisting of several old dikes that did not meet the constructure standard. The risk level was higher in summer and autumn than in winter and spring, due to seasonal variations (typhoon or storm frequency and intensity). When the coastal wetland indicators were included, the presence of coastal wetland vegetation reduced the dike RI values by an average of 13.6% around the Chongming Island. During the flourishing periods of the vegetation, a high rate of wave attenuation reduced the RI levels considerably. We provide a reliable framework to carry out large-scale and high-resolution dike risk assessment to be applied for wetland vegetation restoration, green dike construction, and risk management in coastal areas.

Creating new littoral zones in a shallow lake to forward-restore an aquatic food web

Current rates of habitat loss require science-based predictions on how to restore or newly create lost habitat types. In aquatic ecosystems, littoral zones are key habitats for food web functioning, but they are often replaced by unnatural steep shorelines for water safety. To reverse this trend, knowledge is needed on how to successfully (re)create littoral zones. We quantified the response of an aquatic food web to the large-scale creation of new heterogeneous littoral habitats in shallow lake Markermeer, the Netherlands. Lake Markermeer was formed by dike construction in a former estuary, which created a heavily modified homogeneous 70,000 ha turbid lake lacking littoral habitat. Fish and bird populations declined over the last decades, but classical restoration via return to former marine conditions would compromise water safety and the large spatial scale prohibited biodiversity offsets. Therefore, an innovative “forward-looking restoration” approach was adopted: a 1000 ha archipelago called “Marker Wadden” was constructed without using a historic reference situation to return to. This aimed bottom-up stimulation of the aquatic food web by adding missing gradual land-water transitions and sheltered waters to the lake. After four years, new sheltered shorelines had become vegetated if they were constructed from nutrient-rich sediments. Exposed and sandy shorelines remained free of vegetation. Zooplankton community diversity increased in sheltered waters due to bottom-up processes, which increased food availability for higher trophic levels, including young fish. The creation of sheltered waters increased macroinvertebrate densities threefold, with sediment type determining the community composition. The archipelago became new nursery habitat for 13 of the 24 fish species known to occur in the lake, with up to 10-fold higher abundances under sheltered conditions. We conclude that modifying abiotic conditions can stimulate multiple trophic levels in aquatic food webs simultaneously, even in heavily modified ecosystems. This provides proof-of-principle for the forward-looking restoration approach.

Effects of the Diversity of Flow Velocity on the Upstream Migration Behavior of Grass Carp in the Reaches of Spur Dikes

The construction of spur dikes alters the flow pattern of rivers and affects the upstream migration behavior of fishes. Traditional rock-fill spur dikes and experimental permeable spur dikes with a “Weighted Excess Storage” (WES) profile were evaluated using hydrodynamic experiments and experiments on the upstream migration behavior of juvenile Grass Carp (Mylopharyngodon idella). The swimming ability and upstream migration paths of juvenile Grass Carp in the spur dike were analyzed, and the relationship between the upstream migration success rate of Grass Carp and the diversity of flow velocity was studied. The induced velocity and critical velocity of juvenile Grass Carp with a body length of 5 ± 0.5 cm are 0.1 m/s and 0.7 m/s according to the experiment. The flow velocity diversity index increased roughly in a power function trend with the increase in flow discharge, and under the same flow conditions, the flow velocity diversity index of permeable spur dikes was greater than that of rock-fill spur dikes. When the flow velocity was within the preferred velocity range of Grass Carp, the success rate of upstream migration increased linearly with the diversity of flow velocity. When the velocity was greater than 60% of the critical velocity of Grass Carp, the success rate of upstream migration dropped sharply. Compared with rock-fill spur dikes, the experimental permeable spur dikes provide a passage for the upstream migration of fishes and reduce the impact on the upstream migration of fish. The results of this research provide theoretical support for ecologically optimized designs of spur dikes and the ecological management of rivers.

A novel seismic full waveform inversion approach for assessing the internal structure of a medieval sea dike

AbstractCoastal protection in the form of dike constructions has a long history at the German North Frisian coast dating back to the High Middle Ages. As the vast majority of the dikes built prior to the devastating storm surges of the Middle Ages have been irretrievably destroyed, mostly sparse remains and only a few well preserved of these medieval dikes are found along the German North Frisian coast and within the Wadden Sea. Not all details of their construction and dimensions are yet understood. In the present case study, we investigate the historical Schardeich on the island of Pellworm in the German North Sea in a noninvasive way using shear waves (SH‐waves). For the data interpretation, we applied a combination of seismic full waveform inversion and classical seismic reflection imaging to determine the interior structure of the dike and its underlying layers at the highest possible resolution. The results obtained on land are compared with dike remains found in the tidal flats. These remains show up in marine seismic sections as characteristic reflections, which probably represent a compaction layer caused by the load of the former dike. For ground truthing, we compare the seismic results with internal dike structures found in nearby excavations. The comparison highlights that FWI is a reliable tool for near‐surface archaeological prospecting. We find that SH‐wave FWI provides decimetre‐scale velocity and density models that allow, together with the seismic reflection section, to determine distinct construction phases of the dike. The investigated dike further shows a depression at base level of about 0.75 m, which is of the same order as observed for the dike base reflections in the tidal flats. Transferring these findings to the dike remains mapped in the tidal flats, we derive a height of the former dike from 2.2 to 4.4 m.

Restoration of a fish-attracting flow field downstream of a dam based on the swimming ability of endemic fishes: A case study in the upper Yangtze River basin

The construction of fish passage facilities can mitigate the negative effects of dams and other water engineering construction on river connectivity and have a significant positive effect on the conservation of local fish diversity. To attract target fishes into fish passage facilities effectively, the optimal flow velocity range to attract fish must be determined. Three local endemic species of the Mishi Reservoir were considered as the protection targets. However, their swimming abilities remain unclear. Therefore, the induced swimming speed (Uind), critical swimming speed (Ucrit) and burst swimming speed (Uburst) of three fish species were tested. Based on these results, we identified the optimal flow velocity to attract fish, which falls within the range of 0.15–0.51 m/s. A validated three-dimensional hydrodynamic model was used to simulate different schemes. By comparing the flow field simulation results of different schemes, we obtained the optimal measure to restore the flow field, namely, a multiple engineering measure combining increased the fish attraction flow in the fish collection pond and the construction of a spur dike. This study offers a solution for the specific case and enhances the database of swimming characteristics of endemic fish in the upstream reaches of the Yangtze River. It also provides a valuable reference for designing fish-attracting flows and potential measures for restoring flow fields in similar future projects.

Assessment of Water Quality in a Coastal Region of Sea Dike Construction in Korea and the Impact of Low Dissolved Oxygen Concentrations on pH Changes

To investigate the factors affecting water quality in coastal regions with sea dike constructions, surface water outside a sea dike was monitored for six years from 2015 to 2020 in the Saemangeum region of Korea. Statistical analyses of the six years of high-frequency measurements revealed that the water quality in this system was predominantly governed by natural processes followed by pollutant inputs as the secondary influencing factor. Severe dissolved oxygen (DO) depletion was observed in the surface waters during warm periods, probably owing to the advection of DO-depleted water from elsewhere to the surface layer. Based on the apparent oxygen utilization (AOU)–pH relationship (r = 0.52, n = 1837), the maximum AOU (180 µM) led to a pH decrease from 8.04 to 7.50, which was considerably lower than the estimated value of 7.72. This extra pH drop was probably due to a reduction in the buffering capacity associated with increased CO2 in the water column originating from the atmosphere and in situ production, as well as local water column redox reactions associated with benthic inputs of reduced chemical species. Overall, persistent DO depletion with ongoing eutrophication/hypoxia could accelerate ocean acidification in Korean coastal waters, which could be more acute in coastal regions with artificial coastal constructions.

Trenched and diked contours for sustainable agricultural utilization in changing world; soil hydrological, geomorphological, and physical perspectives from over 70 years of implementation in the Northern Negev

AbstractTrenched and diked contours (TDC) are used in hilly arid regions worldwide to reduce runoff and soil erosion. The TDC is based on three parts: ‘runoff contributing area’, trench, and adjacent soil dike on the hillslope contours. Surveys over the Northern Negev indicate the hydrological interrelation between the inter‐dike surface and the dike. This study hypothesized that all the TDC parts are hydrologically interrelated. The objective is to analyze the soil's physical properties that influence the interrelation from dike construction until maturation and the influences of these interrelations on soil fertility, salinity, and stability. TDC systems, also known as ‘Shikim’, were constructed by the KKL‐JNF (Karen Kayemet L'Israel. The Jewish National Foundation) all over the hills of the Northern Negev, the semiarid region of Israel, from the 1950s until present, which gives the ability to analyze the dynamic of water flows inside the TDC s along their existence. The findings indicate three hydrological interrelations, (i) From the ‘runoff contributing area’ into the trench, which differs between the planted and un‐planted types; (ii) From the trench into the dike; (iii) and water migration in the ‘dike’ medium. Along the TDC maturation, the intensity of biological influences on these interrelations increases, leading to increased water mobilization to the trench (planting strip) and into the dike medium. The water migration in the ‘dike’ leads to forming of a soil bed adequate for sustainable agricultural utilization in its' downslope face. The finding of this study will maximize the agricultural utilization of the TDCs and their profitability.

Effect of planning policies on land use dynamics and livelihood opportunities under global environmental change: Evidence from the Mekong Delta

The Mekong Delta faces significant challenges in supplying Vietnam and its export market countries with agricultural commodities, while ensuring livelihoods and providing living space to its growing population in the context of climate change and the country’s agrarian transition. Anthropogenic factors, such as the construction of dykes to control river flooding, river sand mining, the further development of triple-cropping rice production, and infrastructure development, together with climate change impacts on sediment and water availability, are all combining to threaten agricultural production. One of the key challenges in sustainable development is the need to identify plausible future states of agricultural-based socio-ecological systems which draw upon differing strategies of land management, and to characterise the impacts of these systems on both the landscape and employment. It was hypothesised from the literature and rapid rural appraisals that each land system can only provide a certain number of jobs, which was further demonstrated using binomial regressions. We show that the odds of being employed are lower for intensive agricultural systems (OR=0.78 for triple rice; 0.91 for intensive aquaculture) than for diversified systems (OR=1.16 for rice-aquaculture; OR=1.63 for mixed fruit trees). Drawing from workshops with local and national stakeholders, we then used Earth observation and national census data in a spatial land use systems dynamic framework to simulate two alternative Mekong Delta futures based upon the climate pathway RCP 4.5 in combination with two existing policies (i) Resolution No. 124 (Specialisation) which promotes triple crop rice and aquaculture intensification and (ii) Resolution No. 639 (Diversification), which states that there should be a development of sustainable rice aquaculture and crop diversification. Based on the quantitative objectives of each policy, we estimated likely changes of services provided by land use systems if either policy were to dominate. The estimated impacts of each future scenario on the provision of employment ultimately indicate that policies with a diversification development paradigm will provide more employment (+0.9%) than policies with a specialisation paradigm (−46%), and that current policies have potentially conflicting consequences. Decisions driving towards intensive farming risk triggering rural unemployment and outmigration, potentially exacerbating urban poverty in major cities such as Can Tho and Ho Chi Minh City. On the other hand, decisions aiming at increasing diversified agricultural systems can help secure more job opportunities. Our results indicate that spatial planning policies should rely on a broad-based assessment of land system services that include employment and environmental impacts to ensure a just transition towards resilient and environmentally sustainable rural territories.