Stephen Caruana
The Cocos Fire one month after the 2014 blaze. The May outbreak …
Developing a proactive plan
Municipalities are as much a part of the environment as plants and animals, and any mitigation strategy that doesn’t incorporate human values fails to appreciate the practical interface between people and nature. Budgets must account for the devastating aftereffects of fire.
Integrate erosion controls into infrastructure projects. If roadwork is conducted near a high-risk slope, consider building a retaining wall or sediment-control structure.
Risk evaluations help determine how resources can best be allocated in an emergency event and over the long term. Understanding how slopes may fail is essential to both efforts.
Fire-prone communities should have a probability map, which is easy to compile. Many states, including California, Oregon, and Washington, have prepared LiDAR and landslide maps. The U.S. Geological Survey (USGS) maintains extensive geologic mapping, though many show only deep-seeded geologic conditions. The most relevant maps for pre-fire or post-fire erosion assessment also include surficial conditions.
California’s Department of Forestry and Fire Protection has a fire map website that includes communities at greatest risk. Oregon has the Statewide Landslide Information Database. USGS’s National Geologic Map Database includes state maps. Many large cities and counties also have extensive GIS databases with publicly available maps.
Also compile soil survey data and local vegetation maps that categorize the properties of the soils above underlying bedrock — infiltration rates, slope, and slope length — which contribute to the susceptibility of a site or development to erosion and debris flows. Soil survey data is also available online.
Data should include the length of time since the last fire. Mature plants burn more intensely than weeds and grasses, which affects erosion.
Mapping enables you to better anticipate and manage risk. Characterizing how a slope may fail enables your team to place failure probabilities according to time since last fire, vegetation condition, and secondary effects. You can then allocate resources specifically toward those specific assets and/or locations.
For example, I’m helping a large city determine areas most susceptible to fire and landslides. I combined soil maps that tell me the propensity of the surficial soil to erode with topographic (for steepness of slopes), geologic (underlying bedrock), landslide (history or potential hazard areas), and fire history maps (indicates the last time area burned) — all available in the city’s GIS.
These maps allow me to assess erosion propensity across multiple scenarios, draw conclusions, and make recommendations. The city can take in-situ slope retention measures and stock up on post-fire control measures such as weed-free straw bales, mulches, and grass seeds.
Stephen Caruana is an agronomist and director of environmental planning at Kleinfelder. E-mail scaruana@kleinfelder.com; visit www.kleinfelder.com.
