Client: Natural England
Location: Lyscombe Farm, Dorset, England
Service Provided: Hydrogeological Assessment for Nutrient Mitigation
Background
Lyscombe Farm sits within the upper catchment of Poole Harbour, a designated protected area facing significant pressure from nutrient pollution, particularly nitrogen and phosphorus. As part of a wider nutrient mitigation strategy, Natural England sought to understand how changes in land management at Lyscombe Farm (specifically the cessation of intensive agriculture) would impact nutrient levels in the harbour over time.
The key challenge was to evaluate the time lag between interventions on the farm and observable nutrient reductions in Poole Harbour, factoring in the complexity of overland flow and subsurface water pathways.
Project Objectives
- Assess the hydrogeological setting of Lyscombe Farm
- Determine how water and nutrients move through the landscape
- Estimate time delays (lags) between land-use changes and improvements in Poole Harbour water quality
- Provide recommendations to inform regional nutrient mitigation planning
Our Methodology
1. Desk Study and Site Visit
Initial data collection and a comprehensive site walkover provided a baseline understanding of site conditions, topography, and existing water features.
2. Conceptual Hydrogeological Model
A conceptual model was created to map infiltration, groundwater recharge, and flow mechanisms, focusing on the Chalk aquifer that underlies the site.
3. Water Balance Development
We quantified how rainfall is distributed between overland runoff, evapotranspiration, and infiltration into the aquifer.
4. Time Lag and Nutrient Transport Assessment
Using flow modelling, we estimated how quickly nutrients would travel from the farm to Poole Harbour through both fissure and matrix flow in the aquifer.
5. Reporting and Recommendations
A final report delivered clear findings, time lag projections, and practical next steps for data improvement and model refinement.
Key Findings
- Water Balance:
- 9% of rainfall becomes surface runoff
- 44% is lost to evapotranspiration
- 47% recharges the groundwater system
- Groundwater Flow Dynamics:
- Fissure Flow: Fast-moving water reaches the water table quickly
- Matrix Flow: Slower-moving, progressing at ~1 metre/year
- Time Lag Estimates:
- Nutrients via fissure flow reach springs within 1 year
- Nutrients enter Poole Harbour within 3–5 years
- 55% of rainfall infiltrates through the matrix, significantly delaying nutrient transport
- Regional Impact:
- 35% of rainfall from Lyscombe Farm reaches Poole Harbour within 3 years
- An additional 9% reaches the harbour within 5 years
Recommendations
- Targeted Borehole Drilling
Further drilling in the Lyscombe Bottom area is needed to refine data on groundwater depth and flow characteristics. - Regional Model Integration
Collaborate with the Environment Agency to enhance regional-scale water and nutrient transport models. - Model Refinement
Continued data collection will improve the accuracy of time lag predictions and nutrient transport assessments.
Conclusion
This hydrogeological assessment provided Natural England with actionable insights into nutrient transport timescales from Lyscombe Farm to Poole Harbour. The findings support strategic land-use changes to achieve long-term water quality improvements. Continued refinement of the model and further field data will strengthen the region’s approach to nutrient mitigation.
Interested in nature-based solutions and hydrogeological consultancy?
Contact us today to discuss your nutrient mitigation project and how we can support sustainable land and water management. We have over 30+ years’ experience delivering hydrogeological assessments, and would be very pleased to receive your enquiry.
