The expansion of the built environment, particularly in urban areas, has many impacts on the natural environment. From a reduction in forested areas, to decreased biodiversity, to the urban heat island effect, the need to develop homes and businesses often affects the ability of the natural environment to regulate itself, and operate as it once did. It’s the same with the management of rain and stormwater. In many cities, the increased prevalence of hard surfaces reduces soil capacity to absorb and naturally drain water. This results in excessive runoff during heavy rainfall events which overloads stormwater systems, causing both flooding and erosion. With climate change now driving increasingly unpredictable and severe weather patterns across the country, the effective management of stormwater is an issue that will only grow in importance over time.

Scientists, designers and engineers have explored many ways of mitigating the effects of excessive stormwater including Water Sensitive Urban Design (WSUD) which aims to recreate the natural environment as much as possible within backyards and shared public spaces. A key objective is to reduce the volume of stormwater, often by retaining it in the landscape in order to reduce flooding, harvest rainwater and stormwater, and improve water quality.

This is where stormwater detention and retention systems and water tanks can help. An on-site detention (OSD) system can be easily integrated into any existing (or new) rainwater tank to assist with managing stormwater. The upper section of the tank is used for stormwater ‘detention’, which means the runoff water is captured and detained, before being gradually released back into the stormwater system slowly. This ‘detention tank’ is intended to remain empty except during periods of heavy rainfall. The bottom section of the tank is the ‘retention’ reservoir, where water is retained for its normal uses such as toilets, gardening, washing, and even drinking or showering. This is where a Kingspan Water Tank is a stand out solution where one tank can be used and hydraulic engineers and designers can easily adjust the proportion of detention and retention. This means you can tailor the OSD system to meet your hydraulic specifications.

OSD systems are becoming more commonplace, and are mandated in some council areas where flooding and excess stormwater are major issues. A key benefit is that within the same tank, the detention section can in effect feed the retention section, maximising yield from the tank. The onsite detention/retention of stormwater through rainwater harvesting has numerous environmental benefits that will continue to grow in importance as the effects of climate change are increasingly felt:

‘At source’ stormwater management

Managing stormwater at the source of the problem is more efficient than collecting it downstream where the volume and velocity of the water is greater and it has more pollutants in it. Rainwater harvesting can turn a stormwater problem into a water opportunity. And it’s an accessible solution for every building.

Peak flow reduction

Delaying the stormwater flow from the site can have significant benefits for flooding downstream and the size of stormwater pipes required.

Harvesting or infiltrating rainwater and stormwater

Capturing rainwater volumes protects the stream ecology of local waterways, reduces scouring of stream banks, maintains groundwater flows and more closely replicates natural runoff regimes. Rainwater retention provides more opportunities for watering green spaces, groundwater infiltration and natural flows in our waterways. In a drought, rainwater tanks capture a regular supply of small rainfall events that are simply absorbed by dry catchments. Closed tank systems offer significantly reduced evaporation than open water storage. In a hot summer, dams can evaporate the same amount of water as a city uses.

Improve water quality and urban cooling

The detention and gradual release of stormwater enables water to be released at a rate that approximates baseflow, ensuring the environment’s natural filtration processes can occur. This means that the water entering waterways is ultimately cleaner, which helps to protect aquatic ecosystems. On-site detention can aid in soil cooling by releasing water into the soil at a rate that makes it possible for the water to fully infiltrate the soil.

Kingspan’s innovative OSD system is designed to simply and seamlessly integrate with existing onsite rainwater storage tanks, or comes built into new detention/retention tanks. Easy to install detention kits are supplied with a double junction with inspection cap, detention tank signage and an orifice plate. The orifice plate is designed to restrict the flow of water being released back to the environment and can be easily adjusted onsite to the specified diameter in line with the site-specific requirements.

With the move towards on-site detention already gaining significant momentum across many of our cities, these innovative systems stand to deliver significant environmental benefits, as well as functional and cost gains for property owners. By reducing water flow during heavy downpours, OSD systems can reduce flooding, decrease erosion, and significantly improve the water quality in our waterways, supporting a healthier natural environment and greater biodiversity. By decentralising the management of stormwater, OSD systems also ease the pressure on our municipal stormwater and sewage systems.

With a legacy spanning almost 90 years, Kingspan has earned a reputation as one of Australia's most trusted brands in water tanks, and today, they remain at the forefront of efficient stormwater management. Offering a diverse range of innovative OSD kits, Kingspan empowers industry professionals with versatile solutions that can seamlessly integrate into existing water tanks or enhance new installations. Backed by a highly skilled team experienced in reading hydraulic plans, the company stands as a beacon of excellence, providing comprehensive and tailored solutions - and emerging as the unequivocal choice in the pursuit of improved stormwater management in the cities of the future.

Visit the Kingspan website to explore their outstanding range of premium products and discover how their unparalleled expertise can elevate the potential of your next project, and contribute to a more sustainable and resilient urban environment of the future.

References:

ARR 2019 – A Guide to Flood Estimation

Chapter 3. Philosophy of Urban Stormwater Management

Chapter 4. Stormwater Volume Management