Trench design for new developments

Our aim is to develop solutions that retain large volumes of stormwater in the landscape to support the urban forest.

This design is for use in nature strips of ‘typical’ suburban streets in new developments. It addresses two problems with individual systems, which:

• are costly to maintain, and
• capture small volumes of runoff.

As an alternative, our design:

• uses one inlet to serve multiple trees, and
• has a system/catchment area ratio of 10%, plus an internal water storage.

This design drawn up by Jamie Tainton uses a trench to retain large volumes of runoff for use by street trees.

Description of design

Key elements of the design are:

• an inlet pit which intercepts runoff upstream of a standard drainage pit
• the inlet pit can be designed with a grate to exclude gross pollutants and a sump to collect sediment
• flows are conveyed via solid pipe to a structural soil trench, offset from road infrastructure and below-ground services
• the structural soil trench runs the length of the road, including under driveways, ending at the next downstream standard drainage pit
• slotted pipe in the trench promotes exfiltration into the surrounding soil
• an internal water storage in the structural soil trench is created by connectors spaced according to the slope of the road
• the slotted pipe connects to the next downstream drainage pit with a jump-up connection
• the design has built-in redundancy where, in the case of blockages to the catch pits, flows will be conveyed to side entry pits as before.

Interacting pits and pipes

Links to the standard drawing are below, but we find the 3D representations below a useful way to communicate.

Flows from the upstream trench terminate at the nearest downstream side entry pit (blue). A new catch pit upstream of the side entry pit conveys flows to the downstream trench (yellow). 3D model created by Scott McKendrick, The University of Melbourne.

Interaction between the terminating pipe (blue) connected to the side entry pit via a jump-up connection and the and new pipe (yellow) connected to the grated catch pit. 3D model created by Scott McKendrick, The University of Melbourne.

Feedback

We hope to develop this drawing to the point where it can be integrated into standard practice, e.g. in the Engineering Design and Construction Manual for Subdivision in Growth Areas.

Although we have solved some problems with this design, no doubt we have created new ones and overlooked other requirements.

We need your feedback — please download and annotate the PDF and/or CAD file below and email your ideas to Chris Szota.