Mystery map

Surveys contradict FEMA; question of map origin still remains

Even the Federal Emergency Management Agency (FEMA) isn’t sure where the data came from that it used to update flood insurance rate maps in Mammoth Lakes.

Last month, homeowners in Snowcreeks II and IV were wrestling with, what they believed was a new FEMA map created as part of the Flood Map Modernization Program. The map showed that the Snowcreek properties were now within the floodplain of Mammoth Creek. Concerned about the high cost of flood insurance, the homeowners hired Triad/Holmes Associates to conduct surveys for a second opinion.

The second opinion of Triad/Holmes determined the subdivisions are not located in the floodplain.

FEMA, however, is not agreement. Further, the agency says the information used to determine floodplain status was not new.

“We took the paper map from 1992 and made it digital and added an aerial map background,” explained Senior Engineer for FEMA Region 9, Ed Curtis. “There was no new study information created for the 2011 map. I don’t know where the 1992 information for Mammoth Creek came from.”

According to Curtis, the map for Mono County was fragmented between the incorporated and unincorporated areas and was just a network of roads.

The 1992 map should have been based on the new North American Vertical Datum, updated in 1988 from the original 1929 National Geodetic Survey. Vertical datum is the reference or basis for elevations, and usually refers to sea level.

“The new vertical datum results in higher elevation,” Curtis explained. “The flood depth has stayed the same, it’s just being measured from a different point [in the 1988 data].” The 1988 data is the current standard for flood mapping.

Snowcreeks II and IV were both built in the ‘80s. According to Snowcreek II HOA President Bill Graham, at least in the case of Snowcreek II, construction took place even before Mammoth was tied into the national grid.

So why wouldn’t Snowcreeks II and IV have been told they were in floodplains back in 1992?

“The maps that FEMA was using did not accurately represent the elevation of the pads that were put in [under the buildings] at the time of construction,” Graham explained. “The pads are several feet above the floodplain. So, we’ve spent several thousand dollars to help the federal government correct its mistakes. I plan to send FEMA the bill.”

Wherever the map came from, according to Triad’s surveys, it’s wrong. At the time of The Sheet’s July story, “FEMA drowns local properties” (https://thesheetnews.com/archives/9786), when neither the Town nor the County knew where the map data had come from either, Triad had completed the survey for Snowcreek IV and deemed the buildings were above the level of floodplain. Since then, Triad has also completed a survey for Snowcreek II, which according to Graham, also shows that none of those buildings are within the floodplain either.

So now Snowcreek homeowners must jump through the hoops of submitting Triad’s survey data to FEMA in a Letter of Map Amendment (LOMA).

“If a surveyor finds different information they can submit it to FEMA in a LOMA,” Curtis said. “FEMA responds within 60 days.”

Curtis wasn’t sure if a LOMA had been submitted on Mammoth’s behalf yet, since LOMAs are sent to FEMA’s offices in Virginia.

Graham said that Triad would send the LOMA to the Town, which was then the agency responsible for submitting the information to FEMA.