After high flows, lots of deposition next to weir.
ENGINEERING - ARCHITECTURE - SURVEYING - PLANNING
Platte River Bank Stabilization at Woodcliff
Project Summary Memo
The river bank along the Woodcliff development has a long history of erosion that has threatened the long term integrity of vital infrastructure, such as roads and utilities. Past attempts at stabilizing the river bank have produced mixed results. As such, JEO Consulting Group, Inc. (JEO) was retained by Saunders County Sanitary Improvement District #8 (Woodcliff) for design and permitting services for implementation of a long term, sustainable design. This design will utilize a combination of bioengineering techniques to not only protect vital infrastructure but also restore and enhance the aquatic habitat along the Platte River adjacent to Woodcliff.
The proposed design primarily consists of a system of bendway weirs. Bendway weirs are low lying rock jetties that are angled slightly upstream. These push the low flow channel away from the bank. Higher flows overtop the weirs, but the angle of the weir redirects the flow of water back to the middle of the river, as opposed to directly along the bank. This creates slow moving water near the bank that promotes sediment deposition. Over time, the area between the weirs will silt in and vegetation will establish, forming a small bench between where the bank sits now and where the low flow channel will be after the project is complete.
In addition to the bendway weirs, segments of stone toe protection will be installed in critical areas that are currently most susceptible to damage from further erosion. This consists of a layer of rock placed approximately half way up the bank.
Along the extents of installed bank protection, willow pole plantings will be included. Cuttings from live willow trees will be placed longitudinally along the bank in conjunction with areas of stone toe protection. Additionally, rows of willow poles will be installed perpendicular to the bank at each weir location and in other strategic areas. Some of the willow poles will root and grow into normal willow trees. The poles that do not grow still provide additional bank protection in that they diffuse high water flows on the bank and further promote deposition (similar to how a snow fence works).
The exact schedule and methods of construction can depend on the selected contractor’s preferences. A estimated three (3) month window will be allowed for placing rock. This work involves the delivery of approximately 6000 tons of riprap and rock, which equates to nearly 250 side dump semi loads. On-site placement of the rock will likely be done by a large excavator and skid loaders or track loaders. It should be expected that the roadway will be damaged by the large equipment, especially along the riverbank.
The contractor will be required to leave one lane open to traffic at all times. Inevitably, there may be a few moments where equipment is completely blocking the road due to construction movements, but those moments should be few and limited in time to just a few minutes. Additionally, the contractor will be required to keep the road traversable at all times. Should equipment damage the road to impassable conditions, the contractor will be required to haul in additional gravel or other material to make the road passable by normal passenger vehicles. Placement of rock is anticipated to take approximately 60 days, but could be between 30 and 90 days depending on weather and availability of the quarry to produce the stone.
The contractor will have the option of installing the pole plantings either with the placement of rock or after. If this occurs after rock placement, the poles should be installed within about a two-week period. Skid loaders and an excavator will be required to install the pole plantings. Seeding and restoration of the project area will occur last.
In general, the only trees to be removed will be the ones necessary for construction of the project elements, such as access to the northernmost trees or trees in the immediate proximity to specific project elements. No mass tree clearing is needed or designed.
General Anticipated Schedule
July through November 2016: JEO evaluation and response to USACE requests for additional information
End of December 2016: Re-submittal of 404 Permit Package to USACE
January through February 2017: Public Comment period and initial USACE reviews
March 2017: Respond to USACE requests for information
April through June 2017: USACE evaluation
June-July 2017: Anticipated receipt of permit
July - August 2017: Bidding and Contracting:
Construction: September 2017 through Winter 2017/2018, with final seeding and restoration in Spring 2018
Example Photos of Similar Project
Willow poles immediately after installation.
Weirs being overtopped by high flows.
Willow poles sprouting a month after installation.
2 months after installation.
SID #8 - Sanitary & Improvement District #8 of Saunders County
SID #8 owns and maintains the Woodcliff Lakes Water & Sewer Systems, road drainage, and emergency sirens.
Meeting dates are posted on the Home page calendar.
Minutes of previous meetings are posted below.
Trustees through 2019 are:
S35 Lonnie Mahrt 402-680-4953 Chairman
S105 Tom Sawyer 402-306-7516 Clerk
S1027 Nick Borman 402-753-0103
S1204 Sean Kenney 402-416-0118
S92 Barry Taylor 402-707-8691
Ice forming between the weirs.
Also check this link to a good drone view of what the bend weirs and the Cedar Creek project look like: https://we.tl/vUtMCWCybD
Bendway weir immediately after construction.
2 months after construction.
Ice between the weirs, notice open channel in the middle of the river.
NEXT MEETING IS SCHEDULED FOR: Mon., May 13th, 5:30pm at the Woodcliff Office
5 months after construction.
Placement of rock for a bendway weir.
Recently harvested willow poles
Check out this video showing the river bank work as of April 6, 2018.
(Thank you to Josh Mahrt!) https://youtu.be/PDSYg5TcGcO
MINUTES OF MEETINGS
Minutes are a draft and subject to approval at the next meeting of SID #8.