James Is., Charleston Watershed Senior Design

1. Austin Balser, Daniel Chewning,
Kelly Creswell, Tyler DuBose

2. Introduction
 Overview
 Problem
 Goals
 Constraints
 Literature Review
 Design Methodology and Materials
 Analysis of Information
 Synthesis of Design
 Alternative Design Options
 Approach to Solution and Final Design
 Sustainability
 Budget
 Timeline
 References

3. Problem
 Recognition:
 Urban and suburban development leads to high runoff
rates and low infiltration rates which reduce the quality
of ground and surface water
 Definition:
 Rapid increase of development in Charleston, SC
leading to high volume of runoff and flooding

4. Goal
 Design a stormwater management plan for Sea Aire
subdivision that:
 Meets state regulations by ensuring the peak flow
during a 2 and 25 year storm event doesn’t exceed pre-development
levels
 Ensures the post-development runoff volume doesn’t
exceed pre-development levels

5. Robinson Design Engineers: Site Plan

6. Robinson Design Engineers: Site Plan

7. Constraints
 Ecological: Must work with existing soil, water table,
vegetation, and waterways
 Ultimate use: Residential living and recreational
space
 Skills: Limited knowledge and experience with
stormwater design
 Cost: Budget of $1200 for design process. Must account
for travel expenses, software, and testing services
 Additional: Difficulty working with regulators and
contractors

8. Questions of User, Client and Designer
 User- Residents of Sea Aire
 What is a rain garden, why are there plants in the ditch?
 What do I have to do?
 Client- New Leaf Builders through Robinson Design
Engineers
 Will this meet regulations?
 Will it cost more?
 Designer- The design team and RDE
 Will this be long lived?
 Can this be an amenity?

9. Governing Equations
 Energy Balance
 푃푎푉 +
1
2
2 + mgha = PbV +
푚푣푎
1
2
mvb
2 + mghb
 Mass Balance
 푚푎푠푠푖푛 − 푚푎푠푠표푢푡 ± 푟푒푎푐푡푖표푛푠 = 푎푐푐푢푚푢푙푎푡푖표푛
 Curve Number Method
 푄 =
퐼−0.2푆 2
퐼+0.8푆
, 푆 =
1000
퐶푁
− 10
 Horton’s Equation
 푓 = 푓푐 + (푓0 − 푓푐 )푒−푘푡
 Universal Soil Loss Equation
 T=RKLSCP

10. Stormwater Management
 Conventional Methods versus LID methods
 Conventional methods provide solutions at the bottom
of the site (ponds, basins, ect.)
 Low impact development methods encourage
infiltration from all locations on site in an effort to
mimic the more natural process

11. Comparison of Volume
1 – Pre-development
2 – Conventional Methods
3 – LID Methods
LID methods maintain pre-development
runoff volume
while conventional methods
lead to increased volume

12. Conventional Methods
 Detention basins
 Drains
 Concrete ditches
 Culverts

13. Low Impact Develop Methods
 Green roofs
 Rain water collection
 Constructed Wetlands
 Bioretention cells
 Rain gardens
 Permeable Pavements

14. Constructed Wetlands
 Public area of development will
need a way to catch and retain
stormwater
 Help filter and remove
containments, “Nature’s Kidney”
 Shallow depression in the ground
with a level bottom

15. Design Methodology and Materials
 Analysis of Information
 Synthesis of Design
 Vegetative Roof
 Rain Barrel
 Rain Garden
 Porous Pavement
 Infiltration Trench
 Bioretention Cell
 Elevation of Alternative Options
 Stormwater Pond
 StormwaterWetland
 Selection of Final Approach

16. Analysis of Information
 Rainfall Distribution Data: Type II
 2-year storm: 4.3 inches
 25- year storm: 8.0 inches
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
0 5 10 15 20 25 30
Cummulative Rainfall (in)
Time (hours)

17. Determining Runoff on Site
 Determined weighted curve number for site using
WebSoil Survey Data
 Calculated runoff depth using Curve Number Method
 Used HEC HMS and SWMM to compute and compare
runoff depth for the entire site

18. 2-Year Design Storm Hydrographs
2-Year Storm: Pre- Development
Runoff Depth: 0.62 inches
Peak Runoff Rate: 0.8 cfs
2-Year Storm: Post- Development
Runoff Depth: 2.57 inches
Peak Runoff Rate: 3.5 cfs

19. 25- Year Design Storm Hydrographs
25-Year Storm: Pre- Development
Runoff Depth: 2.70 inches
Peak Runoff Rate: 3.9 cfs
25-Year Storm: Post- Development
Runoff Depth: 5.82 inches
Peak Runoff Rate: 8.0 cfs

20. Average Residential Lot
 Lot Area: 4857 ft2
 Roof Area: 1132.5 ft2
 Driveway Area: 527 ft2
 Garage Area: 264 ft2
Robinson Design Engineers: Site Layout
 Parameters used to determine design values for LID
options within each residential lot.
 40% of the residential lot is impervious

21. Vegetative Roof
 Plants
 Sedum
 Growing Media
 Perlite (30%)
 Vermiculite (20%)
 Crushed brick (20%)
 Sand (10%)
 Coco peat (20%)
 Filter fabric
 Drainage Layer
 Root Protection Layer
 Waterproof Membrane
 Structural Component
http://godfreyroofing.com/wp-content/uploads/2011/09/green-roofing-layers.png
http://www.optigreen.com/produkte/draenageplatten/fkd-40/

22. Design Considerations
 Load capacity of the roof
 Maintenance: 2 per year
 Initial Growth of Vegetation
 Avoiding Leaks
 Cost of Materials
 Access to Roof
 Fire Risk
 Pitch of Roof
 Gutter System
http://i.stack.imgur.com/tW8B8.jpg
http://www.jrsmith.com/uploads/fileLibrary/1010_rdp_lg.jpg

23. Vegetative Roof Holding Capacity
 Designed to hold 50% of the amount of water falling on
the roof during a 2-year storm
 Each layer of a vegetative roof has a certain water capacity
Component Water Holding Capacity Total
Plants - -
Media Layer 40%, 4 inches 148.7 ft3
Filter Fabric - -
Drainage Layer 8 L/m2 32.3 ft3
Root Protection Layer 4 L/m2 14.8 ft3
Waterproof Layer - -
Roof Material - -
 Total Water Storage: 195 ft3

24. Rain Barrels
 Balance between aesthetics and
storage
 Linked barrels  increased
volume without overwhelming size
 Tank Volume: 200 gallon tanks
 Dimensions: 47’’height, 36’’
diameter
 To be placed on both the house and
garage
 Total Storage Capacity: 800
gallons (4 barrels total)
 Overflow management:
Automatic Downspout Diverter
http://gardenwatersaver.com/connector-kits/
http://gardenwatersaver.co
m/connector-kits/
http://www.tank-depot.com

25. Automatic Downspout Diverter
http://www.gardeners.com/buy/downspout-diverter/33-991VS.html

26. Permeable Pavement
http://www.bae.ncsu.edu/stormwater/PublicationFiles/P
ermPave2008.pdf
• Pavement
• Surface
• Storage
• Underdrain

27. Design Considerations
 Permeable Interlocking Concrete Pavements (PICPs)
 Layers (SWMM)
 Maintenance
 Street sweeping
 Pressure washing
 Vacuum truck
 At least once per year, or after evident damage

28. PICP Design
 3-inch pavement layer
 Manning’s n = 0.019
 Surface slope = 2 to 3%
(less than 5%)
 Storage thickness = 6 to 18
inches
 Underdrain pipe = 1 to 4
inches from bottom of
layer
 Overall depth = 1.5 feet
http://www.bae.ncsu.edu/stormwater/PublicationFil
es/ICPIreport2004.pdf

29. Bioretention Cell
 The public area will contain multiple bioretention cells
 The cells will overflow into vegetative swales or
underdrain pipes below the bioretention cell to leave
the site via the wetland/ vegetated enhanced ditch
http://www.northinlet.sc.edu/LID/FinalDocument/loRes/4.2%20Bioretention%20low%20res.pdf

30. Can we do it?
Water Storage Capacities of LID Methods
• If all LID methods were used together the 25 year storm could theoretically be
contained on each property
• Due to spatial and budgetary constraints, not all LID controls will be installed on
a property
• Therefore, management of flow into the main area from individual plots must
still be considered
Design Storm
Pre-Development
Runoff Depth (in)
Post-Development
Runoff Depth (in)
Increase in Runoff
Depth After
Development (with
no LID controls) (in)
Runoff Volume (gal)
2 year 0.62 3.14 2.52 7629
25 year 2.7 6.56 3.86 11686
Green Roof (gal) Rain Barrels (gal) Infiltration Trench (gal) Permeable Pavement (gal) Rain Garden (gal) Total Water Storage (gal)
1465 800 6567 1800 5520 16152

31. SWMM Modeling
http://www.hydraulicmodel.com/sites/hydraulicmodel.com/files/images/epa_logo_1_2.thumbnail.png

33. Life Cycle Assessment
 Vegetative Roof: Material processing (polypropylene,
HDPE, and PVC), importing of media contents
 Rain Garden: Native plant acquisition, capture of
CO2, pollutant decrease, aesthetic advantage
 Porous Pavement: Manufacturing materials (CGP,
PICP, reinforced plastic pavers), transportation,
reusing rock (crushed/gravel), increase water quality
 Infiltration Trench:

34. Life Cycle Assessment (cont.)
 Rain Barrel:
 Bioretention Cell: Material processing (PVC),
transportation of sand and stone, construction
 Wetland/vegetated enhanced ditch:

35. Sustainability
 Ecological – goal of zero impact on the runoff volume
coming from the site as a means of maintaining the
existing ecosystem
 Social – ultimately serves the people living in the
development. Promotes an active lifestyle and provides
an educational opportunity.
 Economic – prevents future flooding and erosion
 Ethical– aim to balance the wishes of the clients and
the biological integrity of the site

36. Sustainability
 Efficiency
 Capture 100% of stormwater runoff on site for design
storm
 Carbon and Water footprint
 Carbon negative
 Gravity fed systems
 Plants will sequester carbon
 Potential for decreased freshwater demands due to
rainwater recycling (rain barrels)

37. Budget
 Vegetative Roof: $5700 not including construction cost
or initial roofing cost, approximately $5/ft3
 See report for cost breakdown
 Rain Garden:
 Porous Pavement: approximately $3.00/sq. ft. (this
value depends on slope, shape…)
 Rain Barrel:
 Infiltration Trench:

38. Timeline
Event 9/8 9/10 9/17 9/24 10/1 10/7 10/8 10/15 10/22 10/29 11/5 11/12 11/19 11/26 12/3
Finish Proposal
Present Proposal
Finish majority of Literature Review
Pick Design
Start Writing Midterm Paper
3- week progress report
Develop preliminary Design
Calculations for Design
Finish Writing Midterm paper
Midterm Presentation and paper due
Cost Analysis for Design
Bring together final design
Write Final Paper
Final Presentation

39. Questions?

40. References
 http://landstudy.org/Resources.html
 Fangmeier, D.D., Elliot, W.J., Huffman, R.L.,
Workman, S.R. 2013. Wetlands. Soil and Water
Conservation Engineering. Seventh Edition. 287-302.
 Best Management Practices Handbook. South
Carolina Department of Health and Environmental
Control.
www.scdhec.gov/Environment/waterquality/stormwat
er/BMPHandbook/