SuDS observatory — Red Kite House

Red Kite House

Sustainable drainage systems (SuDS) are drainage solutions that provide an alternative to the direct channelling of surface water through networks of pipes and sewers to nearby watercourses. The aims of SuDS are to reduce surface water flooding, improve water quality and enhance the amenity and biodiversity value of the environment. The observatory at Red Kite House has been established to identify how these SuDS schemes impact on groundwater.

The aims of this observatory are:

  • to assess the effectiveness of permeable paving in improving recharge to the ground, compared to impermeable surface
  • to assess how effective these systems are at reducing pollution migration from subsurface activities into the shallow subsurface

The SuDS observatory is located at Howbery Park, near Wallingford in Oxfordshire, where a permeable pavement car park was constructed in 2005, outside the Environment Agency offices in Red Kite House. The car park is made up of permeable paving stone at the surface, with a sand and gravel layer and a geotextile for bio-attenuation. The site was designed so that only the car parking bays are permeable and the rest is standard paving blocks.

The underlying geology of the area is made ground and Thames Valley Formation (sand and gravel), underlain by the basal Glauconitic Marl Member of the West Marlbury Chalk Formation (formerly Lower or Grey Chalk).

The SuDS  observatory location and the superficial and bedrock geology. Contains Ordnance Survey data © Crown copyright and database rights 2014.
The SuDS observatory location and the superficial and bedrock geology. Contains Ordnance Survey data © Crown copyright and database rights 2014.

Paving

Impermeable paving

Impermeable paving.

Conventional block paving is made of concrete, compacted together using sand, and is regularly used for car parks, roads and gardens. These areas do not allow water to infiltrate through and water will run over the surface during rainfall events.

Permeable paving

Permeable paving.

Permeable paving blocks have uneven edges that create gaps between the blocks which allows water to flow through them and into the ground below.


SuDS observatory monitoring

To look at how these SuDS systems affect groundwater, two shallow (about 1 m deep) boreholes have been drilled through and underneath the car park paving blocks, and soil moisture probes installed. These will be logged continuously and sensed remotely, so that during storm events it will be possible to monitor how quickly water moves through the ground beneath the car park.

In order to understand how the volume of groundwater recharge under a SuDS scheme compares to recharge in natural ground, two similar boreholes have been installed in an adjacent field. It is generally assumed in runoff modelling that there is limited infiltration and groundwater recharge in urban areas, so this work will help quantify how recharge is enhanced where SuDS are in place.

Soil moisture sensors

Soil moisture measurement volume.
Soil moisture profile probe with 3 x sensors (raised out of access tube.)

The soil moisture probes being installed at the observatory are IMKO Pico Profile units, which consist of modular stackable sections. The units generate a high-frequency pulse, generating an electromagnetic field around the probe. The pulse is reflected back to its source, enabling determination of the propagation velocity, which is primarily dependent on the water content of the subsurface. The units typically measure material about 15 cm outwards from the tubes in which they are mounted. The units are connected to a datalogger which can be downloaded either manually to a notebook PC or remotely by telemetry.


Soil moisture profile probe testing.

The soil moisture probes were tested in a number of materials (soil, sand, gravel) and were trialled during simulated rainfall events before installation to demonstrate their response to these events.

Groundwater level data

Groundwater levels at Red Kite House.

Groundwater levels at the observatory have been measured since 2012, using four shallow boreholes that are located on each of the corners of the car park. These will help us identify how the groundwater is affected by enhanced recharge, rainfall, the River Thames and regional groundwater flows.

This all helps us build up a conceptual model of the hydrological system at the site. We have also carried out two rounds of groundwater quality monitoring to look at the baseline quality of water underneath the car park.

Data collected from the observatory will be uploaded onto the website when it becomes available.

Contact

Please contact Rachel Bell for futher infomration.