Turning stormwater into food

In a corner of the University of Melbourne’s Burnley campus, a bumper crop of vegetables is growing in unique conditions.

Rain is captured from a nearby roof and directly feeds two raingardens, which are covered in intricate monitoring equipment. By way of comparison, they sit alongside two conventional vegetable gardens.

The project is part of Melbourne Water’s 10,000 Raingarden’s initiative, and researchers from the University of Melbourne, Monash University and Melbourne Water want to know if vegetable gardens can be effectively grown using urban stormwater runoff. 

Professor Tim Fletcher from the Melbourne School of Land and Environment (MSLE) says vegetable raingardens allow individuals and communities to create something good for themselves, while protecting local waterways from stormwater damage.

“The urbanisation of cities has led to vast areas of vegetation being cleared and covered in concrete and other impervious surfaces,” Professor Fletcher says. “This process means water can’t be absorbed back into the soil and literally runs off into the sea. It can also lead to flooding.

“Raingardens have been identified as a way to protect waterways while providing a self-watering and attractive landscape feature. We wanted to take this to the next step and see how productive a vegetable raingarden could be for local communities.”

Postgraduate student Paul Richards from MSLE has spent the past two years creating and planting some very sophisticated gardens. 

Dr Richards says that in practice, a backyard raingarden would not need to be so sophisticated, but the team needed to measure water depth and moisture to understand how much stormwater flows into, and remains in the garden soil. 

One of the raingardens is lined so it retains all the water it receives. Rainwater is delivered directly to the bottom of the garden whenever it rains. The water is then filtered as it moves up through layers of gravel and fine sand before reaching plant roots in the top layer.

The second raingarden is unlined, allowing water to infiltrate the ground and recharge baseflows in streams. These raingardens are being compared with conventional vegetable gardens which are surface-watered with traditional irrigation systems using either tap water or tank water.

A wide range of crops is being grown. The team measured productivity by weight and found that while the two raingardens did not produce as much as the traditional vegetable gardens, they did produce a very reasonable crop and achieved their goal of maximising water use efficiency to produce a harvest. In the case of parsley there was no difference in the amount produced between the raingarden and the garden watered conventionally.

Another important finding, coming from work led by David McCarthy and Minna Tom from Monash University, was that vegetables produced were not contaminated by pollutants commonly found in urban environments, and met the guidelines specified by Food Standards Australia New Zealand.

Professor Fletcher says the results are promising because nutrients that might otherwise flow into waterways and cause algal blooms are being put to good use growing vegetables.

“The filter layers in the raingarden are also doing their work by preventing heavy metals from urban water runoff entering our waterways, while also remaining at safe levels in plants. In contrast we revealed that crops irrigated by tapwater actually contained higher levels of copper due to the pipes used.”

Melbourne Water is using the results to develop a user-friendly guide on how to construct a vegetable raingarden.

The research team at MSLE includes Dr Claire Farrell, Dr Nick Williams, as well as Dr David McCarthy and Minna Tom from Monash University, and Keysha Milenkovic from Melbourne Water.

http://www.landfood.unimelb.edu.au/green/water.html#vegetable