October 29, 2011 Catchment Drainage Area Drainage Area totals 940 - - PowerPoint PPT Presentation

Preliminary Results of Hydraulic Analysis October 29, 2011

Catchment Drainage Area

• Drainage

Area totals 940 acres (286 + 654)

• Area circled

in red most likely feeds into stream system downstream

• f 244th Ave.

NE crossing (roughly 250 – 300 acres)

How big of flood was Dec 2010?

Using Bear Creek Current and Future Conditions Report (revised) Catchment E16 represents Allen Lake Outflows

• 2011 Conditions somewhere in

between 1985 and Future conditions.

• December 2010 Event had a

very rough estimate of 26~28 cfs (+/-) with NE 8th overtopped by about 18 inches

• For this study used range of 26

to 30 cfs for December 2010 event which is approximately a 10- to 25-year event hedging towards future conditions, given 1985 is 25 years in the past.

Allen Lake Elevations*

NE 8th St. Road Closes** *Elevations are approximations **Theoretically at 1-ft deep Source: Burton

Stream Alignment

• f Study Area
• Approximately 5500 feet of

stream length between NE 8th

• St. and 244th Ave NE

Modeled Existing Conditions

• At 30 cfs, NE 8th Street overtops approximately 24 inches
• At 27 cfs, NE 8th Street overtops approximately 18 inches
• Bottom of Sediment shown in Red, muck can be > 3 ft deep

6576 6355.66* 6272 6148 6051 5980 5891 5807.45* 5696.18* 5587 5503 5464 5427 5265 5125 5106 4944 4811 4785 4725 4667 4522 4355 3995 3955 3505 3263 3180 3034.25 2972 2892 2699 2689 2665 2525 2335 1975 1607 1337 1103 1012 862 788.* 755 634 510

Allen Lake Feasibility Study 2011 Plan: Existing Conditions 2011-10-31 10/26/2011

Legend WS 30 cfs Ground Bank Sta Ineff Ground Levee

Existing Conditions Flooding

244th Ave NE NE 18th St. Vitale Michelman Reimer / Roome Newfeld 247th Ave NE

Allen Lake Feasibility Study 2011 Plan: 1) ExistingOct31 10/26/2011 2) Early Action 10/27/2011

Existing Conditions & Effect of Early Action

• Remove blockage in

culverts, water depth

• ver NE 8th St

reduces from 24 inches to < 6 inches

• This is predicated
• n channel

conveyances leading up to and exiting below are not significantly blocked.

• High point in

channel will backwater NE 8th at lower flows (but not

• ver the road)

Existing Partial Blocked Culverts Early Action

Clearing channel vegetation is secondary in effectiveness because water can go overbank

200 400 600 800 1000 338 340 342 344 346 348 350

Allen Lake Feasibility Study 2011 Plan: 1) ExistingOct31 10/26/2011 2) Early Action 10/27/2011

Station (ft) Elevation (ft) Legend WS 30 cfs - ExistingOct31 WS 30 cfs - Early Action Ground Bank Sta .055 . 5 .055 100 200 300 400 500 600 700 800 338 340 342 344 346 348 350

Allen Lake Feasibility Study 2011 Plan: 1) ExistingOct31 10/26/2011 2) Early Action 10/27/2011

5573 - Newfeld Station (ft) Elevation (ft) Legend WS 30 cfs - ExistingOct31 WS 30 cfs - Early Action Ground Ineff Bank Sta .055 . 8 .08

Newfeld farm bridge 900 feet upstream

Low flow backwater conditions

Soft Sediment High Point

A local high point (WSEL of 341 ft) in soft sediment deposition will back up culverts under NE 8th St, locally controls lake levels during low flow conditions, but NOT the cause of

• vertopping.

1000 2000 3000 4000 5000 6000 7000 325 330 335 340 345 350

Allen Lake Feasibility Study 2011 Plan: 1) ExistingOct31 10/26/2011 2) Early Action 10/27/2011 3) DryNE8thSt 10/27/2011

Main Channel Distance (ft) Elevation (ft) Legend WS 30 cfs - ExistingOct31 WS 30 cfs - Early Action WS 30 cfs - DryNE8thSt Ground 634 634 Humphrey 755 755 Humphrey 862 D.S. side of 24... 935 244th Ave NE CP 935 - 2... 1103 1103 - Open Space 1337 1337 - Open Space 1607 1607- Begin new survey Ope... 1975 1975 - Last XS of 1995 Open Space 2335 2335 Hanley 2525 2525 Mertens 2665 2665 Christensen 2718 247th Ave Pl CMP 247th Ave NE (Pipe Arch 77x... 2804 MSPT LLC 2892 2897 Merged old survey, new, and LiDAR MSP... 2948.75 NE 18th St CMP NE 18th St (Pipe Arch 77x52) 3034.25 3034 Floyd 3180 Floyd 3263 3235 Floyd 3505 3505 Floyd 3895 3895 Ciliberti 3955 3955 - Ciliberti 4355 4335 Ciliberti 4522 Syn. 4667 Ciliberti 4667 4667 - Old Survey Lidar right bank Ciliberti 4730.5 4730 -Old Survey Ciliberti 4811 Syn. Lidar left bank, 5073 right bank, no sedime... 4944 Syn. channel similar to 5073 Michelman 5073 New Survey - Top of Sediment Michelman 5265 5265 - Old Survey Reimer 5370 Reimer 5435 5435 - Old Survey Newfeld 5497 5497 - copy of 5503 Newfeld 5573 5573 - Newfeld 5640.54* Newfeld 5714.72* Newfeld 5788.90* Roome 5891 Lucarelli 5969 U.S. of Footbridge Lucarelli 6051 Lucarelli 6148 Lucarelli 6212 McCoy 6319 McCoy 6391.16* McCoy 6459.83* McCoy 6547 NE 8th Street NE 8th Street (Culvert 18" and 30") RIVER-1 Reach-1

Existing, Early Action, Dry NE 8th St.

Existing Early Action Dry NE 8th

Summary

 Causes of NE 8th overtopping, are a combination of:

 Partial culvert blockages and sediment filling in  Low gradient (slope) of stream system  Culvert capacities  Vegetation reducing stream conveyance capacity

 Existing Conditions (at 30 cfs)

 Greater than 1.5 ft water over NE 8th St.  Sheet flows over Vitale driveway,  A few inches over Michelman’s,  An inch or so over Reimer/Roome,  Not overtopping Newfeld  December 2010 event was approximately a 10 to 25 year

event in magnitude.

Summary

Proposed Early Actions Results: Less than 6 inches over

NE 8th for that size event

 future 100-yr (39 cfs) overtops

NE 8th approx. 1.5 ft,

Make NE 8th dry for that size of event (aka Dry NE 8th St.) Results: NE 8th is dry (barely!) for that size event

 100 year overtops a few inches

Results are preliminary.