Flood Information

Index

Cottage Grove's Flood Hazard

Willamette River Water Gage

City Provided Resources

Riparian Newsletter Sources

National Flood Insurance Program

Elevation Certificates

Other Sources

Cottage Grove's Flood Hazard

History of flooding in Cottage Grove

The City of Cottage Grove is located immediately south of the confluence of the Row River and the Coast Fork of the Willamette River. These two rivers as well as Silk, Mosby, and Bennett Creeks contribute to the flooding hazard in Cottage Grove. The city itself is located wholly within the Coast Fork Willamette Watershed Basin.

Due to heavy amounts of rain and close proximity to two major rivers and Silk Creek, flooding has occurred in the past in our city. Cottage Grove experienced frequent flooding before Congress authorized the construction of Cottage Grove Dam and Dorena Dam by the US Army Corps of Engineers as part of the Willamette Valley Flood Control Project in 1936. Although the construction of the Cottage Grove and Dorena Dams between 1942-1945 greatly reduced the frequency of flooding in our community, the risk still exists.

The last “big” flood we saw on both rivers at the same time was in December of 1964, when we had what was equivalent to an 80-year flood. Dorena and Cottage Grove Dams saw peak discharges twice their normal averages that December. In December 1996 and February 1997, so much water filled the Dorena Reservoir that it washed over the top of the Dam, in what is now considered a 20-year flood. Silk Creek last flooded over its banks during the flood of 1997.

EXISTING FIRM MAPS (1999):

In 1999, Cottage Grove adopted new Flood Insurance Rate Maps provided by FEMA – these are the existing FIRM maps that we have been using to determine properties within the “100 year floodplain” or “Special Flood Hazard Area”. These maps were based upon aerial photographs of the 1996 floods.

CENTRAL LANE COUNTY (RE)MAPPING PROJECT (2022):

The new Central Lane County Floodplain mapping project began in 2010. It utilizes LiDAR, a method for measuring distances (ranging) by illuminating the target with laser light and measuring the reflection with a sensor. Differences in laser return times and wavelengths are then used to make digital 3-D representations of the target. This mapping technique allowed FEMA to gain a much better understanding of how flood waters might flow across the landscape, leading to new, revised maps that show a vastly different “100-year flood zone” or “Special Flood Hazard” in Cottage Grove.

The new Preliminary FIRM maps show a potential flood risk that impacts a lot more of the City. “Special Flood Hazard Areas” (Zones A or AE, Floodway) are now projected to impact over 750 properties. These maps will be presented to the public for comment in fall 2022. Adoption of the new maps is expected in 2024. You can see the proposed maps and how the FIRM's will change by clicking this link. 

Cottage Grove Development Code Requirements for Flood Damage Prevention:

Title 14 Development Code Chapter 14.37.200 Flood Damage Prevention requires Floodplain Development Permits for all new development (including fill, grading, excavation, new accessory structures, new houses, additions or alterations to existing structures, fences, etc.) for properties in the Special Flood Hazard Area (SFHA). This includes any properties identified as part of the AE, A, or AO zones, or in a designated Floodway.

If you are one of those properties impacted by the SFHA by the current or new FIRM Map, you will need to learn this code. (See below for a link to the Municipal Code.)

Floodplain Development Permits are issued by the Public Works & Development Department prior to or as part of building permit applications. If you are thinking of building anything on your property, or want to talk about ideas you have for development in an area identified as part of a floodplain, please contact our office prior to starting any work and we’ll walk you through the permit process.

For additional information on local floodplain regulations, please contact Floodplain Administrator Eric Mongan, planner@cottagegrove.org, (541) 942-3340.

Community Rating System (CRS) Program:

The City participates in the Community Rating System, a program of the National Flood Insurance Program (NFIP) that helps lower individual flood insurance rates in return for community wide measures taken to enhance the city’s flood management program and reduce the community’s risk to floods. We are currently a Class 6 CRS Community – which means that every eligible NFIP insurance policy holder in Cottage Grove receives a 20% discount based upon the City’s work on floodplain management. City Planner Eric Mongan is the CRS Program Manager. If you have any questions on the City’s current CRS program, please contact him at planner@cottagegrove.org or (541) 942-3340.

Flood Information:

We have a robust library with flood information, which includes printed and video resources that will help you mitigate your risk if you live in a flood area. One of the goals of the Public Works and Development Department is to provide information to the public on flood damage prevention, flood preparation, and flood insurance. Below are links to various resources including some provided by the City's website and some provided by outside sources. Along with these, attached at the bottom is the seasonal Riparian Newsletter, informational fliers regarding flooding, a list of elevation certificates kept on file at the City of Cottage Grove, the FEMA pamphlet Repairing Your Flooded Home, and the US Army Corps of Engineers booklet Local Flood Proofing Programs.

Willamette River Water Gage

In order to find real-time information on the Willamette River temperature, water levels, discharge, and more click here to visit the USGS Willamette River Water Gage.

US Army Corps of Engineers TEACUPS
Real time information on the water levels of the lakes within the Willamette Valley as well as information on bank levels and flood stages as provided by the US Army Corps of Engineers

City Provided Resources

Flood Damage Prevention Code 14.37.200
Chapter from the Cottage Grove Development Code on Flood Damage Prevention.

Flooding Section from Natural Hazard Mitigation Plan
Section from the Cottage Grove Natural Hazard Mitigation Plan on the area's flood hazards.

Flood Definitions & Standards 
Definitions and Standards regarding flooding taken from the Cottage Grove Development Code.

Emergency Preparedness Videos
Videos providing information on emergency preparedness and personal safety created by the City of Cottage Grove Planning Division.

About the Mandatory Purchase of Flood Insurance
Description on the NFIP and information on when Flood Insurance is mandatory.

Natural Hazards Mitigation
Cottage Grove's complete Natural Hazards Mitigation Plan and brief descriptions of potential natural hazards.

Cottage Grove Floodplain Map
Map of Cottage Grove including Floodway and 100-year Floodplain.

Floodplain Development Permit Application

Riparian Newsletter Sources 

Attached at the bottom of the page is our seasonally released Riparian Newsletter and insert providing information on flood preparation, water safety, and upcoming City events. Below are links to some of the complete articles used as sources for the current newsletter as well as a link to the sign up for Lane County Alert Me.

FEMA HOW TO PREPARE FOR A FLOOD

US Army Corps of Engineers Water Safety Tips

Coast Fork Willamette Watershed Council Science Pub

Lane County Alert Me

National Flood Insurance Program

National Flood Insurance Program
The official website for the National Flood Insurance Program courtesy of FEMA.

Flood Insurance Rate Maps
Flood Insurance Rate Maps (FIRMs) for the City of Cottage Grove as well as a link to the FEMA FIRM website.

Other Sources

US Army Corps of Engineers TEACUPS
Real time information on the water levels of the lakes within the Willamette Valley as well as information on bank levels and flood stages as provided by the US Army Corps of Engineers

Oregon Office of Emergency Management
Information on natural hazards and preparedness for the State of Oregon as provided by the Oregon Office of Emergency Management.

FEMA Home Page
The main website for FEMA from which information on emergency preparedness, flooding, flood insurance, and more can be found.

US Army Corps of Engineers Willamette Valley Project
Information on the Willamette Valley Project which oversees both the Cottage Grove Lake and Dorena Lake.

Ready.gov Flood Information
Basic information on flood preparation and flood safety as provided by Ready.gov.

American Red Cross Flood Safety
Basic information on flood preparation and flood safety as provided by American Red Cross.

National Weather Service Cottage Grove Information​
Real time update on climate and weather for the City of Cottage Grove as provided by The National Weather Service.

Floodsmart