1,721,005 research outputs found
The role of groundwater in supporting eco system and cultural services in North West England
No full textThis paper describes the importance of groundwater to the coastal habitats of the sand dunes in North West England. The sand dunes support an aquifer that extends for 20km between Liverpool and Southport. They provide a range of natural habitats, sites of special scientific interest and a number of nature reserves (https://www.sefton.gov.uk/around-sefton/coast-countryside.aspx). It also supports cultural services (landscape, tourism, art) and international quality recreation facilities such as the famous Royal Birkdale Golf Club and others. Groundwater levels in the sand dunes have been monitored monthly since 1972 and at 30 minute intervals since 2010. Seasonal changes in recharge cause groundwater levels to rise and fall 0.5-1.0m between winter and summer. The long term observations suggest a gradual lowering of water levels of 0.15m over the last 45 years, despite the sea level boundary rising by 0.1m over the same period (https://www.ntslf.org/products/sea-level-trends).
The importance of groundwater in the various nature reserves is demonstrated by the emergence of fresh water ponds each winter. These areas are extremely biodiverse, supporting up to 100 plant species per square meter (Houston, 2008, Natural England, 2014) together with IUCN Red List species (www.iucnredlist.org/) such as the Natterjack Toad (Epidalea calamita).
Concerns have been raised that climatic change and human actions such as agricultural drainage in the adjacent areas may adversely affect the groundwater levels which in turn may cause breeding ponds to dry up and the loss of biodiversity (Curreli et. al., 2013). Another impact is a reduction in the natural sub irrigation of the fairways and greens of the numerous golf courses in the area.
Various 1D and 2D groundwater models have been developed to explain the annual and long-term changes in ground water levels (Clarke and Sanitwong, 2009, Abesser et. al., 2017). These have been tested against the 45+ years of monitoring data. Information from this modelling work is enabling conservation planners to identify areas of the dune system that will be of concern to managers. Coastal processes are creating new land that will become suitable for the creation of new nature reserves. A new approach to conservation may become necessary, where ecosystems relocate spatially, and conservation management will have to become more dynamic.
Abesser, C., Clarke, D., Hughes, A. G., & Robins, N. S. (2017). DOI: 10.1007/s11852-017-0525-5 Clarke, D. and Sanitwong Na Ayuttaya (2009). DOI:10.1007/s11852-009-0066-7 Curreli, A., Wallace, H., Freeman, C., Hollingham, M., Stratford, C., Johnson, H. and Jones, L. (2013). DOI: 10.1016/j.scitotenv.2012.11.035 Houston, J. A. (2008). Management of Natura 2000 habitats. 2190 Humid dune slacks. European Commission. Natural England (2014). Survey and analysis of vegetation and hydrological change in English dune slack habitats. Annex 2 - Site report for Sefton Coast: Ainsdale NNR, Ainsdale LNR, Birkdale Hills LNR. publications.naturalengland.org.uk/file/663563621577523
Design of hydraulically efficient power-law channels with freeboard
No full textA power law-channel is a generalized form of the parabolic channel. The exponent of the governing equation is a variable that for certain maximum permissible side slopes can be determined by maximizing the cross-sectional area of flow (or minimizing the wetted perimeter). Using this exponent rather than the constant allows a hydraulically more efficient open channel section to be designed. In earlier work on power law channels freeboard was neglected to simplify the analysis. However as pointed out by several authors, a channel without freeboard is of academic interest only and not practical. All open channels are in practice designed and constructed with freeboard as a factor of safety. In this paper freeboard has been introduced as an additional parameter to be taken into account when designing a power law channel. The work from this paper is applied to an earlier example of a parabolic channel to demonstrate a practical design
The fractionation of phosphorus in UK chalk stream surface waters and its relevance to the regulation and management of water quality
No full textThe regulatory management of river water quality requires measurements of phosphorus that are operationally viable and meaningful in terms of insight into its effects. This need is a particular concern in globally rare and ecologically sensitive chalk streams. P data pertaining to rivers are commonly limited to soluble reactive P; other fractions of P may be of concern but are not routinely monitored. This study seeks to establish the nature and extent of non-regulated forms of P in UK chalk streams. Whilst soluble reactive P in two southern English chalk streams was found to comprise the majority of reactive P in surface waters in the majority of samples, 15-20% of the total reactive P was within other size fractions greater than 0.22 μm. The contribution of reactive P to the total P was highly variable. We conclude that, with some adjustments, the established method of regulatory monitoring of P in UK rivers is viable and valuable. In cases where the levels of reactive P are not consistent with ecological status and/or expected outcomes of programmes of measures, we recommend that targeted analysis of non-regulated forms of P is undertaken as a means to guide and focus management interventions
Predicted effects of climate change, vegetation and tree cover on dune slack habitats at Ainsdale on the Sefton Coast, UK
No full textDune slack habitats are highly dependent on the availability of water to support flora and fauna. Typically this is provided by shallow groundwater. This paper describes the seasonal and long term variation in groundwater levels in part of the Sefton coastline between 1972 and 2007. The effects of climate change, vegetation management and coastline realignment on groundwater levels are modelled. The observed annual water table levels rise and fall with an amplitude of 1.5 m, but longer term variations and trends are apparent. A stochastic water balance model was used to describe the changes in water table levels in slack floors in the open dunes and also in areas afforested with pine trees. It was found that the pine trees evaporated 214 mm/year more than open dunes vegetation, resulting in the water table being 0.5–1.0 m lower under the trees than under the open dunes. The effects of climate change on the ground water was simulated using predictions of future climate conditions based on the UKCIP02 medium high emissions scenario. The increase in temperature and change in rainfall patterns will result in a decrease in mean ground water levels by 1.0–1.5 mm in the next 90 years. Typical patterns consist of sequences of 5–10 years of low water table levels interspersed by infrequent sequences consisting of 2–5 years of relatively high or “normal” levels. These results indicate that that flora and fauna that cannot survive a 5–10 year period of water table levels >2.5 m below ground level are unlikely to survive or persist in many slack areas and a change in the ecology of these slack may become inevitable. Other effects of climate change include sea level rise which will result in a gradual rise in water table levels. Coastal erosion will increase the water table gradient to the sea and result in a slight lowering of the ground water levels. Conversely coastal accretion will reverse this process. The spatial distribution of coastal erosion and accretion along the Sefton coastline and its likely impacts on groundwater levels are discussed. The modelling work described in this paper has identified the factors which have the largest effect on groundwater levels in temperate coastal dune systems
A Quasi-2D Bayesian network model for assessments of coastal inundation pathways and probabilities
No full textCoastal flood assessments often require the analysis of a complex system of flood sources, pathways and receptors. This can be challenging for traditional numerical modelling approaches. In this paper we use a Bayesian networks approach to assess coastal floodplains as networks of inter-linked elements. A Bayesian network (Bn) model is built to describe flood pathways and estimate flood extents for different extreme events. The network of the Bn model is constructed from a quasi-2D Source – Pathway – Receptor (SPR) systems diagram. The Bn model is applied in Teignmouth in the UK, a coastal floodplain of typical complexity. It identifies two key flood pathways and assesses their sensitivity to changes in sea levels, beach widths and coastal defences. The advantages, utility and limitations of the Teignmouth Bn model are discussed. The process of 2D SPR and Bn model construction helps identify gaps in floodplain understanding and description. The Bn model quantifies inundation probabilities and facilitates the rapid identification of critical pathways and elements, before committing resources to further detailed analysis. The approach is transferable and can be readily applied in local-scale coastal floodplains to obtain a systems-level understanding and inform numerical modelling assumptions
Channel capacity under arranged demand irrigation
No full textTo date, arranged demand irrigation and on-demand irrigation were considered as two distinct types of systems. This paper presents the hypothesis that arranged demand is a continuous function with on-demand as one extreme and fully arranged demand as the other. This paper introduces the index of relative timeliness to capture this semantic. This index assumes a value of 1 for an on-demand system and 0 for a fully arranged demand system. This paper then demonstrates that how this index can be incorporated in mathematical modelling. An earlier integer programme is modified to include the concept of relative timeliness. As a case study an existing tertiary unit is simulated using this tool to investigate whether, given its current capacity, the tertiary unit can be operated on an arranged demand basis, and if so what level of service can be expected. The model a] so indicates what capacity is required if the tertiary unit were to be operated on an on-demand basis. The capacity requirements as predicted by the model developed in this work relate well to earlier empirical/ experience guidelines. The model developed is useful for investigating and simulating existing tertiary units, but in its current form cannot be used for general design guidelines for new designs. Some recommendations for further developments are made
Evaluation of a genetic algorithm for the irrigation scheduling problem
No full textA typical irrigation scheduling problem is one of preparing a schedule to service a group of outlets which may be serviced simultaneously. This problem has an analogy with the classical earliness/tardiness problem in operations research. In previously published work an integer program was used to solve this problem, however such scheduling problems belong to a class of combinatorial problems known to be computationally demanding (N-P hard). This is widely reported in operations research. Hence integer programs can only be used to solve relatively small problems usually in a research environment where considerable computational resources and time can be allocated to solve a single schedule. For practical applications metaheuristics such as genetic algorithms, simulated annealing, or tabu search methods need to be used. However as reported in the literature, these need to be formulated carefully and tested thoroughly. This paper demonstrates the importance of robust testing of one such genetic algorithm formulated to solve the irrigation scheduling problem with simultaneous outlets serviced against an integer program formulated to solve the same problem
Algal wastewater treatment systems for seasonal climates: application of a simple modelling approach to generate local and regional design guidelines
No full textAlgal waste stabilisation ponds (WSP) provide a means of treating wastewater, and also a potential source of water for re-use in irrigation, aquaculture or algal biomass cultivation. The quantities of treated water available and the periods in which it is suitable for use or discharge are closely linked to climatic factors. This paper describes the application, at a continent-wide scale, of a modelling approach based on the use of readily available climate datasets to provide WSP design and performance guidelines linked to geographical location. Output is presented in regionally-based contour maps covering a wide area of Russia and central Asia and indicating pond area, earliest discharge date, discharge duration, wastewater inflow:outflow ratio and salinity under user-specified conditions. The results confirm that broad-brush discharge guidelines of the type commonly used in North America can safely be applied; but suggest that a more detailed approach is worthwhile to optimise operating regimes for local conditions. The use of long-series climate data can also permit tailoring of designs to specific sites. The work considers a simple 2-pond system, but other configurations and operating regimes should be investigated, especially for the wide range of locations across the world that are intermediate between the ‘one short discharge per year’ mode and year-round steady-state operation
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