In January 2021 the Environment Agency reported that all the catchments in Hertfordshire have received exceptionally high rainfall over the previous six month period, (170% of the long term average falling between October and January) which has resulted in saturated ground, higher river flows flood warnings and as previously reported to members a number of properties flooding.
The Environment Agency have issued a flood alert for Kimpton / Lilley Bottom
These areas are monitored which allows alerts to be issued so it doesn’t necessarily mean other areas won’t be affected; most likely those areas where groundwater flooding was observed in 2013/14 and possibly 2000/2001 which was a notably wet winter.
Groundwater flow most likely relates to rainfall events which are not recent (possibly months or years ago) and is slower to respond to rainfall than rivers but can last for a long time. It is extremely problematic to manage as it covers significant areas and volumes of water.
Kimpton last suffered groundwater flooding in 2001; http://www.kimptonvillage.tsohost.co.uk/flood.htm
Response February 2021
The county council as the Lead local Flood Authority LLFA were made aware of the rising groundwater levels by EA reports for the Thames and North London Area. North Herts District Council also reported elevated levels from monitoring of a sump on the outskirts of Kimpton. As the LLFA HCC is the authority with powers to manage flood risk from groundwater.
Kimpton and Lilley Bottom
Using existing resilience structure set up for the Covid response, HCC is coordinating a multi-agency group to monitor and prepare for potential flooding in Kimpton. Officers from Hertfordshire County Council the Environment Agency, North Herts District Council and Kimpton Parish Council are meeting regularly to review any response. A review of options based on the findings from 2001 is being carried out infrastructure including the highway drainage has been surveyed and cleaned, Fire and Rescue carried out a trial deployment of their high-volume pump. Planning of preparation and response needs to account for a range of scenarios
It is unclear at present if flooding will occur, or by what mechanism, and it could be several weeks before changes in groundwater levels are seen. Groundwater levels are currently rising and the levels in a sump installed near the Industrial Estate on Claggy Lane are being monitored daily by NHDC. The current groundwater levels are lower than in 2001 when flooding occurred, and higher than those in 2013/14 when flooding did not occur. It is difficult to tell if the current rate of rise in groundwater levels will continue at what point they will significantly slow or fall.
Extensive pumping was carried out in 2001 to help guide groundwater coming from springs higher up the valley through the village. Claggy Road is the area most impacted directly, with the Enterprise Area and several houses being affected. The options for mitigation including pumping are being explored. If required it could need to be in place for 6 to 8 weeks and there is the possibility that not all impacts can be mitigated especially if flows are significant as capacity to move water away from the area is limited and there is potential to increase flood risk downstream.