Mapping Hazard Prone Areas

Natural & Human Caused Risks

Hazard Mitigation has been practiced for centuries, but today’s analysis tools  broaden our positive impacts.

Natural resource hazard mitigation efforts begin by integrating physical site properties into a holistic picture of how geology, soils, precipitation, aquatic systems, vegetation, and people have come together to influence how natural processes interact. Sometimes, hazards are declared based on how people, structures, infrastructure, and natural environments are damaged by natural processes. Sometimes the hazard comes in terms of cascading events of one disaster that causes another disaster, and so forth.

Tsunami Inundation Zone

The image accompanying this discussion, shows an anticipated tsunami inundation at Queets, Quinault Indian Reservation along the Pacific Ocean shorelines in Washington State. This inundation zone is magnified by a significant river system, Queets River, draining alongside the settlement and into the Pacific Ocean. When the tsunami strikes, the water force from the ocean will meet the water from the river causing significant water backup which will continue long after ocean waters are forced back into the sea.

The entire watershed is within a rain-forest ecosystem, supporting salmon species and other animals. The tsunami event is expected to destroy the US Highway 101 bridge at Queets, and flood the community. Upstream of Queets another bridge crosses the river and we predicted that bridge will also be compromised by the combination of tsunmai and Queets River water backup with the detritus that gets relocated in this difficult to predict event.

Mitigation measures often begin with identification and reinforcement of escape zones for local residents and visitors. This is one of the best protection measures possible for the people of this ocean shoreline community.

Tsunami Innundation Zones, Queets, Washington

Wildfire Risks: Fire Prone Landscapes

Fire Prone Landscapes, Mullan, Idaho

Analysis tools to assess the risk exposure to wildland fires are numerous. Each analysis tool has specific applications to unique needs and can be considered in light of the site being addressed; none of them will replace professional expertise of fire behavior analysts on the ground.

Schlosser et al. (2002), developed a methodology to assess the location of fire prone landscapes on forested and non-forested ecosystems in the western US. This assessment technique has been completed for tribal- and county-level fire mitigation plans and FEMA hazard mitigation plans, for Bureau of Indian Affairs and Bureau of Land Management Fire Management Plans and Environmental Assessments on over 60 project areas in Idaho, Alaska, Montana, Nevada, Oregon, Wyoming and Washington to determine fire prone landscape characteristics.

The goal of developing the Fire Prone Landscapes (FPL) analysis is to make inferences about relative risk factors across large geographical regions for wildfire spread. This analysis uses the extent and occurrence of past fires as an indicator of characteristics for a specific area and its propensity to burn in the future. Concisely, if a certain combination of vegetation cover type, canopy closure, aspect, slope, and position on the hillside, have burned with a high frequency in the past, then it is reasonable to extrapolate that they will have the same tendency in the future, unless mitigation activities are conducted to reduce this potential.

The basis of the analysis technique is to bring all of these factors together in a geospatial model (GIS layers) to determine the area of each combination of input variables that is available to burn, and then determine how much of this area actually burned in past fire events.

Landslides & Mass Wasting: Landslide Prone Landscapes

Sturzstrom

A sturzstrom is a rare, poorly understood type of landslide, typically with a long run-out. Often very large, these slides are unusually mobile, flowing very far over a low angle, flat, or even slightly uphill terrain. They are suspected of “riding” on a blanket of pressurized air, thus reducing friction with the underlying surface.

  • Shallow landslide

A shallow landslide is common where the sliding surface is located within the soil mantle or on weathered bedrock (typically to a depth from a few feet to many yards). They usually include debris slides, debris flow, and failures of road-cut slopes. Landslides occurring as single large blocks of rock moving slowly down slope are sometimes called block glides.

Shallow landslides can often happen in areas that have slopes with highly permeable soils on top of low-permeability bottom soils or hardpan. The low-permeability bottom soils trap the water in the shallower, highly permeable soils, creating high water pressure in the top soils. As the top soils are filled with water and become heavy, slopes can become very unstable and material will slide over the low permeability bottom soils. This can happen within the Coeur d’Alene Reservation where a slope with silt and sand as its top soil sits on top of bedrock. During an intense rainstorm, the bedrock will keep the rain trapped in the top soils of silt and sand. As the topsoil becomes saturated and heavy, it can start to slide over the bedrock and become a shallow landslide.

Landslide Prone Landscapes & Fault Lines around Kellogg and Wardner, Idaho

  • Deep-seated landslide

In deep-seated landslides the sliding surface is mostly deeply located below the maximum rooting depth of trees (typically to depths greater than 30 feet). Deep-seated landslides usually involve deep regolith, weathered rock, and/or bedrock and include large scale slope failure associated with translational, rotational, or complex movement.

  • Landslide Prone Landscapes

The materials may move by falling, toppling, sliding, spreading, or flowing. Some landslides are rapid, occurring in seconds, whereas others may take hours, weeks, or even longer to develop. Although landslides usually occur on steep slopes, they also can occur in areas of low relief. Landslides can occur as ground failure of river bluffs, cut-and-fill failures that may accompany road construction and building excavations, collapse of mine-waste piles, and slope failures associated with quarries and open-pit mines.

The primary factors that increase landslide risk are slope and certain soil characteristics. In general, the potential for landslide occurrence intensifies as slope increases on all soil types and across a wide range of geological formations.

The materials may move by falling, toppling, sliding, spreading, or flowing. Some landslides are rapid, occurring in seconds, whereas others may take hours, weeks, or even longer to develop. Although landslides usually occur on steep slopes, they also can occur in areas of low relief. Landslides can occur as ground failure of river bluffs, cut-and-fill failures that may accompany road construction and building excavations, collapse of mine-waste piles, and slope failures associated with quarries and open-pit mines.

The primary factors that increase landslide risk are slope and certain soil characteristics. In general, the potential for landslide occurrence intensifies as slope increases on all soil types and across a wide range of geological formations.

From the Landslide Prone Landscape profile produced, it is possible to depict areas of risk and their proximity to development and human activity. With additional field reconnaissance, the areas of high risk were further defined by overlaying additional data points identifying actual slide locations (although these data were relatively limited), thus improving the resolution by specifically identifying the highest-risk areas.

A risk-rating score of zero represents no relative risk and a score of one hundred is considered extreme risk. In practice, very few areas of the highest risk category (100) are found. This rating scale should be considered as nominal data, producing values that can be ordered sequentially, but the actual values are not multiplicative. This means that a site ranking 20 on this scale is not “twice as risky” as a site ranking 10. The scale provides relative comparisons between sites.

Flood Risks

Flood Risk, Taholah, Washington, Quinault Indian Reservation

Flooding and storm water accumulation is widespread along the edges of rivers and lakes. Flooding can impact any area where water accumulates on the surface and reaches a structure, road surface, or sensitive vegetative area. Flooding is a natural process that occurs when water leaves river channels, lakes, ponds, and other water bodies where water is normally confined and expected to stay. It is also a serious and costly natural hazard when it occurs around buildings and infrastructure. Floods damage roads, farmlands, and structures, often disrupting lives and businesses. Flood-related disasters occur when property and lives are impacted by the flooding water. An understanding of the role of weather, runoff, landscape, and human developments in the floodplain is therefore the key to understanding and controlling flood-related disasters.

In many populated places in the USA, the Federal Emergency Management Agency (FEMA) has mapped 100-year and 500-year flood zones. These serve the effort to create flood risk areas and to provide a means of risk assessment for homeowners who are located in or adjacent to flood zones. Not all areas of the country have been mapped for FEMA Flood zone maps – known as Flood Insurance Rate Maps (FIRM).

When FEMA FIRM data are available, we use them. In many areas these maps have not been created. Absence of flood maps by FEMA does not mean those areas are free from flooding.

Geospatial data are available to make these flood zone estimates. Today, Digital Elevation Models (DEM) are flown using LiDAR technology to record topographic data to a 1 meter accuracy. It takes well designed computer infrastructure and analyst acumen to convert topographic, soils, geology, precipitation, vegetation, and anthropogenic alteration into predictions of where floods are likely to happen.

We have created these flood zones for clients such as rural counties in Idaho, Montana, Wyoming, Neveda, and Washington. We have made flood zone predictions for tribal governments, where FEMA has not completed risk assessments such as flood. These data give people, businesses and governments the ability to protect people, businesses, structures, infrastructure and the way of life known to the region.

Expansive Soil Risks

Expansive soils and expansive clays are substrates that are subject to large-scale settlement or expansion when wetted or partially dried. Expansive soils contain minerals such as smectite clays that are capable of absorbing water. When these soils absorb water they increase volume. The more water these soils absorb the more their volume increases. Expansions of ten percent or more are not uncommon. This change in volume can exert enough force on a building or other structure resting on top of them to cause damage.

Expansive soils such as clay, claystone, and shale can “swell” in volume when wetted and then shrink when dried. This volumetric expansion and contraction can cause houses and other structures to heave, settle, and shift unevenly, resulting in damage that is sometimes severe. Cracks in building foundations, along floors and within basement walls are typical types of damage done by these swelling soils. Damage to the upper floors of the building can occur when motion in the structure is significant.

Expansive soils will also shrink when they dry out. This shrinkage can remove support from buildings or other structures and result in damaging subsidence. Fissures in the soil caused from differential expansion and contraction can also develop. These fissures can facilitate the deep penetration of water when moist conditions or runoff occurs. This produces a cycle of shrinkage and swelling that places repetitive stress on structures.

Expansive Soils on the Coeur d’Alene Indian Reservation

When expansive soils are present they will generally not cause a problem if their water content remains constant. The situation where greatest damage occurs is when there are significant or repeated moisture content changes. An example of this condition can be documented in where rain gutters spill onto the ground at the edge of the foundation, artificially wetting the soil during rainfall periods, leading to soil swelling. When these soils dry in the summer, the soils shrink. The home shown on the adjacent photo has already experienced the detrimental effects of the swelling (wet periods) and shrinking (dry periods) by forming a vertical foundation crack.

This is one of the effects of expansive soils, revealed through geospatial analysis of soils, slope, human habitation and observation. It happened with a home here, but consider if it happens to a bridge support, a water main supplying drinking water to a community, or to the supports of an electrical distribution infrastructure. Mitigation measures are warranted.

Hazard Mitigation Must be Integrated with Public Outreach & Involvement

Benewah County, Idaho, located in the panhandle region of the state, is bordered on the west by Washington State’s Whitman County and is home of the Coeur d’Alene Indian Tribe’s Reservation. Benewah County has been attentive to hazard mitigation activities as “the Big Burn” incinerated much of this region in 1910 as a wildfire ignited in nearby Wallace, Idaho, and burned about three million acres (4,700 sq mi; 12,100 km2) in northeast Washington, northern Idaho, and western Montana. Wildfire mitigation is understood by residents of this county, but true mitigation can only be realized with homes, infrastructure, and businesses all coordinate their efforts.

One of the most powerful analytic strategies used in this region has been development of a Fire Prone Landscapes analysis (lower mapped image) enabled through Geographical Information Systems (GIS) to regress slope, aspect, vegetation, riparian zone characteristics, and associated physical site characteristics to map where wildfire risks are the highest. These are the tools of hazard mitigation in the 21st Century and we enable the analyses, develop meaningful mitigation strategies, and assist people to make the difference in their survival of natural hazards.

In about 2002, the term Wildland-Urban Interface (WUI) was introduced to assist people to contextualize how wildfire risks combine with human habitation. WUI zones (upper map with polygon lines) are segregated into Intermix, Interface, Rural Lands, Wildlands, and Infrastructure zones. The analysis to realize this approach has been developed by Dr. Schlosser to map where structures are placed throughout a region. The juxtaposition of these structures is analyzed in GIS systems to create these polygons seen on the map shown above. It creates a meaningful analytic combination to see where people, structures, and infrastructure are co-located with wildfire risks. These are the areas where wildfire mitigation efforts are prioritized and implemented.

Click on this link to download the discussion and commentary of how to Define the WUI, using examples applied through time in Benewah County and other areas in the western U.S.A.

Defining-the-WUI2013

Click here to read about how to use geospatial analyses to map the WUI.