Head cuts and Head cuts and KnickpointsKnickpoints

Identify, Prevent & StopIdentify, Prevent & Stop

Georganne BowmanGeorganne BowmanSeptember 30, 2011September 30, 2011

outlineoutline

• 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 ResponseStream 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 PowerWork and Power

                                                                                      

Competence vs CapacityCompetence vs Capacity

Restoration In the USRestoration In the US

• Type of projects:– Stream Habitat improvement– Bank Stabilization– Water Quality– Dam removal

RestorationRestoration

Channel StabilizationChannel 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?What is a Headcut?

• Headcut or knickpoint is an abrupt 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 erosionStream erosion

• The stream expends kinetic energy in "trying" to eliminate the nickpoint.

Partch PropertyPartch 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 siteIssues with site

• 3 channels converging• Swampy area

– Horses and vehicles could not cross

– Headcut migrating approximately 2 feet per year.

Step poolsStep pools

Demonstration siteDemonstration 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 LearnedLessons Learned

• It’s 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.