A rapid model for estimating the depletion in river flows due to groundwater abstraction

Abstract

The Environment Agency of England and Wales uses its calibrated regional models to estimate the reduction in river flows resulting from proposed groundwater abstractions. Where there is no regional model, analytical equations can produce quick initial estimates of river flow depletion. However, users often want more confidence in their estimates by representing more faithfully their understanding of the real river–aquifer system. This paper shows that, when using a numerical model designed to predict river flow depletion, it is important to include adjacent catchments and intermittent streams and less important to include river elevations and variations in transmissivity with groundwater head. Recharge does not usually need to be included unless part of the river becomes disconnected or dry. Therefore, for rivers where stream length is constant and transmissivity variations are small, it is valid to use a ‘no-recharge’ depletion model, which can be built quickly (within a month). A case study on the River Leith in NW England illustrates the use of such a model to assess the ecological impact of two groundwater abstraction licences under the European Union Habitats Directive.

The use of groundwater levels and numerical models for the management of a layered, moderate-diffusivity aquifer

“…If groundwater abstraction does not draw groundwater levels significantly below the streambed and/or nonperennial conditions are insignificant, then changes in abstraction impacts on surface water flows should not occur when climatic conditions vary, as long as the relationship between groundwater head and groundwater -surface water flow does not depart too much from linearity. Hulme et al (2012) demonstrate this point in detail. Any variation of the groundwater abstraction impact with climatic conditions would then depend on the location and penetration of the borehole, local aquifer conditions and abstraction rate.…”

Groundwater abstraction impacts on river flows: predictions from regional groundwater models

“…This may be related to natural factors such as the increased length of overflowing river reaches (see also Hulme et al 2012) and springs as groundwater levels rise and, for the Chalk in particular, the enhanced speed of flow response associated with the saturation of more transmissive shallow fissure systems (e.g. Leckford and Worlds End).…”

“…Hantush 1965, and more recently Hunt 1999). Many of these have been built into the Environment Agency's 'Impact of Groundwater Abstraction on River Flows' (IGARF) suite of predictive tools, as summarized initially in Kirk & Herbert (2002), and extended to consider neural network modelling approaches by Parkin et al (2007), and object-oriented code enhancements in Jackson et al (2008) and Hulme et al (2012). Many authors describe the 'real world', non-linear hydrogeological mechanisms illustrated in this paper, which go beyond idealized analytical representations and may result in impacts during low-flow periods being less than such approaches predict (e.g.…”

Introduction: groundwater resources modelling: a case study from the UK

“…This programme consisted of eight regionally based subprogrammes (SW, Southern, Thames, Anglian, Midlands, Wales, NW and NE) covering the Chalk, Permo-Triassic Sandstone, Jurassic Limestone, Carboniferous Limestone, Permian Dolomites (Zechstein) and Lower Greensand (Fig. 3) In some cases the papers provide alternative approaches to conventional groundwater modelling, because of the importance of flow in large conduits or time/cost constraints (Hulme et al 2012). However, the papers from the England and Wales programme and the associated modelling mostly have seven common characteristics:…”