Sustainable Drainage System

The sustainable drainage system, or ponds project as it became known, was the last development funded in the 2017 improvements package.  Unlike other work which improved individual facilities, the scheme involved wide-scale landscape changes along a pivotal axis of the park.  

The scheme had four main elements:

  • A new waterbody at Barn Park.
  • A swale or wide ditch on the lower slopes of Zoo Field and Mawson Meadow to convey spring water and surface water run-offs to the new waterbody.      
  • Path modifications to incorporate stone filter drains and to raise path levels in the vicinity of Barn Park. 
  • A bund or low bank along two sides of Barn Park Field.

The main design drivers were to reduce the incidence of path flooding at Barn Park and to reduce the risk of the downstream sewer network overflowing during exceptional rainfall. 

Path flooding in January 2014 (Andrew Young)

The new waterbody

The new waterbody had to be a minimum size to retain sufficient water and prevent flash flooding during prolonged downpours.  This proved difficult to achieve within the existing layout and topography. Trees were one constraint although it was judged acceptable to fell three widely-admired weeping willows. 

Willows at Barn Park in 2020 (Andrew Young)

Another constraint was the perceived need to keep both of the Barn Park football pitches despite a needs assessment in 2015 and confirmed in 2018, which showed they had four times the required capacity.  Furthermore, the field was very infrequently used for football and had been allocated for a closed-loop cycle track in the adopted masterplan. Rather than impinge on the redundant football pitches, the scheme’s designers chose to make two new ponds, one cut into the lower edges of Mawson Meadow and one sandwiched between the banks of Barn Park Field and Coronation Avenue.  They would be lined to prevent water loss and connected by pipes to the existing pond, which was to be cleared of silt and overgrown vegetation.   

Proposed layout of ponds at Barn Park

The design met significant objections when submitted for planning approval in 2019.  Most prominent were the square corners and straight lines of the northern pond, the use of gabions for retaining structures, the raised bank around Barn Park Field, extensive excavations into Mawson Meadow and the loss of the three weeping willows.  There was also considerable disappointment that the scheme would not deliver the lake which had been in prospect for so long, as well as frustration that the opportunity to address the poor path layout at Barn Park had been dismissed. 

Some changes were made to the design in 2021 which included a more natural shape for the northern pond and higher-quality materials for the retaining structures and fences, but the substantive issues regarding the development’s relationship with the wider park were left unaddressed.  The revised plans were approved early in 2022 and construction work started in November 2022.  

The swale

Improvements to Argyle’s Mayflower stand in 2019 required the separation of foul and surface water discharges. Surface water from Home Park was diverted to a new attenuation tank and piped to a new swale in Zoo Field which ended near Coronation Avenue. Pre-cast concrete headwalls were used near the swale’s head despite representations about their utility nature in a parkland setting, whilst the sinuous water course quickly became overgrown, albeit with an attractive band of summer ox-eye daisies.

In 2023, another swale was dug between the lower end of the Zoo Field swale and the new southern pond at Barn Park, running broadly parallel to Coronation Avenue. It included 19 check weirs to assist water infiltration into the ground and reduce the risk of uncontrolled flows in heavy rainfall.

Path modifications

The original granite-sett drainage channels on either side of Coronation Avenue had become broken in several places.  They were replaced by a gravel filter drain framed by one row of granite setts at the path edge and two rows of granite setts next to the main path.  The gravel strips were to reduce the speed of water run-offs and assist infiltration into the ground.  A similar arrangement was installed on the north side of Jubilee Row below the Family Tree Field.  The gravel strips meant that there was a slight reduction in the width of the paths’ running surfaces, by about 0.3 metres on either side. 

The lower end of Coronation Avenue and its connecting paths were raised in height by up to 0.6 metres to make future path flooding very unlikely.

Newly installed path edge on Coronation Avenue incorporating a stone-filter drain (Andrew Young)

Bund on Barn Park Field

The bund was designed to retain storm water on Barn Park Field rather than let it flow into the ponds below.  It consisted of an earth bank, about 0.5 metre high, around the southern and eastern edges of the field.  The existing banks, a legacy from the 1975 levelling works, already constrained views from Coronation Avenue northwards and made access to and through Barn Park Field difficult, so the increase in height of about 12% would make these problems significantly worse. 

Bank below Barn Park Field in 2023 before being raised with a bund (Andrew Young)

Construction work was hampered by higher than average rainfall during 2023 and the scheme’s main elements were not completed until the start of the Christmas holiday. Large quantities of excavated material had been transported to Reservoir Field for infill by then but a significant amount remained on Barn Park Field, and was planned to follow. With this and the ground saturated, the Council and its contractors agreed to suspend work until conditions became more favourable in 2024.

Unlike most developments in the second half of the 20th century, the drainage scheme was not commercially driven, and the intention was to benefit the park.  However, with flood prevention as the principal design driver, and insufficient prescription in the adopted masterplan, the scheme did not relate well to the wider parkland, nor did it consider the long-standing problems of movement through the park.  It interrupted natural desire lines and added to the visual and physical separation between parkland to the north and south of Coronation Avenue.  The plans met with many objections from the public but despite this, and the very large area that was affected in a strategic greenspace, planning approval was granted by delegated officer powers.