Hertfordshire Chalk Groundwater Model Phase 2

Tender description

The Hertfordshire Chalk Groundwater Model (HCGM) represents 4060km2 of the Chalk aquifer to the north-east of London, including the county of Hertfordshire, parts of Buckinghamshire, Bedfordshire, Oxfordshire, Essex, Cambridgeshire, and London. The model represents a number of Chalk streams that are situated in the Wye, Colne and Lee catchments. These catchments have been previously assessed to suffer from large scale over abstraction through the Catchment Abstraction Management Strategy (CAMS) methodology. The Hertfordshire Chalk Groundwater Model (HCGM) was built between 2017 and 2019. The focus of the HCGM build was to join three existing groundwater models; Vale of St Albans (VSA), Rib-Ash-Stort (RAS) and South West Chilterns (SWC), which covered the area into one single model. Additional input from the Cam, Bedford Ouse (CBO) groundwater model was used where the newly defined boundary of the HCGM extended into the CBO model area. The model is currently used for groundwater management for surface water catchments in the Agency's Hertfordshire and North London (HNL) and Thames areas. The objective of this model merger was to overcome the difficulties in assessing the impact of abstractions where such abstractions were located close to model boundaries. The EA is looking to procure an external contractor to deliver Phase 2 of the project, which will deliver the Formulation of Revised Conceptual Model. This phase will refresh the existing foundation conceptual models and merge them into a single conceptual model that will then be updated. This will then support proposals for further development of the model in Phase 3. The objectives of Phase 2 will be: - To refresh the existing foundation conceptual models and merge them into a single conceptual model - To gather and review necessary datasets and literature to support merged conceptual model update, reporting on initial model conceptual model uncertainty and data gaps - To expand the conceptual model where new data and literature is available for several concepts such as influence of superficial deposits, karstic development, evidence of hydrogeological layering within the Chalk - To report on the updated conceptual model and make recommendations for development and refinement of numerical model in MODFLOW 6 (Phase 3)