Floods are hazards that occasionally affect California landscapes. In the California Supplemental Exam for landscape architects, there may be a question or two about floods and how to mitigate the affects of flooding on project sites.
Floods are covered on the CSE under job task 8 (Identify potentially hazardous conditions that may affect development of project site) and Knowledge Area 403 (Knowledge of potentially hazardous conditions e.g., fire, flood, erosion, storm water). It is reasonable to expect a one or two questions on hazards, including floods.
How To Determine Flood Risk
Landscape architects can investigate a site’s documented flood potential by researching the Federal Emergency Management Agency’s (FEMA) Special Flood Hazard Area (SFHA) maps.
You can find FEMA flood maps on the a special website dedicated to flood mapping. Here is the website: https://msc.fema.gov/portal
“The FEMA Flood Map Service Center (MSC) is the official public source for flood hazard information produced in support of the National Flood Insurance Program (NFIP). Use the MSC to find your official flood map, access a range of other flood hazard products, and take advantage of tools for better understanding flood risk.”
Special Flood Hazard Area Maps
FEMA publishes Special Flood Hazard Area Maps (SFHA). According to FEMA, a Special Flood Hazard Area is defined as “the area that will be inundated by the flood event having a 1-percent chance of being equaled or exceeded in any given year.”
Flood Insurance Rate Maps
After a flood hazard area has been mapped. FEMA and the insurance industry create Flood Insurance Rate Maps. FEMA describes a Flood Insurance Rate Map as “the official map of a community on which FEMA has delineated both the special hazard areas and the risk premium zones applicable to the community.”
Flood Insurance Rate Maps are used to determine flood insurance premiums and assign flood risk to parcels. The construction industry uses Flood Insurance Rate Maps to determine if a property lies within the 100 year flood zone.
What is a 100 Year Flood Zone?
A 100 year flood zone is an area which is below 100 year flood base elevation and is subject to catestrphoic inundation.
The base flood elevation is defined by FEMA as “The computed elevation to which floodwater is anticipated to rise during the base flood. Base Flood Elevations (BFEs) are shown on Flood Insurance Rate Maps (FIRMs) and on the flood profiles. The BFE is the regulatory requirement for the elevation or floodproofing of structures. The relationship between the BFE and a structure’s elevation determines the flood insurance premium.”
Flood Zone Designations
FEMA uses several different zones to describe the probability of flooding in a particular area. The zones are defined below.
Zone A
The flood insurance rate zone that corresponds to the 100-year floodplains that are determined in the Flood Insurance Study by approximate methods. Because detailed hydraulic analyses are not performed for such areas, no Base Flood Elevations or depths are shown within this zone. Mandatory flood insurance purchase requirements apply.
Zone A99
The flood insurance rate zone that corresponds to areas of the 100-year floodplains that will be protected by a Federal flood protection system where construction has reached specified statutory milestones. No Base Flood Elevations or depths are shown within this zone. Mandatory flood insurance purchase requirements apply.
Zone AE and A1-A30
The flood insurance rate zone that corresponds to the 100-year floodplains that is determined in the Flood Insurance Study by detailed methods. In most in- stances, Base Flood Elevations derived from the detailed hy- draulic analyses are shown at selected intervals within this zone. Mandatory flood insurance purchase requirements apply.
Zone AH
The flood insurance rate zone that corresponds to the areas of the 100-year shallow flooding with a constant water-surface elevation (usually areas of ponding) where aver- age depths are between 1 and 3 feet. The Base Flood Elevations derived from the detailed hydraulic analyses are shown at selected intervals within this zone. Mandatory flood insurance purchase requirements apply.
Zone AO
The flood insurance rate zone that corresponds to the areas of 100-year shallow flooding (usually sheet flow on sloping terrain) where average depths are between 1 and 3
You do not have to memorize each flood insurance zone for the California Supplemental Exam for landscape architects. However, know that there are several gradations of what qualifies for a 100 year storm event and the flooding that can occur.
What If A Project Is Located in A 100 Year Flood Zone?
If you have a project located in the 100 year flood zone as designated by a Flood Insurance Rate Map, a landscape architect has a couple of options. First, you can choose a development program which is compatible with occassional flooding. Passive recreation and habitat restoration projects and often occur within the flood zone. A second option is to raise the elevation of the development above the flood base of the patient. this will keep all development out of the flood zone. Not all jurisdictions allow this method so you’ll need to check with the local zoning board or development authority to determine if this method will work for your project site.
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Kansas City District via Compfight cc
USACE HQ via Compfight cc
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John is a landscape architect who is currently preparing to take the California Supplemental Exam to become licensed in California. He is currently a licensed professional landscape architect in Georgia and Florida. John graduated from California State University, Pomona with a BSLA degree in landscape architecture in 1997 and has extensive practice experience in residential and commercial landscape design.