Because of the exceptionally wet weather we experienced in February, and the flooding which occurred as a result of so much rain, we have put together the following information to answer questions about the drainage of Underhill Park and the impact of the proposed development.
Photo by Jim Young
We all know that Underhill Park floods and that it acts as a holding area during times of heavy rain. However, the Council’s engineer has advised that such flooding does not affect third parties or the highway because the Park is so low lying. In his view, the surface water within the Park has to be dealt with on site via natural filtration and evaporation. Natural filtration can be assisted by constructing soakaways and the efficiency of these is determined by the ground conditions.
Thanks to Mumbles Community Council (MCC), a lot of information is available on the ground conditions. MCC commissioned studies by Earth Science Partnership in February 2010 and also in January 2011 and 2012 in which water levels in six boreholes were monitored and infiltration rates tested using two trial pits. The boreholes have also provided information on the changes in ground structure by depth.
Subsequently, land drainage was introduced across the main rugby pitch and large soakaways were constructed to intercept the run off from the access road and car park area.
Impact of the development
The Phase 1 buildings are to be located above the area which often floods but, in order not to exacerbate the problem, any surface water arising from the proposed development area will be recycled or diverted to soakaways. These requirements are built into the plans and costs for Phase 1.
The largest impact will be from the proposed all-weather pitch.
Prior to submitting the 2019 planning application for Phase 1, CB3 Consult were commissioned by MCA to advise on the best location for the all-weather pitch and on the design of suitable soakaways. This work included Earth Science Partnership carrying out further investigations including determining infiltration rates at three locations within the Park. Based on the information, CB3 Consult has advised on the size of soakaways required to take the surface water discharge from the proposed development. Diverting the surface water run-off to soakaways from such a large area of the park should reduce the scale of flooding at times of heavy rain. The cost of providing these soakaways is also included in the cost estimates for Phase 1.
Before work can start MCA need to secure an approval from Natural Resources Wales for a sustainable drainage scheme. This is a requirement of the Flood and Water Management Act 2010 and MCA will therefore be appointing a specialist engineer to prepare this scheme and seek the necessary approval.