1. What are the features of the flood mitigation plan being delivered through this project?
This plan is meant to act as a guide for flood mitigation projects in the Lowe River. Please refer to our one-page summary located on the documents page of the project website.
2. Groins? Dikes? Levees? What is the difference and what do we have now?
In Valdez, we use all three terms interchangeably to describe embankments that hold water from dry land. However, there are differences between each of the terms. Traditionally, the following definitions apply:
The current flood mitigation structures that protect the 10 Mile subdivisions on the Lowe River are technically groins. The groins are positioned to deflect and direct flows from entering the subdivisions without being hydraulically cut off from the river. This is important for the subdivisions as many streams that flow through the area need to drain into the river to prevent flooding.
3. What are the outcomes of this project?
The 2020 survey of Valdez residents indicates that maintenance of existing infrastructure is the most valuable use of public funds. Two construction projects may derive from the work completed through this project 1) gravel extraction in the Lowe River floodplain and 2) dike infrastructure improvements.
The gravel extraction in the Lowe River aims to encourage more of the water in the floodplain to flow away from the dikes at the 10 Mile subdivisions. Modeling indicates that this will reduce the water surface elevation at the dikes.
The dike infrastructure improvements will range from replacing worn rock or replacing rock displaced by storm events to strategically raising the dikes to make sure there is enough space between the top of the dikes and the water level during storms (freeboard).
4. Why is this project needed?
Historically, portions of the Lowe River floodplain have been susceptible to flooding. This project will protect areas of infrastructure through the development of new dikes and revetments, provide maintenance of existing dikes and levees, and identify areas that are susceptible to flooding that may not be preventable. Years that have had significant flood events include 1983, 1995, 2006, 2012, 2015, 2016 and 2018.
5. Why are our homes flooding?
Properties within the Alpine Woods Subdivision are taking on water from two sources: Lowe River and groundwater.
6. What processes are occurring on the Lowe River that influence the risk of flood and/or erosion?
7. Why should I care?
8. Who are the stakeholders in this project?
Everyone in Valdez is a stakeholder in mitigating the risk of Lowe River flood and erosion because of the public and private assets and infrastructure adjacent to the river that are subject to potential failure if that risk is not mitigated. A few of the stakeholders are:
9. What is a braided floodplain?
A braided floodplain is a floodplain that may have more than one river channel flowing through it and each of those channels have the potential to move within the floodplain. The movement of the channels depends on the type of material in the floodplain and the velocity and amount of water flowing through those channels.
10. What is an aggrading floodplain?
This is the term that describes if material is being deposited on to the riverbed or floodplain. The sediment that is carried by the river is either suspended in the water or rolls along the bottom of the riverbed. If the river is aggrading, it means that the material is settling out of the water to the bottom of the river/floodplain. This has the effect of raising the riverbed/floodplain over time.
11. What's so challenging about mitigating flooding on the Lowe River?
A lot! The Lowe River is an aggrading floodplain. The project corridor is a twelve-mile stretch of river with multiple stakeholders who each have different risks, costs, and possible benefits to weigh. In addition, rivers, and particularly glacial rivers influenced as heavily as the Lowe by seasonal precipitation and snow melt, are notoriously difficult to control.
12. What factors determine when a flood or erosion mitigation project will occur?
13. Can the dikes near my home stop all water from the Lowe River?
No, the dikes are constructed to channel or direct water away from infrastructure. This is the case unless dikes contain an impermeable barrier that reduces the seepage through the dike. The amount of water that can seep through or under the dike is minimal compared to the amount of water that is deflected by the dike. The amount of water that can seep through the dike (permeability) is taken into consideration when designing the dikes.
14. What are some examples of other flood mitigation projects in Valdez?
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