Denton Co Levee-CS120412MEMORANDUM
TO:
Board of Directors
Denton County Levee Improvement District Rio. 1
FROM:
Russell Erskine, PE 409e
Mathew L. Busby, EIT
EMAIL:
rerskine @halff.com
rnbusby@halff.com
SUBJECT:
Denton Creek Outfall Erosion Protection
t-tatff Associates, Inc.
12011 North Bowser Road
Richardson. Texas 75081
(214) 346 -6200
Fax (214) 739 -0095
DATE. April 12, 2012
AVO: 28540
Attached is a cost: estimate for implementing erosion protection at several outfalls along Denton Creek,
between MacArthur Boulevard and Denton Tap Road_ Recommendations are based on field observations
conducted on January 17, 2012 and April 10, 2012.
Headwalls located below the normal water surface do not exhibit significant signs of erasion. headwalls
located above the normal water surface could be removed and replaced at a lower elevation to reduce
erosion.
in lieu of this extensive replacement, Halff prepared an estimate for controlling erosion using riprap and
Scour Stop, a vegetated riprap alternative. Scour Stop is used in relatively flat areas with established
vegetation that, with reinforcement, will sustain erosive forces, Riprap is used in areas where velocities
are higher and periods of inundation are longer. Size is based on flow velocities. Riprap size is described
using the median diameter (Dw) of stone to be installed. The riprap layer thickness is based an a depth
twice the median diameter, The stone used for riprap will need to he well - graded for long -term integrity of
the riprap blanket. Geotextile is used for soil separation beneath the riprap. Proper installation of the
riprap is important to longevity.
Before installing erosion protection, existing erosion damage will need to be repaired. In areas where a
structure has been undermined and compaction would be difficult, self - compacting Plowable fill is
recommended to backfill the existing eroded area. Other areas should be backfilled with a cohesive soil
and adequately compacted.
Ouffall. 6 showed more significant structural darnage than the other outfalls. See attached maps for
location. A site visit revealed separation in the pipe joint connecting to the outfall (approximately 2" gap)
as well as a sinkhole near the top of the outfall. This outfall should be reconstructed. it is recommended
that the outfall be located at or below the normal water surface to reduce erosion. Construction below the
water level involves special considerations, such as coffer dams, during construction.
PROJECT* DCLID OUTFALL EROSION PROTECTION
HALFF ASSOCIATES, INC.
PREPARED BY. MLB
AVO: 28544
CHECKED BY. RE
•
PLAN
ITEMS NO. ITEM DESCRIPTION
UNIT
QTY.
UNIT PRICE
BID ESTIMATE
1 18 "ROCK RIP RAP
CY
1 18
87.00
S
7,566.00
2 GEOTEXTILE {8 oz minimum)
5Y
37
1A0
5
37.00
TOTAL:
11
OUTFALL
PLAN
ITEM NO. ITEM DESCRIPTION
UNIT
QTY.
UNIT PRICE
810 EM MATE
1 18" ROCK RSPRAP
CY
53
$
87.00
S
4.611.00
2 24" ROCK RIPRAP
CY
95
$
75.00
$
7.125.00
3 FLOWABLE FILL
CY
5
$
78.00
$
390.00
4 GEOTEXTILE f8 ox. minimum
SY
195
$
1.00
$
195.00
TOTAL
11
a
PLAN
ITEM NO. ITEM DESCRIPTION
UNIT
(QTY.
UNIT PRICE
SID ESTIMATE
1 78" ROCK RIPRAP
CY
67
$
87.001$
5,829.00
2 FLOWABLE FILL
CY
5
$
78.00
$
390.00
3 GEOTESCTILE fA oz, n-liftuaLl
SY
I i
$
i.00
t $
98.00
TOTAL
F1
a
PLAN
ITEM: NO. ITEM DESCRIPTION
UNIT
QTY.
UNIT PRICE
BID ESTIMATE
1 FILL (95% COMPACTION)
CY
s
$
14.00
$
70.00
2 SCOURSTOP MAX
EA
30
$
64.00
$
1,920.00
3 SCOURSTOP ANCHORS
EA
150
$
2.00
$
300.00
4 GEOTEXTH-E 8 oz. minimum
SY
55
$
1.00
$
55.00
TOTAL
FI
OUTFALL
PLAN
ITEM NO. ITEM Dl;Sl RIPTION
UNIT
QTY.
UNIT PRICE
B
1 FILL (95 %a COMPACTION)
CY
5
$
14.00
2 SCOURSTOP MAT
EA
30
$
64.00
3 SCOURSTOP ANCHORS
EA
150
S
2.00
4 GEOTEXTILE 8 oz. minimum
SY
55
$
1.00
TOTAL
11
• UTFALL 6 (RE MOVE AN t REPLAC E)
PLAT!
ITEM NO. ITEM DESCRIPTION
UNIT
QTY.
UNIT PRICE
BID ESTIEATE
1 REMOVE EMS TING ttOU ALL
EA
7 is
400.00
$
400.00
2 42" CLASS III RCP
LF
90
$
90.00
$
8.700.00
3 SLOPED END SECTION 4:1
EA
1
2,750.00
S
2,750.00
TOTAL
1,25o .Do
PLAN
ITEM NO. ITEM DESCRIPTION
UNIT
QTY,
UNIT PRICE
BID ESTIMATE
1 FILL {950/. COMPACTION)
CY
10
14.00
4151,01)
2 24" ROCK RIPRAP
CY
36
$
75.00
S
2,7
3 GEOTEXTILE $ 4Z minimum
SY
55
$
1.00
S
s
2,895.00
SUBTOTAL
$
39,076.00
i
1',
li
OVERALLTOTAL
$
47,000.00
Ttiis statement was prepared utilizing standard cost and/or estimating practises. It is understood and agreed that this is a statement of
probable construction cost only, and the Engineer small not be liable to the Owner or anyThird Party for
any failure to accurately estimate
the cost and/or quantities for the project, or any part thereof.
Notes.
1. Excludes professional engineering fees.
2. Excludes surrey fees for easements by separate instrument or R.O.W. dedication
3. Excludes relocation of any franchise utilities (to be determined)
•" THIS SHEET
None
fvlade by
HALFF'
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Date Dept. Show No.
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1470
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