The Chalk as a karstic aquifer: evidence from a tracer test at Stanford Dingley, Berkshire, UK

Abstract

Karstic features such as swallow holes and dolines are the rule rather than the exception in the Chalk outcrop of southern England, particularly in the region of the Chalk/Tertiary boundary. Previous tracer tests at Bedhampton and Water End have indicated groundwater transport velocities of 2.2 and 5.5km/day. A recent tracer test at Stanford Dingley in Berkshire has indicated comparably high transport velocities in the Chalk: 5.8km/day for peak tracer concentration, and 6.8km/day for tracer breakthrough. In all three cases the swallow hole systems were able to transmit turbid surface run-off contamination over large distances, indicating a short-circuiting of the natural attenuating properties of the unsaturated and saturated zones. In the light of this, the practice of using swallow holes to dispose of agricultural- and road-run-off should be discouraged.

Variability of dissolved CO<sub>2</sub> in the Pang and Lambourn Chalk rivers

“…The Lambourn, for example, has an average stream gauge baseflow index (BFI) of 0.93, whilst the Pang has average BFI of 0.867 (Gustard et al, 1992). In addition to groundwater springs, there are several sink holes in both catchments, the most significant one being in the lower Pang catchment (Banks et al, 1995;Maurice et al, 2006). Significant impermeable Tertiary (Eocene) formations are also found in the lower Pang, including Reading Beds and London Clay.…”

Catchment scale tracer testing from karstic features in a porous limestone

“…The Chalk is a porous fractured limestone that exhibits small-scale karstic features at the surface -sinking streams and dolines, plus an extensive dry valley network. Subsurface karst is also developed to some degree (Banks et al, 1995;MacDonald et al, 1998;Maurice et al, 2006;Worthington and Ford, 2009) but the influence this has on groundwater flow and contaminant transport remains poorly understood. It is not even certain whether an occurrence of dolines and sinking streams is a reliable indication that karst channels exist in the aquifer beneath them, nor how far such channels might extend where they are present.…”

“…More substantial cave networks have been described in Northern Ireland (Barnes, 1999), and geomorphological karst development in the French Chalk (solution features and caves) appears to be much more significant than in England (Rodet, 1991;Rodet et al, 2009). Codrington (1864), Harold (1937), Atkinson & Smith (1974), Rodet (1991), Banks et al (1995), Barnes (1999), Massei et al (2002Massei et al ( , 2006 and Maurice et al (2006) all report tracer tests on sinking streams in chalk with results that are summarised in Table 1. The earliest water tracing in the English Chalk was by Codrington (1864) who introduced dye into a stream sink in Wiltshire and reported its visible reappearance at a spring several kilometres away. Few details are given but the visible recovery suggests that attenuation was low.…”

Characterising groundwater-dominated lowland catchments: the UK Lowland Catchment Research Programme (LOCAR)

“…Its ability to support major flows throughout the year demonstrates a large storage and slow response. On the other hand, historical tracer testing (Banks et al, 1995), confirmed by recent work of Maurice (Maurice et al, in press) has demonstrated travel times of the order of several kilometres per day. While tracer tests provide confirmation of certain flow connections, the contributing area of the Blue Pool has not been fully defined.…”