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Resilient St. Vrain

St. Vrain Floodplain Updates

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Resilient St. Vrain: Restore & Revitalize


Are you in a floodplain? Find out using Longmont's Floodplain Inquiry Map >

The Federal Emergency Management Agency (FEMA) approves the Flood Insurance Rate Maps (FIRM) for communities. The FIRM shows the area of land that could be inundated by a 100-year flood event, known as the Special Flood Hazard Area (SFHA). The SFHA has a 1% chance of flooding in any given year. These maps are also used to rate flood insurance.

The map below overlays the new existing 100-year floodplain areas (shown in red) over the 2012 FEMA FIRMs (shown in blue). The new, existing 100-year floodplain has been submitted to the state (as part of CHAMP) for incorporation into the new FEMA FIRMs, which are planned to be effective in early 2019.

Click on any map to open a PDF file that can be enlarged for easier viewing or saved to your computer. Have questions about these maps and what they mean for your property? Please contact the City of Longmont Floodplain Administrator.

View draft floodplain maps for the unincorporated Boulder County areas west of Longmont >

Learn more about why work on Resilient St. Vrain is being built to 100-year flood flow levels >


CLOMR / LOMR Process

Revisions to the floodplain map through a Conditional Letter of Map Revision (CLOMR) are being proposed for  Sandstone Reach and City Reach 1. The City of Longmont is in the process of notifying property owners of ongoing and upcoming projects that may affect flood elevations along and near St. Vrain Creek.

The maps on this page present three Special Flood Hazard Area (SFHA) stages for the first two Resilient St. Vrain work areas (Sandstone Reach and City Reach 1). Click on any of the maps below to open a larger PDF file that can be downloaded to your computer or enlarged for easier viewing.

 


 

Sandstone Reach

Sandstone Reach follows St. Vrain Creek from County Line Road downstream (eastward) approximately 2.5 miles to the Boulder Creek confluence (point where the two creeks meet) near Highway 119.

Regulatory Floodplain

In 2015, FEMA approved updated Flood Insurance Rate Maps (FIRM) for Weld County. These maps show the 100-year flood risk and are used to rate flood insurance policies. The map below, referred to as the "regulatory floodplain," shows the Special Flood Hazard Area (SFHA) boundaries within the Sandstone Reach.

Sandstone Effective

Existing Conditions Floodplain

After the 2013 flood, the Colorado Department of Transportation (CDOT) and Colorado Water Conservation Board (CWCB) conducted a hydrology study of the watershed to evaluate flood flow rates. CWCB is currently working with FEMA to update the FIRM to reflect the results of the new flow rates; that work is expected to be completed sometime in 2018. The map below reflects the new approved 100-year flood flow rates, as well as the post-flood topography along the creek corridor. The floodplain boundaries shown in this map of the Sandstone Reach are referred to as the "existing conditions."

Sandstone Existing

Proposed Conditions Floodplain

After work to repair the flood damage is completed through the Resilient St. Vrain project, the City of Longmont will submit floodplain revisions to FEMA. Those planned revisions, referred to as the "proposed conditions" floodplain, are shown in the map of the Sandstone Reach below.

Sandstone Proposed


City Reach 1

City Reach 1 follows the St. Vrain Creek from slightly west of Main Street downstream to the confluence (point where the two creeks meet) with Left Hand Creek, east of Martin Street.

Regulatory Floodplain

In 2012, FEMA approved updated Flood Insurance Rate Maps (FIRM) for Boulder County. These maps show the 100-year flood risks and are used to rate flood insurance policies. The map below, referred to as the "regulatory floodplain," shows the Special Flood Hazard Area (SFHA) boundaries within City Reach 1.

City Reach 1 Effective 

Existing Conditions Floodplain

After the 2013 flood, the Colorado Department of Transportation (CDOT) and the Colorado Water Conservation Board (CWCB) conducted a hydrology study of the watershed to evaluate flood flow rates. CWCB is currently working with FEMA to update the FIRM to reflect the results of the new flow rates; that work is expected to be completed sometime in 2018. The map below reflects the new approved 100-year flood flow rates approved from the CDOT study, as well as the post-flood topography along the creek corridor. The floodplain boundaries shown in this map of City Reach 1 are referred to as the "existing conditions."

City Reach 1 Existing Conditions 

Proposed Conditions Floodplain

After work to repair the flood damage and improvements to the creek channel to pass the new 100-year flood flow rates are completed through the Resilient St. Vrain project, the City of Longmont will submit floodplain revisions to FEMA. Those planned revisions are referred to as the "proposed conditions" floodplain

For City Reach 1 "proposed conditions" in the map below, two floodplain areas are shown. The green and purple areas together comprise an interim condition, while the purple area on its own is an estimate of the 100-year floodplain after additional improvements are completed upstream of City Reach 1.

City Reach 1 Proposed Conditions

 


 

For More Information

The Colorado Hazard Mapping Program (CHAMP) is remapping the 100-year floodplain of creeks affected in 2013, including the St. Vrain Creek. Read about the St. Vrain Watershed Risk Mapping Assessment and Planning effort >

Floodplain map changes such as the ones detailed above can affect flood insurance premiums. Learn more in this FEMA brochure >

The National Flood Insurance Program maintains a website, FloodSmart.gov, to share information about flood risks.

For questions about the regulatory, existing, and proposed condition floodplain areas, contact the City of Longmont Floodplain Administrator.

 

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