Conceptualising groundwater flow systems at a national (British mainland) scale Brighid Ó Dochartaigh and BGS Hydro-JULES team 11 September 2019 Seeking answers to 2 questions: How can an integrated & holistic approach to modelling terrestrial hydrology – including groundwater – improve: 1. Simulation of major flooding events, such as 2013-14 floods? 2. Assessment of water resources under drought conditions? Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 2 British mainland (WP4.1) 3D Parameterising Deep geological Saturated GW domain – Unsaturated framework Zone code technique Zone code model Conceptual FY18/19 models of groundwater (GW) flow Parameterising Model Sub-surface GW domain – instance code application FY19/20 Results Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 3 Britain’s diverse geology and hydrogeology Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 4 3D Geological Framework Model +1.5 km to -15 km 1:625,000 scale mapping Newell 2019 Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 5 Model includes 3D information from: borehole geology & geophysics; pre-existing cross sections; geological history & structure; seismic data Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 6 Geology: a physical framework for groundwater flow Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 7 Key groundwater conceptual model parameters Geology Geography Surface water Groundwater Aquifer Chemistry Flow Aquifer Topographic relief Recharge quantity, Groundwater flow Aquifer properties: e.g. Dominant thickness area & mechanism type (fracture; porosity, hydraulic chemistry intergranular) conductivity, transmissivity, storage capacity Depth to Key groundwater flow Discharge Flow path length Response to recharge: Differences in aquifer top & boundaries (e.g. characteristics, spatial & temporal chemistry with base coast, rivers) area and (including memory of depth mechanism (e.g. droughts & floods) springs, baseflow, wetlands) Surrounding Interaction with other Other surface Flow path depth Predictability & Presence of rock types flow systems water interactions variability of aquifer palaeo &/or properties connate water Lithology & Preferential Abstraction variability pathways (e.g. characteristics faults, karst) Structure Groundwater age Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 8 Defined 17 hydrostratigraphic units (aquifer types) 1 Quaternary 2 Neogene and Palaeogene 3 Chalk 4 Upper Greensand to Lower Greensand 5 Wealden 6 Purbeck Group to Ampthill Clay Formation 7 Corallian Group 8 Oxford Clay 9 Great and Inferior Oolite groups (mid-Jurassic) 10 Lias Group 11 Mercia Mudstone Group 12 Sherwood Sandstone Group 13 Permo-Triassic 14 Carboniferous 15 Devonian 16 Silurian, Ordovician, Cambrian 17 Precambrian & Igneous Most productive aquifers Less productive aquifers or unproductive rocks Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 9 Groundwater conceptual models for Hydro-JULES hydrostratigraphic units - Summarise key aquifer, groundwater flow & groundwater chemistry features - Schematic, representative cross sections - Text summaries of key characteristics - Existing models for part or all of 7 units 1 Quaternary 2 Neogene and Palaeogene 3 Chalk 4 Upper Greensand to Lower Greensand 5 Wealden 6 Purbeck Group to Ampthill Clay Formation 7 Corallian Group 8 Oxford Clay 9 Great and Inferior Oolite groups (mid-Jurassic) 10 Lias Group 11 Mercia Mudstone Group 12 Sherwood Sandstone Group 13 Permo-Triassic 14 Carboniferous 15 Devonian 16 Silurian, Ordovician, Cambrian 17 Precambrian & Igneous Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 10 Examples of existing regional conceptual models Dominant groundwater flow Fractures, faults, type bedding and karst Dominant aquifer productivity High (but variable) Dominant groundwater flow 0-1 to >10 km path length Typical groundwater flow Variable <10 m to depth 100’s m Dominant groundwater age Days to decades Dominant baseline Generally oxic, Ca- groundwater chemical type HCO3 dominated Dominant overlying strata Coal Measures, Mercia Mudstone, Quaternary Carboniferous Limestone – Wales (also in England) Ander & Farr (in prep) Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 11 Examples of existing regional conceptual models Dominant groundwater Significantly intergranular flow type (sandstone); Fracture (breccia) Dominant aquifer Moderate to Very High productivity Dominant groundwater 1 km + flow path length Geological control usually dominates over catchments Typical groundwater 100s m flow depth Dominant groundwater Years to millennia age Dominant baseline U Moderately mineralised; oxic groundwater chemical Ca-Mg-HCO3 dominated type Dominant overlying Variable strata Permo-Triassic – Scotland (also in England) Ó Dochartaigh et al. 2015 Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 12 Examples of existing regional conceptual models Carboniferous (mined/unmined) – Scotland / Wales (also in England) Ó Dochartaigh et al. 2015, Ander & Farr (in prep) Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 13 Examples of existing regional conceptual models Dominant groundwater Intergranular flow type Dominant aquifer Low to High productivity Dominant groundwater Unknown flow path length Typical groundwater < 10 m (but up to 100m) Quaternary – Wales (also applicable across much of flow depth Dominant groundwater Modern to decades age England & Scotland) Dominant baseline Unknown groundwater chemical type Ander & Farr (in prep) Dominant overlying Absent or variable other strata Quaternary deposits Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 14 Example of existing detailed conceptual model England – Cotswolds Oolite aquifers HydEF Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 15 Developing remaining regional conceptual models - Upscale existing local / catchment scale conceptual models across relevant regional hydrostratigraphic units 1 Quaternary 2 Neogene and Palaeogene 3 Chalk 4 Upper Greensand to Lower Greensand 5 Wealden 6 Purbeck Group to Ampthill Clay Formation 7 Corallian Group 8 Oxford Clay 9 Great and Inferior Oolite groups (mid-Jurassic) 10 Lias Group 11 Mercia Mudstone Group 12 Sherwood Sandstone Group 13 Permo-Triassic 14 Carboniferous 15 Devonian 16 Silurian, Ordovician, Cambrian 17 Precambrian & Igneous Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 16 What depth is active groundwater flow? Total Dissolved Solids Based on study by Bloomfield et al. (in prep) Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 17 Summary Work to date: • Geological framework model • Define hydrostratigraphic units • Collate existing regional conceptual models of groundwater flow • Develop plan to upscale existing local / catchment scale conceptual models for missing hydrostratigraphic units • Define max. depth of active groundwater flow Outcome: • Solid basis for developing realistic numerical groundwater flow models at a national scale More about Hydro-JULES numerical groundwater modelling at BGS posters & exhibit Centre for Ecology & Hydrology | Hydro-JULES Conceptualising groundwater flow systems at a national (British mainland) scale 18.