Better Maps Help Many Homeowners

Changes to federal floodplain maps for the Matanuska-Susitna Borough are not final yet, but drafts show that at least preliminarily, many more homes here will be moving out of the floodplain than into it.

The map above shows Lucille Creek, west of Wasilla. The red shows the old floodplain designation. The blue is the proposed map. The structures will be moved out of the floodplain designation as shown.

FEMA, the Federal Emergency Management Agency, is updating its floodplain boundaries for the 1-percent and 0.2-percent-annual-chance (100- and 500-year) flood events.

The final maps need to be adopted by FEMA and the Borough Assembly. Adoption is anticipated to be in late 2018.

Initial estimates show 1,500 Mat-Su structures are moving out of the floodplain. This means the land the structure is on will no longer hold the federal floodplain designation.

This could save homeowners overall $10 million to $20 million over 15 years.

Some 200 to 300 other Mat-Su homes are likely moving into the floodplain designation.

Floodplain or flood pathway designations require flood insurance if you have a loan backed by the federal government. Flood insurance can cost thousands of dollars a year.

FEMA is deriving these new maps based on detailed new technology. Previously, the FEMA floodplain maps for the Borough had relied on science and data of 1985.

As President of E-Terra, LLC., Assembly Member Steve Colligan’s expertise is in mapping. 

“The newly collected data is a 100 times better than was available before and will be the basis of the decision-making. Some discrepancies will need fine-tuning, but it is the best available data," Colligan said.

LiDAR is short for Light Detection and Ranging. It is data collected by scanning the earth’s surface using a laser and measured feedback from an airplane to the ground. It creates very accurate measurements of bare earth (terrain) and top of tree canopy and structures (surface). By draping an image over the elevation data of LiDAR, you can create a three dimensional model. The Borough began adding LiDAR in 2011 with the help of nine partners in a $2.1 million project.

Since 1985, FEMA has advanced its hydrology and hydraulic mapping models using these new data sources, along with industry improvements in technology and computer processing power to create more accurate modeling techniques resulting in accurate maps and floodplain definitions.

The data is a snap shot in time that will need updating on a periodic basis to reflect changes from flooding and erosion. The major creeks and rivers in the Mat-Su Borough occasionally leave their banks and cause notable damage. In 2005, flooding here was declared a federal disaster. In 2012, flooding was declared a federal disaster. As recently as 2015, flooding on major waterways closed six roads and dampened a few properties. Erosion damage and sometimes flooding on the meandering Matanuska River is a recurring problem every year.

This overhaul in floodplain mapping is called the Borough Risk Map project. The Borough met with FEMA on Jan. 20 to discuss the fine-tuning of the mapping and the process of solving discrepancies.

FEMA encourages homeowners to have flood insurance if they live near water. Flooding also happens outside of floodplains. A homeowner’s flood insurance will be a fraction of the cost if the property designation is not in a floodplain.

The Borough will directly notify affected Mat-Su property owners. Floodplain technicians are able to answer specific questions at 861-7822.

Reach us by email This email address is being protected from spambots. You need JavaScript enabled to view it.  or phone at (907)861-7822 with questions or make an appointment to come in and discuss your property.

Visit the Borough floodplain web page at http://www.matsugov.us/flood-plain-development-info

Reporters call Alex Strawn, Manager of Development Services, at (907)861-8574.