Search

Enhancing crop production, particularly by growing a crop in the typically-fallow dry season is a key strategy for alleviating poverty in the Ganges delta region. We used a polder water and salt balance model to examine the impact of several crop management, salt management and climate change scenarios on salinity and crop evapotranspiration at Dacope and Amtali in Bangladesh and Gosaba in India. A key (and unsurprising) finding is that salt management is very important, particularly at the two drier sites, Dacope and Gosaba. Good salt management lowers salinity in the shallow groundwater, soil and water storage ponds, and leads to more irrigation. Climate change is projected to alter rainfall, and this in turn leads to modelled increases or decreases in runoff from the polders, and thence affect salt concentrations in the soil and ponds and canals. Thus, the main impacts of climate change are through the indirect impacts on salt concentrations, rather than the direct impacts of the amount of water supplied as rainfall. Management practices to remove salt from polders are therefore likely to be effective in combatting the impacts of projected climate change particularly at Dacope and Gosaba. [ABSTRACT FROM AUTHOR]

• The impact of polders' land use change on river nutrient conditions was quantified. • Polder N and P export has a contribution of 23.7% and 122.3% to nutrient in River Zhong. • Polder N and P export will increase with more residential areas and paddy lands. • Polder N and P export will decrease in case that water areas were increased. Excess nutrient export from lowland artificial watersheds (polders) led to severe eutrophication and harmful algal blooms of their surrounding rivers and lakes. Taking River Zhong in Lake Taihu basin as the study area, this study attempted to quantify the impacts of polders' land use changes on river nutrient conditions. A Nitrogen (N) Dynamic Polder model and a Phosphorus (P) Dynamic Polder model was used to estimate N and P export from lowland polders in the context of land use change. The investigation results showed that N and P contribution to River Zhong increased by 7–30% in case that 30% of agricultural lands (paddy lands or dry lands) were changed into residential areas. In case that 30% agricultural lands were changed into water areas, N and P contribution can be decreased by 6% and 35%, respectively. Fertilization period especially during rainy season (from June to August) were the hot moments of nutrient loss, accounted for above 50%. Infiltration was the main pathway of N and P export from polders, accounting for more than 60%. Therefore, from management perspective, we argued controlling urban areas, maintaining water areas and controlling fertilization for polders could be potential strategies for reducing river nutrient concentration in River Zhong. [ABSTRACT FROM AUTHOR]

Highlights • Aus-aman-rabi systems using modern high yielding varieties were evaluated in the low salinity coastal zone of Bangladesh. • System aus-aman-maize rice equivalent yield (REY) ranged from 16 to 20 t/ha/yr • System aus-aman-sunflower REY ranged from 14-20 t/ha/yr. • Rabi crop yield was strongly affected by sowing date, and was the main determinant of system yield and profitability. • With 100% of labour costed, gross margins of up to USD 1,200/ha/yr and BCR up to 1.3 were achieved. • Good water management (especially drainage) was the key to such highly productive and profitable aus-aman-rabi systems. Abstract Cropping intensity and agricultural productivity in the polders of the coastal zone of Bangladesh are much lower than that of most of the country. The main reasons for this are waterlogging, the late harvest (December/January) of the rainy season rice crop (known as 'aman'), and the lack of readily accessible fresh water during the dry season in the polders. Waterlogging prevents the production of high yielding and earlier maturing rainy season rice varieties (HYV aman), and of high yielding/value rabi (dry season) crops such as maize and sunflower. However, gravity drainage of excess water from the polders is physically feasible. Furthermore, the rivers surrounding the polders in the central coastal zone (Barisal Division) contain large volumes of fresh river water throughout the year. Research was therefore undertaken to evaluate, under good water management, the feasibility of intensifying to high yielding rice-rice-rabi cropping systems in the low salinity central coastal zone. A replicated cropping system experiment was conducted for two years at Patuakhali using a short duration modern 'aus' variety (aus is the name of the rice crop grown during the early rainy season) (BRRI dhan65), a medium duration modern aman variety (BRRI dhan44), and high yielding/value rabi crops. The cropping systems included four aus sowing dates (20 March, 5 and 20 April, 5 May) which resulted in four aman and four rabi sowing dates. Two rabi crops were compared within each sowing date (maize – Pacific 984, sunflower – Hysun 33). Annual cropping system rice equivalent yield (REY) ranged from 13.7 to 20.0 t/ha. All systems were profitable with 100% of labour purchased, although benefit cost ratios (BCR) were not always >3, suggesting low attractiveness to farmers. However, most polder farms are small, with 30–60% of labour provided by the family. With 75% or less of labour purchased (the rest provided by family), all cropping systems were financially attractive, even with a 10% decline in grain price. Rabi crop yield was the main determinant of total system REY and profitability, both of which declined as sowing date of the rabi crops was delayed beyond 15 December. Optimisation of sowing date of the rabi crops should therefore be the first consideration in cropping system intensification for the low salinity coastal zone. The optimum sowing date of both the maize and sunflower was mid-December. For adequate "turn around" time between all crops, for the varieties used in this study, the aus crop should be sown in mid-April and the aman crop in mid-August. This research shows that, with good water management, it is possible to implement highly productive and profitable aus-aman-rabi cropping systems in the low salinity coastal zone of Bangladesh. [ABSTRACT FROM AUTHOR]

Exploring the hydrological regulation of a lowland polder is essential for increasing knowledge regarding the role of polders associated with pumping stations in lowlands. In this study, the Lowland Polder Hydrology and Phosphorus modelling System (PHPS) was applied to the Jianwei polder as a case study for quantifying the regulation effects of a lowland polder with pumping on discharge and phosphorus loads. The results indicate that the polder significantly affected the temporal distribution and annual amount of catchment discharge. Compared with a no-pumping scenario, an agricultural polder with pumping stations generated a sharper discharge hydrograph with higher peak-values and lower minimum-values, as well as an 8.6% reduction in average annual discharge. It also decreased the phosphorus export to downstream water bodies by 5.33 kg/hm 2 /yr because of widespread ditches and ponds, a lower hydraulic gradient, and increased retention times of surface water in ponds. [ABSTRACT FROM AUTHOR]

Excess nitrogen (N) export from lowland artificial watersheds (polders) is often assumed to be a major contributor to the cultural eutrophication of downstream aquatic ecosystems. However, the complex transport processes characterizing lowland areas pose significant challenges in accurately quantifying their actual role. In this study, we developed a dynamic model to track N sources and transport pathways in lowland polders. The model is able to accommodate all the unique characteristics of polder dynamics, including artificial drainage, and interactions among surface water, groundwater and soil water. Our model was calibrated and validated against water level data and nitrogen concentrations measured in a lowland polder (Polder Jian) in China during the 2014–2016 period. Model performance was satisfactory with an R 2 value of 0.55 and an NS value of 0.53 for total N concentrations. The characterization of the various components of water budget and N cycle derived by the model was on par with local empirical estimates. N export from Polder Jian was approximately 57 kg ha −1 yr −1 and was distinctly higher than values reported from nearby non-polder areas. The largest fraction of N export stemmed from seepage. To our knowledge, this is the first dynamic model to quantify N export from a watershed with artificial drainage network and can be used to design remedial measures of ecosystem degradation. [ABSTRACT FROM AUTHOR]

Ensemble Kalman Filter (EnKF) is potential in optimizing parameters of an environmental model, but may lead to a worse performance of the model in case that improper parameters were updated. To overcome this weakness, EnKF was improved by coupling with a dynamic and multi-objective sensitivity analysis. The improved EnKF was applied to update the parameters of a coupled phosphorus model for simulating phosphorus dynamics of Polder Jian located in Lake Taihu Basin, China. Two parameters that were most sensitive to particulate and dissolved phosphorus were identified at each sub-period, and were then updated using EnKF. To evaluate the performance of the improved EnKF, four simulations with different parameter update strategies were implemented, and compared with measured data. The simulation with the improved EnKF well simulated DP dynamics in Polder Jian with a d value of 0.65 and a RMSE value of 0.015 mg/L. This model fit is better than that of other three simulations with different parameter update strategies, implying a success of the improved EnKF in updating parameters of the coupled phosphorus model. This improved EnKF has the advantage to update several parameters simultaneously, and can be applied in other models with minimal changes. [ABSTRACT FROM AUTHOR]

Culling prior to final harvest has shown many advantages in improving the marketable yield in freshwater prawn farming. This study is an attempt to compare three harvesting techniques on the production and population structure of Macrobrachium rosenbergii farming in a wetland ecosystem of South India. The study also compares the marketable yield structure and economics of farming of these prawns in three quadruplicate sets of polders following either complete harvest (T1) or traditional partial harvest through dewatering and cast netting (T2) or a modified cull harvest (T3) with a newly designed drag seine. Results showed better yield and faster morphotype transformation among treatments that followed cull harvesting. Among them, better results on mean weight and survival rate (64 g and 54% respectively) were recorded from T3. The results also showed that irrespective of the type of cull harvesting, their inclusion in polders facilitated faster morphotypic transformation and thenceforth the preponderance of terminal morphotypes in the harvested population. Likewise, larger sized male morphotypes were significantly higher (35% and 25% respectively) in T2 and T3. The net production also varied significantly within the treatments from 140 kg ha−1 in T1 to 515 kg ha−1 in T3. From a marketability point of view also, the total marketable prawns (>50 g group) varied considerably from 94% (T2) and 92% (T3) to 78% in T1. While working out the harvest economics through benefit-cost analysis, it was inferred that the introduction of the new harvest technique was more profitable compared to the traditional systems prevailing in Kuttanad. This study also emphasizes the need for resorting to modified partial harvesting through the use of drag seines, as it considerably reduces the cost on harvesting in a waterlogged ecosystem such as Kuttanad. [ABSTRACT FROM AUTHOR]

The urban agglomeration polders type of flood control pattern is a general flood control pattern in the eastern plain area and some of the secondary river basins in China. A HEC-HMS model of Qinhuai River basin based on the flood control pattern was established for simulating basin runoff, examining the impact of urban agglomeration polders on flood events, and estimating the effects of urbanization on hydrological processes of the urban agglomeration polders in Qinhuai River basin. The results indicate that the urban agglomeration polders could increase the peak flow and flood volume. The smaller the scale of the flood, the more significant the influence of the polder was to the flood volume. The distribution of the city circle polder has no obvious impact on the flood volume, but has effect on the peak flow. The closer the polder is to basin output, the smaller the influence it has on peak flows. As the level of urbanization gradually improving of city circle polder, flood volumes and peak flows gradually increase compared to those with the current level of urbanization (the impervious rate was 20%). The potential change in flood volume and peak flow with increasing impervious rate shows a linear relationship. [ABSTRACT FROM AUTHOR]

A choice experiment was used to analyse the preferences of residents neighbouring the Erstein polder (Alsace, France) for the different services that it provides. The heterogeneous nature of these preferences was shown through the use of a latent class model. Whilst the population as a whole values the improvement in water quality and the contribution, even partial, to flood protection, preferences differ when it comes to biodiversity and public access to the site. This study shows the potential conflicts between the different uses of the Erstein polder. These conflicts represent different communication themes for the site managers. [ABSTRACT FROM AUTHOR]

In semiarid Sahelian region, the dynamics of soil organic carbon (SOC) and water are key to sustainable land management. This work focuses on the behaviour of carbon. A total of 33 soil profiles in four polders, ranging from 10 to 65 years in age, were sampled, analysed (0–1 m), and matched with marsh soil profiles in recent sediments considered as reference ( t 0 ) for carbon stocks determination. SOC and soil inorganic carbon (SIC) stocks show a spatial variability between polders. SOC stocks were t 0 200 ± 0.8; t 60 183 ± 34; and t 65 189 ± 1.1 MgC·ha −1 , whereas the SIC stocks were negligible. These results show the highest stocks of soil carbon observed for this climatic region. The SOC stocks were also calculated for the equivalent soil mass at a defined depth (0–0.3 m); the corrected calculation of SOC stocks ( S corr ) for 2450 Mg·ha −1 of equivalent soil mass is t 0 64 ± 1.9, t 60 59 ± 9.8, and t 65 53 ± 2.2 MgC·ha −1 ; the stocks decrease by −7.8% and −17.2% from t 0 to t 60 and t 65 . Carbon was inherited from the pre-existing·marsh and the polders have conserved high stock values. [ABSTRACT FROM AUTHOR]

Hydrological processes in lowland polders, especially those for paddy rice planting, are affected by complicated factors. The improved Wageningen Lowland Runoff Simulator (WALRUS) model incorporates an irrigation and drainage scheme, and a new stage-discharge relationship to account for hydrological processes in multi-land-use polder with paddy fields and pumping stations. Here, this model was applied to assess how climate and land use changes affected the runoff of a Chinese polder in Poyang Lake basin in the past two decades. Simulated results showed that the runoff in the autumn-winter transition and midsummer months increased significantly, whereas those in the other months decreased slightly during the period of 1996-2005, primarily affected by climate change. For the period of 2006-2014, the runoff in the autumn-winter transition and midsummer increased, while that in the other months declined, affected by both climate and land use/cover changes. The land use/cover change resulting from the conversion of rice-wheat rotation to dominantly double-rice cropping and the expansion of residential area, increased the runoff during this period by demanding more irrigation water from the outside basin. [ABSTRACT FROM AUTHOR]

Phosphorus (P) export from lowland polders has caused severe water pollution. Numerical models are an important resource that help water managers control P export. This study coupled three models, i.e., Phosphorus Dynamic model for Polders (PDP), Integrated Catchments model of Phosphorus dynamics (INCA-P) and Universal Soil Loss Equation (USLE), to describe the P dynamics in polders. Based on the coupled models and a dataset collected from Polder Jian in China, sensitivity analysis were carried out to analyze the cause-effect relationships between environmental factors and P export from Polder Jian. The sensitivity analysis results showed that P export from Polder Jian were strongly affected by air temperature, precipitation and fertilization. Proper fertilization management should be a strategic priority for reducing P export from Polder Jian. This study demonstrated the success of model coupling, and its application in investigating potential strategies to support pollution control in polder systems. [ABSTRACT FROM AUTHOR]

We start with the well-known expression for the vacuum polarization and suitably modify it for 21-dimensional spin-orbit coupled (SOC) fermions on the low-buckled honey-comb structured lattice plane described by the low-energy Liu-Yao-Feng-Ezawa (LYFE) model Hamiltonian involving the Dirac matrices in the chiral representation obeying the Clifford algebra. The silicene and germanene fit this description suitably. They have the Dirac cones similar to those of graphene and SOC is much stronger. The system could be normal or ferromagnetic in nature. The silicene turns into the latter type if there is exchange field arising due to the proximity coupling to a ferromagnet (FM) such as depositing Fe atoms to the silicene surface. For the silicene, we find that the many-body effects considerably change the bare Coulomb potential by way of the dependence of the Coulomb propagator on the real-spin, iso-spin and the potential due to an electric field applied perpendicular to the silicene plane. The computation aspect of the Casimir-Polder force (CPF) needs to be investigated in this paper. An important quantity in this process is the dielectric response function (DRF) of the material. The plasmon branch was obtained by finding the zeros of DRF in the long-wavelength limit. This leads to the plasmon frequencies. We find that the collective charge excitations at zero doping, i.e., intrinsic plasmons, in this system, are absent in the Dirac limit. The valley-spin-split intrinsic plasmons, however, come into being in the case of the massive Dirac particles with characteristic frequency close to 10 THz. Our scheme to calculate the Casimir-Polder interaction (CPI) of a micro-particle with a sheet involves replacing the dielectric constant of the sample in the CPI expression obtained on the basis of the Lifshitz theory by the static DRF obtained using the expressions for the polarization function we started with. Though the approach replaces a macroscopic constant by a microscopic quantity, it has the distinct advantage of the many-body effect inclusion seamlessly. We find the result that for the nontrivial susceptibility and polarizability values of the sheet and micro-particle, respectively, there is crossover between attractive and repulsive behavior. The transition depends only on these response functions apart from the ratio of the film thickness and the micro-particle separation (/) and temperature. Furthermore, there is a longitudinal electric field induced topological insulator (TI) to spin-valley-polarized metal (SVPM) transition in silicene, which is also referred to as the topological phase transition (TPT). The low-energy SVP carriers at TPT possess gapless (massless) and gapped (massive) energy spectra close to the two nodal points in the Brillouin zone with maximum spin-polarization. We find that the magnitude of the CPF at a given ratio of the film thickness and the separation between the micro-particle and the film are greater at TPT than at the TI and trivial insulator phases. [ABSTRACT FROM AUTHOR]

Simulating the rain-runoff process in lowland polder will lead to improvements to hydrological modeling of entire floodplain catchments. The lumped Wageningen Lowland Runoff Simulator (WALRUS) provides an efficient and reliable model for simulating the hydrological processes in lowland catchment with shallow groundwater. However, this model needs to be improved before being applied to Chinese polders, which have multiple land use types and pumping stations. This study proposes an improved version called WALRUS-paddy that accounts for the discharge from multi-sources, including drylands, paddy fields, residential areas, and water areas. A water management scheme is incorporated to control the irrigation and drainage operation in paddy rice fields and the groundwater flow between the paddy field and the adjacent dryland is considered. In addition, a new stage-discharge relation function is introduced to represent the discharge process of the polder with pumping stations and culverts. Then, the model is validated in the Jianwei polder of east China. The modeled results agree well with the observed discharge and show that the improved model can provide good estimates of the discharge in this polder district. Thus, the improved model is feasible and helpful for water resources management of Chinese polders. [ABSTRACT FROM AUTHOR]

[Display omitted] • A model was proposed for mountain-lowland watershed with a average model fit of R2 = 0.66. • Domestic sewage and crop pollution contribute 56% and 42% of nitrogen (N) and phosphorus (P) loading. • Polders showed a large potential of N and P reduction, with a rate of 61.69% and 64.93%. Quantifying nitrogen (N) and phosphorus (P) sources and their contributions at a watershed scale is a primary step to design best management practices. This task is challenging for a mixed watershed with both mountain and lowland areas, because most existing watershed models were developed for mountain areas with clear water flow directions. To solve this challenge, we coupled the Soil and Water Assessment Tool (SWAT) for mountain watersheds, Phosphorus Dynamic model for lowland Polder systems (PDP) and Nitrogen Dynamic model for lowland Polder systems (NDP) for lowland artificial watersheds (i.e., polders) to characterize N and P loading for a typical mountain-lowland mixed watershed, Lake Chaohu Basin in China. The coupled model was calibrated based on eight-year (2011–2018) meteorological, hydrological and water quality datasets, and had a satisfactory performance for both hydrological and water quality variables (R2 > 0.6, NS > 0.6). Our eight-year investigation in the five watersheds of Lake Chaohu Basin revealed that 1) the estimated N and P loading had an annual averaged amount of 10,832 and 781 t/yr, and an intensity of 15.72 and 1.33 kg/ha/yr, respectively. Three watersheds (Nanfei, Pai and Baishitian River Watersheds) had relatively high loading intensity for N (35.16, 18.34 and 13.34 kg/ha/yr) and P (2.49, 1.25 and 2.72 kg/ha/yr), and contributed 67.6% (N) and 68.5% (P) to the loading of the five investigated watersheds. 2) Polders in Lake Chaohu Basin can be N and P sources or sinks for their surrounding rivers, depending on the polder-river interaction. Within Nanfei, Pai and Baishitian River Watersheds, N and P retention ability was higher in polders than that in mountain watersheds. 3) Population density, precipitation intensity and soil erosion were critical drivers of N and P loss and showed positive correlation with N and P loss intensity. This study demonstrated the high value model coupling to characterize N and P loading in a mountain-lowland mixed watershed system, and thus to improve our understanding on its N and P cycling. [ABSTRACT FROM AUTHOR]

[Display omitted] • A model was proposed for mountain-lowland watershed with a average model fit of R2 = 0.66. • Domestic sewage and crop pollution contribute 56% and 42% of nitrogen (N) and phosphorus (P) loading. • Polders showed a large potential of N and P reduction, with a rate of 61.69% and 64.93%. Quantifying nitrogen (N) and phosphorus (P) sources and their contributions at a watershed scale is a primary step to design best management practices. This task is challenging for a mixed watershed with both mountain and lowland areas, because most existing watershed models were developed for mountain areas with clear water flow directions. To solve this challenge, we coupled the Soil and Water Assessment Tool (SWAT) for mountain watersheds, Phosphorus Dynamic model for lowland Polder systems (PDP) and Nitrogen Dynamic model for lowland Polder systems (NDP) for lowland artificial watersheds (i.e., polders) to characterize N and P loading for a typical mountain-lowland mixed watershed, Lake Chaohu Basin in China. The coupled model was calibrated based on eight-year (2011–2018) meteorological, hydrological and water quality datasets, and had a satisfactory performance for both hydrological and water quality variables (R2 > 0.6, NS > 0.6). Our eight-year investigation in the five watersheds of Lake Chaohu Basin revealed that 1) the estimated N and P loading had an annual averaged amount of 10,832 and 781 t/yr, and an intensity of 15.72 and 1.33 kg/ha/yr, respectively. Three watersheds (Nanfei, Pai and Baishitian River Watersheds) had relatively high loading intensity for N (35.16, 18.34 and 13.34 kg/ha/yr) and P (2.49, 1.25 and 2.72 kg/ha/yr), and contributed 67.6% (N) and 68.5% (P) to the loading of the five investigated watersheds. 2) Polders in Lake Chaohu Basin can be N and P sources or sinks for their surrounding rivers, depending on the polder-river interaction. Within Nanfei, Pai and Baishitian River Watersheds, N and P retention ability was higher in polders than that in mountain watersheds. 3) Population density, precipitation intensity and soil erosion were critical drivers of N and P loss and showed positive correlation with N and P loss intensity. This study demonstrated the high value model coupling to characterize N and P loading in a mountain-lowland mixed watershed system, and thus to improve our understanding on its N and P cycling. [ABSTRACT FROM AUTHOR]

The distribution of non-pollen palynomorphs (NPP) in a core from Cook's Bay, Lake Simcoe, shows a response to changes in water quality accompanying agriculture, urbanization and industrialization. Low concentrations of nutrients in sediments with little non-arboreal pollen (NAP) record low disturbance prior to European settlement ∼1850s. These sediments are rich in desmids such asCosmariumspp.,Euastrumspp., andStaurastrumspp., an assemblage indicative of oligotrophic conditions. A decline in desmids together with an increase in dinoflagellates and thecamoebians up-core is consistent with increased nutrients. Abundant phytoliths in sediments that are relatively rich in Poaceae and other NAP records the draining of the Holland Marshes. A sharp increase in nutrient levels, together with a transition from high nitrite (NO2) to high nitrate (NO3) concentrations, records a sudden increase in biological oxygen demand leading to depletion of dissolved oxygen associated with the creation of polders in the 1920s and 1930s. A second influx of phytoliths immediately preceded the sharp rise inAmbrosia, recording rapid land clearing accompanying the five-fold post-World War II population boom in the Cook's Bay watershed. TheseAmbrosia-rich sediments are rich in metals and have high total phosphorus and NO3, with abundantPediastrumspp. andPeridiniumspp., notablyPeridinium willeiandPeridinium volzii, recording eutrophication. The abundance of the ciliateCodonella crateraand the difflugiid thecamoebiansCucurbitella tricuspisandDifflugia protaeiformisin palynological preparations as well as in washed thecamoebian samples from the upper part of the core records low dissolved oxygen associated with continued eutrophication of Cook's Bay. [ABSTRACT FROM PUBLISHER]

Abstract: Evidence is presented from three estuarine tide gauges located in the Sundarban area of southwest Bangladesh of relative sea level rise substantially in excess of the generally accepted rates from altimetry, as well as previous tide-gauge analyses. It is proposed that the difference arises from the use of Relative Mean Sea Level (RMSL) to characterise the present and future coastal flood hazard, since RMSL can be misleading in estuaries in which tidal range is changing. Three tide gauges, one located in the uninhabited mangrove forested area (Sundarban) of southwest Bangladesh, the others in the densely populated polder zone north of the present Sundarban, show rates of increase in RMSL ranging from 2.8mma−1 to 8.8mma−1. However, these trends in RMSL disguise the fact that high water levels in the polder zone have been increasing at an average rate of 15.9mma−1 and a maximum of 17.2mma−1. In an area experiencing tidal range amplification, RMSL will always underestimate the rise in high water levels; consequently, as an alternative to RMSL, the use of trends in high water maxima or ‘Effective Sea Level Rise’ (ESLR) is adopted as a more strategic parameter to characterise the flooding hazard potential. The rate of increase in ESLR is shown to be due to a combination of deltaic subsidence, including sediment compaction, and eustatic sea level rise, but principally as a result of increased tidal range in estuary channels recently constricted by embankments. These increases in ESLR have been partially offset by decreases in fresh water discharge in those estuaries connected to the Ganges. The recognition of increases of the effective sea level in the Bangladesh Sundarban, which are substantially greater than increases in mean sea level, is of the utmost importance to flood management in this low-lying and densely populated area. [Copyright &y& Elsevier]

The creation of a national identity shared by the whole population becomes increasingly difficult in individualizing and globalizing national societies. The national population fragments into many lifestyle groups with very different social and cultural orientations. The enactment of these different lifestyle identities during leisure activities accentuates these differences. However, these different identities are sometimes performed on the same spatial stage. The main part of this article analyses the use of the dike along the river Linge, a part the Rhine estuary, which, lined with apple trees, cuts through an iconic Dutch river landscape with polders, old villages and meadows with quietly grazing cattle. Especially during the weekends, it is a stage crowded by walkers, cyclists, classic car drivers, and motorcyclists. The importance attached to this river dike is linked to a shared traditional form of Dutch collective national identity. The different uses of the river dike are based to the diverging values on which the different lifestyles are based. This results in conflicts over the use of and access to the dike. The role of the state in regulating these conflicts results in a more limited form of national identity. [ABSTRACT FROM AUTHOR]

The frequent occurrence of floods recently has motivated discussions by experts on reviewing the safety of flood protection structures. The simulation of flood discharges belongs among transient flow tasks. Due to the randomness of the phenomenon, as well as the often unknown geological composition of the environment in which the flooding occurs, this question has become very complicated. The finite element method (FEM) is one of the methods for reviewing risk factors endangering the stability of hydraulic structures. In this article the application of FEM is mentioned in assessing the stability of the subsoil of the Borša polder in Slovakia. [ABSTRACT FROM AUTHOR]

Flooded grasslands of Šilutė municipality are a unique area of Lithuanian nature with both natural value and economic activity potential, which is now fully utilized. Today, due to lack of funding condition of the Nemunas River polder system is continuously deteriorating; the polders cannot serve their purpose: to timely remove the excess amount of water from the flooded areas and to ensure good economic condition of those areas. As a result, vegetation in the territory declines, certain types of sem-inatural habitats and species extinct, and so the natural value of the area is declining. On the other hand, more and more unused and uncut grass that could be used as a source for energy and other needs of the region is left in these areas each year. Semi-natural grassland mowing is necessary to preserve open spaces for flora and fauna. Without further measures, grasslands overgrow with shrubs, landscape changes, and meadows lose their attractiveness and cannot perform any other so-called eco-services. The research aim is to examine the importance of multifunctional agriculture in strengthening the Nemunas River polder systems with regard to competitiveness of the area. To achieve the aim the following objectives have been set: - To analyze the characteristics and design features of agricultural private and public goods; - To identify the economic efficiency of the polders, to determine key issues; - To assess the environmental impact of the main problems and failures; - To submit proposals for: a) further improvement of efficiency of functioning of polder systems, b) environmental requirements to carry out economic activities at polders, c) opportunities for development of economic activities (agricultural production and other businesses, use of straws for energy purposes), d) research necessary to carry out; - To assess the need for funds, funding sources and mechanisms to implement the proposals. - To assess the Šilutė flooded meadows and polder systems, their economic status and economic viability; - To assess the potential of multifunctional agriculture in increasing economic, environmental, social LFA competitiveness. The object of the research is flooded meadows, natural and economic potential to carry out business there, economic viability of technological devices at flooded grasslands, potential utilization of potential improvement trends and sources of funds to realize the objectives. To address these challenges the following methods are used: scientific literature logical analysis and synthesis, induction and deduction, agricultural and rural development document analysis and generalization. Research methods: analysis of scientific information and literature, legal and other documents, secondary data analysis, analogies, logical comparison, induction and deduction. Sources of information are relevant laws of the Republic of Lithuania, official information of Taurage County, Šilute district, Lithuania, Flooded Meadows Improvement Study carried out by the Lithuanian Agriculture Livestock Research Institute in 1994, and other sources of information and data. Foreign and Lithuanian monographs, scientific publications, online articles, publications, Lithuanian and European Union agricultural and rural development strategic documents for economic cooperation and development, laws of Lithuania, Lithuanian agricultural corporations data have been referred to. Some flooded areas are within the protected areas where economic activity is strictly regulated by law. Operational limitations of the Nemunas Delta Regional Park and the state reserves are regulated by the Law on Protected Areas that prohibits construction of complex wind turbines in the state parks and natural reserves. Agricultural activities in the Nemunas Delta Regional Park are regulated by the plan for management of scenic areas. Today, all the operators that have submitted the necessary documents and satisfy the requirements can expect to get support under RDP for 2007-2013. Currently, under the measure "Payments to farmers in disadvantaged areas other than mountain areas" 195 LTL per ha shall be paid under the measure "Natura 2000" and payments linked to Directive 2000/60/EC, reimbursement of 138 LTL per ha and for lost income. [ABSTRACT FROM AUTHOR]

Abstract: A spatially explicit dynamic model was developed that combines water quantity and quality processes for an average Dutch peat polder. The model has been used to calculate the consequences of climate change for surface water level, groundwater level and nitrogen and phosphorus fluxes, based on time series (2036–2065) of the two most extreme climate change scenarios for the Netherlands (G and W+) developed by the Royal Dutch Meteorological Institute. It was calibrated using measured data from two existing polders. The results suggest that surface water levels will not change much in both scenarios. Hence, the current practice of letting extra water in during dry summer periods to maintain sufficient water levels will probably remain a viable solution to temporary summer droughts in the near future as the required water volumes are not likely to increase greatly. Late summer groundwater levels decrease substantially in the W+ scenario but not in the moderate G scenario. This drop in groundwater level would accelerate the on-going process of peat oxidation, resulting in increased soil subsidence, greenhouse gas emissions and nutrient release from mineralisation. The W+ scenario also led to higher nitrogen concentrations and lower phosphorus concentrations in the ditch network. Probably the reduced stream velocity in the W+ scenario results in an increased sedimentation of (adsorbed) phosphate. Sedimentation is a less important process in the nitrogen cycle, and the increased nitrogen concentrations anticipated in summer according to the W+ scenario are therefore probably the consequence of a reduced outlet of water due to increased evaporation. Additionally, an increased delivery of nitrogen through mineralisation could also contribute to the increased nitrogen concentrations in summer. [Copyright &y& Elsevier]

Abstract: Most geological and soil maps are not detailed enough to represent the high lateral and vertical textural variability in the subsoil of coastal lowlands. Intensive sampling campaigns need to be carried out to quantify this variability. As an alternative, a proximal soil sensing procedure based on a single survey with an electromagnetic induction instrument was used to map a 6.5ha Holocene tidal area in Belgium. We investigated the effectiveness of a multi-receiver apparent electrical conductivity (ECa) survey for mapping the trace of tidal paleochannels. From a limited number of augerings, a three-layered soil was observed composed of a clayey top layer, a clayey infilling of the tidal channel above a subsoil consisting of coarse sandy material. A fitting procedure allowed modelling the conductivities of both subsurface layers, after which the four simultaneous ECa measurements were combined to model the depth of the interfaces between the three layers. The predictions were validated by 16 depth observations along a 150m transect. A correlation coefficient of 0.91, with an average error of 0.23m, was found between the predicted and measured depths of the clay-sand interface. We concluded that the dense ECa measurements (2 by 2m resolution) allowed reconstructing a precise three-dimensional representation of the tidal channels. [Copyright &y& Elsevier]

The Taihu Basin is located in the east coast of China, with a total area of 36,895 km2. Low-lying floodplain areas occupy about 83% of the basin. The threat of frequent floods to this economically important area has stimulated construction of enormous flood-defense projects along the complex system of rivers and lakes. Digital modeling of flooding processes and quantitative assessment of flood damages in this basin remain challenging due to the complexity. This article reports on an approach to simulate the flooding processes, which integrates hydrological and hydraulic modeling with dike-reliability analysis and socioeconomic information within a GIS platform. A new algorithm is introduced to calculate the influence of the flood-defense systems on spatial distributions of floodwater and consequential damages. Scenario analysis indicates that the modeling is particularly sensitive to the assumed rainfall, dike reliability, and the pump capacities within local polders. The model is validated by comparison with observations from historical flood records. The analysis reveals that the defense systems have significantly reduced the basin-wide flood risk and changed the spatial distributions of floodwater. Such a GIS-based approach can be potentially used to assess the benefit from construction of flood defenses and to avoid unintended spatial redistribution of flooding. [ABSTRACT FROM AUTHOR]

Abstract: This study tested the hypothesis that raising canal water levels with 30cm beyond the growing season in intensively managed lowland grassland (2.4–3.7m above sea level) in Belgium decreases the agronomic value of pastures The study ran 3 years before and 3 years after the water elevation. Using five pairs of plots inside and outside the wetted perimeter, it was not possible to demonstrate significant impacts of the elevated water level on dry matter yield, forage quality, botanical composition, and penetration resistance of the top soil layer of the grassland. In an ex situ lysimeter experiment, simulating the effect of a water level in canals up to 50cm beneath the surface of the pastures indicated a significant decrease of the penetration resistance of the top soil layer. Results are discussed and confronted with the difficulties of field research addressing the elevation of water levels. [Copyright &y& Elsevier]

The existing water management in Dutch polders is based on independent water systems for each polder. These are featuring artificial stabilized ground and surface water levels. As a result of the local climate the water levels in the polders are not continuously at a constant level. To maintain a stable water table in the polders, the surplus of relatively clean rainwater has to be pumped away during the cold seasons into canals or rivers, which are located on a higher level. During the summer relatively polluted water from these waterways is led into the polders to top up the declining water levels. This procedure leads to various problems regarding water quantity and water quality. The described existing system is not adaptable to climate change and includes the risk of flooding, particularly from torrential rain. Therefore it is crucial to develop, preferably self-sufficient, rainwater management systems in the polders. They should allow the fluctuation of the water levels inside the polders for seasonal storage and flood control. The described concept is adopted in the present water policy in the Netherlands as well as in research and recent urban development projects in Dutch polders. [ABSTRACT FROM AUTHOR]

Summary: As upward seepage of saline groundwater from the upper aquifer is leading to surface water salinization of deep polders in the Netherlands, we monitored the processes involved in the Noordplas Polder, a typical deep polder. Our results show three types of seepage: (1) diffuse seepage through the Holocene confining layer, (2) seepage through paleochannel belts in the Holocene layer, and (3) intense seepage via localized boils. They differ with regard to seepage flux, chloride concentration, and their location in the polder; thus, their contributions to surface water salinization also differ. Permeable, sandy paleochannel belts cut through the lower part of the Holocene layer, resulting in higher seepage fluxes than the diffuse seepage through the Holocene layer where there are no paleochannels. The average chloride concentration of paleochannel seepage is about 600mg/l, which is sixfold higher than the average concentration of diffuse seepage. The highest seepage fluxes and chloride concentrations are found at boils, which are small vents in the Holocene layer through which groundwater preferentially discharges at high velocities. This results in upconing of deeper and more saline groundwater, which produces an average chloride concentration of 1100mg/l. Despite the fact that seepage fluxes are difficult to measure, we were able to calculate that boils contribute more than 50% of the total chloride load entering the Noordplas Polder and they therefore form the dominant salinization pathway. [ABSTRACT FROM AUTHOR]

Abstract: The clumping index measures the spatial aggregation (clumped, random and regular) of foliage elements. The global mapping of the clumping index with a limited eight-month multi-angular POLDER 1 dataset is expanded by integrating new, complete year-round observations from POLDER 3. We show that terrain-induced shadows can enhance bi-directional reflectance distribution function variation and negatively bias the clumping index (i.e. indicating more vegetation clumping) in rugged terrain. Using a global high-resolution digital elevation model, a topographic compensation function is devised to correct for this terrain effect. The clumping index reductions can reach up to 30% from the topographically non-compensated values, depending on terrain complexity and land cover type. The new global clumping index map is compared with an assembled set of field measurements from 32 different sites, covering four continents and diverse biomes. [Copyright &y& Elsevier]

The article sketches the history of the Flood Action Plan 20 (FAP-20), an experiment with polder compartmentalization, seeking to integrate flood management, drainage, and irrigation, and make it more democratic in response to the destructive 1987 and 1988 floods in Bangladesh. As a transferred technology the project took too little cognizance of local physical, social, institutional, and economic context and practices to be able to work successfully. The project did bring previously unavailable amenities to the region that served as a shelter area in the floods of 1998. [ABSTRACT FROM AUTHOR]

Abstract: Hurricane Katrina caused devastating flooding in St. Bernard Parish, Louisiana. Storm surge surrounded the polder that comprises heavily populated sections of the Parish in addition to the Lower 9th Ward section of Orleans Parish. Surge propagated along several pathways to reach levees and walls around the polder''s periphery. Extreme water levels led to breaches in the levee/wall system which, along with wave overtopping and steady overflow, led to considerable flood water entering the polder. Generation and evolution of the storm surge as it propagated into the region is examined using results from the SL15 regional application of the ADCIRC storm surge model. Fluxes of water into the region through navigation channels are compared to fluxes which entered through Lake Borgne and over inundated wetlands surrounding the lake. Fluxes through Lake Borgne and adjacent wetlands were found to be the predominant source of water reaching the region. Various sources of flood water along the polder periphery are examined. Flood water primarily entered through the east and west sides of the polder. Different peak surges and hydrograph shapes were experienced along the polder boundaries, and reasons for the spatial variability in surge conditions are discussed. [Copyright &y& Elsevier]

Abstract: We study the computerized generation of operational strategies for the management of temporary storage of drainage water from several polders in a network of small lakes and canals (Dutch: polder–boezem system). This network of lakes and canals functions as an intermediate storage reservoir. Pumps empty the intermediate reservoir into rivers or the sea. We suggest a way of prioritizing the allocation of pumping capacity when a prediction of future drainage to the intermediate reservoir is provided. We show that there is a greedy algorithm that allocates pump capacity for several time steps in advance and that respects the priority rules. [Copyright &y& Elsevier]

Gaining insight into how natural trait variation is manifest in populations shaped by differential environmental factors is crucial to understanding the evolution, ecology and sensory biology of natural populations. We have demonstrated that lab-reared Lymnaea detect and respond to the scent of a crayfish predator with specific, appropriate anti-predator behavioral responses, including enhanced long-term memory (LTM) formation, and that such predator detection significantly alters the electrophysiological activity of RPeD1, a neuron that is a necessary site for LTM formation. Here we ask: (1) do distinct populations of wild Lymnaea stagnalis respond only to sympatric predators and if so, can these traits be quantified at both the behavioral and neurophysiological levels, and (2) does the presence of a non-sympatric predator elicit anti-predator behaviors including augmentation of LTM? We tested three different populations of wild (i.e. not lab-reared) snails freshly collected from their natural habitat: (1) polders near Utrecht in The Netherlands, (2) six seasonally isolated ponds in the Belly River drainage in southern Alberta, Canada and (3) a 20-year-old human-made dugout pond in southern Alberta. We found strain-specific variations in the ability to form LTM and that only a sympatric predator evoked anti-predatory behaviors, including enhanced LTM formation and changes in RPeD1 activity. [ABSTRACT FROM AUTHOR]

River polders are retention basins contained by levees alongside rivers into which water from the main river channel is diverted during extreme floods in order to cap the peak discharge of the flood hydrograph and to alleviate downstream flood risk by reducing the water levels. The retained water, however, is stagnant and the organic material in the water and the bottom sediments imposes a strong oxygen demand on the water. This paper presents a quasi two-dimensional computer-based methodology to assess the environmental risk exhibited by the operation of polders with which the concentration of dissolved oxygen in river and polder water can be simulated. A Monte-Carlo analysis allows the probability distribution of all the outcomes of the minimum dissolved oxygen levels in the water to be derived. From this analysis, the environmental risk of the dissolved oxygen concentrations in the polder water falling below 2 mg O2/L (the level considered critical for aquatic ecosystems) can be determined. The August 2002 extreme flood event on the Elbe River, Germany, with a proposed polder system variant was used to calibrate the model. A daily time step was used to for the simulations for a time frame 12–21 August 2008. The results show plausible spatial and temporal variations in the dissolved oxygen concentrations within the polders. The quasi-2D approach was successful in simulating the spatial distribution of water quality constituents in the polder system. There is up to approximately 20% risk that dissolved oxygen levels fall below 2 mg/L in the polders. This risk can potentially increase if sediment oxygen demand increases due to crop residue and water temperatures in polders increase. High nutrient transport in the river during flooding can cause a spurt of phytoplankton growth in the polders. [Copyright &y& Elsevier]

Abstract: Land surface albedo is one of the key parameters in the radiation budget, the hydrological cycle and climate modeling studies. It is now widely understood that large errors may occur in the estimation of surface albedo without taking into consideration the anisotropy reflectance effect, which is a general feature of the earth surface. Two major anisotropic correction methods exist for the retrieval of land surface albedo under clear sky conditions. One method involves linearly converting from top of the atmosphere (TOA) albedo to surface albedo, and another is based on the inversion of the Bidirectional Reflectance Distribution Function (BRDF) model of the surface. In the present study, a new approach that utilizes an empirical model for estimating surface albedo has been proposed for snow free land surfaces under clear sky conditions. We analyzed the bidirectional reflectance data set with numerous samples representing various land cover types, which derived from POLDER/ADEOS-1 multi-angle imagery data and distributed by MEDIAS-France. Through the analysis, an empirical relation between bidirectional reflectance and albedo was established and has been discussed in detail. The proposed model can be used for direct estimation of surface albedo from a single BRF observation when the sun-target-sensor geometry is known. No BRDF model inversion scheme is necessary. The present model has no or weak dependence on the existing land surface classifications, and is insensitive to wavelength. The theoretical absolute accuracy of the estimated albedo is approximately 0.010 for visible (0.4–0.7 μm), 0.023 for near infrared (0.7–3.0 μm) and 0.016 for shortwave (0.2–3.0 μm), respectively. Albedo consistency with viewing geometry has been verified, resulting in good agreement for albedo estimated from various viewing directions. Validation of the satellite estimated albedo derived by the proposed method, using field observations were also presented and results show it can give reasonably accurate estimation. The proposed method is expected to be a suitable candidate for practical applications of albedo estimation for sensors that do not perform multi-angle observations. [Copyright &y& Elsevier]

In the Stimulation Program System-oriented Ecotoxicological Research (SSEO) three sites in The Netherlands were investigated for field effects of the grey veil of pollutants. At each site several studies were performed in order to arrive at an adequate weight of evidence and to improve causal inference of pollutant effects. This paper contains a synthesis of results of the studies, performed at one of the sites, the Demmerikse polder. This site is characterized by an anthropogenic layer of soil (in old Dutch: ‘toemaakdek’) on top of the natural peat. Lead, copper and zinc concentrations were elevated, with lead concentrations above a Netherlands environmental quality criterion (Intervention Value) in 66% of the samples. Issues discussed in the paper are: the sampling strategy, selection of maximum gradient and suitable community end-points, both in space and in time. Specific emphasis was given to causal inference of ecological effects of pollutants, related to direct versus indirect effects, functioning of ecosystems, normal operation range and risk assessment. The plausibility of metal effects could be demonstrated on a number of occasions. In the Demmerikse polder changes in the bacterial and nematode communities could be related significantly to metal concentrations and separated from other environmental variables, such as organic matter content and pH. [Copyright &y& Elsevier]

In flood modeling, many one-dimensional (1D) hydrodynamic and water quality models are too restricted in capturing the spatial differentiation of processes within a polder or system of polders and two-dimensional (2D) models are too demanding in data requirements and computational resources, especially if Monte-Carlo techniques are to be used for model uncertainty analyses. The first goal of this paper is to show the successful development of a quasi-2D modeling approach which still calculates the dynamic wave in 1D but the discretisation of the computational units is in 2D, allowing a better spatial representation of the flow and substance transport processes in the polders without a large additional expenditure on data pre-processing and simulation processing. The models DYNHYD (1D hydrodynamics) and TOXI (sediment and micro-pollutant transport) were used as a basis for the hydrodynamic and water quality simulations. An extreme flood event on the Elbe River, Germany, with a proposed polder system variant was used as a test case. The results show a plausible differentiation of suspended sediment and zinc concentrations within the polders both spatially and temporally. This fulfills the second goal of this research. The third goal of this work is to provide an example methodology of carrying out an environmental risk assessment in inundated areas by flood waters, as required by the European Union floods directive. The deposition of zinc in polders was used for this example, due to its high contamination potential in the Elbe River. The extended quasi-2D modeling system incorporates a Monte-Carlo uncertainty analysis to assess the environmental impact of heavy metal deposition in the polders during extreme flooding. The environmental risk computed gives a 48% chance of exceeding the inspection value of 500 mg zinc/kg sediment for a flood such as the August 2002 event. [Copyright &y& Elsevier]

Poland's approximate 500-km coastline predominantly comprises sandy, low-lying beaches and populated coastal lowlands. They are exposed to a range of threats from recently observed intensified climate changes and anticipated accelerated sea-level rise. Sediment starvation is already indicated by the growing necessity for dune and cliff protection that has been exacerbated by sea-level rise. The current study is both a summary and extension of existing Polish studies, and analyses current and predicted influences of accelerated sea-level rise on the coast. First, the Polish coast was divided into three areas according to coastal and socioeconomic characteristics. Then, considering two scenarios of accelerated sea-level rise [(i) 30 cm/100 y and (ii) 100 cm/100 y], an analysis of the threats of land loss and flood risk was carried out, and economic and social costs and losses assessed. This analysis included two adaptation scenarios: retreat (do nothing) and full protection. These analyses show that the greatest impacts of accelerated sea-level rise would occur in the far-eastern and western regions of the Polish coast with lesser impacts along the central region. Threatened areas include the conurbation of Gdansk, the Zulawy polders, and the low-lying areas around the Szczecin Lagoon and the Odra river mouth. Because both the Szczecin Lagoon region and the Vistula River delta are of key importance for the Polish economy and are densely populated, a carefully planned response is required to manage these threats. [ABSTRACT FROM AUTHOR]

The Belgian coastal plain and the Schelde estuary are threatened by sea-level rise. While of great economic importance with a threatened population of some 0.8 million (of a total population of 10 million), assessments of these risks are limited. This article describes the physical characteristics of the coast and undertakes a qualitative interpretation of its vulnerability. Low-lying polders are the most vulnerable to sea-level rise where a major problem is water drainage during rainy periods; their varying vulnerability to sea-level rise and increase in rain intensity is assessed, including the relationship between drainage levels and saltwater seepage. Freshwater lenses developed within the dunes are also vulnerable to sea-level rise, leading to threats to drinking water supplies from saltwater intrusion. Belgian coastal defence structures and their effectiveness are discussed. Historical sea-level rise during the past century, wave and wind data, and the evolution of erosion and accretion along the coast are interpreted. For Antwerpen, a harbour city on the river Schelde, the effects of sea-level rise are far from clear. Included here are historical data on changes in tidal amplitude during the 20th century. Future research needs should focus on the quantitative interpretation of data to understand the effect of sea-level rise on beach erosion, flood risk, and fresh and salt groundwater distribution. Furthermore, a thorough socio-economic study should be undertaken to assess the vulnerability of the Belgian coast and the Schelde estuary. [ABSTRACT FROM AUTHOR]

Question: The vegetation in a polder after partial tidal restoration does not resemble the targeted salt-marsh vegetation. Is this difference in vegetation due to lack of dispersal or unsuitable abiotic conditions ? What could be done for a better restoration of the site? Location: Northwestern France. Methods: Seeds were trapped at the single inlet of the polder with a 200-µm mesh net to estimate inputs of seeds from the bay. In parallel, seed dispersal was studied in the polder by placing Astroturf® seed traps on the surface of the sediment at three different elevations in three distinct areas. Abiotic conditions such as flooding frequency, water table level and soil salinity were monitored. Results: All but one species from the adjacent salt marshes were trapped at the inlet. Not all of these species were on the seed traps inside the polder. Seed dispersal was not homogeneous in the polder and seed trap content mostly discriminated in function of their elevation. Salinity and water logging at the bottom of the slope were very high compared to tolerance of most halophytes but decreased rapidly higher up the slope. Conclusions: The development of salt marsh target species is highly restricted by limited hydrochory inside the polder but also by unfavourable soil conditions induced by the actual hydrological regime. Halophytes are excluded at the bottom of the slope by abiotic conditions and out-competed by sub-halophytes higher up. In order to restore salt marsh vegetation inside the polder, a larger opening should be induced in order to increase the flooded surface, and diminish water logging and flooding frequencies. [ABSTRACT FROM AUTHOR]

Managed realignment has aroused increasing interest over the past decade, reflecting a growing awareness of the high cost of holding the line, the widespread trend of coastal squeeze, and the potentially adverse effects of accelerated sea level rise. This comparative study of England's and Germany's approaches to managed realignment sought to explore similarities and differences and hence provide insights on its future use. Although consideration of managed realignment is widely perceived as a positive development, important and sometimes surprising differences were found concerning its application. This reflects various factors ranging from the physical landscape and the state of coastal defences to cultural factors. Existing schemes are mostly concentrated on the coasts of eastern England and the German federal states of Lower Saxony and Mecklenburg-Western Pomerania. Managed realignment in England, and to some extent on Germany's Baltic Sea coast, seems driven by longer term factors, such as the desire to create more sustainable flood defences and to provide new intertidal habitats, although these are often combined with the more immediate need to upgrade defences. On Germany's well-defended North Sea coast, managed realignment has only been undertaken for specific compensation reasons, although broader conservation concerns might become an important future driver for managed realignment in summer polders. Thus managed realignment is now firmly on the agenda in both countries, reflecting a radical departure from the recent past, in which protection was the only possible response. However, application is likely to differ significantly both between and within these countries. [ABSTRACT FROM AUTHOR]

Western Europe's de-polderisation policy was launched in the 1980s and has since spread along the coasts, especially in the UK, where it is governed by coastal defence objectives through ''managed realignment'' and environmental objectives that are predominant elsewhere. Various means of de-polderisation exist: through tidal gates, breaches, or sea dike removal. Although physical studies on de-polderisation should be continued, it is equally important to examine the social context, favouring or not, of marsh restoration because acceptance of any de-polderisation scheme largely depends on public opinion. The results of five opinion surveys carried out in France and the UK were thus compared and revealed diverging opinions or unexpected indifference toward de-polderisation. A profile of those opposed shows that they are relatively old and regularly frequent the de-polderised sites or live near them. "Negative" reactions, however, are also linked to a lack of knowledge about the marsh environment and of the effects of de- polderisation. Other explanations surface as well: that today coastal environments are quite simply viewed as ''land- scape,'' the degree of human intervention in the implemented schemes, the physical and eustatic context, and the degree to which people are informed. Public knowledge could be improved and mentalities changed through better communication methods, especially on a local level. Furthermore, the creation of a "variables bank" capable of explaining public attitudes and perceptions more systematically would also improve ''social management'' of the de-polderisation policy. [ABSTRACT FROM AUTHOR]

Minerotrophic peatlands play an important role in the regulation of water quality and quantity but due to drainage and agricultural land use most of these systems have lost this function. In Central Europe, many re-wetting projects have been implemented to restore wetlands for multifunctional purposes during the last years. The Pohnsdorfer Stauung (Northern Germany) is a eutrophic fen which was used for intensive agriculture for 40 years. The peatland is divided in two subareas by a small stream. In the scope of re-wetting measures, one subarea (westpolder) was flooded by blockading the main drainage ditch in 1996/97, a second subarea (eastpolder) was re-connected to the stream by an inlet and outlet in 2001. Nitrogen and phosphorus dynamics were investigated in the surface water of these systems over a 5-year (westpolder) and 3-year (eastpolder) period, and balances were calculated. In both polders high dynamics of nitrogen and phosphate concentrations were observed in the surface water. Nitrate peaked in the winter months, whereas ammonium, phosphate and organically bound nitrogen (Norg) revealed highest values during summer. Daily balances for the eastpolder and annual balances for both polders were calculated. In both polders nitrate was retained but phosphate and Norg were exported. Differences of the nutrient dynamics and the absolute and relative balances between the polders were due to the different hydrology: the eastpolder received a high nitrate load by the stream, in the westpolder nutrient loads are low and internal nutrient cycles are dominating. During the summer months, high ammonium concentrations, oxygen depletion, and phosphate release occur in the warm, stagnant water of both polders. Normally, high phosphate and ammonium concentrations did not coincided with discharge phases from the polders. However, in August 2002 after heavy rainfall high phosphorus and ammonium discharge was observed. One important factor influencing the detected nutrient dynamics and balances is the change from a drained and fertilized peatland to a flooded wetland in only a few years. We conclude that continuous water flow and stable water levels are desired for flooded peatlands to prevent high concentrations of ammonium and phosphate and to utilize the potential for nitrate retention. In degenerated peatlands, flooding should only be regarded as an easy technological solution in order to conserve the peat mineralization, and to form the foundation for the further development of the peatland to a more efficient nutrient retaining system. [Copyright &y& Elsevier]

Optimum ground-water conditions of a drained mass of a polder system having one conducting channel were simulated with account for a rain or snow fall-out. The calculations were conducted with the use of an invariant (independent of the number of conducting open channels and their configuration) nonstationary mathematical polder system, involving a strategy for control of the ground-water level in a drained mass (a system of Saint-Venant differential equations for an open channel, a two-dimensional Boussineq equation, and a differential equation for the transfer of water in drains were simultaneously solved). [ABSTRACT FROM AUTHOR]

The Ketenisse polder is a former intertidal brackish marsh of 30 ha situated between the fortress of Liefkenshoek and the Kallo sluice on the left bank of the Schelde estuary, Belgium. In the 19th century its central part was embanked as a polder. During the construction of a traffic tunnel in the late eighties, the excavated soil was dumped between a lower summer dike and the damming dike. The area was restored in 2002 as compensation for the construction of a container terminal on a mudflat in 1994-1995. The rubble of the summer dike and the dumped material were removed and the area was levelled with the intention of creating the optimal starting conditions for the development of new tidal mudflats and marshes. Developments concerning morphology, sediment characteristics and sedimentation-erosion processes are monitored. Six transects with sedimentation-erosion plots were placed perpendicular to the shoreline. This article discusses those monitoring results, mainly for the first year after levelling. Sedimentation as well as erosion between 0 and 30 cm was observed in the first year. Local changes in stream current patterns caused erosion on some parts of the former mudflats; sheltered depressions filled up relatively fast. Median grain size showed large variation, both spatial and temporal. Organic matter content of the sediment varied between 0.5 and 15% and was closely related to sediment median grain size. [ABSTRACT FROM AUTHOR]

One of the impacts drainage has on the downstream part of a water system is a higher risk of peak flows caused by heavy precipitation. In the polders of the Netherlands this is a well-known problem. The heavy precipitation flows easily from paved areas and with some delay from unpaved areas into many small canals and through these canals towards the downstream pump station. Here, high water levels can result in an unacceptable high groundwater table. This problem has grown over the past years as more area has been paved and storm events have become more extreme. Until recently in the Netherlands, the solution for this problem was to increase the pump capacity, but nowadays the Dutch Government's opinion and that of the local Water Boards about solving this problem is changing. Rather than shifting the problem to more downstream lying parts of the water system, the philosophy has become “first retain, then store, only then discharge” (Nationaal Bestuursakkoord Water, 2003. Dutch National Policy on Water Management for the 21st Century). A way to retain water in upstream parts of the waters system is to use real-time control structures in the upstream canals. In this paper a control method is presented that can effectively retain water in the upstream parts, until the downstream part can accommodate this amount of water. The method is based on upstream Proportional Integral-control with adaptation of the set point. The control is referred to as Cascade PI-Control. Basically, the goal of the control method is to fill the available storage equally in the whole area. Tests have been performed with a calibrated model of an existing polder in the Netherlands. Results show that application of the control method is sufficient to avoid such drainage problems. [ABSTRACT FROM AUTHOR]

Abstract: In the Netherlands, the design of dikes and other water retaining structures is based on an acceptable probability (frequency) of overtopping. In 1993 a new safety concept was introduced based on total flood risk. Risk was defined as the product of probability and consequences. In recent years advanced tools have become available to calculate the actual flood risk of a polder. This paper describes the application of these tools to an existing lowland river area. The complete chain of calculations necessary to estimate the risk of flooding of a polder (or dike ring) is presented. The difficulties in applying the present day tools and the largest uncertainties in the calculations are shown. [Copyright &y& Elsevier]