Polder System Research Articles

Coastline change detection with satellite remote sensing for environmental management of the Pearl River Estuary, China

The Pearl River delta area in Guangdong Province has one of the highest economic development rates of China. Rapid industrialization and urbanization has resulted in extensive changes in land use, including the construction of harbours and embankments. The lack of sustainable coastal zone management has caused severe environmental problems, such as land subsidence, intrusion of sea water, siltation of river channels and coastal erosion. For the analysis of the changes of the coastlines, multi-temporal Landsat images and a SPOT scene have been used, in combination with topographical and nautical data. From the change analysis, it can be concluded that the largest variations in the position of the coastline over time occurred in the Nansha Development Zone, situated in the Northern part of Lingdingyang bay. Sedimentation and land reclamation was responsible for the growth of the islands in the period 1960 to 2000, which however decreased slightly in the years after. Various large changes occurred also in the East of the bay along the coast of Shekou peninsula, caused by extensive harbour construction and growth of polder systems. Based on the research of the coastline change in recent decades, suspended sediment plume distribution and its sedimentation, it is suggested that the western part of the waterway in the estuary may not be suitable for large number of construction for harbours, due to the sedimentation and fill up. One of the most important impacts of the coastline changes in the Pearl River Estuary is the narrowing down and extension of river channel which results in more floods in the upper part of the river.

Simulation of the ground water level of substantial polder systems

A method of a communal matrix synthesis of the transformation of the coordinates C(α L ) from local reference systems (LRS) into a communal reference system (CRS) for any configuration of polder systems, supplying the formation of the groundwater level (GWL) in a communal reference system is designed. The GWL numerical accounts in a CRS give an adequate representation about the time-space allocation of groundwater for the entire drained mass, permitting the quantitative valuation of the qualities of the polder systems.

Quantifying structural uncertainty due to discretisation resolution and dimensionality in a hydrodynamic polder model

In flood modelling, the structure of conceptual models may have a large influence on the simulation results. Hence, the focus of this paper is on the structural uncertainty in hydrodynamic flood modelling systems. Three different conceptual models with an increasing order of complexity of the spatial discretisation of the flow through a polder system were compared in order to investigate the effect of spatial resolution and dimensionality on flood modelling. The hydrodynamic 1D model DYNHYD was used as a basis for the simulations. The model was extended to incorporate a quasi-2D approach and a Monte Carlo analysis was used to show the effect of structural uncertainty on the resulting flow characteristics of the diverted flood waters. Two flood events of the River Elbe were used to calibrate and test the model. The results of the velocity fields indicate that the simplest 1D model revealed more predictive uncertainty than the other two more complex models. The differences in model structure does not cause large differences in the capping of the peak discharges, but may substantially influence the results of subsequent modelling of sediment and contaminant transport.

Environmental risk of dissolved oxygen depletion of diverted flood waters in river polder systems – A quasi-2D flood modelling approach

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 O 2/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.

A quasi-2D flood modeling approach to simulate substance transport in polder systems for environment flood risk assessment

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.

Coastal flood management in Semarang, Indonesia

Semarang is one of the biggest cities in Indonesia and is nowadays suffering from coastal flooding. Land subsidences, high water tide, and inadequate structural measures play important roles in the coastal inundations. Structural and non-structural methods for controlling coastal flooding including dykes, drainage systems, pump stations, polder systems, coastal-land reclamations, coastal planning and management, public education, as well as the establishment of an institutional framework for disaster management have been implemented in the Semarang coastal area. Although some improvements have been made, the current flood management system has generally failed to address a wide range of coastal inundation problems. Some improvement actions have been proposed including stakeholders involvement on the disaster mitigation. For a long period coastal management, accelerated sea level rises due to global warming should also be taken into account.

The effectiveness of polder systems on peak discharge capping of floods along the middle reaches of the Elbe River in Germany

Abstract. In flood modelling, many one-dimensional (1-D) hydrodynamic models are too restricted in capturing the spatial differentiation of processes within a polder or system of polders and two-dimensional (2-D) models are very demanding in data requirements and computational resources. The latter is an important consideration when uncertainty analyses using the Monte Carlo techniques are to complement the modelling exercises. This paper describes the development of a quasi-2-D modeling approach, which still calculates the dynamic wave in 1-D but the discretisation of the computational units are in 2-D, allowing a better spatial representation of the flow in polders and avoiding large additional expenditure on data pre-processing and computational time. The model DYNHYD (1-D hydrodynamics) from the WASP5 modeling package was used as a basis for the simulations and extended to incorporate the quasi-2-D approach. A local sensitivity analysis shows the sensitivity of parameters and boundary conditions on the filling volume of polders and capping of the peak discharge in the main river system. Two flood events on the Elbe River, Germany were used to calibrate and test the model. The results show a good capping effect on the flood peak by the proposed systems. The effect of capping reduces as the flood wave propagates down stream from the polders (up to 0.5 cm of capping is decreased for each additional kilometer from the polder).

Optimum control of the ground-water level with account for a rain or snow fall-out

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).

Preliminary Analysis on the Polder Construction in the Jiangsu-Zhejiang-Shanghai Boundary District of the Lower Reaches of Taihu Basin

The Jiangsu Zhejiang Shanghai boundary district of the lower reaches of the Taihu Basin is a plain area with low lying terrains and complicated hydrological system; it is a region where the threat of flood and waterlogging is most serious and the water environment deterioration most obvious. In the meantime, the water resources contradiction stands out because of its location-in the fringes of three administrative areas. To mitigate flood and waterlogging disasters, the fringe polder constructions as well as the maintenance are one of the key problems to the water resource utilization and water environment improvement in the district. After analyzing the development history and situations about fringe polder distribution along the boundary area, the polder system problems within the given district are discussed from the following aspects: the polder area change, water area ratio and the length of polder dykes, and so on. The appropriate polder scale and the drainage power of waterlogging are suggested. Finally, several suggestions on fringe polder development are proposed.

Water and Energy Relations in Lithuania

Water and energy links have changed considerably over the course of the centuries. Since ancient times water has been used in Lithuania for domestic needs (preparing meals, thirst slaking and hygienic necessities) and in agriculture for watering plants, etc. When handicrafts and industries began to develop, water power was used for working purposes: to turn the wheels of mills, sawmills' mechanisms and wool-carding workshop equipment and later to generate electricity. The first small hydropower plant started working in 1900. In 1935 there were 96 small hydropower plants or mixed hydrostations from 309 electricity-producing ones. In the Soviet period (1940-90) water and energy links quickly changed and their development on a large scale depended on the general needs of the Soviet empire. An attempt is made in the paper to discuss briefly the development of water and energy relations in the fields of electricity production, dam quality, water use and wastewater treatment, polder systems and irrigation during the last decade in Lithuania.

PARAMETER UNCERTAINTY IN RAINFALL‐RUNOFF MODELING FOR POLDER SYSTEM DESIGN1

ABSTRACT: An approach is developed for incorporating the uncertainty of parameters for estimating runoff in the design of polder systems in ungaged watersheds. Monte Carlo Simulation is used to derive a set of realizations of streamflow hydrographs for a given design rainstorm using the U. S. Soil Conservation Service (SCS) unit hydrograph model. The inverse of the SCS curve number, which is a function of the antecedent runoff condition in the SCS model, is the random input in the Monte Carlo Simulation. Monte Carlo realizations of streamfiow hydrographs are used to simulate the performance of a polder flood protection system. From this simulation the probability of occurrence of flood levels for a particular hydraulic design may be used to evaluate its effectiveness. This approach is demonstrated for the Pluit Polder flood protection system for the City of Jakarta, Indonesia. While the results of the application indicate that uncertainty in the antecedent runoff condition is important, the effects of uncertainty in rainfall data, in additional runoff parameters, such as time to peak, in the hydraulic design, and in the rainfall‐runoff model selected should also be considered. Although, the SCS model is limited to agricultural conditions, the approach presented herein may be applied to other flood control systems if appropriate storm runoff models are selected.

Stability of channels of large canals on large-scale erodible models

i0. .7. O. Hinze, Turbulence, McGraw-Hill, New York (1959)o Ii. N. K. Nikitin, "Generalization of the semiempirical theory of turbulence to flows near a rough surface with various regimes of manifestation of the roughness properties," in: Turbulent Flows [in Russian], Nauka, Moscow (1970). 12. G. Vo Vasil'chenko, "Calculation of steady fluid flow over roughness," in: Water Management and Hydraulic Engineering [in Russian], Vysh~ishaya Shkola, Minsk (1981). 13. G. V. Vasil'chenko, "Investigation of the relation between the turbulent characteristics of a flow in the bottom region and in it underlaying cohesionless soil," in: Dynamics and Thermics of Rivers [in Russian], Moscow (1973). 14. G. Vo Vasil'chenko, "Hydraulic substantiation of the placement of polder systems in a river floodplain," in: Reclamation and Development of the Pripyat' Floodplain [in Russian], Uradzhai, Minsk (1982)o