What are bushfires? They are uncontrolled fires that occur either naturally or by human intervention through areas that Australians call “the bush”. In other countries these are called forest or wild fires. Bushfires can be slow moving (depending on conditions) but still generate higher heat output hence they smolder for days regardless of their spread time. Bushfires in Australia are common because the climate is mostly hot, dry and prone to drought. After the terrible bushfires in 2019/2020, this year has started with severe fires on the outskirts of Perth, which destroyed close to 100 properties and 11,000 hectares of bushland. Erosion and sediment control after bushfires in Australia is non-negotiable the debris from bushfires generates erodible materials that are susceptible to wind and water which increases sediment yields. The factors affecting bushfires include fuel load, fuel moisture, ambient temperature, relative humidity, slope angle and ignition source. Different products are available for dust suppression related to bushfires and the most effective solutions factor in vegetative recovery that includes techniques such as hydroseeding and hydromulching. In Australia and New Zealand, Global Road Technology has been at the forefront of efforts related to erosion and sediment control after bushfires. The article seeks to highlight erosion and sediment control techniques after bushfires in Australia focusing on post bushfire recovery efforts and Global Road Technology products which can be utilized for post bushfire erosion and sediment control. 

Uncontrolled v managed fires

Fires in Australia have become part and parcel of the Australian environment evident in natural ecosystems that have evolved with fire, and both historic and recent fires have shaped the landscape along with its biological diversity. In many parts of the country, indigenous communities managed the landscape using fire for many thousands of years. Native Australian plants are known to be very combustible whilst several species depending on fire to for their reproduction cycle. However, uncontrolled bushfires can be devastating; such as the recent fires near Perth mentioned above. The spread of ash was cited from as far as 50 km away from the fire-front with blankets of smoke across the city of Perth. Residents from the north-eastern suburbs such as Ellenbrook, Averley and Brigaddon were immensely affected and had to be evacuated immediately. The timing of the bushfires could not be any worse, with them happening at time when Perth has been enduring high temperatures with extended dry conditions hence the moisture deficit in the soil in addition to gusty winds that have created hotspots within the fire area. 

Once the fires have gone out…

There are several techniques that can be implemented as part of bushfire recovery efforts and these include: 

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This article will mostly focus on hydroseeding and hydromulching, but further information can be sourced on polymer stabilisation by clicking the links above. Hydroseeding, as described in one of our articles, is a hydraulic planting method in which a slurry mix of water and seed are sprayed onto a planting surface for revegetation purposes and it is one of the many available seeding techniques. In general, seeding rates are determined by the method of seeding, the selected plant species which might not necessarily be grass alone and the purity of the seed. In scenarios where the seeds are mixed, their development should be based on pure live seed to account for species that have low germination rates or mixes that might have a high amount of inert material which includes dirt or other plant parts. In cases of bushfires, species performances at the germination stage determines the success of hydroseeding with evidence showing that species are able to germinate earlier and at high germination rates more successfully than species with low germination rates especially during periods of water scarcity which is the case of the Australian climate and environment. Given the adaptation of native plants in Australia to the frequency of bushfires, the use of native plants for revegetation is recommended with enough support from seed germination tests to determine percentage of viable seeds that have the potential to germinate under amicable conditions which better informs optimum seeding rates and developing preconditioning treatments to promote uniform germination. 

Hydromulching is a hydraulic technique to efficiently apply a mixture of organic material known as mulch, a binding chemical known as a tackifier, fertilizers, and seed as a slurry in water onto open or disturbed ground to prevent erosion while supporting revegetation. Before we get deeper into hydromulching it is key to highlight the differences between hydroseeding and hydromulching in that hydromulching does not necessarily contain seed. There are two different hydromulch methods of application which are:

  • Ground hydromulch treatment 
  • Aerial hydromulch treatment

Ground hydromulch treatment is a technique that involves spraying from specialized water trucks that incorporate a tank, agitators, and spraying equipment such as hoses and cannons. The vehicles apply the water-based slurry of the mulch, tackifiers and seed at a certain liter per hectare with spraying limited at maximum spray distance from infrastructure such as roads. On the contrary, aerial hydromulch treatment involves use of an aircraft and the hydromulch is applied as a water-based slurry at a certain liter per hectare usually with the same seed mixture as for ground hydromulch treatment and can also include soil-binding agents such as polyacrylamide. The advantages of using aerial hydromulch is that applications are not limited to road or rail access however the application skill set is far less common with site research showing that aerial hydromulch treatment has greater initial and long term effect on ground cover than ground hydromulch treatment. 

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Bushfire recovery efforts

Bushfire recovery involves reduction of post-fire runoff and erosion in which hydromulching has been utilized effectively although after the first year the treatment becomes ineffective as result of the deterioration of the mulch layer. Other schools of thought and practical examples show that hydroseeding is more effective for erosion control post bushfires although sediment yields can be limited in severity of the storm depending on its intensity. For all revegetation needs Global Road Technology offers tackifier chemistries as well as seed germination and strike rate through their biocatalyst technology in GRT: Enviro-Binder, a spray over liquid polymer that provides erosion control and nutrients to increase germination and strike rate for the short and long term hence can be effectively utilized as a key solution for preventing erosion while seeds establish. GRT: Enviro-Binder allows for mobility and increased uptake of nutrients by plants and is an ideal product to give excellent growth, root development and sustainable vegetation health. This was seen in both the regeneration of the landscape in the Nelson hills in NZ as well as in Australia’s 2019/2020 season.

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