Water Sensitive Urban Design

Water sensitive urban design (WSUD) is an engineering and land planning approach which marries factors of the urban water cycle including all of the following; groundwater, stormwater, water supply and wastewater management into general urban design with the intention of minimizing environmental degradation while simultaneously improving beauty and the recreational appeal of the same environment.

It is necessary to know that the term Water Sensitive Urban Design is peculiar to Australia and the middle east but refers to the same thing as Low Impact Development (LID) as used in the United States and Sustainable Drainage Systems (SuDS) as used in the United Kingdom.

One may wonder, validly, what makes WSUD different from traditional development patterns or methods in urban areas and city centers. The answer is quite simple; traditional or standard industrial and urban development focused on changing surfaces from semi-permeable vegetative surfaces to interwoven or interconnected surfaces that  are impervious which resulted in high quantities of stormwater runoffs.

This development model considered stormwater runoffs as a nuisance and a liability which posed a threat to human life and property and it was treated like the enemy. How?  Focus was put on developing stormwater management systems which immediately channels stormwater as soon as they become available into streams and rivers without consideration going into preserving the ecosystem. This approach led to what was termed the Urban Stream Syndrome.

Water Sensitive Urban Design, on the other hand, is a plan that integrates stormwater and other such natural occurring water sources into planning rather than resist or try to annihilate. It allows or provides a system wherein the stormwater is factored into the planning with green areas provided for to absorb stormwater with whatever is left channeled into filtration systems and reused.

WSUD has proven to be most accepted in areas that suffer drought either because of their unique environments or because of climate change. With WSUD, stormwater is no longer considered as a nuisance with destructive tendencies, it is now regarded as an asset that can improve the life of both the people and the state of the environment.

Cornerstone Principles of Water Sensitive Urban Design

•  Protecting and enhancing sanity and biodiversity of wetlands, creeks and rivers around and within urban settlements.

•  Restoring water balance in urban areas by greater reuse of greywater, recycled water and stormwater.

•  Efficient use of water resources by reuse and focus on system efficiency.

• Protection and improvement of quality of water draining from urban settlements into wetlands, creeks and rivers.

•  Integrating stormwater reuse and treatment into the landscape so that it offers multiple beneficial uses such as wildlife habitat, water quality treatment, open public space and recreation.

•  Integrating stormwater into the landscape to improve and achieve urban design and visual, cultural, social and ecological ethos.

•  Cost effective and easy implementation of Water Sensitive Design in order to allow widespread implementation.

Applying these principles have provided a cost-effective means of limiting the impact of development on waterways around urban areas, make provision for places that are greener and cooler and engender healthier communities that are connected and protective of their waterways.

Such communities are central to the idea and execution of WSUD as one factor that has mitigated the use and spread of this system are a lack of ability or willingness, organization cultures that are unsupportive and restrictive policies which easily limit the implementation of WSUD to realize the desired goals.

Common Examples of WSUD Processes

The WSUD practices discussed here are common in Australia.

Bioretention Swales and Systems: Bioretention swales are vegetated, shallow, landscaped depressions which have sloped sides. Their purpose is to capture stormwater from runoffs, infiltrate and treat them as it moves from surface areas. Swales are inexpensive to build but require more space in order to function optimally since the water channeled has to infiltrate the soil, be conveyed and filtered.

Bioretention systems are broader systems that involve bioretention swales and may include bioretention basins. It involves water treatment by vegetations set up for that purpose. This step is done prior to the filtration of the sediments contained in the water by medium set up for the purpose. The vegetation provides for natural absorption of nutrients contained in the stromwater such as phosphorus, nitrogen and other such soluble nutrients and contaminants which can be absorbed by plants.

The advantage of bioretention systems over other WSUD systems is that it leaves lesser footprints than other constructed systems such as wetlands. Other advantages include the fact that it reduces what dirt is left to go through filtration systems. On the other hand, it poses challenges of complication where it has to be used on a larger scale thus the availability of other media even though this could be just as effective. In general, bioretention systems are most advisable when dealing with small areas.

Infiltration trenches/systems: Infiltration trenches are surface excavations which are filled with permeable materials such as rocks or gravels. Their purpose is to create subsurface reservoirs which hold stormwater during runoff and gently release them into nearby soil and underwater systems without distorting their natural pH levels or compositions.

These systems are not built as treatment systems for runoffs but as we have noted fleetingly above, it has the ability to retain materials and sediments which can act as pollutants. They’re also intended to slow the release of runoffs into underwater tables by gently releasing them instead of doing so abruptly by first capturing the runoff and then slowly infiltrating it back into the water table.

Since the function of infiltration systems is the discharge of lightly filtered stormwater back into underground water sources, it is often positioned as the final layer in a WSUD. It also more effective when positioned on flat surface rather than on sloppy or unstable surfaces areas. Geotextile fabrics and laid at the bottom of the excavation to prevent soil going into the rock/gravel fill. It is also advisable where in soils that have good infiltration systems as against usage in soil that is less permeable.

Maintenance is also necessary where this system is used to ensure that infiltration is kept at desired levels and not reduced by clogged residue.

Sand filters: this is a material-based variation to the infiltration system. Material-based in the sense that instead of stones or gravel, the excavation is filled with sand instead. Also, there are installed much deeper than the infiltration systems which are installed higher up than them. It is the last step of filtration before the water drops back into the underground water system. The main difference between an infiltration system and its counterpart, the infiltration system has no plant filter since sand cannot absorb nutrients like the gravel and rock filter.

Porous paving: this filtration system is a more WSUD alternative to normal impervious systems of urban development. It allows runoff of stormwater into the soil or to a water reservoir dedicated for the purpose situated below the surface. It is more appropriate for flat surfaces and areas such as roads, car parks and driveways. This has quite effective filtration properties and improves water quality through removal of contaminant. There are mainly two kinds of porous paving systems and there are the monolith and modular systems.

Importance of WSUD

• One importance of Water Sensitive Urban Design is that where it is effectively done, it reduces the demand for scarcely available water reduces by providing an alternative supply.

• WSUD aids in the improvement of environmental aesthetics. This engenders care and connection to the environment and those who live in it.

• Urban design helps in the reduction and prevention of water related natural disasters such as flooding in areas where it is properly considered and implemented. This is because stormwater runoff is quickly absorbed back into the ground and infiltrated instead of running on the surface thereby reducing their impact on the land and people’s properties.

• Another importance is the care the environment, especially water bodies, receive as a result of the proper implementation of WSUD; they are kept free of contaminants and pollutants as these are already collected by the various WSUD systems in use which collects waste according to their various capacity. Bigger sized pollutants are collected by systems such as the infiltration systems and at most the sand filled system.

• Where it is properly implemented, the Water Sensitive Urban Development removes the burden of water wastage and ensures that all waters are properly utilized and efficiently reused.

In conclusion, this is quiet a new system of engineering, but it nonetheless is one way to care for the environment and help in mitigating the problems of climate change and it is recommended that it should be widely adopted.