Public Works hosts FEMA flood risk maps review

Snohomish County Public Works Planning and Development Services held an informational public meeting on Dec. 12 to review preliminary flood risk maps issued by the Federal Emergency Management Agency.

FEMA consulting firm Starr II Regional Service Center Lead Josha Crowley introduced the new maps, giving an overview of FEMA’s process, which has been ongoing for several years.

The purpose of the meeting was to review the new Digital Flood Insurance Rate Maps (DFIRMs) and examine changes to flood risk areas along the Skykomish and Sultan rivers. In addition to updating existing paper maps to an easier-to-use digital format, the preliminary DFIRMs offer increased accuracy over the current maps, which are referred to as the effective maps. 

Once formally adopted by FEMA in roughly 2018, the DFIRMs will supersede the effective maps.   

The maps are a component of the National Flood Insurance Program (NFIP), which seeks to reduce the impact of flooding by providing flood insurance to property owners and encouraging communities to engage in floodplain management activities to reduce risk. The goal of the program is to help cities and counties facilitate long-range planning to reduce risk to life and property, Crowley said, as flooding is the most predictable of the natural hazards.

Crowley said the most impactful piece of the flood insurance program is the mandatory purchase requirement for homeowners in special flood hazard areas. Two separate federal statutes mandate the purchase of flood insurance, which is required by lenders.  

“If your home is located in a special flood hazard area and you have a mortgage, your mortgage provider will require you to carry flood insurance,” Crowley said.

The purpose of mandated flood insurance is to take a proactive approach at mitigating loss by reducing the impact of flooding on private and public structures.

Since 1977, there have been 79 flood insurance claims in the city of Monroe, totaling $927,820.70, according to FEMA. In Sultan, there have been 191 claims, equaling $2,776,159.11. Flood insurance claims in unincorporated areas of Snohomish County have exceeded $23 million since 1977, according to FEMA documentation.   

The NFIP preliminary flood risk maps are meant to quantify flood risk and assign insurance rates, which are dependent on the amount of flood risk; the higher the flood risk, the higher the insurance premium. The maps analyze the risks associated with a 1 percent annual chance flood event, formerly referred to as the 100-year flood or base flood.

“What we’re talking about is the 1 percent annual chance event, or the 100-year flood,” Crowley said. “They’ve, within the last 10 years or so, changed the terminology from 100-year to 1 percent annual chance just to remove that impression that it’s only going to happen once every 100 years.”

Just because a major flood event happened one year, does not mean it can’t happen the next.

“It has a 1 percent chance of happening every year,” he said.

One of the noticeable differences between the effective maps and the preliminary maps are changes to the base flood elevation (BFE), which is the elevation the floodwater is expected to rise during a 1 percent annual chance event. In the preliminary maps, FEMA used an updated system called NAVD 88 for relating ground and flood elevations to determine a more accurate zero level, called a datum.

The effective maps use a system called NGVD 29, which is based on mean sea level. The shift to NAVD 88, which is based on the density of the earth, has resulted in a zero-level variation of 3.6 to 3.9 feet depending on the location. It’s a much more accurate system, Crowley said, but the transition resulted in some changes to the maps.

“There will be several areas where we haven’t actually changed the base flood elevation but it will look like the base flood elevation is almost four feet higher,” Crowley said. “That’s a result of the datum shift and not a result of a new study.”

In addition to digital formatting and the datum shift, the maps incorporate updated studies that took place along the north and south forks of the Skykomish River, the Sultan River and May Creek. Most of the additional study took place from 2006 through 2010 in partnership with Snohomish County, Crowley said, using on-site river gauge analysis, on-the-ground physical study and topographical study using Light Detection and Ranging (LiDAR), a technology that measures distances with laser beams.

“The topography is LiDAR-based,” Crowley said. “This is physically an aircraft flying overhead, shooting lasers, and timing the return of these laser beams.”

In creating the updated maps, the new data was used in conjunction with recent high water marks and data obtained using a modeling software system called HEC-RAS to predict flood outcomes.

“We’re modeling this 1 percent annual chance flood, which is a statistically-based flood, but we can use that model and compare it with actual measured events and make sure that the model’s producing base flood elevations for the measured events that match what was observed,” Crowley said.

The majority of the new data was released in 2010 with the intent of updating the maps at that point, Crowley said, but a new Levee Analysis Mapping Procedure (LAMP) changed things. As a result of the updated LAMP criteria, the maps were put on hold as FEMA sought the best way to assess hazard reduction associated with levees not accredited to protect against the 1 percent annual chance flood.

Previously, FEMA used an approach called “without levee” for areas with non-accredited levees. This meant that non-accredited levees were treated as though they had no effect on the area behind the levee, known as the landward side. In 2011, Congress asked FEMA to discontinue that approach in favor of more comprehensive flood modeling.

The LAMP was developed by a FEMA-led team made up of FEMA representatives, the U.S. Army Corps of Engineers and engineering and academic individuals considered experts in the study of non-accredited levee systems. 

Levee analysis procedures are relevant to the Sky Valley since there is a system of two levees directly east of Sultan near Startup, a portion of which is non-accredited. The first was built in 1965 as a flood control device to prevent Skykomish River flows from entering the Wallace River. The Skykomish River-Wallace River Levee was modified in 1969 to add the Startup Training Federal Levee, a 2,700-foot-long levee to protect nearby farmland. 

In order to show an area as protected on the preliminary flood risk maps, a levee must be hydraulically significant, it has to have an owner, it has to be operated by that owner and it has to be certified to NFIP standards that it was designed to offer protection during the 1 percent annual chance flood.

“It’s a pretty strict and stringent process to certify a levee,” Crowley said. “It is not trivial.”

The LAMP has added an element of complexity, and there are more flexible ways to examine non-accredited levees. There are ways to grant partial accreditation, where one part of a levee might be certified while another part of the same levee is not. Because of this, FEMA made the decision to seclude areas containing non-accredited levees until they can be restudied based on LAMP. In areas of seclusion, the preliminary maps will remain unchanged. 

In the case of the Startup Levee, FEMA has issued a Provisionally Accredited Levee (PAL) status, so it will be recognized on the map as protected due to flood control measures.

“This applies to the Startup Levee, which is just upstream of here,” Crowley said. “That is a levee that we are fairly confident can be certified.”

The PAL is valid from April 15, 2016 through April 15, 2018. According to FEMA, “if levee certification is not provided by that time, then this area will be put in the queue for a future flood study using the new Levee Analysis and Mapping Procedure.”

Crowley said there will be a note on the map indicating the PAL. Hopefully, the Startup Levee can be certified in the given two-year timeframe, at which point the PAL notation would drop off with no change to the risk level. If the levee isn’t certified, then the risk could change, which could impact nearby property owners, Crowley said.

Sultan resident Dick Prendergast has lived in the Trout Farm Road area of Sultan for 26 years. He’s been flooded once in that time, he said. His mortgage company requires him to carry flood insurance, for which he pays more than $1,000 a year. He described flood insurance as being like a car payment, except he never gets to enjoy the car.

The maps will go through extensive public process before they are made effective. First issued in July, an appeal period will run from January through April 2017. FEMA hopes to issue a letter of final determination in fall of 2017, and the new maps would become effective in spring of 2018.

For more information on the new maps, visit http://snohomishcountywa.gov/3750/Flood-Hazard-DFIRM. For more information on living behind a non-accredited levee, visit http://snohomishcountywa.gov/DocumentCenter/View/38394.