Pauw P.S.,Deltares |
Groen J.,Acacia Water |
Groen M.M.A.,Acacia Water |
van der Made K.J.,Wiertsema en Partners |
And 2 more authors.
Journal of Hydrology | Year: 2017
Submarine groundwater discharge is an important part of the hydrological cycle, but remains under-investigated for confined aquifers with no surface outcrop at the beach. This paper considers the offshore directed flow of fresh groundwater in the unconfined and confined aquifers along the coast of the Western Netherlands. Salinity patterns based on hydrological, geological, and geophysical field data are presented in five shore-normal hydrogeological cross-sections, extending from the beach to 4. km inland. The offshore continuation of the fresh groundwater is discussed using analytical models and cone penetration tests (CPTs) performed at the beach. All CPTs taken around the low water line of the intertidal zone reveal that changes from saline to fresh groundwater are always associated with a low-permeable layer. Such a low-permeable layer, which can be as thin as a few decimetres, may form the confining layer between the unconfined and confined aquifers, or can occur within of the unconfined aquifer. Due to its high vertical resolution, a CPT is an effective method to detect these variations in salinity and lithology. At each of the investigated locations, freshwater was present in the confined aquifer. Assuming that this fresh groundwater is part of an active flow system, the submarine freshwater tongue is estimated to extend at least a few hundred meters offshore, based on analytical model calculations. Hydrochemical data from an old offshore borehole, however, suggest this may be an underestimate and that the submarine freshwater tongue originates from former times when the coastline was located further westward than nowadays. © 2017 Elsevier B.V.
Sultana S.,University of Dhaka |
Ahmed K.M.,University of Dhaka |
Mahtab-Ul-Alam S.M.,University of Dhaka |
Hasan M.,University of Dhaka |
And 6 more authors.
Journal of Hydrologic Engineering | Year: 2014
Fresh water resources are scarce in rural communities in the southern deltaic plains of Bangladesh where both shallow and deep groundwater is frequently brackish, and fresh water ponds have been increasingly salinized by inundation during storm surges and brackish-water aquaculture. Low-cost aquifer storage and recovery (ASR) schemes were constructed at 13 villages in three coastal districts by developing storage in shallow confined fine to medium sand aquifers overlain by variable thicknesses of silt and clay. A typical ASR scheme consisted of a double-chambered graded sand filtration tank with a volume of 19.5 m3 that feeds filtered pond water to four to six large diameter (d = 30.5 or 56 cm) infiltration wells through PVC pipes fitted with stop valves and flow meters. The infiltration wells were completed at 18-31 m below ground and filled with well-sorted gravel capped with a thin layer of fine sand that acts as a second stage filter. Infiltration rates at 13 sites averaged 3 m3/day (range: 3-6 m3/day) over one year of operation. At 11 sites where water was abstracted, the recovery rate ranged from 5 to 40%. The source pond source water frequently had turbidity values of ≥100 NTU. After sand filtration, the turbidity is typically 5 NTU. Despite this, clogging management involving frequent (monthly to weekly) manual washing to remove fine materials deposited in the sand filtration tank and the infiltration wells is found to be necessary and effective, with post-manual-washing operational infiltration rates restored to annual average values. E. coli counts in recovered water are greatly reduced compared to raw pond water, although E. coli is still detected in about half of the samples. Arsenic in recovered water was detected to be at level of > 100 μg/L repeatedly at three sites, suggesting that As risks must be carefully managed and require further investigation. © 2014 American Society of Civil Engineers.
Velstra J.,Acacia Water |
Groen J.,Acacia Water |
Groen J.,VU University Amsterdam |
de Jong K.,Water Board Noorderzijlvest
Irrigation and Drainage | Year: 2011
In studies concerning rainwater lenses on a parcel scale in brackish polder areas it is assumed that infiltrated rainwater flows through the rainwater lens and seeps to the watercourses. This freshwater system is supposed to be superimposed on the brackish diffuse upward seepage system. This study investigates the influence of field drainage on the dynamic behaviour of fresh rainwater lenses and the risk of salinization of the root zone. Observations presented in this paper show that shallow water and salt movements in clayey polders are more complex and more dynamic than previously thought. On 18 parcels 2D geo-electrical resistivity imaging profiles were measured, which give a good spatial and temporal representation of the salinity distribution of the groundwater. It appears that during wet periods upconing of brackish groundwater appears under pipe drains and ditches, which drain a mixture of fresh meteoric water and deep brackish groundwater. Between drainpipes small rainwater lenses develop. During the dry season, when the groundwater table drops below the drainage level, brackish soil moisture stays behind. Transpiration of the crops rooted in the clayey polder soils result in strong capillary rise of salts, which may even reach the root zone in some places. © 2011 John Wiley & Sons, Ltd.
Foster S.,Global Water Partnership |
Tuinhof A.,Acacia Water |
van Steenbergen F.,Meta Meta Research
Water SA | Year: 2012
In numerous countries of Sub-Saharan Africa the strategic agenda of the water-sector is undergoing substantial change because of demographic pressure, climate change and economic transformation. Two new policy questions are arising from the need to make better use of available groundwater storage to improve water-supply security: • What is the scope for promoting much increased groundwater use for irrigated agriculture, and how might the investment risks be reduced and sustainable outcomes ensured? • How can the demand to expand urban groundwater use, for both further supplementing municipal water-supply systems and for direct in situ water supply, be best channelled to maximise the benefits whilst minimising the risks? This 'new agenda' poses very different challenges from the long-standing requirement to provide rural water supplies of adequate coverage, reliability and quality (which, while still not yet fully addressed, is outside the scope of this paper). Balanced answers to these new questions are needed to provide a sound basis for appropriate investment policies on managed groundwater development and adequate institutional provisions for their implementation. They are discussed here from the standpoint of the GW-MATE experience in some World Bank-supported projects in eastern Africa during 2001-2010, together with a review of some developments in western Africa and insights from parts of Asia and Latin America.