HA Req 1: Sites of Avoidance + Repair: 500-Year Floodplain, Storm Surge + Sea Rise – Above Green

(Required)

INTENT

Selecting a location for a structure is an important part of the design process. Understanding the importance of selecting the location and the impact to the design is an important first step in design. Where a structure is located impacts the safety and security of the structure and its residents.

Uncontrolled water, like floods and intense storms, can cause human and economic damage. Areas adjacent to ocean tides are at an increased risk from rising sea levels due to global warming/climate change. Avoiding these areas when building can substantially reduce risks to life, property, infrastructure (including water, wastewater removal + treatment, power, roads, transit, food supply/consumer access), health care delivery/ access, solid waste, retail/consumer access, and business during extreme events.

Communities protecting flood and surge prone areas reduce the impact of loss by prohibiting permanent structures and improving buffering and water adsorptive capacity. Parkland or golf course creation are secondary uses that reduce risk of loss.

STRUCTURE AND COMMUNITY REQUIREMENTS

Floodplain

Avoid areas within 500-year floodplain. Statistically, the traditional 100-year floodplain has been found vulnerable to extreme events and sea level rise. Even in areas with prolonged drought, storm events, when they occur, are more intense, making the 500- year floodplain level appropriate for underwriting.

Sites Not Permitted

Building on green field sites below the 500-year floodplain is not permitted.

Provide a permanent flood control mitigation system for new facilities on previously developed locations and/or within existing, built environments such as cities or towns located within the 500-year floodplain. The permanent flood control mitigation system must protect the entire facility and/or protect critical infrastructure and locate key functions and service areas above the 500-year floodplain to provide for business continuity.

If the 500-year floodplain is not available/has not been mapped, use the 100-year floodplain and add 3’ (three feet) to that measurement. If neither floodplain is available, a civil engineer/engineering team must conduct an analysis to determine the 500-year floodplain.

Sea Level Rise

Avoid coastal zones inundated by 2’-6” of sea level rise, or provide an engineering solution as follows:

Complete by 2020: areas inundated by more than 4’ up to 5’ sea level rise
Complete by 2022 (and beyond): areas inundated by more than 5’ up to 6’ sea level rise

Storm Surge

Based on the sea level rise defined above, projects (except for significant, high-risk and/ or mission-critical projects) should:

Accommodate a Category 2 hurricane and storm surge with minimal or no interruption to the services, provided from the facility, beyond the immediate time frame of the storm.
Provide for Category 4 hurricane and storm surge mitigation with expectation that there may be an interruption to non-essential functions and services provided by the facility beyond the immediate time frame of the storm.
Provide permanent infrastructure as required to protect the entire facility and/or protect critical infrastructure.
Protect or locate key functions and service areas above the Category 4 surge elevation to provide for emergency operations.

(Significant, high-risk and/or mission-critical projects should accommodate and mitigate Category 3 and Category 5 storms respectively.)

Use NOAA SLOSH Model data to interpolate storm surge. In the absence of SLOSH Model data use the Surging Seas Threat Map and Forecasting Tools to establish storm surge scenarios that take into account sea level rise. Sea Level Rise and Storm Surge for 2022 and beyond should use the NOAA 2012 Sea Level Rise “High Scenario” combined with a 1 in 100-year flood (“Extreme” flood scenario) to determine water levels for planning purposes.

Develop an Inundation Map for the project as described by Architecture 2030 using the following tools:

2. Innundation Mapping. Inundation Mapping Swatch - 2030 Palette

3. Implement Coastal Adaptation Strategies. Coastal Adaptation Strategies Swatch - 2030 Palette

4. Implement Living Shoreline Strategies. Living Shorelines Swatch - 2030 Palette

5. Design for the Following:

Increased injury & loss of life
Decreased operating expenses including energy
Increased equipment life
Increased property life
Increased property value
Reduced capital outlays for repairs
Reduced insurance costs
Reduced maintenance costs
Reduced unexpected repairs, equipment downtime, business interruptions

Notes on Sea Level Rise

The year 2100 sea level rise based on the IPCC RCP8.5 Mean “High” Scenario with a Medium Confidence Rating or “Likely” rating is approximately 0.745 Meters or roughly 2-1/2 feet (about 2’-6”) (the actual change will vary based on local conditions). This level is below the NOAA “Intermediate High” scenario of 3’-9” and below the high level of 4’-9” or greater rise expected by 70 global sea level experts (see guidance, below). However, it is generally above the U.S. Army Corps of Engineers’ “Intermediate” scenario of roughly 1’-9” (Sea-Level Change Curve Calculator 2014.88). The 6’ increase recognized by the checklist roughly corresponds to the high case scenario of 6’-6” or 2 meters established by NOAA. Sea level-experts anticipate a 6’-6” to 9’-8” (2-3 meter) rise through 2300 (see guidance, below) and the 8’ minimum rise for higher-risk projects helps to limit the economic, social, health and environmental exposures from sea level rise that may otherwise overrun facilities that operate for extended time frames (or set baseline elevations for extended infrastructure) and could pose a significant risk to communities due to toxic exposures through flooding and/or failure to provide vital services such as energy generation or sewage processing.

There are several variables impacting sea level scenarios. Two important variables are: (1) climate change mitigation (or lack of mitigation) and (2) reinforcing feedback loops.

Aggressive mitigation of climate forcing gases (CO2, CH4, etc.) could reduce the extent of sea rise, but current indicators are not strong for near-term aggressive mitigation. NOAA’s “intermediate high” scenario sets a 3’-9” or 1.1 meter increase based on projected ocean warming + current levels of ice sheet melting. A lack of mitigation would increase the impact of reinforcing feedback loops and/or the strength of feedback loops could be greater than anticipated (which appears likely given the faster than expected decrease in Arctic sea ice), resulting in higher levels of warming and greater sea level rise due to thermal expansion and most importantly, greater ice sheet melting, particularly in Greenland and West Antarctica.

Guidance:

“Sea-level rise: What the Experts Expect” Nov 2013, Realclimate.org
Underwriting Documentation: Recognized Map Showing Location Outside 500-Year Floodplain
“Global Warming of 1.5°”, October 2018, Intergovernmental Panel on Climate Change