Restoring your client’s turf after a natural disaster

Donald Gray, professor emeritus of civil and environmental engineering at the University of Michigan, says it’s crucial for landscaping and turf professionals to control erosion through mulch, vegetative seeding, blankets and other measures.

Upheaval from natural disasters such as fires, floods, hurricanes, windstorms and landslides can pose significant challenges in restoring your clients’ turf and landscaping to its previous condition.

One of the biggest post-disaster challenges is erosion, which can pose a significant property and environmental threat. It’s critical that turf and landscape professionals act quickly and comprehensively to address those challenges on behalf of their clients, as to mitigate potential problems with erosion.

Previous natural disasters can offer lessons on measures to take that can minimize damage should there be a future reoccurrence.

Soils vulnerable after fires

Fires, an ongoing issue in areas such as California, are an example of natural disasters with predictable results for the landscape. Soil is quite vulnerable after a fire because a fire season often precedes a rainy season in many areas of the country, bringing the potential for large amounts of vulnerable soils to wash off slopes and into other areas, such as waterways. Also, waterways clogged with sediment and debris can create flooding problems.

Flooding, whether seasonal or otherwise, can overtop stream banks. Coastal flooding can result in erosion and other types of damage.

Another natural disaster that follows long rainy seasons in some regions of the country is landslides, which can create significant damage as well. Afterwards, the problem is a “very disturbed condition that is vulnerable to a whole host of erosion processes,” says Donald Gray, professor emeritus of civil and environmental engineering at the University of Michigan.

Gray points out that landslides disturb the slope and weaken the soil, making it vulnerable to advanced erosion, such as gullying. At that point, turf and landscape professionals should consider potential scenarios for stopping the gullies from forming.

Ten principles of effective post-disaster landscaping and turf reconstruction

Donald Gray, professor emeritus of civil and environmental engineering at the University of Michigan, says the following 10 principles have proven to be effective when applied after a natural disaster:

1. After the disaster hits and it’s time to provide damage control, assess the site and fit the redevelopment or erosion control plan to the site, says Gray. “Avoid extensive grading and earthwork in erosion-prone areas,” he adds. “Adopt a landform grading approach that mimics stable natural slopes.”

2. Installing hydraulic conveyance facilities such as ditches, curbs and down drains can go a long way in handling increased runoff. “Decrease hydraulic gradients by lengthening channels as much as possible,” Gray says.

3. Keep runoff velocities low and reduce tractive stresses by spreading flow out in wide swales and installing slope breaks, benches and grade control structures.

4. Construct interceptor drains and berms to divert runoff from steep slopes and denuded areas.

5. Gray advises to save native site vegetation whenever possible, although he concedes this may not be an option after a fire. “Discourage growth of fire-adapted plants or vines that are poorly suited for erosion control, such as licorice (Glycyrrhiza),” he adds.

6. If it appears that vegetation must be removed, clear the site in small, workable increments, advises Gray. Limit the duration of exposure while doing so. Gray says that to prune or coppice trees is the most appropriate measure to take in order to minimize future blowdowns.

7. Landscape and turf contracts can protect cleared areas with mulches, compost and temporary, fast-growing herbaceous covers. “That is particularly important after a fire,” Gray points out.

8. After a natural disaster, construct sediment basins to prevent eroded soil or sediment from leaving the site.

9. Gray says the most important factor to keep in mind is to install erosion control measures as early as possible.

10. After installation, inspect and maintain control measures, Gray adds.

Beyond typical approaches

While landscaping and turf professionals can use the usual approaches to control erosion through mulch, vegetative seeding, erosion control blankets and other measures, it’s crucial to transcend all of those approaches to techniques that address more channelized erosion in areas typically prone to the condition, Gray says.

Check dams are one approach, says Gray. The temporary or permanent barriers can slow velocity and serve to prevent erosion. However, if they are not properly set, there can be washout around them, Gray cautions.

Another effective solution is the soil bioengineering technique of live gully repair. This technique uses alternating layers of live branch cuttings and compacted soil to repair small rills and gullies.

Gray has developed a series of basic soil and erosion control principles that turf and landscape professionals can apply to post-disaster job sites. Lessons learned from disasters in the past point to the need for a sound plan as opposed to a “haphazard application of different measures,” says Gray.

With respect to fires, Gray points out that the primary fallout from a fire is that it burns off the vegetal cover and the vegetation – in particular, low canopy vegetation and herbaceous vegetation – grass and, to a lesser extent, bushes. Unless that is mitigated, it is quite often followed by serious erosion problems in the year following the burn, he adds.

A case in point is the Oakland Hills, Calif., fire of October 1991. Flames fanned by hot, dry winds blowing from the Central Valley consumed 1,800 acres of the Oakland and Berkeley hills, resulting in 25 deaths and the destruction of 2,903 dwellings. Because of extensive revegetation work that was done in the hills, the erosion was minimized in the following year, says Gray.

Hypothetical case

Gray offers a hypothetical example of how to apply erosion control principles following a fire on a hillside landscaped with bushes and grasses.

Following a fire, “clear the hillside of burned vegetation and protect these cleared areas with mulches, compost blankets and fast-growing herbaceous covers,” he says. “Remove surviving fire-adapted plants and vines that are poorly suited for erosion control.”

Next, adopt a landform grading approach that avoids uniform, planar grading and instead introduces concave and convex shapes that mimic stable surrounding natural hillsides, says Gray. “Introduce wide drainage swales that spread out the flow and that are curvilinear to lengthen out flow paths,” he adds.

Divert runoff from critical areas, such as erosive soils and steep slopes, by using berms and ditches. Revegetate drainage swales and concave shaped areas with woody plants, and use grasses and herbaceous plants in the drier, convex interfluve areas, says Gray. Then, build a sediment basin that is properly sized and constructed to retain eroded soil on-site.

Next, install stepped-pools, grade control structures or rock armor when necessary to control scour erosion in runoff conveyance channels, says Gray. He adds that the most important lesson learned from previous natural disasters is to apply repair measures as early as possible.

“Vegetation takes awhile to get established,” he says. “There has to be a grace period before the rain starts when you hope you can get your grasses and herbaceous materials established.”

Once established, it’s important to periodically inspect and maintain the measures put in place, he adds.

Carol Brzozowski is a member of the Society of Environmental Journalists and has written extensively about environmental issues for numerous trade journals for more than a decade. She resides in Coral Springs, Fla.