Drainage Report#1A
24 NATIVE DRIVE–CONCEPT DRAINAGE REPORT-2/18/19
In response to the Town of Queensbury request for a Storm water management
calculation for the impact of the Tenant required Site Plan Modifications for the
existing 24 Native Drive Site , a drainage plan review assessment was prepared for the
proposed less than an acre area of disturbance review. The Proposed Sheet Labels Inc. is
a proposed isolated area fit up review of roughly 28,000 SF within the existing 115,892
SF PEMB shell at 24 Native Drive, situated on existing Site Plan of 14.28 Acre Site for
proposed minor dock and parking driveway improvements . The post development (.4
ac) storm area of the proposed northeastern side Site Entrance and parking area
currently drains via an existing CB network to the designated front SWM area of the
existing site. The Pre-development runoff area of can be protected with Sediment
Erosion Structure Inlet Controls of the existing CB’s, and silt fence at all adjacent
affected contours, and propose no change in sheet flow as an area volume of review .
Although the existing gravel driveway area is to be paved , by commercial standards, the
same sheet flow overland flow is conducted via previously paved pad areas surrounding
each catch basin. The proposed 19,098 SF area of disturbance currently drains to the
existing CB /SWM network so no re-sizing of the SWM area, or impacts to the side
entrance is anticipated. The proposal will have a negligible impact on the area , other than
improving what is proposed to satisfy the demand of an otherwise vacant building , by
the applicant and proposed Tenant.
On the proposed area of exterior of workon the west side , to comply with the Tenant
request for graded dock doors and drive –in truck area, the Site requires 23, 645 SF of
disturbance review to re-align the existing gravel fire lane and also proposes (3) isolated
Drywells to take the Dock runoff at the west rear location of the Site. Since the front
SWM pond discharge design points are more remote, the (3) Drywells are proposed
independent to the existing front drainage network . The Drywells are proposed to be
interconnected with an 8” equalizer pipe , each having an internal volume of 698 CF of
storage . These Drywells should address the immediate proposed graded are to
accomplish the Tenant dock area plan . The new SWM DW inlet protections and
proposed silt fence containing the area of work are proposed on (SP-1) and Site Details
and profiles of the DW’s on (SD-1 & SD-2) . The Goal#1 of proposed review will
retain the calculated 2,094 CF volume of accumulated Site Are Storage Volume at the
west side site work . SWM storage from runoff determined from the Fire lane upland,
as well as the drive door ramp and dock area pervious sheet flow drainage ,being
channeled to the improved fire lane contour elevation 384 to 380 inlet of the (3)
Drywells . The 8” PVC connector pipes will equalize flow and accumulate and transfer
runoff thru and to the (3) DW’s to receive the total proposed infiltration system of the
2,094 CF Volume of Storage .
Although the whole site area is (14.28 AC) , the western and eastern areas of work are
isolated at the rear and analyzed independently within a disturbed area review of less
than an acre combined between the west side and the east side . The West Rear Dock
drainage area is analyzed separately as it’s own discharge point to the 2,094 CF
Volume of Drywell storage . The SWM design point, having a disturbed area review of
23,645 sf: The longest time of drainage concentration was selected for the gravel
Driveway approach and Area along with the Fire lane and dock Grading Area, since
grading will be analyzed, assuming a gravel driveway with asphalt pads to remain. The
existing property Pre-Development area depicts the west (.54 Ac) site area draining the
area of proposed work , while the east draining with approximately ( .44 acres) . The
areas are relatively flat , although the west side fire lane is proposed to drain (-4’) change
in height in approximately 148 lf horizontal gravel fire lane (2.7% slope) at the West
Site. The existing fire lane at the East side is to be resurfaced with no grading cut
required , which is 2 Ft drop in 40 Ft horizontal , or 5% existing fire lane grade.The Site
Post Construction is proposed to be improved with a re-alignment of the fire lane around
the proposed docks on the west side and re-surface pavements at the existing gravel fire
lane on the East. post construction all disturbed areas proposed with stabilized lawn
slopes . The Pre & Post Development areas are calculated for the Time of Concentration
(Tc) analysis review for 25 year and 100 year storm events.
The purpose of this report is to establish an on-site storm water design which is
reasonable and consistent with the storm water management goals of the Town Of
Queensbury, to limit discharge within the site areas and preserve the existing
downstream slopes/ site from any erosion during development. Calculations analyzing
Pre-development and Post-development for a 25 year storm analysis are offered as a basis
design . Goal #2 analyzes Water Quality The Site is also noted to pass the Standard 1.5
gals /SF disturbed area calculation Review. The longest West sideTime of Concentration
analyses for Pre (Tc=8 Min.) was determined to be the west site area drainage path and
Post Development improved to (Tc=4.5 Min.) were utilized, assuming the developer
maintains the agreement to install an assumed graveldriveway . Similarly, longest East
sideTime of Concentration analyses for Pre (Tc=7.5 Min.) was determined to be the east
site area drainage path , after a paved condition, quickens the and Post Development
improved to (Tc=5.5 Min.) were utilized.. The methodology of the rational formula
calculations and the New York State charts are attached .
Existing Site West side Docks-25 yr (Pre) :
-Pre-developed- Site (Dock Area) is 152 LF of 4’(elevation 384 -380) over gravel
slope =2.7% (Tc=8 minutes off chart)
C=.8 analysis for overland flow:
-Therefore Tc= 8 minutes existing site, where
-coefficient total (c) =.8, undisturbed
-Drainage Dock Site Area Disturbance = 23,645 SF(.54ac)
-25 year storm tc off chart, I=4.7 inches/hour
-Q25 pre(Dock) Fire lane Site Existing =CIA=(.8)(4.7)(.54)=2.03 CFS Drainage
Site- Pre Development
Post Development 25 Yr.(Post):
-Post-developed-Dock Area, pervious sheet flows , improved storm control areas ,
(.54 acre) site drainage area to 380 CF SWM basin to be controlled .
C= Drive analysis, localized grading review toward DW’s , 23,645 SF(.54 ac)
-Drainage path Fire Lane (Tc=4.5 ) minutes .
-Most remote Tc tracked driveway site travel is 4.5 minutes
-Therefore Tc= 4.5 minutes proposed for revised graded driveway site analyzed
for the disturbed area. Rainfall Intensity is 5.3 inches /hour off 25 Hour Rainfall
Chart .
-1162 SF Asphal t Paved Apron (.024 ac), Site Gravel drive resurfaced (.516)
-25 year storm tc off chart =4.5 minutes Dock Area Drive Site, I=5.3 inches/hour
-Q25 post (Gravel Lane ) Dock Area Proposed =CIA=(.8) (5.3) (.516)=2.188 CFS
-Q25 post (Paved Apron ) Dock Area Proposed =CIA=(.9) (5.3) (.024)=.1145 CFS
-Sum of CFS at West Side Dock =2.3 CFS
Storage Volume Analysis is the difference between the existing and proposed 25 year
runoff volume
Qv pre=64(2.03 ) 60/2= 3,898 CF Volume pre- development 25 year –to Dock Area
Qv post=64(2.3)60/2= 4,416 CF Volume of post development 25 year-Dock Area –
with Paved Apron
The Delta Post Development Volume of Storage is 4,416 CF-3,898 CF=518 CF.
Volume of Storage is accommodated with the build out with the 1162 SF paved
apron at the (3) DW’s, , so the design runoff is addressed . Each 8Ft effective
drywell with the stabilized 5.5 minute perc rate , drains down in 528 minutes or
8.8 hours. The deep test pit depth by the Contractor was made early in October
anticipating the use of Drywells to satisfy the Tenant requirement for additional
Docks to inspect soils at a depth of 18 Ft to the bottom of the proposed DW
system Pit where no ground water was found . No additional drainage storage
proposed outside of the Drywell combined volume need be analyzed required
beyond the 2,094 CF is proposed as a reasonable management solution, to
address the 25 yr storage requirement .
Therefore, Goal #1 is addressed if Volume of Storage for infiltration SWM
Drywells at 5.5 min/inch is utilized to improve the Post Development Volume of
Storage of 2,094 CF at the West Side Dock Area, is actually more than the Pre-
Development condition of 518 CF requirement storage for 25 year analysis .
Existing Site East Side Fire lane (Pre) :
-Pre-developed- Site (Dock Area) is 118 LF of ’(elevation 385 -383) over gravel
slope =1.7% (Tc=7.5 minutes off chart)
C=.8 analysis for overland flow:
-Therefore Tc= 7.5 minutes existing site, where
-coefficient total (c) =.8, undisturbed
-Fire lane Site Area Disturbance = 19,098 SF(.44ac)
-25 year storm tc off chart, I=4.75 inches/hour
-Q25 pre East side Fire lane Site Existing =CIA=(.8)(4.75)(.19)=.722 CFS
Drainage Site- Pre Development
-Q25 pre East side lawn buffer Site Existing =CIA=(.3)(4.75)(.25)=.356 CFS
Drainage Site- Pre Development
-Sum of Pre-CFS 25 Yr. =1.078 CFS
Post Development (Post):
-Post-developed-East side Fire Lane Area, pervious sheet flows , improved storm
control areas , (.44 acre) site drainage area to catch basin to be controlled .
C= Drive analysis, localized grading review toward , 19,098 SF(.44 ac)
-Drainage path Fire Lane (Tc=5.5 ) minutes .
-Most remote Tc tracked fire lane site travel is 5.5 minutes
-Therefore Tc= 5.5 minutes proposed for revised graded driveway site analyzed
for the disturbed area. Rainfall Intensity is 5.1 inches /hour off 25 Hour Rainfall
Chart .
-12,763 SF Asphal t & Concrete Dr. pad (.293 ac), Site Gravel drive resurfaced
with Pavement
-25 year storm tc off chart =5.5 minutes Fire lane Site, I=5.1 inches/hour
-Q25 post (Paved) Fire lane Area Proposed =CIA=(.9) (5.1) (.29)=1.33 CFS
-Q25 post (Lawn Buffer ) Fire lane Proposed =CIA=(.3) (5.1) (.145)=.22 CFS
-Sum of CFS at East Side Fire Lane =1.55 CFS
Storage Volume Analysis is the difference between the existing and proposed 25 year
runoff volume
Qv pre=64(1.078 ) 60/2= 2,070 CF Volume pre- development 25 year –to East
SideArea
Qv post=64(1.55)60/2= 2,976 CF Volume of post development 25 year-Fire lane
Area –with Pavements
The Delta Post Development Volume of Storage is 2,976 CF less 2,070CF=906
CF.Volume of Storage is accommodated with the build out with pavement at
the fire lane . Since the original design runoff area has not changed , and was
previously designed for pavement , no improvements , other than new
landscaping in the buffer is being proposed .Although drywells were not tested
on the east side, if (2) 8Ft effective drywells were proposed , assuming the
tested same stabilized 5.5 minute perc rate , an additional 1396 CF Volume of
Storage could be proposed within the area of the diagonal parking to address
the increase in pavement at the area of improvement, additional 906 CF
determined Volume of Storage , or additional grading within the already sized
SWM Basin could be proposed as mitigation , but seems contrary to what had
already been designed which exists . No additional drainage storage proposed
outside of the preexisting SWM basin is proposed as a reasonable management
solution. Although the Contractor may consider scraping (.33’) or 4” off of the
bottom of the existing 3616 SF SWM Basin which would offset the Drainage
Volume By 1,194 CF > 906 CF required (which should also address the 50yr.
Therefore, Goal #1 at the east side Fire Lane is to improve with pavement with
no additional SWM infiltration .
, Analysis Goal #2 summary is as follows:
If Goal #2 is required with a Water Quality (WQv to be reviewed. WQv=CPA/12,
where .8 runoff coefficient was established within the statistic for gravel drive
impacts, where the regional target 90% rule rainfall is (1”) , where the disturbed area
is (23,645-.54 ac’s). Therefore WQv={(.8)(1)(23,645)}/12=1576 CF .
The current rear yard infiltration SWM design is 2,094 CF +- ,which is greater than
1576 CF , WQv for the West Side Dock Area Review . No additional improvements
for water quality other than continued maintenance and landscaping is proposed on
the East side Fire lane . See supplemental handout for Eastside Fire Lane.
Lastly, proposed SWM Basin Sizing proposed on application as a Standard for
Warren County Region , being generally accepted is 1.5 Gals/SF Area of Disturbed
Impervious Calculated. Assuming West Side dock area is partially paved around the
(3) Drywells the 1162 SF Impact X 1.5 Gals=1743 Gals Min. Volume/ 7.48 Gals
/CF=233 CF Minimum Storage Volume For the proposed west side development.
The Provided Volume Of Storage for the Project is 2,094 CF , At the West side Dock
Area , having mostly reserve potential given the other scenario reviews that were
explored for this project, all passing . Given the tests for a stabilized less than .5
minute percolation rate of the soil for drywells , each drywell at the 8Ft depth (96
inches )X .5 minutes =48minutes/ 60 =.8 hours to drain . No additional
improvements for water quality other than continued maintenance and landscaping
is proposed on the East side Fire lane at this time , unless the Contractor is required to
remove up to 12” of existing SWM Basin and Reseed until stabilized . . See
supplemental handout for Eastside Fire Lane.
,Warren County having pond sizing review for less 1 acre disturbance review
should not require any further protection to
accommodate drainage discharge for the developed site areas .
If analyzed 50 Yr. Storm per Chazen Comments :
Existing Site West side Docks-50 yr (Pre) :
-Pre-developed- Site (Dock Area) is 152 LF of 4’(elevation 384 -380) over gravel
slope =2.7% (Tc=8 minutes off chart)
C=.8 analysis for overland flow:
-Therefore Tc= 8 minutes existing site, where
-coefficient total (c) =.8, undisturbed
-Drainage Dock Site Area Disturbance = 23,645 SF(.54ac)
-50 year storm tc off chart, I=6.2 inches/hour
-Q50 pre(Dock) Fire lane Site Existing =CIA=(.8)(6.2)(.54)=2.68 CFS Drainage
Site- Pre Development
Post Development Westside Docks-50 Yr.(Post):
-Post-developed-Dock Area, pervious sheet flows , improved storm control areas ,
(.54 acre) site drainage area to 380 CF SWM basin to be controlled .
C= Drive analysis, localized grading review toward DW’s , 23,645 SF(.54 ac)
-Drainage path Fire Lane (Tc=4.5 ) minutes .
-Most remote Tc tracked driveway site travel is 4.5 minutes
-Therefore Tc= 4.5 minutes proposed for revised graded driveway site analyzed
for the disturbed area. Rainfall Intensity is 5.6 inches /hour off 50Hour Rainfall
Chart .
-1162 SF Asphal t Paved Apron (.024 ac), Site Gravel drive resurfaced (.516)
-50 year storm tc off chart =4.5 minutes Dock Area Drive Site, I=5.6 inches/hour
-Q50 post (Gravel Lane ) Dock Area Proposed =CIA=(.8) (5.6) (.516)=2.31 CFS
-Q50 post (Paved Apron ) Dock Area Proposed =CIA=(.9) (5.6) (.024)=.12 CFS
-Sum of CFS at West Side Dock =2.43 CFS
Storage Volume Analysis is the difference between the existing and proposed 25 year
runoff volume
Qv pre=64(2.68 ) 60/2= 5,146 CF Volume pre- development 50 year –to Dock Area
Qv post=64(2.43)60/2= 4,666 CF Volume of post development 50 year-Dock Area –
with Paved Apron
Storage Volume Analysis is the difference between the existing and proposed 50
year runoff volume. Volume Post is actually less than pre-Development , but the
Storage Volume delta is 480 CF. The Storage Volume of the proposed Drywells
is 2,094 CF
If analyzed 50 Yr. Storm per Chazen Comments :
Existing Site East Side Fire lane (Pre) :
-Pre-developed- Site (Dock Area) is 118 LF of ’(elevation 385 -383) over gravel
slope =1.7% (Tc=7.5 minutes off chart)
C=.8 analysis for overland flow:
-Therefore Tc= 7.5 minutes existing site, where
-coefficient total (c) =.8, undisturbed
-Fire lane Site Area Disturbance = 19,098 SF(.44ac)
-50 year storm tc off chart, I=5.65 inches/hour
-Q50 pre East side Fire lane Site Existing =CIA=(.8)(5.65)(.19)=.859 CFS
Drainage Site- Pre Development
-Q50 pre East side lawn buffer Site Existing =CIA=(.3)(5.65)(.25)=.424 CFS
Drainage Site- Pre Development
-Sum of Pre-CFS 25 Yr. =1.28 CFS
Post Development (Post):
-Post-developed-East side Fire Lane Area, pervious sheet flows , improved storm
control areas , (.44 acre) site drainage area to catch basin to be controlled .
C= Drive analysis, localized grading review toward , 19,098 SF(.44 ac)
-Drainage path Fire Lane (Tc=5.5 ) minutes .
-Most remote Tc tracked fire lane site travel is 5.5 minutes
-Therefore Tc= 5.5 minutes proposed for revised graded driveway site analyzed
for the disturbed area. Rainfall Intensity is 6.05 inches/hour off 50 Hour
Rainfall Chart .
-12,763 SF Asphal t & Concrete Dr. pad (.293 ac), Site Gravel drive resurfaced
with Pavement
-50 year storm tc off chart =5.5 minutes Fire lane Site, I=6.05 inches/hour
-Q50 post (Paved) Fire lane Area Proposed =CIA=(.9) (6.05) (.29)=1.58 CFS
-Q50 post (Lawn Buffer ) Fire lane Proposed =CIA=(.3) (6.05) (.145)=.263 CFS
-Sum of CFS at East Side Fire Lane =1.84 CFS
Storage Volume Analysis is the difference between the existing and proposed 50 year
runoff volume
Qv pre=64(1.28 ) 60/2= 2,458 CF Volume pre- development 50 year –to East
SideArea
Qv post=64(1.84)60/2= 3,532 CF Volume of post development 50 year-Fire lane
Area –with Pavements
Storage Volume Analysis is the difference between the existing and proposed 50
year runoff volume. Volume Post is greater than pre-Development , (3532-2458)
Storage Volume delta is 1,074 CF. The Storage Volume of the Original Pond
Scrape down and seed 12”. (3617 SF X FT=3617 CF)