Section 3: Hydraulics & Hydrology
1
Section 3: Hydraulics & Hydrology Design
Final Design Report
Prepared For:
Capstone Developers
306 Lowry Hall
Clemson, SC
Date:
November 28, 2012
Prepared By:
Freeman Mach Consulting (2-1)
Frederick Paige
Armen Zadoorian
Mason Smith
Christopher Stubbs
Hydraulic and Hydrology Specialist
Mason Smith
Calculations Deliverable Manager
Armen Zadoorian
Final Report Deliverable Manager
Christopher Stubbs
Section 3: Hydraulics & Hydrology
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Table of Contents
Section 3: Hydraulics and Hydrology Calculations Report
3.1: Objective and Scope……………………………………………………………………………………………………..……3
3.2: Pre-Development Site Description…………………………………………………………………………………..…4
3.3: Pre-Development Flow Pattern Description……………………………………………………………….………4
3.4: Pre-Development Curve Number and Time of Concentration…………………………………………….5
3.5: Pre-Development IDEAL Work Space and Hydrographs..……………………………………………………6
3.6: Post-Development Site Description…………………………………………………………………………….………8
3.7: Post-Development Flow Pattern Description………………………………………………………………………8
3.8: Post-Development Curve Number and Time of Concentration…………………………………………11
3.9: Post-Development IDEAL Work Space and Hydrographs………..……………………………………..…13
3.10: Hydrology & Hydraulics Methodology………………………………………………………………………………16
3.11: Analysis and Results…………………………………………………………………………………………………………22
3.12: References………………………………………………………………………………………………………………….……23
3.13: Sample Calculations………………………………………………………………………………………….……………..24
3.14: Lessons Learned……………………………………………………………………………………………….………………28
3.15: Drawings………………………………………………………………………………………………………………….………29
Section 3: Hydraulics & Hydrology
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3.1 Objective and Scope
The Museum of Clemson History, located off Perimeter Rd across from the Botanical Gardens, is under
the jurisdiction of Greenville County Stormwater Ordinance and the Master Plan established by Clemson
University. Key design parameters and restrictions that are to be satisfied in the design are as follows:
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Install storm water management facilities to limit the 2-year and 10-year developed peak
discharge rates to pre-developed peak discharge rates using a duration of 24 hours with a SCS
Type II design storm and pass the 100 year 24 hour storm event resulting in a minimum of 2ft of
free board on storm water pond.
Return periods, rainfall intensities, pipe sizes, etc should follow the requirements outlined in the
Greenville, SC Stormwater Management Design Manual.
All pipes shall be designed to flow as open channels. Pressurized flow in any pipe is not
acceptable for the 10-year rainfall design event.
Gravity-driven flow only, i.e. no pumps.
For 100-year storm event pressurized flow in pipes is acceptable.
No pipes shall be designed under the building pad.
Finished grade spot elevations for structures and invert elevations must be notes on the
appropriate drawing(s).
IDEAL can be used for pipe sizing, calculating runoff hydrographs, and for the designing the
Stormwater pond.
Erosion control during construction does not need to be designed, but prevention measures
shall be specified for the finished site.
Water on rooftops should be collected in a gutter and downspout system.
Pavement must be drained with curb and gutter, drainage inlets, or appropriately designed
channels.
Both a primary and emergency outlet must be designed for the Stormwater pond. The water
level in the pond must not me higher than 2ft below the tope of the pond during the 100-year
rainfall event.
The design of the Stormwater pond must account for the setbacks specified by Professor
Csernak.
Pervious parking lots cannot be used as detention/retention pond.
This reports outlines how the stormwater is to be managed including the design of pipes, inlets, roof
drainage, swales, and stormwater pond. All essential components and properties are outlined through
tables and figures including a comparison of pre-development runoff with post-development runoff to
ensure compliance with code.
Section 3: Hydraulics & Hydrology
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3.2 Pre-Development Site Description
The property is approximately 4.5 acres of mostly open area covered primarily with good
condition maintained grassland. The northern section of the lot, towards Commons Court, is
covered by a wooded area of approximately 1.05 acres, which extends from midway between
markers 14-15 to Newman Road Extension. The site is currently used as open park space for
students and residents to enjoy recreational and leisure activities.
The site has a moderate slope across the entire lot from a maximum elevation of approximately
808 ft to a low point of 780.67 ft which is the top elevation of a catch basin already existing on
the site. The resulting change in elevation is approximately 28 ft. The existing catch basin is
located on a sag and collects water from the project site and an adjacent property. The catch
basin on site measures 3ft by 4ft with an open area of approximately 6 square feet. The
majority of the lot results in a natural flow eastwardly toward the existing catch basin. What
flows into the catch basin through the top grate and the pipe under Newman Rd. The site is
considered to have 3 sub-basins which are displayed in drawing H1 of Section 3.15. The flow
from sub-basins 1 and 2 fall into an existing ditch which runs parallel to Perimeter Rd. Sub-basin
3 was determined to flow into the parking lot north of the property along Commons Court.
There are several existing trees on site adjacent to Perimeter Rd that run parallel to the ditch.
The design of the storm water plan will focus on the preservation of these trees. The soil type
is primarily composed of sands and silts resulting in a classification of soil group B and soil type
Pacolet.
3.3 Pre-Development Flow Pattern Description
The pre-development state can be divided into 3 sub basins as shown in drawing H1 to allocate
the runoff to the shared outlet point. The highest elevation on the property, 808ft, is located
about 50ft south of marker 15. From this point the majority of the flow will move south and
become collected in the existing ditch along Perimeter Rd. The ditch disperses the water east
and west to the shared outlet point. The northern most sub-basin, denoted as sub-basin 2 in
H1, flows northwardly towards Commons Court where the water is dispersed into existing catch
basins.
Section 3: Hydraulics & Hydrology
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3.4 Pre-Development Curve Number and Time of Concentration
Table 1: Average Curve Numbers
Sub-Basin
Grass Cover [acres]
Wood Land [acres]
Total Area [acres]
CN, Grass Cover
CN, Wood Land
CN, Avg
1
2.215
0.27
2.485
61
55
60.5
2
0.268
0.76
1.028
61
55
56.56
3
0.977
0.977
61
55
61
Using the Greenville County Storm Water Management Design Manual, the curve numbers for
each sub basin were determined. Two different land use types were selected, open space with
good grass cover and good condition wood land. From the soils report it was determined that
the property satisfied the conditions of hydrologic soil group B. Weighing the respective curve
numbers with their areas yielded the average curve numbers shown in Table 1 above.
Table 2: 2Yr-24Hr Storm Event Time of Concentration
2Yr-24Hr Storm Event
Sub-Basin
Sheet Flow Tt [hrs]
Shallow Concentrated Flow Tt [hrs]
Time of Concentration [hrs]
1
0.3156
0.0857
0.4013
2
0.1622
0.1622
3
0.3139
0.0208
0.3347
2
0.1343
0.1343
3
0.2599
0.0208
0.2806
Table 3: 10Yr-24Hr Storm Event Time of Concentration
10Yr-24Hr Storm Event
Sub-Basin
Sheet Flow Tt [hrs]
Shallow Concentrated Flow Tt [hrs]
Time of Concentration [hrs]
1
0.2613
0.0857
0.347
Section 3: Hydraulics & Hydrology
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The time of concentration for each sub basin was computed using the formulas provided by
Greenville County’s design manual which can be seen in the sample calculations of section 3.13.
The time of concentration was equal to the sum of the sheet flow travel time (first 300’) and
the shallow concentrated flow travel time. To use these formulas the hydraulic grade was
determined along with the manning sheet flow coefficient (n) and average overland flow
velocity (v) for each sub-basin.
3.5 Pre-Development IDEAL Work Space and Hydrographs
Figure 1: Pre-Development IDEAL work space
Using the software IDEAL, a pre-development workspace was created to model the existing flow
conditions and features on the site. From the workspace shown above in Figure 1, two hydrographs
were produced for 2Yr and 10Yr-24Hr storm events. Several inputs were used in the model including but
not limited to the curve numbers, areas, time of concentrations, and slopes of each basin. Growing
season was assumed for the pre-development case to lower the peak discharge for the outlet. This in
return provides a more conservative design when paired with a dormant season post-development site.
Existing catch basin on site included the dimensions, open area, and elevations. The peak discharge for
the 2Yr and 10Yr storm events were 4.448 cfs and 10.54 cfs respectively.
Section 3: Hydraulics & Hydrology
Figure 2: Pre-Development 2Yr-24Hr Storm Event Hydrograph
Figure 3: Pre-Development 10Yr-24Hr Storm Event Hydrograph
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Section 3: Hydraulics & Hydrology
8
3.6 Post-Development Site Description
The post-development site is composed of approximately 1.69 acres of impervious cover (roof,
access road, parking lot, sidewalks) and 2.81 acres of pervious good condition grassland. The
site will mostly serve academic visits and events as well as tailgating adventures on the
weekends.
The property will host a 12,500 square foot building pad and roof. The building was designed
with a traditional gutter and downspout to remove and disperse the water from the roof
surface. Northeast of the museum lies an 84-space parking lot designed to accommodate the
guests and service vehicles. Several combination inlets were strategically placed around the
parking lot to capture the runoff. The facility also features an access road off Newman Rd Ext
directly across from the entrance of the commuter lot R-1. Two slotted drain inlets are located
at the beginning and end of the entrance road to prevent runoff from spreading from the
parking lot onto the access road and also to eliminate runoff from flowing onto Newman Rd
Ext. To allow water flow under the entrance road a culvert was installed as seen in drawing H3.
To the north west of the entrance road a stormwater pond was designed to satisfy the
hydrologic requirements and setback requirements as outlined by the universities’ master plan
and Greenville County Stormwater Ordinance. At 10ft deep, including the 2ft freeboard
requirement, the pond has a top stage area of 0.119 acres. The existing ditches along Perimeter
Rd. as well as the existing catch basin were included in the stormwater design.
Several trees were cut down to satisfy the design requirements. The soil type remains the same
as pre-development conditions, Type B Pacolet.
3.7 Post-Development Flow Pattern Description
The post-development site can be divided into 17 sub basins as shown in drawing H2. All flow
paths are designated with arrows showing the directions of flow within each sub-basin. In the
basin delineation 4 major land cover areas were determined for design: roof drainage, parking
lot drainage, pervious areas, and the stormwater pond.
Section 3: Hydraulics & Hydrology
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Building Roof Drainage
The museum’s roof has a surface area of 12,500 square feet. Due to its irregular shape the roof
plan was sloped in two different directions. The two areas were modeled as sub-basins 9 and 10
which can be seen in drawing H2. Sub-Basin 9 of the roof drains northeast where the water is
collected in a 5 inch gutter and directed down through 3 inch diameter spaced leaders into the
horizontal storm drain pipe GP1. Similarly, Sub-Basin 10 of the roof drains southeast were the
water is collected in a 4 inch gutter and distributed into 2 and 3 inch diameter spaced leaders to
the horizontal ground pipe GP2. For efficiency the two horizontal ground pipes were connected
at a junction located at the northeast face of the building. The junction consists of a 6” ground
pipe and 8” ground pipe converging into a 12 inch concrete pipe denoted as P9 in figure 4.
Parking Lot Drainage
As seen in drawing H2 the parking lot can be divided into 9 sub-basins. Each sub-basin features
an inlet to capture the water and direct it to either the storm water pond or off site to the
shared final outlet point. The parking lot slopes 2% in one direction toward Marker 15 at the
north end of the property. Several islands and 6 inch raised curbs required the Water Drop
command in AutoCAD Civil 3D to achieve accurate delineation. Sub-Basin 11 flows northwest
where the flow if captured in SD3, a 0.67ft x 30ft slotted drain inlet, and then piped through P5
into the next inlet of the network. Sub-Basin 12 flows north following the raised curb and is
collected in I1, a 2ft x 3ft combination inlet. From Inlet I4 the flow is piped through P4 to the
outfall structure O1. Sub-Basin 13 flows north and is collected along the 6 inch raised curb
connecting the parking lot islands. At the north end of the curb the flow is collected in Inlet I4, a
2ft x 3ft combination inlet. Sub-Basin 14 flows north and collected in I3, a 2ft x 3ft combination
inlet. As shown in drawing H3 the ground pipe junction connects to Inlet I4, which connects to
I3 where finally the water is piped through P7 to the outfall structure. Sub-Basin 15 flows north
into I5 where the water flows through pipe P10 to inlet I3. From Inlet I3 the water is piped
through P7 to the outfall structure. Sub-basin 16 flows directly toward the access road where a
0.5ft x 40ft slotted drain inlet, SD2, was designed to capture and prevent the flow from
spreading down toward Newman Rd Ext.
Section 3: Hydraulics & Hydrology
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Pervious Areas
Several areas around the site remained undisturbed from the pre-development conditions.
These include sub-basins 1, 2, 4, 5, and 17. Sub-basin 1 and 2 become collected in the existing
ditch along Perimeter Rd. The ditch disperses the water east and west to the shared outlet
point. The northern most sub-basin, denoted as sub-basin 5 in H2, flows northwardly towards
Commons Court where the water is dispersed into existing catch basins. Sub-basin 4 flows
southeast under the access road through a 15” RCP culvert to the existing catch basin on site.
Sub-basin 17 lies within the grading of the stormwater pond so runoff will naturally flow into
the pond.
Access Road and Road Surrounding Building
As seen in drawing H2 the access road is defined as sub-basin 3 and the road surrounding the
building pad is labeled as sub-basins 6,7, and 8. Sub-Basins 6 and 7 flow southwest where they
share inlet I2, a 2ft x 6ft combination inlet. Inlet I2 is piped through P6 where it joins the
network at slotted drain Inlet SD3. Sub-basin 8 is located at an elevation lower than the
stormwater pond so water was collected in inlet SD4, a 0.67ft x 22ft slotted drain inlet, and
then piped through SP2, an 8 inch PVC pipe, to swale 2 where the water is dispersed to the
shared outlet point. The connection of SP2 and swale 2 is riprapped to reduce scouring and
erosion when the flow hits the ground surface and also to allow for increased time of
infiltration. The access road is sloped toward Newman Rd Ext. To capture the runoff a 0.5ft x
40ft slotted drain inlet, SD1, was placed at the intersection of the access road and Newman Rd
Ext. From SD1 the water is sent through SP1, a 6 inch PVC pipe, (with Riprap protection) to
swale 1 where the water is collected in the grate of the existing catch basin on site.
Storm Water Pond (Refer to Drawings H3,H4,H5)
The first step in designing the storm water pond was recognizing the setbacks established by
Clemson’s master plan. With a 25ft setback from the access road, Newman Rd Ext, and
Commons court the pond was polygon shaped to fit within the setbacks. The size of the pond
was determined using the hydrograph of outfall structure O1 before the stormwater pond was
introduced to the post-development IDEAL file. The run-off volume was approximately 1.13 acft or 1823 yd3. The lowest elevation of the pond was determined to be 780ft allowing for a total
Section 3: Hydraulics & Hydrology
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depth of 10 ft including the 2 ft freeboard requirement. With the limited space the pond slope
was designed at 2H:1V to maximize the total volume. Greenville County Stormwater Ordinance
requires that pond slopes shall be no steeper than 3H:1V but erosion control measures on a
2H:1V slope satisfy the requirements. TRMs (Turf Reinforcement Mats) are recommended in
the design to enhance the ability of plants to stabilize the soil and prevent erosion of the pond
side slopes. The maximum top stage area was 0.119 acres and bottom stage area was 0.0135
acres. To reduce the peak runoff an open top barrel riser was designed with several orifices at
varying heights which is displayed in H5. Once water enters the barrel riser flow travels through
pipe P1, an 18” RCP, to the existing catch basin on site. A 5ft wide rectangular emergency
spillway located at 7.5ft from the bottom of the pond was included for 100Yr storm events.
Riprap protection outside the spillway was provided to reduce erosion and scouring when in
use and shown in drawing H5.
3.8 Post-Development Curve Number and Time of Concentration
Table 4: 2Yr-24Hr Storm Event Average Curve Number and Time of Concentration
2yr-24Hr Storm Event
Sub-Basin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Area [acres]
0.998
0.831
0.051
0.0845
0.587
0.17
0.297
0.05
0.115
0.172
0.138
0.24
0.245
0.087
0.202
0.071
0.034
Curve Number, Avg
61
61
98
61
56.2
84.27
75.2
92.8
98
98
98
98
98
98
98
98
61
Flow Path [ft]
367.28
437.9
83.71
124.6
104.2
216
187
108.62
150
150
155.72
192.04
243.6
111
186.68
98.4
5.52
Hydraulic Grade
[ft/ft]
0.075
0.041
0.087
0.064
0.08
0.025
0.02
0.021
0.02
0.02
0.027
0.023
0.025
0.029
0.024
0.032
0.732
Travel Time [hrs]
0.335
0.420
0.009
0.166
0.131
0.034
0.031
0.020
0.026
0.026
0.024
0.030
0.035
0.018
0.029
0.015
0.005
Table 5: 10Yr-24Hr Storm Event Average Curve Number and Time of Concentration
10yr-24Hr Storm Event
Sub-Basin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Area [acres]
0.998
0.831
0.051
0.0845
0.587
0.17
0.297
0.05
0.115
0.172
0.138
0.24
0.245
0.087
0.202
0.071
0.034
Curve Number, Avg
61
61
98
61
56.2
84.27
75.2
92.8
98
98
98
98
98
98
98
98
61
Flow Path [ft]
367.28
437.9
83.71
124.6
104.2
216
187
108.62
150
150
155.72
192.04
243.6
111
186.68
98.4
5.52
Hydraulic Grade
[ft/ft]
0.075
0.041
0.087
0.064
0.08
0.025
0.02
0.021
0.02
0.02
0.027
0.023
0.025
0.029
0.024
0.032
0.732
Travel Time [hrs]
0.281
0.352
0.007
0.137
0.109
0.028
0.026
0.016
0.022
0.022
0.020
0.025
0.029
0.015
0.024
0.013
0.004
Section 3: Hydraulics & Hydrology
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Table 6: 100Yr-24Hr Storm Event Average Curve Number and Time of Concentration
100yr-24Hr Storm Event
Sub-Basin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
0.998
0.831
0.051
0.0845
0.587
0.17
0.297
0.05
0.115
0.172
0.138
0.24
0.245
0.087
0.202
0.071
0.034
61
61
98
61
56.2
84.27
75.2
92.8
98
98
98
98
98
98
98
98
61
Flow Path [ft]
367.28
437.9
83.71
124.6
104.2
216
187
108.62
150
150
155.72
192.04
243.6
111
186.68
98.4
5.52
Hydraulic Grade
[ft/ft]
0.075
0.041
0.087
0.064
0.08
0.025
0.02
0.021
0.02
0.02
0.027
0.023
0.025
0.029
0.024
0.032
0.732
Travel Time [hrs]
0.221
0.276
0.006
0.106
0.084
0.022
0.020
0.013
0.017
0.017
0.015
0.019
0.022
0.011
0.018
0.010
0.003
Area [acres]
Curve Number, Avg
Using the same methods as the pre-development case, the curve numbers and time of
concentration for each sub basin were determined. Two different land use types were selected,
open space with good grass cover and paved surfaces. Weighing the respective curve numbers
with their areas yielded the average curve numbers shown in the tables.
The time of concentration for each sub basin was computed using the formulas provided by
Greenville County’s design manual which can be seen in the sample calculations. The time of
concentration was equal to the sum of the sheet flow travel time (first 300’) and the shallow
concentrated flow travel time. To use these formulas the hydraulic grade was determined along
with the manning sheet flow coefficient (n) and average overland flow velocity (v) for each subbasin.
Section 3: Hydraulics & Hydrology
13
3.9 Post-Development IDEAL Work Space and Hydrographs
Figure 4: Post-Development IDEAL work space
Using the software IDEAL, a post-development workspace was created to model the flow features and
conditions displayed in drawing H3. Dormant season was assumed for the post-development case to
increase the peak discharge for the outlet. This in return provides a more conservative design when
paired with a growing season used on the pre-development site. From the workspace shown above in
Figure 4, four hydrographs were produced for 2Yr and 10Yr 24Hr storm events. Two hydrographs before
and after the storm water pond was inputted into IDEAL. From the pre-development case the peak
discharge for the 2Yr and 10 Yr storm events where 4.448 cfs and 10.54 cfs respectively. Without the
stormwater pond the post-development yielded a 2Yr and 10Yr storm event peak discharge of 10.39cfs
and 16.85cfs respectively. With the stormwater pond the post-development yielded a 2Yr and 10Yr
storm event peak discharge of 4.246cfs and 9.822cfs respectively.
Section 3: Hydraulics & Hydrology
Figure 5: Post-Development (W/Out Pond) 2Yr-24Hr Storm Event Hydrograph
Figure 6: Post-Development (W/Out) 10Yr-24Hr Storm Event Hydrograph
14
Section 3: Hydraulics & Hydrology
Figure 7: Post-Development (With Pond) 2Yr-24Hr Storm Event Hydrograph
Figure 8: Post-Development (With Pond) 10Yr-24Hr Storm Event Hydrograph
15
Section 3: Hydraulics & Hydrology
16
3.10 Hydrology & Hydraulics Methodology
Pipes & Inlets
The design of the stormwater system was completed using the computer program IDEAL. IDEAL is a
computer software used to model stormwater runoff. Several inputs and storm events can be tested to
accurately produce hydrographs and other environmental impacts on the soil and water. The initial
IDEAL file was setup without a storm water pond. The design of the inlets and pipes above the storm
water pond elevation needed to satisfy the 2Yr and 10Yr requirements as stated in the Greenville
County Stormwater Ordinance. Using the information from tables 4, 5, and 6 each sub-basin was
created in the workspace as shown in figure 4. Sub-basins were selected as pervious, impervious or
combined areas. Areas, curve number, peak rate factor, and time of concentration were imputed for
each individual sub-basin. All soils were selected as Pacolet from the provided soils report. With the subbasins arranged each was connected with the appropriate feature (Non-Routed Connector, Pipe
Structure, or Circular Conduit) based on drawing H3. Sub-basins that drained off site away from the
existing catch basin were connected to the shared final outlet. Before IDEAL was ran several design
guidelines were established on top of the requirements set by Greenville County.
1.
2.
3.
4.
Maximum Spread of 3ft (6-feet is Actual Max GCSO 6.5.1.7)
Maximum Spacing of 300ft.
Minimum Pipe Slope of 0.5% (GCSO 6.5.1.5)
The minimum fill over on all pipes shall be 1-foot (GCSO 6.5.1.6)
To be conservative a maximum spread of 3ft was established and a maximum spacing of 300ft was
selected to treat the runoff as sheet flow.
Initially all pipe sizes were assumed to be 15” RCP pipes and all combinations inlets assumed to be 2ft x
3ft combination inlets with a 4” throat height. Slotted drain inlets spanned the width of the road and the
grates were assumed to be either 6 or 8 inches wide depending on the pavement slope. Combination
inlets were selected because they provide both trash and water removal. Slotted drain inlets were
selected to separate parking lot and road areas for delineation purposes as well as reduced flow paths.
All sub-basins that flowed over the surface were treated as non-routed connectors to their respective
inlets. With all assumptions and properties inputted IDEAL was validated and run. The report following
displayed spreads, surcharges, and error messages. All conduits and inlets that were surcharged were
increased until the error message cleared. The error message “Convergence criteria is not met. Flow is
routed as simple translation” was ignored. This process was repeated until all pipes and inlets met
design requirements but yet remained cost effective. With the maximum spacing between inlets 300ft
this did not affect any of the design.
Section 3: Hydraulics & Hydrology
17
Roof Drainage
The roof drainage design can be seen in Roof Drainage Calculations of the sample calculations in section
3.13. Following the guidelines provided by the 2000 International Plumbing Code (IBC) the roof drainage
design satisfies the 100-YR-1Hr Rainfall events for this particular area. A traditional downspout and
gutter was chosen for the Museum of Clemson History. As seen in the calculations the roof plan was
divided into 3 areas to simplify the irregularly shaped roof. From figure 1106.1 of the IBC the 100-Yr-1Hr
rainfall was determined to be 4.0 inches for the Clemson area. A 3-inch diameter vertical leader was
assumed from table 1106.2. Spacing for the leaders was then determined and checks to ensure the
assumed leader diameter satisfied the requirements. Both gutter size and horizontal storm drainage
piping were selected at ¼” slope in 12. From tables 1106.6 and 1106.3 the gutter size and horizontal
storm drain piping were determined. These steps were followed for each of the three roof areas. Areas
2 and 3 converge to form a single 3-inch diameter leader to satisfy both areas to the left and right of the
dashed line as depicted in the sample calculations.
Table 7: Combination Inlets
Structure
I1
I2
I3
I4
I5
Size (ft)
2X3
2X6
2X3
2X3
2X3
Throat Height (in)
4.0
6.0
4.0
4.0
4.0
Opening Area (ft2)
3.0*
6.0
3.0*
3.0*
3.0*
* Not included in IDEAL for inlets on grade.
Table 7 displays the final dimensions for the combination inlets. Inlet I2 was the only one surcharged
during the 10Yr event so the size was doubled to reduce the spread down below the 3ft goal.
Table 8: Slotted Drain Inlets
Structure
SD1
SD2
SD3
SD4
Size (ft)
0.5X40
0.5X40
0.67X30
0.67X22
Opening Area (ft2)
8.0*
8.0*
6.0*
4.0*
* Not included in IDEAL for inlets on grade.
Section 3: Hydraulics & Hydrology
18
Table 8 displays the final dimensions for the slotted drain inlets. 6-inch wide grates were used for low
slope areas and 8-inch wide grate for steeper slopes and/or increased catchment area.
Table 9: Pipe Dimensions and Properties
Pipe
Diameter (in)
Length (ft)
Slope
Material
P1
18
130
0.007
RCP
P2
18
5
0.02
RCP
P3
15
60
0.005
RCP
P4
15
80
0.0063
RCP
P5
15
120
0.0058
RCP
P6
12
170
0.0165
RCP
P7
15
22
0.01
RCP
P8
15
22
0.01
RCP
P9
12
150
0.03
RCP
P10
15
80
0.05
RCP
GP1
6
54
0.02
PVC
GP2
8
58
0.02
PVC
SP1
6
20
0.075
PVC
SP2
8
50
0.04
RCP
PIPE UNDER PERIMETER RD
20
120
0.0125
RCP
Abbreviations: PVC - Polyvinyl Chloride RCP - Reinforced Concrete Pipe
Table 9 displays the pipe schedule with appropriate dimensions, slope, and material. The diameter of P1,
P2, and the pipe under Perimeter Rd had to be increased to prevent surcharging. The increase in the
diameter of the pipe under Perimeter required the invert elevation at the existing catch basin to be
lowered to 778.5ft to accommodate the increased pipe diameter. GP1, GP2, and SP1 were all selected to
be PVC to reduce costs.
Section 3: Hydraulics & Hydrology
Table 10: Structure Rim Elevations and Pipe Invert Elevations
Structure
Rim Elevation (ft)
P4
I1
791.8
787.5
P6
I2
793.6
791
P7
I3
793
787.4
P8
I4
793.85
787.8
P10
I5
795.25
791.4
SP1
SD 1
787
785.5
P3
SD 2
794.2
787.3
P5
SD 3
794.6
788.2
SD 4
797.3
O1
790
Swale 1
785
Swale 2
795
Invert Elevation (ft)
P5
787.5
P8
787.4
P10
787.4
P6
788.2
SP2
795
P3
P4
787
787
SP1
784
SP2
793
Pipe Under Perimeter
Pipe Under Newman
779.07
Existing Catch Basin on
Site
780.67
778.5
Catch Basin
780
Pipe Under Perimeter
777
P7
787
Table 10 displays all the rim elevations of the stormwater system structures. Each structure has the
invert elevations of all pipes entering or exiting the structure. All pipes remained at a minimum 1ft
below the ground surface to satisfy the fill requirements. All pipes were also designed at a minimum
pipe slope of 0.5% to meet code.
19
Section 3: Hydraulics & Hydrology
20
Table 11: Swale Dimensions
Type
Length (ft)
Width (ft)
Max Depth (ft)
Slope (ft/ft)
Side Slope (ft/ft)
Mannings Coeff. (n)
Swales
SW1
Trapazoidal
52
2
1
0.01
0.3
0.24
SW2
Trapazoidal
150
2
1
0.01
0.3
0.24
As seen in drawing H3 two swales were designed to increase the flow path of the runoff from SP1 and
SP2 to the existing catch basin and shared outlet point respectively. The dimensions of the swales were
all assumed based on common design surrounding the university. Sod was used to cover the swales due
to an increased manning coefficient and time of concentration.
Table 12: Pre and Post-Development Hydrograph Properties
Hydrograph Properties
2-Yr Storm Event Peak Flow (cfs)
10-Yr Storm Event Peak Flow (cfs)
2-Yr Storm Event Peak Discharge Time (hrs)
10-Yr Storm Event Peak Discharge Time (hrs)
2-Yr Storm Event Runoff Volume (ac-ft)
10-Yr Storm Event Runoff Volume (ac-ft)
PreDevelopment
4.448
10.54
12.1
12.1
0.5862
1.222
PostDevelopment
4.246
9.822
12.1
11.0
0.7083
1.62
Table 12 displays the tabulated output from figures 2,3,7 and 8 for the pre and post-development
hydrographs. The post-development 2Yr and 10Yr storm event peak flow satisfies the design
requirements set by the Greenville County Stormwater Ordinance. The post-development 10Yr storm
peak discharge time was reduced from the effects of the stormwater pond.
Section 3: Hydraulics & Hydrology
21
Table 13: Pond Properties
Pond Properties
Depth (ft)
10
Stage-Area 0ft (acres)
0.0135
Stage-Area 10ft (acres)
0.119
Riser
Type
Open Top
Shape
Circular
Height (ft)
7.5
Diameter (in)
24
Orifices
Diameter (in)
1 @ 0ft
1.5
1 @ 3ft
1.5
3 @ 6ft
3
Barrel
Diameter (in)
18
Length (ft)
25
Slope
0.02
Material
RCP
Emergency Spillway
Type
Broad-Crested Weir
Shape
Rectangular
Crest Height (ft)
7.5
Width (ft)
6.0
Table 12 displays the pond properties during the 2,10, and 100Yr-24Hr storm events. With the confined
area from the parking lot and property setbacks the pond surface area was at its max. With a 2H:1V
grading the stage area at the top of the pond was 0.119 acres and bottom equal to 0.0135 acres. A 7.5ft
tall 24-inch diameter open top riser was designed to control the outflow from the pond. The storm
water pond was tested at 2yr, 10yr, and 100yr storms to determine the elevations and number of
orifices along the riser. The barrel was designed to be 25ft long with an 18inch diameter composed of
RCP. The emergency spillway was designed at 7.5ft above the bottom surface of the pond. Rectangular
in shape the broad-crested weir spans 6.0ft wide. Riprap protection on the opposite side of the weir
provides erosion control from scouring when the emergency spillway is in use. A plan and profile view of
the stormwater pond can be seen in drawings H4 and H5.
Section 3: Hydraulics & Hydrology
22
3.11 Analysis and Results
Table 14: Pre-Development Peak Flow versus Post-Development Peak Flow
2-Yr Storm Event
10-Yr Storm Event
Peak Flow (cfs)
Pre-Development
4.448
10.54
Post-Development
4.246
9.822
As stated in the Greenville County Stormwater Ordinance the post-development peak flow shall not be
greater than the pre-development peak flow rate. With the given stormwater design the posdevelopment satisfies this requirement for both the 2Yr and 10Yr-24Hr storm events.
Table 15: Inlet Spreads
Inlet
I1
I2
I3
I4
I5
Spread (ft)
1.97
2.82
1.35
2.66
1.85
As stated by the Greenville County Stormwater Ordinance the maximum spread in the travel lane must
not exceed 6-feet during the 10Yr storm event. A 3-feet maximum spread was used in the design during
IDEAL so this requirement is satisfied.
Table 16: Stormwater Pond Peak Stage
Peak Stage (ft)
2-Yr Storm Event
10-Yr Storm Event
100-Yr Storm Event
5.37
7.393
7.937
As stated by Capstone Developers a minimum freeboard of 2-foot above the 100-year 240hr design
storm water elevation must be maintained. Additionally the emergency spillway must be utilized by the
100-year storm only. During the 2Yr-24Hr storm event he pond rises to 5.37ft using the first two sets of
orifices on the barrel riser. During the 10Yr-24Hr storm event the water level rises 7.393ft utilizing the
last set of orifices at 6ft above the bottom surface of the pond. With an emergency spillway elevation of
Section 3: Hydraulics & Hydrology
23
7.5ft above the bottom of the pond the emergency spillway is being utilized during the 100-yr storm
event only. The maximum pond depth is 10ft including the freeboard requirement concluding that the
peak stage of 7.937ft lies below the 8ft maximum required in design.
The stormwater design for the Museum of Clemson History satisfies all design requirements established
by the Clemson University Master Plan and the Greenville County Stormwater Ordinance.
Technical Specification included in the stormwater design:
Division 33:
334100
3.12 References
Greenville County Storm Water Management Design Manual
2000 International Plumbing Code
“Hydrology and Hydraulic Systems”, Gupta, Ram S. 3rd Edition
IDEAL® Software
PowerPoint’s provided by Dr. Earl Hayter Clemson University
Section 3: Hydraulics & Hydrology
3.13 Sample Hand Calculations
Time of Concentration, Tc
Pre-Development Sub-Basin 1:
Flow Line A: 577.8ft
𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝐺𝑟𝑎𝑑𝑒 𝑓𝑜𝑟 𝑓𝑖𝑟𝑠𝑡 300′ =
𝐸𝑙𝑒𝑣𝑎𝑡𝑖𝑜𝑛 1−𝐸𝑙𝑒𝑣𝑎𝑡𝑖𝑜𝑛 2
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝐺𝑟𝑎𝑑𝑒 𝑓𝑜𝑟 𝑓𝑖𝑟𝑠𝑡 300′ =
𝑆ℎ𝑒𝑒𝑡 𝐹𝑙𝑜𝑤 𝑇𝑟𝑎𝑣𝑒𝑙 𝑇𝑖𝑚𝑒, 𝑇𝑡 =
𝑇𝑡 =
808𝑓𝑡 −785.81𝑓𝑡
300𝑓𝑡
= 0.074
0.007(𝑛𝐿)0.8
𝑃2 0.5 𝑆 0.4
0.007(0.24 ∗ 300)0.8
= 0.3156 ℎ𝑟𝑠
3.70.5 0.0740.4
𝑆ℎ𝑎𝑙𝑙𝑜𝑤 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑒𝑑 𝐹𝑙𝑜𝑤 𝑇𝑟𝑎𝑣𝑒𝑙 𝑇𝑖𝑚𝑒, 𝑇𝑡 =
𝑇𝑡 =
277.8𝑓𝑡
3600∗0.9𝑓𝑡/𝑠
𝐿
3600𝑣
= 0.0857 ℎ𝑟𝑠
𝑇𝑖𝑚𝑒 𝑜𝑓 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛, 𝑡𝑐 = 𝑆ℎ𝑒𝑒𝑡 𝐹𝑙𝑜𝑤 𝑇𝑡 + 𝑆ℎ𝑎𝑙𝑙𝑜𝑤 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑒𝑑 𝐹𝑙𝑜𝑤 𝑇𝑡
𝑡𝑐 = 0.3156ℎ𝑟𝑠 + 0.0857ℎ𝑟𝑠 = 0.4013 ℎ𝑟𝑠
Curve Number, CN
Pre-Development Sub-Basin 1:
Total Area: 2.485 acres composed of grass and wood land.
Good Condition Open Space Grass Cover = 2.215 acres
Good Condition Wood Land = 0.27 acres
CN Grass Cover = 61
CN Wood Land = 55
𝐶𝑁𝐴𝑣𝑔 =
𝐶𝑁𝐴𝑣𝑔 =
𝐴𝑟𝑒𝑎1 𝐶𝑁1 + 𝐴𝑟𝑒𝑎2 𝐶𝑁2
𝐴𝑟𝑒𝑎 1 + 𝐴𝑟𝑒𝑎 2
2.215 ∗ 61 + 0.27 ∗ 55
= 60.3
2.485
24
Section 3: Hydraulics & Hydrology
Page 1 of roof calcs
25
Section 3: Hydraulics & Hydrology
Page 2 of roof calcs
26
Section 3: Hydraulics & Hydrology
Page 3 of roof calcs
27
Section 3: Hydraulics & Hydrology
28
3.14 Lessons Learned
In the design of the stormwater system several lessons were learned. From a software standpoint
AutoCAD Civil 3D was heavily used in the pre-development and post-development basin delineation.
Features like Water Drop were a useful tool to gain a visual perspective of how water would flow over
the created surface. IDEAL created a computer model of the basin delineation that could be analyzed
through several storm events displaying reports for the inlets, pipes, pond, and runoff values.
Following the design requirements from Capstone Developers and the Greenville County Stormwater
Ordinance required a lot of checklists and management duties to ensure the design was compliant with
the minimum standards and also the higher standards on top of the GCSO.
Communication and planning between Freeman Mach Consulting played a crucial role in an efficient
stormwater design. Grading the site to use natural gravity flow while leaving sufficient area on a
confined plot for the storm water pond required several inputs from the transportation, construction,
and hydrologic design specialist.
Section 3: Hydraulics & Hydrology
Section 3.15 Hydraulics & Hydrology Drawings
H1: Pre-Development Sub-Basin Delineation
H2: Post-Development Sub-Basin Delineation
H3: Building and Parking Lot Flow Features
H4: Stormwater Pond Plan View
H5: Stormwater Pond Elevation View
29