HARPENDEN TOWN COUNCIL
NON CONFIDENTIAL
COMMITTEE:
ENVIRONMENT
DATE:
19 MARCH 2014
REPORT BY:
TOWN CLERK
SUBJECT:
HARPENDEN COMMON DRAINAGE
1.
Summary
1.1
The main vehicular access/egress point on the Common is via the Baa Lambs
car park. It is used throughout the year for events ranging from Classics on the
Common, Discovery Day, the Fairs and Circus when cars, vans and heavy lorries
all access the site.
1.2
There have been issues with effective drainage of the access/egress point for
some time. The Common does generally recover well after vehicle movements
during inclement weather but the main entrance remains compacted and worn.
2.
Recommendation
2.1
It is recommended that the options tabled are considered and the Clerk advised
of the preferred action.
3.
Background
3.1
In 2006, some drainage works were undertaken to the area by the Councils
grounds maintenance contractor. A soak away and perforated pipe were
installed running from the main entrance across the Common to outfall near the
ponds. Unfortunately these works do not appear to have worked as water has
not been seen running through the pipe.
3.2
In 2007, The Town Council purchased 40 trakmats (see figure 1) to help alleviate
damage and rutting to the access/egress point of the Common. These have
worked well but to a point. During periods of inclement weather and heavy
vehicle movements they become ineffective as the photo in figure 2 illustrates.
Figure 1
Figure 2
3.3
A report was presented to the Environment Committee in June 2010 about
reducing the number of fairs on the Common thus the number of heavy vehicles
using the site. The report also suggested that a solid surface could be
considered by Members to be laid.
3.4
Any form of new, solid surface such as tarmac that is proposed to be laid on
common land would need permission from the Planning Inspectorate who act on
behalf of the Secretary of State for Environment, Food and Rural Affairs.
3.5
In 2012 Ringway the Hertfordshire County Council Highways contractors
undertook some remedial work to raise the height of the kerb along the A1081 by
the turning into the Baa Lambs car park (see figures 3 and 4) and raise the
camber of the footpath/cycleway to deflect water back into the road. The aim of
this work was to direct the road runoff further down the road so that it did not run
directly down the driveway and pool at the entrance to the Common. This
scheme has been moderately successful.
Figure 3
Figure 4
3.6
Specialist land drainage consultants have been approached for advice/options on
how to best with the drainage issues experienced on this site. The solutions
proposed are listed in the following table.
3.7
It is suggested that the works will only need to apply to the main access to the
Common not the secondary access to the right hand side of the driveway.
Members are advised that option 1 is simply a drainage solution and option 2 is a
surfacing solution.
Contractor
1
2
3
Option 1 & cost
Excavate for an Aco (see figure 5) drain at the entrance point off the car
park.
Supply and lay approx. 3m of Aco drain c/w heavy duty grating bedded
and haunched in concrete. Leave a spigot for connection of a 150mm land
drain.
Install a 150mm land drain along the described route approx.. 70m
discharging via the existing headwall into the bank.
All excavated material to be removed from site and the drain backfilled
with 20mm shingle to within 100mm of ground level then topped off with
2-6mm shingle. £2645 +VAT
Supply and install a herras panel compound to store machinery,
equipment and materials for the duration of the works.
Supply and install 4m of Aco drain along the entrance into the common
adjacent to the bollards.
Investigate and connect this up to the existing twin walled plastic pipe (see
figure 7) leading down to the pond. If the existing drainage pipe is found
to be damaged or unusable:
Supply and install a 70m length of 150mm twin walled plastic drainage
pipe connected up to the Aco drain and run down to the pond as per the
previous drainage pipe. £2640 +VAT
Option 2 & cost
Supply and install Golpla (see figure 6)
geotextile matting backfilled with rootzone (a
blended sand/soil product) and seeded over the
haul route approx.. 225m2 £6650 + VAT
Excavate a track to a width of up to 4m and to a
depth of approximately 200mm from the car
park down to the bund and the white post.
All arisings will be used to re-profile the existing
bund.
Lay a geotextile membrane and re-surface the
track to allow lorry access to the common.
Specification: MOT Type 1 (50mm dia.) granite
sub-base and compact with a twin drummed
vibrating roller as per Hertfordshire County
Council specification.
All arisings from the track will be spread along
the existing bund and re- profiled.
Upon completion of the works the bund will be
reseeded. £10,620 +VAT
Erect herras panel compound.
Scrape of vegetation and topsoil from track,
Excavate trench 500mm deep, cast and level arisings on bottom side of cast and level.
track.
Supply and place geotextile. Supply and place
Supply and lay 150mm perforated twin wall pipe and backfill to surface 200mm limestone type 1 and compact. Supply
with clean 40mm shingle. £3654.85 + VAT
and compact 20mm depth limestone dust.
£12,795
Figure 5 – Two different types of Aco drainage solutions
Figure 6 – Golpla geotextile. UV stable, non-toxic, weatherproof, visually unobtrusive, can withstand
heavy vehicle weights
Figure 7 – twin walled perforated pipe
4.
Financial Implications
4.1
If Members support the proposals to provide a solution to the drainage issue,
option 1 costs can be met from the existing grounds maintenance budget.
However, if Members are seeking to undertake option 2 works then it will be
necessary to use earmarked reserves which will require authority from the Policy
and Finance Committee.