Combatting the effects of heavy rainfall – a two-pronged approach

Gully machine

The Transport for Buckinghamshire (TfB) Network Improvement Team had a busy year in 2019, particularly in one of its key areas of work – drainage improvement schemes.  In all, 29 schemes were included in the countywide programme for 2019 – 20 with the team on target to complete this programme in this financial year.

The TfB team work very closely with the Buckinghamshire County Council Strategic Flooding Team on all schemes, aiming to increase capacity and efficiency of drainage. Eastern Dene, Hazelmere is one example of many such schemes, solving a complex drainage problem through:

  • Upgrading the entire drainage system in June 2019
  • Increased gulley maintenance on the A404
  • Creating new boreholes
  • Installing a 300mm pipe under the A404 to allow the overspill of surface water to cross the road and use the holding capacity at this location
  • Use of a ‘water gate’ system to give extra protection to a property.

A local resident of Eastern Dene gave feedback on the new scheme which was completed in December: “It is really reassuring to know that you are continuing with strategies to relieve the flooding issue in our area. With the heavy rain on Thursday, the drains between Eastern Dene and Park Lane worked well and the new drains by the new catch pit coped with the water before it entered the road.”

Ironically the drainage programme was hampered by extreme periods of heavy rainfall that can be attributed to climate change. Scientists say that as the world has warmed by 0.7C, with the atmosphere able to hold 4% more moisture, which means more potential rain. The persistent wet weather started in mid-August and continued throughout the latter part of 2019, with a series of downpours in late November bringing one of the wettest weeks in the last 50 years, causing major disruption.

Over the past few years and with the threat of increasing heavy rainfall, the TfB team developed a matrix to prioritise proposed drainage schemes.  The flood management team also advised on flood risk areas in order to include schemes to tackle flooding before they become an issue to residents.

The matrix is completed to score each proposed scheme against a set of criteria which includes road safety, property damage, local reports and time weighting. From this matrix a rolling programme of works is developed with approximately 30 schemes prioritised for delivery each year.                   

What else has TfB been doing to tackle the wet weather and flooding? 

As well as the 29 drainage schemes the highway maintenance teams carry out a range of activities including routine gully clearing to keep the drainage flowing.

Over the last few months of extreme rainfall, it has been a challenge to keep on top of the significant additional reactive work of clearing sites where flooding or standing surface water has been identified. Often, problems lie within underground drainage pipes, or more recently the issue of a lot of water trying to enter the drainage at once, overwhelming the system.

Even if sufficient capacity exists,  gullies and pipes can also become blocked with debris, especially during autumn leaf fall.  An additional machine was brought in by TfB for a twelve week period in order to supplement the efforts of the three full time teams in the depots in the North and South of the County. Additionally, new gully machines have been purchased to upgrade existing ones, operating from the depots at Aylesbury, High Wycombe and Amersham. This will double the number of gully emptiers active on the network between April and June, combatting the effects of the winter period and preparing the network for the autumn and winter weather of 2020/21.

A new asset management software system (GullySMART) is now in use to manage over 79,000 gullies in Buckinghamshire.  The system combines mobile technology with mapping data, available on a hand held device and building a forward looking profile of required maintenance based upon historical knowledge of attendance and condition. This innovative technology will enable TfB to build a picture of the condition of the gully data, which will ultimately lead to a more focussed ‘needs based’ approach to the gully-clearing programme, concentrating on those gullies that need more frequent cleansing.

Mark Shaw Deputy Leader and Cabinet Member for Transportation keeps a keen eye on all work in progress to manage flooding and said: “I am satisfied that this two pronged approach to gully clearing plus major schemes to address the more problem areas of highway flooding will have a significant impact however, we can’t get complacent. I am pleased that we will also be adding an additional £1 million to the routine gully clearing programme from April 2020.  We will have an extra 3 gully machines on the network between April and June giving us 6 machines to get ahead of ourselves this year, should we experience another wet autumn.”