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FAQ’s on the Big Wood River Flooding and the Hailey Greenway 2019

Why is the Big Wood River flooding despite flows being lower than the former flood levels?

Gravel-bed rivers like the Big Wood are constantly changing and flooding is part of their inherent nature. 2017’s record flooding altered the Big Wood River throughout its drainage by eroding banks, creating new channels and moving bedload (gravel, rocks, and sediment along the bottom of the river). Bedload migration caused in 2017, as well as previous spring run-offs,  has elevated the river bed in various locations, which has created new flooding areas and flooding at lower flows than had been seen in recent history. Rivers that are connected to the floodplain are far healthier in ecosystem and natural flood mitigation function.  The long-term strategy of the Land Trust and its partners is to develop larger projects within the Hailey Greenway to help reconnect the river to its floodplain to get those natural flood mitigation functions.

 

What has been done “on the ground” to help alleviate flooding?

Unfortunately, there is no simple solution to alleviate flooding issues with the Big Wood River, especially in the reach that encompasses the Hailey Greenway. Any impact or alteration that may seem positive for one reach of the river could, and often does, cause problems elsewhere. Many of the issues the Big Wood River is now facing have been created by alterations made to the river and its floodplain over the last century. The Big Wood River is not owned or managed by a single entity. It also runs through numerous communities and impacts thousands of people and miles of private property, public property, and wildlife habitat. Every manmade impact regarding the river must take into account the health of the entire watershed.

Following the flooding of 2017, the City of Hailey and the Land Trust incorporated various flood mitigation concepts into the Hailey Greenway Master Plan. The County, City, and the Land Trust have begun implementing some of the projects outlined in the Hailey Greenway Master Plan. One of these projects designed to reduce low-flow flooding was the recent completion of the Heagle Park side-channel activation. This recently reactivated side-channel should help alleviate flows at flood levels by diverting approximately 300 cfs away from the Della Neighborhood; the side channel starts on the Draper Preserve. Additionally, the City of Hailey has been installing culverts within the Della View neighborhood as an effort to help drain floodwaters and lower the duration of inundation.

 

What future work is planned to help alleviate flooding?

The City of Hailey, Blaine County, Big Wood Flood Control District 9, and the Wood River Land Trust continue to explore options to alleviate flooding in residential areas without causing problems elsewhere. Man-made alterations to the river, including its channelization upstream, are a major cause of flooding downstream. Grants and assistance for this stretch in Hailey have been requested by Blaine County from the Army Corps of Engineers. The process of altering rivers is extremely expensive, time-consuming and includes many legal challenges, but we continue to try to find solutions.

Currently, stream alteration permits have been completed and submitted to the appropriate parties in order to begin work around our Colorado Gulch Preserve area of the river downstream from Della View. We hope that the restoration around this area of the river will reactivate channels to help reduce the impacts of flooding and protect the new pedestrian bridge. We are also currently working with our partners to explore temporary and immediate options to reduce low-level flooding for residents of the Della View neighborhood.

 

Why can’t you fill in the main trail of the Draper Preserve to stop it from conveying water into the neighborhood?

The main trail in Draper Preserve is actually a sewer easement road. Underneath the main trail lays an active City sewer line. This line requires maintenance, and therefore the trail in which it runs under cannot be obstructed.

As part of the Hailey Greenway Master Plan projects, however, we have decommissioned and “roughened” two other trails located near War Eagle Drive as part of our efforts to reduce water flow into the neighborhood.

 

What’s the difference between groundwater and river water flooding?

As recent findings have shown, groundwater and river water in gravel-bed rivers like the Big Wood are fully connected and ever-changing. What happens within the banks of the river is directly impacted and connected to the groundwater or aquifer. Flooding episodes can come over the top of the ground, as happens along the river in the Hailey Greenway, or can rise up from the aquifer underground; in some cases, both scenarios can occur. This has happened within the Della View neighborhood before.

 

Are there any general public health issues we should be aware of?

The City will notify the public if there are any general health and safety issues. The flooded river itself is fast-moving and dangerous during spring run-off, and people and pets should use extreme caution when near it. At certain flood levels, Draper Preserve will be closed to the public at the request of the City’s Fire Chief. Please be aware and on the lookout for trail closure signs when this occurs.

 

Is there any other information available?

To learn more about how the City of Hailey handles a flood event, and how individual homeowners can prepare, please see the City of Hailey’s resource list: https://www.haileycityhall.org/Announcements/City%20of%20Hailey%20Flooding%20Preparat ion%20and%20Policies%20-%20Before%20a%20Flood.pdf

Development in the floodplain is hard to undo, and yet will always be challenged by flooding. The Wood River Land Trust prioritizes acquiring open land in the floodplain where it’s still available to try to avoid problems like this in the future. The Land Trust owns and manages properties throughout the Big Wood drainage. To learn more about some of these properties and how reconnected floodplains can help alleviate flooding, please call Matt Steinwurtzel at 208- 788-3947 for more information.

 

*For more information on lessons in flood control and river management, you can view the presentation given at the Community Library from Hannah Sanger, Science and Environment Division Administrator for the City of Pocatello. Hannah recently spoke on the history of flood control efforts on the Portneuf River, and how those lessons apply to management in the Wood River Valley. You can view the presentation here.

 

Additionally, we encourage you to read this Idaho Mountain Express story on our approach to river restoration and management, which explains the Land Trust’s intentions to protect active floodplain areas from development, remove unnecessary flood structures, and adopt regulations to prevent the continuation of past mistakes.

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