Rationale for groundwater monitoring in the context of the Lowland Permeable Catchment Research Programme (LOCAR)

The purpose of this short report is to discuss the rationale behind the design of hydrogeological monitoring networks. More specifically, to provide the background necessary for an assessment of the options for establishing hydrogeological baseline monitoring networks in three lowland permeable catchments that are being developed by the NERC Lowland Catchment Research (LOCAR) Thematic Programme. The aim of LOCAR is to undertake detailed, interdisciplinary programmes of integrated hydroenvironmental research relating to the storage-discharge cycle and groundwater-dominated aquatic habitats in three lowland catchments, the Pang-Lambourn, the Tern, and the Dorset Frome. In addition to the hydrogeological monitoring networks, instrumentation will also be established to monitor surface and atmospheric water and the ecology of each of the catchments. The LOCAR Programme will address five central questions, these are: - (i) What are the key hydrogeological processes controlling surface water-groundwater interactions and the movement of groundwater in lowland catchments? (ii) What are the key physical, chemical and biological processes operating within the valley floor corridor that affect surface water and groundwater? (iii) How do varying flow regimes control in-stream, riparian and wetland habitats? (iv) How does land use management impact on lowland catchment hydrology, including both water quantity and quality? (v) How can the hydrological, hydrogeological, geomorphalogical and ecological interactions resulting from natural or anthropogenic changes be predicted using integrated mathematical models? Data and observations from the hydrogeological monitoring networks and instrumentation will be principally used to address questions (a), (b) and (e), but will also be used along with data from the other monitoring networks in investigations and studies related to questions (c) and (d). The LOCAR Programme has identified a number of specific tasks or topics that may influence the design of the hydrogeological monitoring network and instrumentation. These may be summarized as follows: - • Flow and transport in the Chalk and Triassic Sandstone aquifers are poorly understood and the relationships between flow and transport properties at different scales, i.e. pore scale, borehole scale and catchment scale needs elucidating. • Aquifer heterogeneity is a dominant influence on contaminant dispersion and is not yet adequately characterized. The role of fracture flow in the Chalk and sandstones need particular attention. • The role of drift deposits in influencing recharge and pollution pathways needs investigation. • Chemical interactions need an understanding of pore and fracture scale processes (including heterogeneiety and scaling properties), and the role of, and constraints on, microbial degradation, and hence the scope for natural attenuation of pollutants, require investigation. • The spatial functioning of the surface water system must be mapped onto an understanding of surface water-groundwater interactions.