HomeMy WebLinkAboutFile Documents.287 McSkimming Rd.0044.2018 (34).ARBK1
Drainage Report
287 MCSKIMMING RD
ASPEN, CO 81611
August 17, 2017
Prepared by
Richard Goulding, P.E.
Roaring Fork Engineering
592 Highway 133
Carbondale, CO 81623
09/26/2017
Reviewed by Engineering
12/18/2017 4:35:25 PM
"It should be known that this review shall not
relieve the applicant of their responsibility to
comply with the requirements of the City of
Aspen. The review and approval by the City is
offered only to assist the applicant's
understanding of the applicable Engineering
requirements." The issuance of a permit based
on construction documents and other data shall
not prevent the City of Aspen from requiring the
correction of errors in the construction
documents and other data.
2
Drainage Report
287 MCSKIMMING RD
ASPEN, CO 81611
I HEREBY AFFIRM THAT THIS REPORT FOR THE IMPROVEMENTS AT 287 MCSKIMMING ROAD WAS
PREPARED BY ME FOR THE OWNERS THEREOF IN ACCORDANCE WITH THE PROVISIONS OF THE CITY
OF ASPEN URBAN RUNOFF MANAGEMENT PLAN AND APPROVED VARIANCES AND EXCEPTIONS
LISTED THERETO. I UNDERSTAND THAT IT IS THE POLICY OF THE CITY OF ASPEN THAT THE CITY
OF ASPEN DOES NOT AND WILL NOT ASSUME LIABILITY FOR DRAINAGE FACILITIES DESIGNED BY
OTHERS.
RICHARD GOULDING, P.E.
RFE Project # 2017-04
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Table of Contents
1.0 General .................................................................................................................................................... 4
1.1 Existing Site ........................................................................................................................................ 4
1.2 Proposed Conditions ........................................................................................................................... 4
1.3 Previous Drainage Studies .................................................................................................................. 4
1.4 Offsite Drainage & Constraints ..................................................................................................... 5
1.5 Existing Easements .............................................................................................................................. 6
2.0 Drainage Basins and Sub-basins ............................................................................................................. 6
2.1 Drainage Basins .................................................................................................................................. 6
2.2 Peak Discharge Calculations ............................................................................................................... 7
3.0 Low Impact Site Design .......................................................................................................................... 9
3.1 Principles............................................................................................................................................. 9
4.0 Hydrological Criteria ............................................................................................................................ 10
4.1 Storm Recurrence and Rainfall ......................................................................................................... 10
4.2 Storage Volumes Methodology ........................................................................................................ 10
5.0 Hydraulic Criteria ................................................................................................................................. 12
5.1 Inlets .................................................................................................................................................. 12
5.2 Pipes .................................................................................................................................................. 14
5.3 Outlet Structure ................................................................................................................................ 15
5.4 Rip Rap Sizing .................................................................................................................................... 16
6.0 Proposed Facilities ................................................................................................................................ 16
6.1 Proposed structures ........................................................................................................................... 16
6.2 Infiltration ......................................................................................................................................... 17
6.2.1 Drywell ...................................................................................................................................... 17
7.0 Operation and Maintenance .................................................................................................................. 17
7.1 Drywell ............................................................................................................................................. 17
8.0 Appendices ............................................................................................................................................ 19
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1.0 General
1.1 Existing Site
The residence under evaluation is located at 287 McSkimming Road in Aspen, Colorado. This property is
a 0.813 acre (35,075 square feet) parcel and is located within the Smuggler/Hunter Drainage Basin. The
site is currently undeveloped. The site is bounded by Skimming Lane to the Northwest, 521 McSkimming
Road to the Northeast, McSkimming Road to the Southeast and 283 McSkimming Road to the Southwest.
The existing vegetation on this lot includes aspen and pine trees of various sizes and native grasses and
shrubs.
HP Geotech (now known as HP Kumar) completed a subsoil study for this lot on December 5, 2005 and
completed a site visit and update to this study on March 5, 2013. Per the consultation, the subsurface
conditions for the site consists of sand and gravel that is silty with cobbles and possible boulders. A
percolation test completed on July 10, 2017 showed a percolation rate of 4 minutes per inch for the soil on
this site.
1.2 Proposed Conditions
This project is classified as a βMajor Projectβ as per Table 1.1 of the URMP. The proposed development is
over 1000 square feet (sf) and disturbs an area of approximately 16,893 sf., roughly 48% of the site. The
intent of this report is to demonstrate compliance with the requirements of the URMP. The Low Impact
Design (LID) Principles in the introduction of the manual were used as a guide throughout the design
process.
The proposed project consists of the construction of a two-story, single family residence with multiple
patios, a spa and a snow melted driveway and walkway. There are a number of plantings and landscaped
areas associated with this project as well.
The runoff from impervious surfaces will be collected through a system of swales and inlets, roof drains,
and a trench drain that are all routed to a drywell located to the northwest of the building. Refer to sheet
C-106 of the civil set for the proposed grading and drainage of this site.
1.3 Previous Drainage Studies
This property is within the blue mudflow area as defined by the COA Urban Runoff Management Plan
mudflow maps, or an area within 200 feet of slopes greater than 30%. RFE met with April Long and Jack
Danneberg of the City of Aspen Engineering Department during the week of February 6, 2017 to discuss
this mudflow zone. During this meeting we were informed that this area would be removed from being
considered a mudflow concern on the updated mudflow maps that the city is in the process of adopting.
Additionally, HP Kumar performed an evaluation of the site and surrounding conditions for this property
in order to determine if the area was a risk for mud or debris flows. Through their evaluation, HP Kumar
concluded that this lot does not have a credible risk for debris or mudflows and that a further analysis, in
their opinion, is not warranted. A stamped letter stating this opinion has been included with this drainage
report. Based on these facts, a mudflow analysis was not conducted for this site.
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The city of Aspen provided us with two previous drainage reports that included this property in their
offsite analysis. The first drainage report was completed by High Country Engineering on October 23,
2009 and reviewed on Mar 30, 2010. The work considered in this drainage report included improvements
to Skimming Lane. The second drainage report was completed by Sopris Engineering on July 16, 2014
and reviewed on September 18, 2010. This drainage report was completed for the Access and
Infrastructure Permit for 189 Skimming Lane. These drainage reports were referenced when considering
offsite flows from the site and how they are dealt with downstream.
1.4 Offsite Drainage & Constraints
There is a single offsite basin to the northeast that flows onto this property (see sheet C-103 for the
delineation of this basin). This offsite basin consists of an undeveloped hillside that is vegetated primarily
with native grasses, shrubs and some trees. Since this basin is primarily located outside of the soil map
provided in the URMP, an analysis was performed using the National Resources Conservation Service
(NRCS) web soil survey online software. Based on the findings of this analysis, which can be found in
the appendices of this report, the primary soil type within this basin can be classified as Hydrological Soil
Group A. The below tables show the calculated size, time of concentration and the 100-year peak flow
rate from this basin.
The runoff from this basin will be captured by a large swale that runs along the eastern and northeastern
edge of the property. This swale collects runoff from both on and offsite; however, the inlet located in the
depression at the northeastern end of this swale has been sized to only convey the on-site runoff volume.
In the event of a major storm, the offsite runoff will bypass this inlet and will be released onto the hillside
following its current historic runoff path towards Skimming Lane. Rip-rap will be placed at the outfall of
this swale to protect the slope at this location from erosion and to reduce the velocity of the flow below 7
ft/s (see section 5.4 for a discussion of the procedure used to size this rip-rap).
Overland Flow Time (To)
(Eq. 3-4 from URPM)
Channelized Flow Time (Tf )
(Eq. 3-5 from URPM)
Top Elevation 9312 ft.Channelized Flow Y Y or N
Bottom Elevation 9150 ft.Top Elevation 9150 ft.
Overland Distance (Lo)500 ft.Bottom Elevation 8116 ft.
Slope (So)0.324 ft./ft.Channelized Distance (Lf )2700 ft.
5 Year Runoff Coefficient, C 0.00 5 yr. runoff coeff. for basin Slope (S f)0.383 ft./ft.
Overland Flow Time (To)14.09 Min.Conveyance Coefficient (K )4.5 From Table 3-3
Flow Velocity (V f )2.78 ft/s
Channelized Flow Time (Tf )16.16 Min.
Time of Concentration (Tc)30.25 min
Time of Concentration Offsite Basin 1
Only valid for 300ft of developed area or 500ft
of rural area
Only valid for 300ft of developed area or 500ft
of rural area
Offsite 100 Year Peak Discharge Developed Calculations
1 Hour(P1)1.23
Return Period 100
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 752540.00 272.00 0.04%0.200 30.25 2.24 7.74
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The runoff from this offsite basin, as well as that from the onsite basin, will flow downhill towards
Skimming lane following the historic pattern of this site. This runoff will flow over an existing soil nail
wall along the Eastern edge of Skimming Lane and will be captured by the eastern roadside swale. This
roadside swale slopes towards an inlet located at the Eastern corner of 189 Skimming Road that connects
to an existing drywell. As discussed in the drainage report completed by High Country Engineering, if the
capacity of this drywell were to be exceeded, additional runoff would surcharge the roadside swale and
sheet flow across the road towards the slope on the western side matching the historical pattern.
1.5 Existing Easements
An existing waterline easement of varying width runs along the Eastern and Northeastern property lines
of this site. The eastern swale, which collects on and offsite stormwater, crosses into this easement
resulting in some proposed grading within the easement. All grading activity will occur 5 feet or more off
of the surveyed waterline and will not reduce the depth of cover over it. Additionally, since no trees or
shrubs will be planted within 10 feet of the waterline, access to this easement will not be affected by the
proposed development.
2.0 Drainage Basins and Sub-basins
The site can be considered a single onsite basin with a point of concentration located at the propose
drywell, which can then be subdivided into smaller sub-basins. Basin and Sub-basin delineations are
shown on sheet C-104 and C-105 of the civil permit drawings. These sheets list impervious areas, runoff
coefficients, peak flows, and the required volume of runoff to be detained. The sub-basins were created to
calculate the concentrated flow from each impervious area, including patios, decks and roofs. These sub-
basin peak flows were then used to size the proposed infrastructure.
2.1 Drainage Basins
Basin 1 is the only major basin on site and consist of the entire disturb area from the construction of the
proposed residence and associated landscaping. This basin has a total area of 16,893 square feet (sf) and
is 54% impervious. Impervious sections of the basin include the roof structure, patios, walkways and the
driveway. The remainder of the basin is made up of pervious landscaped areas that surround the
residence. This basin was divided into a total of 9 sub-basins.
Sub-basin 1.1 collects runoff from the southwestern portion of the roof structure, the northwestern
portion of the driveway and surrounding landscaped areas. The runoff from this sub-basin is collected by
a series of swales that feed to an inlet. These swales will serve as a form of water quality control to treat
the driveway runoff before it enters the storm system, avoiding the need for a sand oil separator.
Sub-basin 1.2 consists of the southeastern portion of the driveway and adjacent landscaping. The runoff
from this basin is collected by a swale and trench drain which connect to a single inlet. As discussed
above, this swale will function as a form of water quality treatment for the driveway runoff.
Sub-basin 1.3 consists of the remainder of the roof structure, the front walkway, two patios along the
northeastern side of the building and the surrounding landscaped area. The runoff from this sub-basin is
collected by a large swale along the eastern and northeastern edge of the disturbed area which then feeds
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to a single inlet at the northeastern end of the swale. This swale also collects runoff from the offsite basin;
however, the inlet is only designed with enough capacity for the onsite runoff, and the remaining offsite
flow will bypass this inlet and will be released onto the hillside during larger storms.
Sub-basins 1.4 through 1.9 consist of portions of the back patio and each have a single inlet associated
with them.
All inlets connect into a storm system that drains to a drywell located to the northwest of the rear patio.
This drywell is 6 ft. in diameter and 11.5 ft deep (rim elevation to sump elevation).
2.2 Peak Discharge Calculations
The peak flows were calculated for the Major Basin for 5 and 100 year storm events using the Rational
Method. The Rational Method is an acceptable method to calculate runoff for this basin as the area is
under 90 acres. Rainfall intensity was calculated using a Time of Concentration (Td) of 5 minutes. The
actual time of concentration for this site is less than 5 minutes, but according to the City of Aspen URMP,
equations used to calculate rainfall intensity are only valid for a time of concentration of 5 minutes or
greater so the smallest valid time of concentration value was used. The 1 hour Rainfall depths (P1) used
for these calculations was taken from Table 2.2 of the URMP and is equal to 0.64 inches for the 5-year
event and 1.23 inches for the 100-year event. Equation 2.1 was referenced when solving for the Rainfall
Intensity (I).
π°= ππ.π π·π
(ππ+π»π )π.πππ (πΆπππποΏ½βππ 2.1)
Runoff Coefficients (C), a function of the Soil Group (in this case B for the onsite basin) and the
percentage of impervious area within each sub basin were developed using Figure 3.3. The Runoff
Coefficient (C) was then multiplied by the Rainfall Intensity (I) and the area of the Major Basin (A, in
acres) to determine the peak discharge.
π·π=πͺπ°π¨
ππ=ππππ πΆοΏ½βπποΏ½ππππ (πππ)
πΆ=ππππππ πΆπππποΏ½βποΏ½βπππ
οΏ½ =πποΏ½βπππππ οΏ½ ππππποΏ½βππ¦ (οΏ½βπποΏ½ππ πππ οΏ½πππ)
π΄=π΄πππ (πππππ)
These peak flow values were used to calculate the size of the proposed detention and conveyance
structures, such as drywells, inlets and pipes. The tables below contain the peak flows for developed and
undeveloped conditions for 5 and 100 year storm events for the major basin, and the 100 year peak flow
rate for the sub basins.
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5 Year Peak Discharge Developed Calculations
1 Hour(P1)0.64
Return Period 5
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 16893.00 9199.00 54.45%0.350 5 3.29 0.45
5 Year Peak Discharge Pre Development Calculations
1 Hour(P1)0.64
Return Period 5
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 16893.00 0.00 0.00%0.080 5 3.29 0.102
100 Year Peak Discharge Developed Calculations
1 Hour(P1)1.23
Return Period 100
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 16893.00 9199.00 54.45%0.520 5 6.33 1.28
100 Year Peak Discharge Pre Development Calculations
1 Hour(P1)1.23
Return Period 100
Basin ID Total Area Imp. Area Impervious C Value Time of C Intensity Q Max
See(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)
1 16893.00 0.00 0.00%0.350 5 6.33 0.859
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3.0 Low Impact Site Design
Low Impact Development (LID) aims to mimic the natural pre-development hydrologic pattern. The goal
is to manage storm water as close to its source as is possible. This entire developed site is approximately
54% impervious. The treatment train approach is used on all runoff to increase water quality and
percolation.
3.1 Principles
Principle 1: Consider storm water quality needs early in the design process.
The Grading and Drainage design was coordinated between the architect, landscape architect and civil
engineering teams throughout the design process and water quality requirements were discussed early on.
Multiple site visits ensured proper understanding of existing conflicts and opportunities to improve
existing drainage patterns.
Principle 2: Use the entire site when planning for storm water quality treatment.
Storm water quality was considered in the design of every part of the site that is being affected by the
proposed construction. A system of swales was incorporated into the site to collect the vast majority of
the onsite runoff.
Principle 3: Avoid unnecessary impervious area.
The total impervious area on the site was kept to a minimum while meeting the architectural design goals
by incorporating pervious landscaped areas throughout the site.
Principle 4: Reduce runoff rates and volumes to more closely match natural conditions.
All runoff from impervious surfaces on the property is collected and routed to a drywell. This drywell has
been sized to capture and infiltrate the WQCV and to detain the 100-year runoff volume and release it at
100 Year Sub Basin Peak Discharge Developed Calculations
1 Hour(P1)1.23
Return Period 100
Sub Basin Total Area Imp. Area Impervious C Value Time of C Intensity Sub Basin Flow Rate
(Name)At (ft2)Ai (ft2)Ai/At (%)From Table (Td)I=88.8P1/(10+Td)01.052 Qsub (ft3/sec)
1.1 3165.00 2136.00 67.49%0.590 5 6.33 0.27
1.2 1597.00 1068.00 66.88%0.590 5 6.33 0.14
1.3 7729.00 4132.00 53.46%0.520 5 6.33 0.58
1.4 905.00 687.00 75.91%0.650 5 6.33 0.09
1.5 99.60 18.40 18.47%0.430 5 6.33 0.01
1.6 245.00 135.00 55.10%0.540 5 6.33 0.02
1.7 122.00 55.60 45.57%0.510 5 6.33 0.01
1.8 142.00 142.00 100.00%0.950 5 6.33 0.02
1.9 162.00 92.60 57.16%0.540 5 6.33 0.01
1.3A 260.00 260.00 100.00%0.950 5 6.33 0.04
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the historic peak flow rate for the site. The release point for the drywell has been designed to match the
natural condition of the site.
Principle 5: Integrate storm water quality management and flood control.
The use of swales to collect runoff and a drywell for storage acts to integrate water quality BMPs with
flood control methods.
Principle 6: Develop storm water quality facilities that enhance the site, the community and the
environment.
The use of the two-chambered drywell for water quality reduces the runoff of sediment and contaminants
from the site. This reduces the siteβs effect on the Roaring Fork River and the community.
Principle 7: Use treatment train approach.
The combination of swales, which collect the vast majority of the runoff from the site, that eventually
connect to a drywell serves as a treatment train that adds two levels of treatment to storm water from the
site.
Principle 8: Design sustainable facilities that can be safely maintained.
Inlets and piping will be vacuumed or flushed periodically to maintain adequate flow. Proper grading
reduces dangerous slopes and proper drainage to reduce ice buildup. The drywell will be easily
accessible for maintenance.
Principle 9: Design and maintain facilities with public safety in mind.
Proper drainage and grading of the driveway, walkway and patios reduces ice buildup and dangerous icy
conditions. All grading was done with safety in mind.
4.0 Hydrological Criteria
4.1 Storm Recurrence and Rainfall
The property is located outside of the commercial core and isnβt served by any storm system so this
property classifies as a βSub-urban area not served by public storm sewerβ. Therefore, the storm
system for the site was designed to meet detention requirements for the 5 and 100-year historical storm
events.
The 1 hour Rainfall depth (P1) is given in Table 2.2 as 0.64 inches for the 5-year event and 1.23 inches for
the 100-year event. The Intensity in inches per hour for different storm duration (Td) was calculated using
Equation 2.1 from the City of Aspen URMP.
4.2 Storage Volumes Methodology
The storage requirements for this site were calculated using the total impervious area along with the
historic and developed peak runoff rates that were established in section 2.2. Based on the requirements in
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the URMP for this development, the total storm water storage volume for this site must satisfy both the
Water Quality Capture Volume (WQCV) and the modified FAA storage volume. The modified FAA
method was performed for the 5 and 100-year events using the historic peak flow rate for the onsite basin.
This storage volume was then added to the calculated WQCV to get the total storage volume. The below
tables summarize these calculations.
5 Year Modified FAA Storage Calculation - Basin 1
Rainfall Duration
(minutes)
Intensity (inches/Hour)
EQ 5-1 Volume In ft3 EQ 5-2 Volume Out ft3 EQ 5-3
Volume Difference
ft3 EQ 5-4 C 0.350
(Td)I=88.8P1/(10+Td)1.052 Vi=(1/720)*C*I*Td*A Vo=30(1+Tc/Td)*Qa*Td Vd=Vi-Vo A 16893.00 ft2
5 3.29 135.13 30.63 104.50 Tc 5 min
8 2.72 178.48 39.82 138.65 Qa 0.102 cfs
11 2.31 208.67 49.01 159.66 P1(5)0.64 in
14 2.01 230.77 58.20 172.57
17 1.77 247.57 67.39 180.17
20 1.59 260.70 76.58 184.12
23 1.44 271.20 85.77 185.43
26 1.31 279.76 94.96 184.80
29 1.20 286.84 104.15 182.69
32 1.11 292.77 113.34 179.43
35 1.04 297.80 122.53 175.27
Maximum Difference 185.43
100 Year Modified FAA Storage Calculations- Basin 1
Rainfall Duration
(minutes)
Intensity (inches/Hour)
EQ 5-1 Volume In ft3 EQ 5-2 Volume Out ft3 EQ 5-3
Volume Difference
ft3 EQ 5-4 C 0.520
(Td)I=88.8P1/(10+Td)1.052 Vi=(1/720)*C*I*Td*A Vo=30(1+Tc/Td)*Qa*Td Vd=Vi-Vo A 16893.00 ft2
5 6.33 385.85 257.56 128.29 Tc 5 min
7 5.54 473.55 309.07 164.47 Qa 0.859 cfs
9 4.93 541.61 360.58 181.03 P1(100)1.23 in
11 4.44 595.82 412.10 183.72
13 4.03 639.88 463.61 176.28
15 3.70 676.32 515.12 161.20
17 3.41 706.89 566.63 140.26
19 3.16 732.84 618.14 114.69
Maximum Difference 183.72
FAA Storage
WQCV Detention
Required Calculated Volumes Required Total
Basin Total Area Impervious Area Impervious WQCV Tbl. Val.Volume 5-yr 100-yr Volume Volume BMP
(ft2)(ft2)(%)(in)(ft3)(ft3)(ft3)(ft3)(ft3)
1 16893.00 9199.00 54.45%0.102 143.6 185.43 183.72 186.0 329.6 Drywell
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5.0 Hydraulic Criteria
This property is not connected to the COAβs storm water infrastructure. All hydraulics are sized for onsite
infrastructure.
5.1 Inlets
Onsite basin 1 was divided into sub-basins according to which inlet they discharged into. The peak flows
for the 100-year event in each sub-basin were used as the flowrate to size the proposed inlets and the
trench drain. Equations 4.17 through 4.20 from the URMP were used in these calculations. The equations
incorporate a 50% clogging factor and assume a 40% opening in the grates. Water depths used in these
calculations are based on the grading around each inlet and safe ponding levels above the inlets. The
tables on the following page summarize the calculations for each inlet as well as for the trench drain.
Inlet-B1, located at the north end of the eastern swale, has been sized for a flow rate that reflects only the
contributing onsite sub-basin (i.e. it has been size for sub-basin 1.3). In the event of a major storm, the
additional flow in the eastern swale from the offsite basin will bypass this inlet, flow over the depressed
area the inlet is located in and continue down the slope past the swale. (See section 5.4 for rip-rap sizing
to protect the slope at this location). In the event of smaller storms, this inlet will accept flows from both
the onsite basin as well as from the offsite basin. Due to the difference in the time of concentration from
the onsite basin (less than 5 minutes) and the offsite basin (30 minutes), runoff from the onsite basin will
be collected before that of the offsite basin. Therefore, the runoff from the onsite basin will be captured
by the drywell and will be treated, while runoff from the offsite basin will be released by the outlet
structure of the drywell.
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Sub Basin and Circular Inlet Calculations 1 Hour(P1)1.23m=40%Return Period100Cg=50%Co=0.65Inlet IDBasin IDTotal Area Imp. Area Impervious C ValueTime of ConcentrationIntensityQ MaxInlet TypeDiameterEffective Open Area(EQ. 4-20)YsInlet Capacity (EQ 4-19)Has CapacitySee(D1)(ft2)(ft2)(%)From Table (Td)I=88.8P1/(10+Td)1.052 ft3/secWo (inches)Ae=(1-Cg)mAftQ=CoAeβ2gYs(Yes/No)INLET-A11.21597.001068.0066.88%0.59056.330.1378" Round80.0700.200.163YesINLET-A21.13165.002136.0067.49%0.59056.330.27112" Round120.1570.200.366YesINLET-A31.9162.0092.6057.16%0.54056.330.0136" Round60.0390.100.065YesINLET-A41.7122.0055.6045.57%0.51056.330.0096" Round60.0390.060.050YesINLET-A51.6245.00135.0055.10%0.54056.330.0196" Round60.0390.060.050YesINLET-A61.8142.00142.00100.00%0.95056.330.0204" Round40.0170.050.020YesINLET-B11.37729.004132.0053.46%0.52056.330.58415" Round150.2450.210.586YesINLET-B21.4, 1.51004.60705.4070.22%0.62056.330.0906" Round60.0390.200.092YesSub Basin and Rectangular Inlet Calculations 1 Hour(P1)1.23m=40%Ys=.04 (Depress inlet by 0.04')Return Period100Cg=50%Co=0.65Inlet IDBasin IDTotal Area Imp. Area Impervious C ValueTime of ConcentrationIntensityQ MaxInlet TypeInlet WidthInlet LengthEffective Open Area (EQ. 4-20)Inlet Capacity (EQ 4-19)Has CapacitySee(D1)(ft2)(ft2)(%)(From Table) (Td)I=88.8P1/(10+Td)1.052 (ft3/sec)RectangularWo (inches)Lo (inches)Ae=(1-Cg)mWoLoQ=CoAeβ2gYs(Yes/No)TRENCH DRAIN-A11.21597.001068.0066.88%0.59056.330.1374" x 17'42041.1331.182Yes09/26/2017
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5.2 Pipes
Pipes used for the storm system will be SDR35 PVC with a Manningβs coefficient (n) of 0.01. The pipes
were sized to accommodate peak flows for a 100-year event from all contributing sub-basins. The below
table lists the sub-basins that contribute to each section of pipe.
Pipe sizes were tested for hydraulic capacity at 80% of their full flowrate. Design charts giving Qdesign / Q
full were downloaded from FHWA and the equations in Section 4.8.4 were used as the basis for these
calculations. Calculated pipe sizes and depth of flow for onsite pipes are shown below.
Storm System Pipes
Pipe System Pipe Contibuting Sub-Basins Design Flow Rate
Qdes
A1 1.2 0.14
A2 1.1 0.27
A3 1.1, 1.2 0.41
A4 1.1, 1.2 0.41
A5 1.1, 1.2, 1.9 0.42
A6 1.1, 1.2, 1.9 0.42
A7 1.1, 1.2, 1.6, 1.7, 1.9 0.45
A8 1.1, 1.2, 1.6, 1.7, 1.9 0.45
A9 1.1, 1.2, 1.6, 1.7, 1.8, 1.9 0.47
A10 1.1, 1.2, 1.6, 1.7, 1.8, 1.9 0.47
A11 1.6 0.02
A12 1.6, 1.7 0.03
A13 1.6, 1.7 0.03
A14 1.6, 1.7 0.03
A15 1.8 0.02
B B1 1.3 0.58
B2 1.3 0.58
B3 1.3 0.58
B4 1.3-1.5 0.68
B5 1.4, 1.5 0.09
DOWNSPOUT DS 1.3A 0.04
OUTLET PIPE OP Drywell 100 year Release Rate 0.86
A
K=0.462
Pipe Design Flow
Rate
Proposed
Slope
Manning
Coefficient
Required Pipe Diameter
Equation 4-31
Required Pipe
Diameter
Proposed Pipe
Diameter
Qdes (ft3/sec) S (%)n d (ft) = {nQdes/KβS}3/8 Dreq (in) Dpro (in)
A1 0.14 2.0%0.01 0.23 2.82 4.0
A2 0.27 2.0%0.01 0.30 3.64 4.0
A3 0.41 1.9%0.01 0.36 4.28 6.0
A4 0.41 2.5%0.01 0.34 4.07 6.0
A5 0.42 7.2%0.01 0.28 3.37 6.0
A6 0.42 7.2%0.01 0.28 3.37 6.0
A7 0.45 7.2%0.01 0.29 3.46 6.0
A8 0.45 7.2%0.01 0.29 3.46 6.0
A9 0.47 11.3%0.01 0.27 3.23 6.0
A10 0.47 11.3%0.01 0.27 3.23 6.0
A11 0.02 2.0%0.01 0.11 1.35 4.0
A12 0.03 8.4%0.01 0.10 1.19 4.0
A13 0.03 8.4%0.01 0.10 1.19 4.0
A14 0.03 8.4%0.01 0.10 1.19 4.0
A15 0.02 20.0%0.01 0.07 0.88 4.0
B1 0.58 1.0%0.01 0.46 5.52 6.0
B2 0.58 7.6%0.01 0.31 3.78 6.0
B3 0.58 1.0%0.01 0.46 5.52 6.0
B4 0.68 1.2%0.01 0.47 5.64 6.0
B5 0.09 25.0%0.01 0.13 1.51 4.0
DS 0.04 2.0%0.01 0.14 1.70 4.0
OP 0.86 2.0%0.01 0.47 5.61 6.0
Pipe Sizing
09/26/2017
15
5.3 Outlet Structure
The drywell will be constructed with a 6β outlet pipe installed with its invert at the WQCV elevation
(8099.67β, see section 6.1). This outlet pipe will protrude into the drywell and a PVC end cap will be
installed on it with a 3.9β diameter orifice drilled into the end cap. This orifice will function to restrict the
flow from the drywell to the historic peak flow rate of 0.859 cfs calculated for the onsite basin in section
2.2. Equation 5-10 was referenced for the calculation of the size of this orifice and a coefficient of
discharge of 0.6 was used to reflect a square edged uniform orifice. The outlet pipe has been sized to
avoid further constricting this flow rate. The outlet pipe will be connected to a level spreader in order to
disperse the flow from the drywell thereby protecting the downhill slope and soil nail wall. The required
length of the level spreader was calculated using the above referenced peak flow rate. A factor of safety
of 2 was used for this calculation. The tables below summarize the calculations for the outlet pipe orifice
and the level spreader.
Pipe Design Flow
Rate
Proposed Pipe
Diameter Slope 80% of Proposed
Pipe Diameter
Manning
Coefficient
Full Pipe Cross
Sectional Area Full Pipe Flow Rate Q Design /
Q Full d/D Hydraulic Grade Line
(Depth of Flow)
Depth of Flow Less Than
80% of Pipe Diameter
Qdes (ft3/sec) Dpro(in)S (%)Dpro*.8 (in)n A (ft) = Ο (Dpro/2)2 Qfull (ft3/s) = A(1.49/n)((Dpro/48)2/3)S1/2 Qdes/Qfull (from Chart)d (in) = (d/D)*Dpro (Yes/No)
A1 0.14 4.0 2.0%3.2 0.01 0.087 0.351 0.39 0.49 1.94 Yes
A2 0.27 4.0 2.0%3.2 0.01 0.087 0.351 0.77 0.73 2.90 Yes
A3 0.41 6.0 1.9%4.8 0.01 0.196 1.008 0.40 0.50 3.00 Yes
A4 0.41 6.0 2.5%4.8 0.01 0.196 1.156 0.35 0.47 2.82 Yes
A5 0.42 6.0 7.2%4.8 0.01 0.196 1.962 0.21 0.35 2.10 Yes
A6 0.42 6.0 7.2%4.8 0.01 0.196 1.962 0.21 0.35 2.10 Yes
A7 0.45 6.0 7.2%4.8 0.01 0.196 1.962 0.23 0.37 2.19 Yes
A8 0.45 6.0 7.2%4.8 0.01 0.196 1.962 0.23 0.37 2.19 Yes
A9 0.47 6.0 11.3%4.8 0.01 0.196 2.457 0.19 0.34 2.01 Yes
A10 0.47 6.0 11.3%4.8 0.01 0.196 2.457 0.19 0.34 2.01 Yes
A11 0.02 4.0 2.0%3.2 0.01 0.087 0.351 0.05 0.18 0.70 Yes
A12 0.03 4.0 8.4%3.2 0.01 0.087 0.719 0.04 0.16 0.62 Yes
A13 0.03 4.0 8.4%3.2 0.01 0.087 0.719 0.04 0.16 0.62 Yes
A14 0.03 4.0 8.4%3.2 0.01 0.087 0.719 0.04 0.16 0.62 Yes
A15 0.02 4.0 20.0%3.2 0.01 0.087 1.109 0.02 0.08 0.32 Yes
B1 0.58 6.0 1.0%4.8 0.01 0.196 0.731 0.80 0.74 4.43 Yes
B2 0.58 6.0 7.6%4.8 0.01 0.196 2.015 0.29 0.41 2.43 Yes
B3 0.58 6.0 1.0%4.8 0.01 0.196 0.731 0.80 0.74 4.43 Yes
B4 0.68 6.0 1.2%4.8 0.01 0.196 0.801 0.84 0.77 4.59 Yes
B5 0.09 4.0 25.0%3.2 0.01 0.087 1.240 0.07 0.20 0.80 Yes
DS 0.04 4.0 2.0%3.2 0.01 0.087 0.351 0.10 0.25 1.00 Yes
OP 0.86 6.0 2.0%4.8 0.01 0.196 1.034 0.83 0.77 4.59 Yes
Hydraulic Grade Line and Pipe Capacity
Design Maximum Release Rate, Q (cfs)0.859
Coefficient of Discharge, Cd 0.60
Height above Orifice, h (ft)4.8
Orifice Shape circular
Orifice Area, ft2 0.081
Circular Orifice Diameter, d (in)3.9
Drywell Outlet Orifice Sizing
Input
Output
Circular Orifice
π΄= π
Orifice Equation
π= πΆ π΄2ποΏ½
Square Orifice
π΄=π
π= 2.2 ππ π
09/26/2017
16
5.4 Rip Rap Sizing
The outfall of the eastern swale will be armored with rip rap to protect the steep slope from failure as well
as to reduce the velocity of the offsite flow down the slope. Rip-rap was sized based on the equations
from the USDA βDesign of Rock Chutesβ paper based on the recommendation of the UDFCD criteria
manualβs section on rip-rap lining of steep sloped channels. This paper also provided a recommended
equation to calculate the manningβs coefficient for rip-rap lined channels. The resulting coefficient was
used to calculate the flow velocity down the slope in order to ensure that the velocity did not exceed 7 fps.
These calculations can be found in the appendix of this report.
6.0 Proposed Facilities
6.1 Proposed structures
A Drywell is being utilized to meet URMP requirements for storm water management. Detention
volumes were calculated using equations 5-1 through 5-4 from the City of Aspen URMP.
The proposed Drywell is located to the northwest of the rear patio and collects all runoff from all
impervious portions of the onsite basin. This drywell has a diameter of 6 ft., an effective storage depth of
8.5 ft. and is surrounded by 18 in. of screened rock, giving the drywell a storage capacity of 330 ft3. The
total capacity for the drywells meets the required detention volume of 330 ft3 for the onsite basin as
calculated in section 4.2. The portion of the required capacity for the WQCV is 144 ft3 which will require
a storage depth of 3.7 ft. The proposed drywell has been designed with an outlet pipe 3.7 ft. above the
sump elevation so that the full WQCV is allowed to infiltrate. The required detention volume of 186 ft3
takes up the remaining 4.8 ft. of effective storage. The release rate for the detention volume is controlled
by the previously mentioned outlet pipe which has been designed to release at the historic peak flow rate
of 0.859 cfs. The below tables summarize the calculations for the storage volume of the drywell.
Design Peak Discharge, QD (cfs)0.859
100 Year Water Elevation, EL100 (ft)8104.47
Level Spreader Elevation, ELLS (ft)8098.5
Factor of Safety, FS 2
Number of Slots per Row, NR 2
Slot Spacing, S (in)5
Slot Diamter, D (in)0.5
Head above Level Spreader, H (ft)5.970
Area of Slot, A (in2)0.19635
Number of Slots per foot, N 4.8
Discharge per Slot, QO 0.016
Discharge per foot of pipe, QF 0.077
Required length of Level Spreader, LR (ft)22.3
Design Length of level Spreader, LD (ft)25
Level Spreader Sizing
General Parameters
Output
Perforate Pipe Properties
Area of Circular Slot
π΄= π
Orifice Equation
π = πΆ π΄2ποΏ½
π= 2.2 ππ π
Head Above Level Spreader
οΏ½= πΆ πΆ
πΆ = .
Required Level Spred Length
=π
π
π =π
09/26/2017
17
6.2 Infiltration
6.2.1 Drywell
According to the URMP, a drywell needs to be able to drain the full WQCV in 24 hours. The minimum
active area of a drywell (or the portion of the drywell that is perforated) is 4 ft. The calculation performed
in the below table shows that the active area of the proposed drywell has a sufficiently large perforated
area for the drywell to drain within 24 hours using the percolation rate of 4 min per inch (or 15 inches per
hour) determined by HP Geotech. Section 8.5.4.2 of the URMP was referenced for these calculations.
7.0 Operation and Maintenance
7.1 Drywell
Drywells must be inspected and maintained quarterly to remove sediment and debris that has washed
into them. Minimum inspection and maintenance requirements include the following:
β’ Inspect drywells at least four times a year and after every storm exceeding 0.5 inches.
β’ Dispose of sediment, debris/trash, and any other waste material removed from a drywell at suitable
disposal sites and in compliance with local, State, and Federal waste regulations.
β’ Routinely evaluate the drain-down time of the drywell to ensure the maximum time of 24 hours is
not being exceeded. If drain-down times are exceeding the maximum, drain the drywell via
pumping and clean out the percolation area (the percolation barrel may be jetted to remove
Drywell Storage
Drywell Basins Diameter Storage Depth Internal Volume External (18" of Screened Rock) Volume Total Capacity Required Capacity
(Name)(#)D (ft)H (ft)Ο*H*(D/2)2) (ft3)0.3*Ο*H*((D/2)+1.5)2 - (D/2)2) (ft3)(ft3)(ft3)
1 1 6 8.5 240 90 330 330
1A 1 WQCV 6 3.7 105 39 144 144
1B 1-Detention Volume 6 4.8 136 51 187 186
Drywell Percolation Area
Needed Perforation Area
Infitration Rate 15 in/hr.
Hydraulic Gradient (dh/dl)*-1.0 ft/ft
Clogging Factor*50%
Hydraulic Cond. (K)0.0003 ft/sec
Required Detention (V)330.00 ft3
Required Percolation Area (APr)22.00 ft2
Drywell Diameter (Dd)6.0 ft
Percolation Depth (Hp)4.0 ft
Screened Rock Width (w)1.5 ft
Proposed Percolation Area (AP)113.10 ft2
Time To drain Required Volume T 4.67 hr
* per recommended values in the URMP
π΄π =
From URMP
π= π΄
Darcy's law
=
.
π΄ππ= πΆοΏ½= πΆ +2 οΏ½π
09/26/2017
18
sediment accumulated in perforations. If slow drainage persists, the system may need to be
replaced.
09/26/2017
19
8.0 Appendices
09/26/2017
Hydrologic Soil GroupβAspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties
(287 McSkimming RD Offsite Basin)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/1/2017
Page 1 of 443390004339100433920043393004339400433950043396004339000433910043392004339300433940043395004339600344000344100344200344300344400344500344600344700344800344900345000
344000 344100 344200 344300 344400 344500 344600 344700 344800 344900 345000
39° 11' 32'' N 106° 48' 25'' W39° 11' 32'' N106° 47' 40'' W39° 11' 9'' N
106° 48' 25'' W39° 11' 9'' N
106° 47' 40'' WN
Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84
0 200 400 800 1200
Feet
0 50 100 200 300
Meters
Map Scale: 1:4,990 if printed on A landscape (11" x 8.5") sheet.
Soil Map may not be valid at this scale.
09/26/2017
MAP LEGEND MAP INFORMATION
Area of Interest (AOI)
Area of Interest (AOI)
Soils
Soil Rating Polygons
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Lines
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Soil Rating Points
A
A/D
B
B/D
C
C/D
D
Not rated or not available
Water Features
Streams and Canals
Transportation
Rails
Interstate Highways
US Routes
Major Roads
Local Roads
Background
Aerial Photography
The soil surveys that comprise your AOI were mapped at
1:24,000.
Warning: Soil Map may not be valid at this scale.
Enlargement of maps beyond the scale of mapping can cause
misunderstanding of the detail of mapping and accuracy of soil
line placement. The maps do not show the small areas of
contrasting soils that could have been shown at a more detailed
scale.
Please rely on the bar scale on each map sheet for map
measurements.
Source of Map: Natural Resources Conservation Service
Web Soil Survey URL:
Coordinate System: Web Mercator (EPSG:3857)
Maps from the Web Soil Survey are based on the Web Mercator
projection, which preserves direction and shape but distorts
distance and area. A projection that preserves area, such as the
Albers equal-area conic projection, should be used if more
accurate calculations of distance or area are required.
This product is generated from the USDA-NRCS certified data as
of the version date(s) listed below.
Soil Survey Area: Aspen-Gypsum Area, Colorado, Parts of
Eagle, Garfield, and Pitkin Counties
Survey Area Data: Version 7, Sep 22, 2014
Soil map units are labeled (as space allows) for map scales
1:50,000 or larger.
Date(s) aerial images were photographed: Aug 12, 2011βSep
22, 2011
The orthophoto or other base map on which the soil lines were
compiled and digitized probably differs from the background
imagery displayed on these maps. As a result, some minor
shifting of map unit boundaries may be evident.
Hydrologic Soil GroupβAspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin Counties
(287 McSkimming RD Offsite Basin)
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/1/2017
Page 2 of 4
09/26/2017
Hydrologic Soil Group
Hydrologic Soil Groupβ Summary by Map Unit β Aspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin
Counties (CO655)
Map unit symbol Map unit name Rating Acres in AOI Percent of AOI
76 Mine loam, 12 to 25
percent slopes
A 2.9 16.7%
77 Mine loam, 25 to 65
percent slopes
A 14.4 83.3%
Totals for Area of Interest 17.3 100.0%
Description
Hydrologic soil groups are based on estimates of runoff potential. Soils are
assigned to one of four groups according to the rate of water infiltration when the
soils are not protected by vegetation, are thoroughly wet, and receive
precipitation from long-duration storms.
The soils in the United States are assigned to four groups (A, B, C, and D) and
three dual classes (A/D, B/D, and C/D). The groups are defined as follows:
Group A. Soils having a high infiltration rate (low runoff potential) when
thoroughly wet. These consist mainly of deep, well drained to excessively
drained sands or gravelly sands. These soils have a high rate of water
transmission.
Group B. Soils having a moderate infiltration rate when thoroughly wet. These
consist chiefly of moderately deep or deep, moderately well drained or well
drained soils that have moderately fine texture to moderately coarse texture.
These soils have a moderate rate of water transmission.
Group C. Soils having a slow infiltration rate when thoroughly wet. These consist
chiefly of soils having a layer that impedes the downward movement of water or
soils of moderately fine texture or fine texture. These soils have a slow rate of
water transmission.
Group D. Soils having a very slow infiltration rate (high runoff potential) when
thoroughly wet. These consist chiefly of clays that have a high shrink-swell
potential, soils that have a high water table, soils that have a claypan or clay
layer at or near the surface, and soils that are shallow over nearly impervious
material. These soils have a very slow rate of water transmission.
If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is
for drained areas and the second is for undrained areas. Only the soils that in
their natural condition are in group D are assigned to dual classes.
Hydrologic Soil GroupβAspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin
Counties
287 McSkimming RD Offsite Basin
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/1/2017
Page 3 of 409/26/2017
Rating Options
Aggregation Method: Dominant Condition
Component Percent Cutoff: None Specified
Tie-break Rule: Higher
Hydrologic Soil GroupβAspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin
Counties
287 McSkimming RD Offsite Basin
Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Survey
5/1/2017
Page 4 of 409/26/2017
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Apr 21 2017
287 McSkimming Rd Eastern Swale Capacity
User-defined
Invert Elev (ft) = 8115.63
Slope (%) = 1.69
N-Value = Composite
Calculations
Compute by: Q vs Depth
No. Increments = 43
(Sta, El, n)-(Sta, El, n)...
( 0.00, 8116.50)-(2.63, 8115.63, 0.030)-(7.16, 8116.00, 0.030)-(9.48, 8116.50, 0.030)
Highlighted
Depth (ft) = 0.63
Q (cfs) = 8.891
Area (sqft) = 2.75
Velocity (ft/s) = 3.23
Wetted Perim (ft) = 7.76
Crit Depth, Yc (ft) = 0.62
Top Width (ft) = 7.62
EGL (ft) = 0.79
-1 0 1 2 3 4 5 6 7 8 9 10 11
Elev (ft)Depth (ft)Section
8115.00 -0.63
8115.50 -0.13
8116.00 0.37
8116.50 0.87
8117.00 1.37
Sta (ft)
09/26/2017
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Jul 14 2017
287 McSkimming Rd, - Driveway Swale 1
Triangular
Side Slopes (z:1) = 7.50, 8.80
Total Depth (ft) = 0.29
Invert Elev (ft) = 8115.56
Slope (%) = 2.90
N-Value = 0.030
Calculations
Compute by: Known Q
Known Q (cfs) = 0.18
Highlighted
Depth (ft) = 0.13
Q (cfs) = 0.180
Area (sqft) = 0.14
Velocity (ft/s) = 1.31
Wetted Perim (ft) = 2.13
Crit Depth, Yc (ft) = 0.13
Top Width (ft) = 2.12
EGL (ft) = 0.16
0 1 2 3 4 5 6 7
Elev (ft)Depth (ft)Section
8115.00 -0.56
8115.25 -0.31
8115.50 -0.06
8115.75 0.19
8116.00 0.44
Reach (ft)
09/26/2017
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Jul 14 2017
287 McSkimming Rd. - Driveway Swale 2
Triangular
Side Slopes (z:1) = 3.40, 4.20
Total Depth (ft) = 0.24
Invert Elev (ft) = 8115.44
Slope (%) = 1.00
N-Value = 0.030
Calculations
Compute by: Known Q
Known Q (cfs) = 0.18
Highlighted
Depth (ft) = 0.21
Q (cfs) = 0.180
Area (sqft) = 0.17
Velocity (ft/s) = 1.07
Wetted Perim (ft) = 1.65
Crit Depth, Yc (ft) = 0.17
Top Width (ft) = 1.60
EGL (ft) = 0.23
0 .5 1 1.5 2 2.5 3
Elev (ft)Depth (ft)Section
8115.00 -0.44
8115.25 -0.19
8115.50 0.06
8115.75 0.31
8116.00 0.56
Reach (ft)
09/26/2017
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Friday, Jul 14 2017
287 McSkimming Rd, - Driveway Swale 3
Triangular
Side Slopes (z:1) = 4.30, 4.30
Total Depth (ft) = 0.42
Invert Elev (ft) = 8115.25
Slope (%) = 2.40
N-Value = 0.030
Calculations
Compute by: Known Q
Known Q (cfs) = 0.14
Highlighted
Depth (ft) = 0.16
Q (cfs) = 0.140
Area (sqft) = 0.11
Velocity (ft/s) = 1.27
Wetted Perim (ft) = 1.41
Crit Depth, Yc (ft) = 0.15
Top Width (ft) = 1.38
EGL (ft) = 0.19
0 .5 1 1.5 2 2.5 3 3.5 4 4.5 5
Elev (ft)Depth (ft)Section
8115.00 -0.25
8115.25 0.00
8115.50 0.25
8115.75 0.50
8116.00 0.75
Reach (ft)
09/26/2017
09/26/2017
Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc. Tuesday, Jul 18 2017
287 McSkimming - Eastern Swale Rip-Rap Outfall Channel
Trapezoidal
Bottom Width (ft) = 3.00
Side Slopes (z:1) = 7.35, 13.51
Total Depth (ft) = 0.30
Invert Elev (ft) = 8110.00
Slope (%) = 40.80
N-Value = 0.059
Calculations
Compute by: Known Q
Known Q (cfs) = 7.74
Highlighted
Depth (ft) = 0.27
Q (cfs) = 7.740
Area (sqft) = 1.57
Velocity (ft/s) = 4.93
Wetted Perim (ft) = 8.66
Crit Depth, Yc (ft) = 0.30
Top Width (ft) = 8.63
EGL (ft) = 0.65
0 1 2 3 4 5 6 7 8 9 10 11 12
Elev (ft)Depth (ft)Section
8109.75 -0.25
8110.00 0.00
8110.25 0.25
8110.50 0.50
8110.75 0.75
8111.00 1.00
Reach (ft)
09/26/2017