Presentation on theme: "Head cuts and Knickpoints Identify, Prevent & Stop Georganne Bowman September 30, 2011."— Presentation transcript:
Head cuts and Knickpoints Identify, Prevent & Stop Georganne Bowman September 30, 2011
outline Stream Response to flow changes Stream restoration in the US –Challenges and expenses Channel stabilization –Headcuts and knickpoints How to Identify, prevent and stop
Stream Response Streams form over time in response to flow regime and geology (conductance and resistance) Urbanization changes the frequency, magnitude and duration of flood events These in turn increase the amount of work that the river/stream can do. This causes channel incision and destabilization
Work and Power
Competence vs Capacity
Restoration In the US Type of projects: –Stream Habitat improvement –Bank Stabilization –Water Quality –Dam removal
Channel Stabilization Streams are dynamic systems reacting to: –stream flow, –slope or –velocity changes The new channel –Cut off from previous flood plain
What is a Headcut? Headcut or knickpoint is an a brupt change of gradient of a stream. It is often attributed to a fall in base level: this initiates a knick point which then travels upstream. It may alternatively be due to a change in rock type or load size, or to tributary entry.
Stream erosion The stream expends kinetic energy in "trying" to eliminate the nickpoint.
Partch Property 7 acres with 25 acres draining to it. Pasture land, grazing for horses/goats Dashed blue line, channelized Objectives: –Livestock safe access to pasture –Stop erosion –Ability to drive across stream –Budget $3000
Issues with site 3 channels converging Swampy area –Horses and vehicles could not cross –Headcut migrating approximately 2 feet per year.
Demonstration site John Sullivan did the design & ordered the supplies Homeowner did the backhoe work and stone placement Grasspave donated and used for driving lane
Lessons Learned Its not enough to slow the velocity at the outlet structure. We also have to consider the change in elevation from the bottom of the discharge to the stream bed Stream restoration is expensive and rarely works.