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The Ganges-Brahmaputra Delta (GBD) in Bangladesh exists at a nexus of stability and vulnerability, as the rivers annually carry ~ 800–1000 MT of sediment from the Himalayan Mountains, yet coastal poldering and sediment extraction within the rivers remove elevation capital from the low-lying delta plain. Recent research in the GBD has begun to unravel how the world's largest fluvio-deltaic mangrove forest—the Sundarbans—is keeping pace with sea level rise (SLR); however, this is contingent on adequate sediment supply delivered to the platform during semi-diurnal tides and the seasonal monsoon. Little is known about the elevation dynamics within human-modified polders by comparison, other than an elevation deficit of 1–1.5 m exists. In this study, seasonal data from Rod Surface Elevation Tables (RSETs) installed within a polder in the southwest region (Polder 32) are compared to the Sundarbans. Over ~ 8 years, results show that surface elevation is gaining within the Sundarbans at a more significant rate (~ 58.4%), and this is due to the higher vertical accretion rates measured in the Sundarbans (~ 67%) from abundant sources of allochthonous material. Elevation gain in the polder, particularly close to the embankment, appears to be attributed to sediment supplied from eroded embankments and local sluice gates, in addition to seasonal subsurface clay swelling during the monsoon. Shallow subsidence within both study areas appears to take place seasonally, but with less delivery of new sediment, the rate of shallow subsidence is lower in the polder compared to the Sundarbans. Despite seasonal shallow subsidence, the elevation change is net positive in both study areas if taken as a whole; however, interior poldered regions exhibit net elevation loss. This comparison in change of elevation, vertical accretion, and shallow subsidence shows how human modification has drastically changed the natural processes. Furthermore, our results are compared to rates of relative and effective SLR, which show that the Sundarbans is keeping pace in this region, while Polder 32 is not. These results are vital to inform embankment mitigation and flood risk in this dynamic delta system. [ABSTRACT FROM AUTHOR]

The aim of the study was to determine an effective variant of operation of the Golina polder to reduce flood hazard in the Warta River valley. We implemented a trial-and-error method for the development of computational variants. Our approach was based on staged analyses of alternatives, which took into account different locations and parameters of the inlet and outlet-controlling structures. Various control scenarios for flooding and draining the polder were also considered. A hybrid hydrodynamic model consisting of a 1D part for the main river area and a 2D part for the polder area was used for calculations. The model was built based on a digital elevation model (1 m resolution) and channel sections of the Warta River. The calibration was based on data collected during the flood in 2010 from the water gauge Sławsk (located directly at the Warta River) and water surface elevation measurements carried out in the polder area. Alternatives in subsequent stages were determined based on the results of previous stages, as well as experiences from the 2010 flood and consultations with the Regional Water Management Board in Poznań. The performance of the alternatives was evaluated according to six criteria that described the effectiveness of the polder operation in terms of its practical use and effectiveness in reducing flood hazard. The results showed that our approach made it possible to identify an effective variant of polder operation. Additional calculations were also performed to determine the magnitude of flows for which flooding of the polder should be considered to reduce downstream flooding. [ABSTRACT FROM AUTHOR]

Copyright of Landscape Architecture Frontiers is the property of Higher Education Press Limited Company and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Community Livelihood Adaptation (CLA) can have significant impacts on polder management. • The shift from rice to shrimp, as unanticipated livelihood pathway for salinization, has changed the polder functionality. • Tidal River Management has risen as livelihood adaptation to waterlogging led by social (un)acceptance of polder management. • Delta planners should listen to CLA, and accommodate uncertainties resulting from CLA for robust and adaptive investment. To deal with large uncertainties about future climate and socio-economic developments, planners in deltas are adopting an integrative and adaptive planning approach referred to as Adaptive Delta Management (ADM). Bangladesh has used the ADM approach for the development of its adaptive plan; Bangladesh Delta Plan 2100 (BDP 2100). The success of policy strategies in an adaptive delta plan critically depends on a specific adaptation of livelihoods of local communities (Community Livelihood Adaptation; CLA), especially in an agriculture-oriented society like Bangladesh. For example, while triple rice cropping might be evaluated as a robust strategy in all futures considered, its success eventually depends on whether farmers' will actually make that choice, which is deeply uncertain. In this paper, we use literature review, insights from interviews and field observations to examine how the uncertainty in CLA impacts (adaptive) delta management. We study two historical cases of livelihood adaptation of farmer communities confronted with salinization and waterlogging in the polders of southwest Bangladesh since the 1960s. We conclude that historically the uncertainty about CLA in polders has been ignored in the development of policy plans, leading to the failure of anticipated policy outcomes. We recommend planners in Bangladesh and other deltas worldwide to take account of CLA as uncertainty when developing long-term adaptive plans. [ABSTRACT FROM AUTHOR]

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]

Polders in the Netherlands are protected from flooding by flood defence systems along main water bodies such as rivers, lakes or the sea. Inside polders, canal levees provide protection from smaller water bodies. Canal levees are mainly earthen levees along drainage canals that drain excess water from polders to the main water bodies. The water levels in these canals are regulated. During the last decades, probabilistic approaches have been developed to quantify the probability of failure of flood defences along the main water bodies. This paper proposes several extensions to this method to quantify the probability of failure of canal levees. These extensions include a method to account for (i) water-level regulation in canals, (ii) the effect of maintenance dredging on the geohydrological response of the canal levee and (iii) survival of loads in the past. The results of a case study demonstrate that the proposed approach is capable of quantifying the probability of failure of canal levees and is useful for exploring the relative benefit of risk mitigating measures for canal levees. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Abstract: Polders are one of the most common artificial hydrological entities in the plain river network regions of China. Due to enclosed dikes, manual drainage, and irrigation intake operations, polders have had a significant impact on the hydrological processes of these areas. Distributed hydrological models are effective tools to understand and reproduce the hydrological processes of a watershed. To date, however, few models are able to simulate the drainage and irrigation intake interactions of polders at a watershed scale. This study develops a modified version of the Soil and Water Assessment Tool (SWAT) model, which is designed to better represent polders (SWATpld). The SWATpld model simulates drainage and irrigation intake processes by calculating the excess‐water storage in the inner rivers and irrigation schedule for paddy rice in the polder. Both SWAT and SWATpld models were tested for the Liyang watershed. SWATpld outperformed SWAT in simulating the daily discharge and intake of the experimental polder and predicting the monthly peak flow at the outlet of the Liyang watershed, which suggests that the modified model simulates the hydrological responses of the study watershed with polder operations more realistically than the original SWAT model does. Further evaluation at various locations and in various climate conditions would increase the confidence of this model. [ABSTRACT FROM AUTHOR]

Implementing new concepts and measures for flood risk management may be restricted by hydromechanical processes. These processes govern the movement of water masses within rivers and their floodplains. Different hydraulic processes are still not fully understood or cannot be described satisfactorily by hydro‐numerical models due to uncertainty in input data. The choosing of the correct surface roughness has a huge influence on the results of hydro‐numerical calculation of historical and design flood events and their reliability for the assessment of flood risk mitigation measures like floodplain restoration. The authors try to outline the various effects of channel and floodplain roughness on fluvial flood routing and give examples. A method is presented for peak discharge calculation of historical flood events. [ABSTRACT FROM AUTHOR]

The Amsterdam area, a highly manipulated delta area formed by polders and reclaimed lakes, struggles with high nutrient levels in its surface water system. The polders receive spatially and temporally variable amounts of water and nutrients via surface runoff, groundwater seepage, sewer leakage, and via water inlets from upstream polders. Diffuse anthropogenic sources, such as manure and fertiliser use and atmospheric deposition, add to the water quality problems in the polders. The major nutrient sources and pathways have not yet been clarified due to the complex hydrological system in lowland catchments with both urban and agricultural areas. In this study, the spatial variability of the groundwater seepage impact was identified by exploiting the dense groundwater and surface water monitoring networks in Amsterdam and its surrounding polders. A total of 25 variables (concentrations of total nitrogen (TN), total phosphorus (TP), NH4, NO3, HCO3, SO4, Ca, and Cl in surface water and groundwater, N and P agricultural inputs, seepage rate, elevation, land-use, and soil type) for 144 polders were analysed statistically and interpreted in relation to sources, transport mechanisms, and pathways. The results imply that groundwater is a large source of nutrients in the greater Amsterdam mixed urban-agricultural catchments. The groundwater nutrient concentrations exceeded the surface water environmental quality standards (EQSs) in 93% of the polders for TP and in 91%for TN. Groundwater outflow into the polders thus adds to nutrient levels in the surface water. High correlations (R2 up to 0.88) between solutes in groundwater and surface water, together with the close similarities in their spatial patterns, confirmed the large impact of groundwater on surface water chemistry, especially in the polders that have high seepage rates. Our analysis indicates that the elevated nutrient and bicarbonate concentrations in the groundwater seepage originate from the decomposition of organic matter in subsurface sediments coupled to sulfate reduction and possibly methanogenesis. The large loads of nutrient-rich groundwater seepage into the deepest polders indirectly affect surface water quality in the surrounding area, because excess water from the deep polders is pumped out and used to supply water to the surrounding infiltrating polders in dry periods. The study shows the importance of the connection between groundwater and surface water nutrient chemistry in the greater Amsterdam area. We expect that taking account of groundwater-surface water interaction is also important in other subsiding and urbanising deltas around the world, where water is managed intensively in order to enable agricultural productivity and achieve water-sustainable cities. [ABSTRACT FROM AUTHOR]

Identifying phosphorus (P) sources, distribution and export from lowland polders is important for P pollution management, however, is challenging due to the high complexity of hydrological and P transport processes in lowland areas. In this study, the spatial pattern and temporal dynamics of P export coefficient (PEC) from all the 2539 polders in Lake Taihu Basin, China were estimated using a coupled P model for describing P dynamics in a polder system. The estimated amount of P export from polders in Lake Taihu Basin during 2013 was 1916.2 t/yr, with a spatially-averaged PEC of 1.8 kg/ha/yr. PEC had peak values (more than 4.0 kg/ha/yr) in the polders near/within the large cities, and was high during the rice-cropping season. Sensitivity analysis based on the coupled P model revealed that the sensitive factors controlling the PEC varied spatially and changed through time. Precipitation and air temperature were the most sensitive factors controlling PEC. Culvert controlling and fertilization were sensitive factors controlling PEC during some periods. This study demonstrated an estimation of PEC from 2539 polders in Lake Taihu Basin, and an identification of sensitive environmental factors affecting PEC. The investigation of polder P export in a watershed scale is helpful for water managers to learn the distribution of P sources, to identify key P sources, and thus to achieve best management practice in controlling P export from lowland areas. [ABSTRACT FROM AUTHOR]

Large tracts of land in the Sacramento-San Joaquin Delta are subsided because of agricultural practices, creating polders up to 10 m below sea level that are vulnerable to flooding. As protective dikes breach, these become shallow, open-water habitats that will not resemble any historical state. I investigated physical and biotic drivers of novel flooded polder habitat, using a Native Species Benefit Index (NSBI) to predict the nature of future Delta ecosystems. Results suggest that flooded polders in the north Delta will have the ecology and fish community composition of a tidal river plain, those in the Cache-Lindsey Complex (CLC) will have that of a tidal backwater, those in the confluence of the Sacramento and San Joaquin rivers a brackish estuary, and those in the south Delta a freshwater lake. Flooded east-side Delta polders will likely be a transitional zone between south Delta lake-like ecosystems and north Delta tidal river plains. I compared each regional zone with the limited available literature and data on local fish assemblies to find support for NSBI predictions. Because flood probabilities and repair prioritization analyses suggest that polders in the south Delta are most likely to flood and be abandoned, without extensive intervention, much of the Delta will become a freshwater lake ecosystem, dominated by alien species. Proactive management of flooded tracts will nearly always hedge risks, save money, and offer more functional habitats in the future; however, without proper immediate incentives, it will be difficult to encourage strong management practices. [ABSTRACT FROM AUTHOR]

Se pretende tener una visión amplia del paisaje dentro de la pintura, un género que surgió con fuerza especialmente después de la época medieval con la entrada de la Edad Moderna en el siglo XV, y consigue su auge en el siglo XVII hasta la llegada de la Escuela de Barbizon y los impresionistas con su “plein air”, y que alcanzan un siglo XX polémico, alejado de lo clásico, de vanguardia, que transcurre en una vía paralela el paisaje académico frente a nuevos retos y formas de expresión.

Urban agglomeration polders (UAPs) are often used to control flooding in eastern China. The impacts of UAPs on individual flood events have been extensively examined, but how flood risks are influenced by UAPs is much less examined. This study aimed to explore a three-dimensional joint distribution of annual flood volume, peak flow and water level to examine UAPs’ impact on flood risks based on hydrological simulations. The dependence between pairwise hydrological characteristics are measured by rank correlation coefficients and graphs. An Archimedean Copula is applied to model the dependence structure. This approach is applied to the Qinhuai River Basin where UAPs are used proactively for flood control. The result shows that the Frank Copula can better represent the dependence structure in the Qinhuai River Basin. UAPs increase risks of individual flood characteristics and integrated risks. UAPs have a relatively greater impact on water level than the other two flood characteristics. It is noted that the impact on flood risk levels off for greater floods.

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]

For early modern societies, distributing the costs of flood defences between the stakeholders in an equitable way was difficult. Institutions were abused by powerful groups to shift the financial burden to poorer groups. According to Epstein, such elite abuse of institutions was possible because in pre-modern states political and economic power were not separated, which made it possible for elite groups to hijack the decision-making process. By studying how three 'states' in the South-Western Netherlands distributed the high costs of dike maintenance, this paper partly confirms Epstein's thesis. No separation existed between political and economic power in the province of Zeeland and here this caused a stalemate because cities represented in the provincial government protected their elites' interests. In Holland and the territories of the States-General, however, taking quick and efficient measures for the repair and financing of sea defences was possible. Here the powerful cities had less significant interests in the areas concerned and were prepared to leave decision-making to technical and financial experts. [ABSTRACT FROM AUTHOR]