HomeMy WebLinkAboutBank Protection for BLD2008-00318 - BLD Engineering / Geo-tech Reports - 7/17/2008 July 17, 2008
Doug Neyhart
2297 Tahuya River Road
Tahuya, Washington
RE: Bank Protection for Property Located at 2297 Tahuya River
Road, Tahuya, Mason County, Washington
Dear Mr. Neyhart,
Envirotech Engineering completed an engineering assessment and design for the
referenced bank protection near the recently constructed bridge abutments. The bank
protection will consist of rock and riprap in order to reduce river bank erosion hazards
near the bridge abutments. Two design drawings are enclosed depicting the
recommended construction.
The size and extents of riprap used for this project exceed the guidelines provided in the
engineering circular "Design of Riprap Revetment" by the Federal Highways
Administration, March 1989. For this design, river geometry is based on a flow depth
exceeding the current 100yr— 24hr storm event. These guidelines estimate the median
stone size based on the average velocity of the river (estimated from Manning's equation
for open channel flow), average flow depth, riprap material's angle of repose, bank
angle, and a conservative stability factor based on floating debris. The following
parameters were used in the design:
• Manning's Coefficient= 0.035
• Slope= 0.62%
• River Depth = 6.5 feet
• Riprap angle of repose =45 deg
• Bank angle = 27 deg
• Stability factor= 2.0
The general flow pattern is depicted on the attached drawings. For the proposed
conditions, erosion potential due to the normal flow is resisted by a combination of
ecology blocks and riprap armoring.
River migration is a natural process, and may be directed towards the east bank. The
rate of migration is difficult to assess, and may not be detrimental during the design life
of the bridge abutments and the nearby existing barn. It is our opinion that the bank is
adequately protected in the interim. However, the bank protection design provided
should be implemented prior to the next wet season. Future maintenance may be
required periodically after intense rainfall. Inspection should be completed after every
large storm event, such as the 10yr-24hr storm event or greater. Maintenance should be
completed as soon as possible, if necessary. Maintenance may include replacing riprap
that have been dislodged or additional armoring. If necessary, design and extents of
additional armoring should be recommended by a professional engineer.
If you have any questions or need any further assistance, please call me at 360-275-
9374.
Sincerely,
Envirotech Engineering
Michael Staten, P.E.
Project Director
Page 2 of 2
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SCALE- 1 INCH = 10 FEET
to
89 FT
79 FT
EXISTING BRIDGE DECK
----300-YR ELEV 0
EXISTING REINFORCED (APPROX)
CONCRETE ABUTMENT (TYP)
— —100-YR ELEV V
PROPOSED 8' TO 12' (APPROX) 10 FT
RIPRAP, 2FT THICK
PROPOSED 8' 2 MIN
TO l2' RIP 1
RAP, 2 FT
THICK
— — — _ORDINARY HIGH 0
WATER ELEV
EXTRU ;V20499 C66M
CONCRETE
EXISTING OLD
ABUTMENT TO 3 F T PROPOSED TOE ROCK, I- TO
REMAIN 2-MAN IN SIZE
EXISTING
RIPRAP TO -40 FT �--- 2-3 FT
REMAIN
CROSS SECTION LOOKING UP-STREAM
1.5FT
4
1
PROJECT/ LOCATION,
BANK PROTECTION
SIDE VIEW 1 1 3FT
DOUG A 1
2297 TAHUYA RIVER ROAD
TAHUYA, WASHSHINGTON
DRAWN BY- DATE-
MCS 08/01/08 ENGINEER, 7,5 F T (--
DESIGNED BY, DATE-
Michael Staten, P.E. 08/01/08 ENVIROTECH ENGINEERING
74 NE HURD ROAD
SHEET BELFAIR, WASHINGTON 98528 SECTION A-A NTSGE PROTECTION
PHONE, (360) 275-9374
SHEET 1 OF 2 FAX, (360) 275-4789
�--30' STEPS PROPOSED /
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ECOLOGY PROPOSED TOE N
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EXISTING ECOLOGY BLOCKS
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BLOCKS MAY BE ADJUSTED
LANDWARD
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SECTI❑N B-B STEPPED ECOLOGY BLOCKS (T P)ESTEPPEDLOCKS
N T S TRANSITION. ALL ABOVE
ORDINARY HIGH WATER
EXISTING REINFORCED MARK
CONCRETE ABUTMENT (TYP)
PROPOSED 8'
TO 12' RIP
RAP, 2 FT
THICK
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EXISTING OLD
ABUTMENT 0
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11
> 12FT 12F
° ¢ o
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7FT MIN o
PROJECT/ LOCATION-
BANK PR❑TECTI❑N
TOP VIEW A
DOUG NEYHART
2297 TAHUYA RIVER ROAD PROPOSED 8'
TO 12' RIP
PROPOSED TOE ROCK, 1- TO
TAHUYA, WASHINGTON ,K2
2-MAN IN SIZE RAP C FT
DRAWN BY; DATES THI
MCS 08/01/08 ENGINEER- NEW ECOLOGY BLOCKS
DESIGNED BY+ DATE <TYP). VERTICAL
Michael Staten, P.E. 08/01/08 ENVIROTECH ENGINEERING
74 NE HURD ROAD
SHEET BELFAIR, WASHINGTON 98528
PHONE, C360> 275-9374
SHEET 2 OF 2 FAX- (360) 275-4789