OR/15/038 Recommendations

Gareth Farr (with contributions from Luz Ramos Cabrera). 2015. Nedern Brook Wetland SSSI Phase 1 hydrological monitoring. British Geological Survey Internal Report, OR/15/038.

The current study has helped to answer some recommendations from Haskoning UK Ltd (2013) regarding the hydrology of the Nedern SSSI / Nedern Brook, however it is acknowledged that the scope was limited and did not cover water balance, geological investigations or water chemistry.

1  Hydrological monitoring
There is still a lack of long term water level data in the Nedrn Brook and extreme events such as drought or flood have not been characterized, thus the limits of flooding and flood duration are poorly understood. The lack of spot gauging within the Nedern Brook also limits the calculation of a stage discharge relationship for flow within the brook. This data is very important to underpin future river restoration plans. There is no groundwater monitoring within the River Terrace Gravel deposits, and thus the role of gravels in groundwater supply to the wetland is not known.

It is proposed that monitoring of groundwater and surface water levels should continue in the Nedern Brook to better characterise the hydrology of the area. Surface water spot gauging during high flow and low flow should be repeated upstream at Tyne Cottages and downstream (Nedern DS) to allow a stage discharge relationship to be formed. This data, which can be back calculated for the monitoring period, will address the key knowledge gap of understanding flow within the Nedern Brook.

Should funding become available then borehole/s drilled into the River Terrace Deposits should be instrumented with data loggers to help better understand the role of the river terrace deposits on groundwater supply to the wetland. On site precipitation data is preferable but not necessary as existing NRW stations at Llanvaches and Collister Pill can be used.

2.  Water balance
Currently there is no water balance for the Nedern brook wetland. Without this we cannot quantify inflows and outflows of water into the wetland, or design appropriate river restoration plans. An initial water balance should be possible once stage discharge relationships for flow are calculated as described in recommendation 1. This would require flow volumes in the Nedern Brook both upstream and downstream of the wetland (as detailed in recommendation 1), rainfall and evapotranspiration (from existing stations), ground and surface water abstraction returns (NRW database) and flow from direct inputs such as drains. An initial water balance would directly benefit the understanding of how the site works, underpinning future management or restoration options.

3.  Geological properties
There is a lack of information on the superficial deposits within the wetland area. It is likely that the superficial deposits will be heterogeneous, some areas being highly permeable — allowing the movement of groundwater and others less so resulting in the impediment or retention of water. The implication is that different areas within the wetland will function differently dependent upon their geology.

The recommendation from Haskoning UK Ltd (2013) to ‘Undertake an investigation to determine the thickness, spatial extent and permeability of the alluvium and river terrace gravels within the study area’ remains however should only be undertaken if river restoration plans are to go ahead. Geological mapping by the BGS see Lawrence et al (2013) could be built upon with a series of small boreholes across the site and lab testing required.