The Vecht area: history, problems and policy
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Abstract:
The Vecht area is a plain with wetlands, located between the river Vecht in the west (Fig. 5.1) and the sandy ice-pushed hill ridge ‘Het Gooi’ approximately 8km to the east. To the north, a former sea (‘Zuiderzee’), now reclaimed, bounds the area; 20km to the south near the city of Utrecht, the hill ridge and the river almost meet (Fig. 5.2). The area is a wetland region with many shallow lakes. Even where a solid soil is present, the groundwater table is close to the surface. The soil diversity is represented by the presence of three types of soil: close to the river and the former sea, there are deposits of clay soils; the centre of the plain is covered by a peat layer some metres in depth; and in the eastern direction this peat layer gets thinner until it reaches the sandy soil of the hill ridge. The area straddles two provinces (North-Holland and Utrecht) and includes 10 municipalities. The number of inhabitants in these areas is restricted. The centres with significant population sizes are mostly at the border of, or just outside, the area (see Table 5.1).Keywords:
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Water distribution and shallow groundwater evaporation in soil with different groundwater table under three irrigation treatments were investigated through soil column experiments in lab.Results showed irrigation schedule and groundwater table had a great influence on the shallow groundwater evaporation.The evaporation of shallow groundwater would decrease substantially when irrigation frequency increased at the same groundwater table and same irrigation quantity.The evaporation of shallow groundwater decreased at low irrigation frequency under the same groundwater table when the quantity per irrigation increased.Deeper the groundwater table,less the evaporation.
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The aims of the study were to reveal changes in the water-table depth and peat subsidence due to land-use change in West Kalimantan. The location of the study is peatland in Kubu Raya District-West Kalimantan, namely on four types of peatland-use, including secondary peat forest (SPF), shrubs (SB), oil palm plantation (CPP) and corn field (CF). The research parameters include depth of groundwater and peat subsidence. The results show that the conversion of peatland to other peatlands causes an increase in peat subsidy. The research parameters include water-table depth and peat subsidence. The results show that the land-use change of peatlands to other peatlands causes an increase in peat subsidence. The increase in subsidence in measurement II (October 2016) coincides with an increase in water-table depth and measurement V (April 2017) of 74.6%-90.9%. There is a tendency to increase water-table depth in August and October 2016 and January 2017, especially on SB, OPP and CF. SPF has a deeper water-table depth and deeper subsidence than other land. This is due to the deeper peat soil depth of the SPF (509 cm) while the other relatively shallow areas range from 108.2 to 115.5 cm. The correlation between water-table depth and subsidence shows a close relationship and significant (p<0.01, r = 0.824).
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Over-exploitation of groundwater has existed before 2000 in Su-Xi-Chang area. From the start of 2000, the program about prohibition of pumping groundwater was implemented stage by stage by Jiangsu provincial government, and the prohibition program was first conducted in over-exploitation area. By the end of 2005, an overall prohibition of pumping groundwater in Su-Xi-Chang was realized and the velocity of land subsidence was slowing down and groundwater table was recovered gradually. According to systematic subsidence monitoring data and observed groundwater table data in the study area in the recent years, the change laws of groundwater table and land subsidence are analyzed before and after prohibition of pumping groundwater, which show there are the tight relationship between recovery of groundwater table and the decrease of land subsidence. Simultaneously, the geological environmental effects were evaluated after prohibition of pumping groundwater. Some countermeasures and proposals are provided for geological environmental protection in the study area.
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Groundwater-related subsidence
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Groundwater is one of the most important natural resources in to sustain the human habitat on earth. It serves us as the major source of drinking water as well as the fresh water resource to be utilized in agriculture and industries. Over the decades the groundwater pumping has been increased few fold and that is raising serious concern about the depth of groundwater level at different parts of earth. The south western Punjab is facing the problem of fluctuating groundwater table due to the heavy agricultural practices in this state. Our study focuses on the observation of change and prediction of groundwater table the in the Muktsar district of south west Punjab, based on the village wise collected well data. Curve fitting technique though MATLAB software has been taken into account for this purpose and it showed a increase in depth to groundwater table for all the four blocks of Muktsar district by 2025. The study highlights the need of raising awareness and establish new laws to ensure sustainable groundwater management in the study area to avoid the scarcity of groundwater in the near future.
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Groundwater resources
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Groundwater utilization as a source of clean water for the community increases, both for domestic and non-domestic needs, thus lowering the groundwater table. The Dayeuhkolot area is part of the Bandung-Soreang Groundwater Basin, which has a groundwater table decline resulting from excessive groundwater utilization. The Experimental Station of Groundwater modeled the groundwater condition in 2010-2020 concluded that the groundwater decline for a particular area reaches up to 50 m. This study aims to analyze the potential for groundwater table restoration that can be carried out at the research location by reducing groundwater utilization through the substitution of surface water use. The prospect of surface water that can be utilized can be identified by identifying its quantity and quality for the feasibility of using surface water as a substitute for groundwater utilization to implement the concept of conjunctive use. Groundwater modeling is carried out with a substitution scheme for groundwater utilization with surface water. Modeling results show that the reduction in groundwater utilization positively impacts the restoration of the water table level. Based on the model result, the groundwater level can recover as high as 2.37 m from 2020 conditions.
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Groundwater model
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Measurements of CH 4 flux from drained and undrained sites in three northern Ontario peatlands (a treed fen, a forested bog, and a treed bog) were made from the beginning of May to the end of October 1991. In the drained portions, the water table had been lowered between 0.1 and 0.5 m, compared to the water table of the undrained portion of the peatlands. The mean seasonal CH 4 flux from the undrained portions of three peatlands was small, ranging from 0 to 8 mg m −2 d −1 , but similar to the CH 4 flux from other treed and forested northern peatlands. The mean seasonal CH 4 flux from the drained portion of the peatlands was either near zero or slightly negative (i.e.,uptake): fluxes ranged from 0.1 to −0.4 mg m −2 d −1 . Profiles of CH 4 in the air‐filled pores in the unsaturated zone, and the water‐filled pores of the saturated zone of the peat at the undrained sites, showed that all the CH 4 produced at depth was consumed within 0.2 m of the water table and that atmospheric CH 4 was consumed in the upper 0.15 m of the peatland. On the basis of laboratory incubations of peat slurries to determine CH 4 production and consumption potentials, the lowering of the water table eliminated the near‐surface zone of CH 4 production that existed in the undrained peatland. However, drainage did not alter significantly the potential for CH 4 oxidation between the water table and peatland surface but increased the thickness of the layer over which CH 4 oxidation could take place. These changes occurred with a drop in the mean summer water table of only 0.1 m (from −0.2 to −0.3 m) suggesting that only a small negative change in soil moisture would be required to significantly reduce CH 4 flux from northern peatlands.
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The problem of groundwater overexploitation in the article of discussion Ⅰ was analysed by the exploitation rate of groundwater.The problem of groundwater overexploitation once more will be discussed by the restrained groundwater table.The limit research on restrained groundwater table's confirmation was made,to confirm the critical and restrained groundwater table on the basis of ideal groundwater table and buried depth theory will be helpful.Partitions and typical farms of Sanjiang Plain,the groundwater table were in perfect condition since the groundwater was mined on large scale and the groundwater sill had tremendous development potential.
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Sanjiang Plain
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Abstract Peat specific yield ( S Y ) is an important parameter involved in many peatland hydrological functions such as flood attenuation, baseflow contribution to rivers, and maintaining groundwater levels in surficial aquifers. However, general knowledge on peatland water storage capacity is still very limited, due in part to the technical difficulties related to in situ measurements. The objectives of this study were to quantify vertical S Y variations of water tables in peatlands using the water table fluctuation (WTF) method and to better understand the factors controlling peatland water storage capacity. The method was tested in five ombrotrophic peatlands located in the St. Lawrence Lowlands (southern Québec, Canada). In each peatland, water table wells were installed at three locations (up‐gradient, mid‐gradient, and down‐gradient). Near each well, a 1‐m long peat core (8 cm × 8 cm) was sampled, and subsamples were used to determine S Y with standard gravitational drainage method. A larger peat sample (25 cm × 60 cm × 40 cm) was also collected in one peatland to estimate S Y using a laboratory drainage method. In all sites, the mean water table depth ranged from 9 to 49 cm below the peat surface, with annual fluctuations varying between 15 and 29 cm for all locations. The WTF method produced similar results to the gravitational drainage experiments, with values ranging between 0.13 and 0.99 for the WTF method and between 0.01 and 0.95 for the gravitational drainage experiments. S Y was found to rapidly decrease with depth within 20 cm, independently of the within‐site location and the mean annual water table depth. Dominant factors explaining S Y variations were identified using analysis of variance. The most important factor was peatland site, followed by peat depth and seasonality. Variations in storage capacity considering site and seasonality followed regional effective growing degree days and evapotranspiration patterns. This work provides new data on spatial variations of peatland water storage capacity using an easily implemented method that requires only water table measurements and precipitation data.
Ombrotrophic
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Water storage
Surficial aquifer
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To understand the dynamic of groundwater table in Gongyi City,provide some basis for the groundwater resources in Gongyi City,and achieve the high-efficient use of groundwater resources,the monitoring points of groundwater table were laid in the urban area of Gongyi City. Based on the monitoring datum of monitoring points of groundwater table in nearly 3 years,we analyzed the influence of the annual and inter-annual precipitation on the dynamic of groundwater table,the depth to groundwater table and the change trend of groundwater drawdown funnel. The results show: in the research area,the depth to groundwater table is shallower,the precipitation is the main influence factor of the dynamic fluctuation of groundwater table; the annual fluctuation of groundwater table is mainly the seasonal fluctuation,the inter-annual groundwater table is in a state of dynamic balance; the aquifer of confined water is the main supply source of the research area,but the long-term excessive mining results in larger groundwater drawdown funnels; under the condition of limit mining,the groundwater drawdown funnel will keep stable,and the groundwater will basically realize the balance between mining and recharging.
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Groundwater model
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Improper utilization of surface and groundwater resources has caused water logging problem in some cases and depletion of groundwater resources in other. Scientific exploitation of groundwater meets irrigation water need and controls rising water table. However, if tubewells are drilled indiscriminately and without proper assessment of exploitable groundwater, it results in an adverse impact on the groundwater regime. The research farm of Indian Agricultural Research Institute (IARI), New Delhi has witnessed varied groundwater situation in past 60 years. This paper describes over the how the excess use of canal water during the forties and fifties and indiscriminate drilling of tubewelIs after that resulted in waterlogging till mid sixties and depletion of groundwater resources thereafter. Analysis of long term data of water table fluctuations at JARI farm revealed that it has been rising till 1964, reaching to ground surface at several places. Subsequent drilling of a large number of tubewells and reduced canal water supply caused decline of the groundwater table. At present, groundwater table is 14 m deep at some places. This paper also stresses the need for comprehensive water balance study before undertaking any water resources development and utilization project in an area.
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