Fact Sheets - Erosion Control at CFB Petawawa

Environmental Success Story At Land Force Central Area (LFCA)

Aim

he story of successful erosion control at Canadian Forces Base (CFB) Petawawa's Drop Zone Anzio shows the Canadian Forces (CF) is capable of safe, realistic military training while being environmentally responsible.

Introduction

CFB Petawawa is the home of 2 Canadian Mechanised Brigade Group, one of three regular force brigades in the Canadian Army. These soldiers need an area to safely practice their parachuting skills. Drop Zone (DZ) Anzio at CFB Petawawa is a 1 x 3 km field, designated as the Base's primary parachute drop zone. The DZ is aligned with the prevailing winds to reduce the chances of a parachutist landing in trees outside the designated area. Here, parachutists can hone their skills in a safe, but challenging environment.

The DZ is also part of a mechanised manoeuvre corridor. Dozens of combat vehicles and troops fight their way across the open spaces during mock battles. The gently rolling grassland of the DZ gets churned up during this training, exposing bare soil to the effects of erosion. High winds sweeping down the DZ blow away exposed soil. For Base personnel, high winds mean a few more acres of grassland turned into desert each year.

Facts

Issues and challenge

Wind erosion can be a serious problem if it goes unchecked. In some spots, patches of grass stubbornly remain, while the wind blows away the surrounding soil. This leaves them sticking up like raised islands. Some of these islands of grass were more than three feet high, which provided an indication of how much erosion had occurred. Moreover, the seeds that land on the DZ are continuously scoured away by the winds before they can germinate and take root.

DZ Anzio's soil consists of fine, nutrient poor sand where few plants can survive. Also, native blackberry bushes were periodically controlled with herbicides to prevent parachute entanglements. Herbicides, however, further limited the number of plant species available to combat soil erosion. The erosion was also uncovering logging debris, which has been buried decades earlier during construction of the DZ. Both posed a safety hazard for parachutists.

Blowing sand can also form sand dunes downwind. These sand dunes slowly shift, covering up and smothering plants beneath them. Plant seeds that are buried too deeply by the drifting sand will die because their sprouts cannot reach all the way to the surface. The largest sand dune measured 100 metres long and 10 metres high and was steadily moving south-east along the eastern side of the drop zone.

Wind erosion had opened up bare spots and turned 260 acres of this 800-acre battleground into desert. At the same time, several stands of trees that had been acting as a windbreak were cut to control a serious insect infestation. These factors, combined with increased training demands, were causing the erosion to worsen.

Mitigation and plan constraints

The mitigation plan had to meet a number of conditions. Budget constraints meant low cost restoration and the solution could not require expensive maintenance, such as watering and fertilising. The plan had to consider the safety and health of soldiers using the land. The training area had to remain open for training during the restoration. The plan also had to allow for ploughing or cultivating to level tire ruts and other damage without killing the remaining vegetation.

The use of plants appeared to be a conceivable solution, given the fact they are an excellent source of protection for the soil. Plants anchor soil in place with their roots and keep rainfall from dislodging soil particles. They shield the soil from wind and flowing water that would carry away loose particles. Dead plant matter (humus) enriches and strengthens the soil. The most effective erosion-controlling plants are perennial grasses and legumes.

Nevertheless, any plants used to keep the sand in place must not grow so tall and dense that parachutists could not see wheel ruts and obstructions when landing. The final vegetation had to be resistant to the effects of vehicle traffic and re-grow from root fragments if the topsoil was sheared away by vehicle traffic. If possible, the plan should also preserve the biodiversity of the area by protecting local plant species.

Restoration plan

In response to the threat, the Base's environmental experts, in concert with Mother Nature, experimented with ways to restore DZ Anzio's windswept plains to fertile grass-covered fields.

Therefore, on 100 acres, treated sewage sludge was delivered from the local treatment plant and injected 6 inches below the surface using special equipment. The goal of the use of sludge was to fertilise and to condition the soil in advance of the planting of new vegetation. The injection of the sludge underground also allowed to control odours and to prevent any health risks to the troops.

A crop specialist was hired to choose a plant species that met all the planting criteria. It was recognised early on that local plants were the best choice. However, the seeds were not commercially available. A repair species had to be found that would allow these native plants to re-establish on the bare sand. Many different species were test planted on selected sites. The most promising types were then tested in combination with the sludge-injected areas. The specialist recommended fall rye, a forage grass that can be planted in spring or fall.

Results

Sewage sludge injection was key to repairing eroded areas. By fertilising, the soil itself improved with more moisture and less drifting. This also solved a sludge disposal problem for the municipality, which in turn was willing to pay for delivering and injecting the sludge.

A 100-acre sludge-treated area was seeded with fall rye. It stood up to traffic during the intensive spring training season, when the plants were young and green. In late summer, when it cannot tolerate heavy traffic, fall rye turns a golden brown colour. The golden colour helped drivers of military vehicles to spot and avoid the areas under active repair. Repair seeding stabilised the sand, added organic matter, trapped wind-blown seeds and acted as a cover crop. This cover crop sheltered the native seeds from wind and traffic while they became established.

After two years, fall rye will begin to die out, if not replanted. This allowed a natural transition to a hardy mix of low maintenance, local species. Mother Nature provides the seed mix from native vegetation in upwind areas. As an added benefit, they fall rye plantations have provided food and shelter for animals such as deer.

Follow-up plans

It is planned to shift sludge injection operations to different sections every two years. Vehicle ruts will be repaired in the more severely impacted areas, the treated and seeded with a repair crop. This will gradually repair the existing erosion areas and control new damage, permitting continued use of the DZ. The process will be continually improved as new lessons are learned. The estimated annual cost for the maintaining of the program is under $15 000.

Conclusion

Ecological use of sewage sludge at Drop Zone Anzio has shown excellent results up to now. Moreover, mitigation and restoration plans implemented, by controlling erosion and restoring native plants in a cost-effective way, have permitted re-enhancement of military training activities at CFB Petawawa.

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