Hydraulic Analysis and Embankment Protection Conceptual Design
Hydraulic Analysis and Embankment Protection Conceptual Design
Hydraulic Analysis and Embankment Protection Conceptual Design
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50 th Annual ASCE Environmental <strong>and</strong> Water Resources <strong>Design</strong> Conference<br />
<strong>Hydraulic</strong> <strong>Analysis</strong> <strong>and</strong> <strong>Embankment</strong> <strong>Protection</strong><br />
<strong>Conceptual</strong> <strong>Design</strong><br />
Presented by Andy McCoy, PhD, PE In conjunction with:<br />
Water Resources Engineer at HDR Engineering Iowa DOT &<br />
Des Moines, Iowa HGM <strong>and</strong> Associates
Acknowledgements<br />
• Iowa DOT – Dave Claman, Bill Kaufman<br />
• HDR – Mike Schubert, Justin Anderson<br />
• HGM – Paul Kline, Brian Higginbotham
Introduction <strong>and</strong> Overview – Context<br />
• Record Missouri River flooding in 2011 – but<br />
also 2008 & 2010<br />
• I-680 severely damaged <strong>and</strong> rebuilt fall 2011<br />
• Iowa DOT investigating permanent<br />
embankment protection<br />
• <strong>Hydraulic</strong> implications of overtopping -typical<br />
sections
Presentation Overview<br />
• Damage Inspection at I-680<br />
• Study approach<br />
• <strong>Hydraulic</strong> analysis <strong>and</strong> results<br />
• <strong>Embankment</strong> protection ti concepts<br />
• Next steps – site specific design
Overview<br />
• Damage Inspection at I-680.<br />
• Study approach<br />
• <strong>Hydraulic</strong> analysis <strong>and</strong> results<br />
• <strong>Embankment</strong> protection ti concepts<br />
• Next steps – site specific design
Damage Investigation
Damage Investigation<br />
• Erosion most severe along the outside edges of the pavement<br />
• Severity of the erosion appeared to increase from north to south.<br />
• A majority of the embankment side slopes appeared to have remained<br />
intact<br />
• Isolated areas where the embankments were entirely breached
Overview<br />
• Damage Inspection at I-680.<br />
• Study approach<br />
• <strong>Hydraulic</strong> analysis <strong>and</strong> results<br />
• <strong>Embankment</strong> protection ti concepts<br />
• Next steps – site specific design
Study Approach<br />
• What type of embankment protection could be<br />
constructed on existing IaDOT roadway system<br />
where roadways subject to potential overtopping?<br />
• What range of maximum velocities result from<br />
varying headwater, tailwater, unit flow rate, typical<br />
section (4 lane versus 2 lane), <strong>and</strong> embankment<br />
height?<br />
• Could a design be developed that could be applied at<br />
multiple locations?
Study Approach<br />
• Analyze the hydraulics of typical IaDOT roadway<br />
sections over a range of conditions
Overview<br />
• Damage Inspection at I-680<br />
• Study approach<br />
• <strong>Hydraulic</strong> analysis <strong>and</strong> results<br />
• <strong>Embankment</strong> protection ti concepts<br />
• Next steps – site specific design
<strong>Hydraulic</strong> <strong>Analysis</strong> <strong>and</strong> Results - Overview<br />
• USBR 2D flow solver – SRH-2D<br />
• Created typical models for 2-lane <strong>and</strong> 4-lane<br />
roadway configuration<br />
• Varied parameters:<br />
Table 1. Combinations for modeling<br />
Roadway Tailwater (ft) Unit Flow Rate <strong>Embankment</strong><br />
Combinations (cfs/ft) Height (ft)<br />
2 Lane 2 to 8 5 to 40 2 to 7<br />
4 Lane 2 to 8 5 to 40 2 to 7<br />
• Looked at resultant maximum velocities<br />
• Combine information into useful figure to<br />
inform future decisions
<strong>Hydraulic</strong> <strong>Analysis</strong> <strong>and</strong> Results - Mesh<br />
Modeled Roadway <strong>and</strong> <strong>Embankment</strong> in<br />
plan view - 4 Lane Divided Highway –<br />
Contours. Crest Elevation = 991,<br />
Floodplain Elevation = 983 ft.<br />
Computational Mesh - Modeled<br />
Roadway <strong>and</strong> <strong>Embankment</strong>. The inset<br />
area shows the refined mesh in the<br />
area of the road embankment.
<strong>Hydraulic</strong> <strong>Analysis</strong> <strong>and</strong> Results – Water <strong>and</strong><br />
<strong>Embankment</strong> Profile
<strong>Hydraulic</strong> <strong>Analysis</strong> <strong>and</strong> Results – Maximum<br />
Velocity Versus Head Differential<br />
Maximum Velocity versus Head differential for all<br />
simulations. Note the area within the black oval<br />
represent the estimated conditions for I-680 for the<br />
flood experienced in 2011.
<strong>Hydraulic</strong> <strong>Analysis</strong> <strong>and</strong> Results – Conclusions<br />
• In 4-Lane – downstream embankment provides shielding for<br />
the upstream embankment<br />
• Maximum velocities are 14 - 18 feet per second (fps) as the unit<br />
flow rates <strong>and</strong> the head differential between upstream <strong>and</strong><br />
downstream increase<br />
• Secondary maximum velocity at downstream shoulder of the<br />
upstream embankment (4 – 9 fps)<br />
• Maximum velocity <strong>and</strong> maximum velocity location depends on<br />
degree of submergence but near edge of pavement to further<br />
down slope in low tailwater condition
Overview<br />
• Damage Inspection at I-680<br />
• Study approach<br />
• <strong>Hydraulic</strong> analysis <strong>and</strong> results<br />
• <strong>Embankment</strong> protection ti concepts<br />
• Next steps – site specific design
<strong>Embankment</strong> <strong>Protection</strong> Concepts<br />
• Vegetated Cover – The majority of existing IaDOT embankments are currently protected<br />
with a vegetated ttd grass cover. This option would consist it of maintaining ti i the existing iti<br />
embankment protection, which would provide protection against lower estimated flow<br />
velocities <strong>and</strong> short flood durations.<br />
•<br />
• Reinforced Vegetation – Permanent turf reinforcement mats like those manufactured by<br />
North American Green ® , Scourstop ® , <strong>and</strong> Green Armor System ® can be incorporated for<br />
higher estimated flow velocities.
<strong>Embankment</strong> <strong>Protection</strong> Concepts<br />
d k i l i i l i bl k b<br />
• Hard Armor –Rock riprap, concrete slope paving, or articulating concrete blocks can be<br />
placed along the embankment slopes with a geotextile.
<strong>Embankment</strong> <strong>Protection</strong> Concepts<br />
• Reinforced Vegetation/Hard Armor –Geoweb ® slope protection is a geosynthetic web<br />
filled with crushed aggregate, which h allows for vegetative ti growth, representing a<br />
combination of both hard armor <strong>and</strong> reinforced vegetation.
<strong>Embankment</strong> <strong>Protection</strong> Concepts<br />
Vegetated<br />
Cover Reinforced Vegetation Hard Armor<br />
Reinforced<br />
Vegetation/<br />
Hard Armor<br />
Grass Cover<br />
(Seeding)<br />
North<br />
American<br />
Green<br />
Scourstop<br />
Green<br />
Armor<br />
System<br />
Rip-Rap<br />
Articulating<br />
Concrete Block<br />
Slope<br />
Paving<br />
Geoweb<br />
Max Permissible<br />
Velocity (fps)<br />
3.5 to 8 (1) 25 21 fps 20 5 to 18 (1) >18 fps (1) >18 (1) 10 to 26.5<br />
<strong>Design</strong> Life<br />
Very Long<br />
Short<br />
(3 yr)<br />
Medium to<br />
Medium to<br />
Medium to Long<br />
Long<br />
long<br />
Long<br />
long (50+ yr) (50+ yr)<br />
(25+ yr)<br />
(25+ yr)<br />
Long<br />
(50+ yr)<br />
Maintenance<br />
Considerations<br />
Mowing<br />
Mowing<br />
No mowing,<br />
must spray<br />
Mowing<br />
Crack<br />
sealing<br />
No Mowing<br />
Mowing<br />
Constructability Easy Easy Medium Medium Difficult Medium/ Difficult<br />
Material Availability High High<br />
Depends on<br />
Area<br />
High<br />
High<br />
High (2 Iowa<br />
Distributors)<br />
Construction Cost<br />
Low to<br />
Medium (2)<br />
Medium<br />
Medium ($9-<br />
10/sf)<br />
Medium High (2) High High<br />
Medium (2) to<br />
High<br />
Maintenance Cost Low (2) May require periodic reseeding. Low (2) Low Low Low (2)<br />
Notes:<br />
• Reference (Fischenich, 2001)<br />
• Reference (IDNR, 2006)
<strong>Embankment</strong> <strong>Protection</strong> Concepts –<br />
What could work at I-680?<br />
Vegetated<br />
Cover Reinforced Vegetation Hard Armor<br />
Reinforced<br />
Vegetation/<br />
Hard Armor<br />
Grass Cover<br />
(Seeding)<br />
North<br />
American<br />
Green<br />
Scourstop<br />
Green<br />
Armor<br />
System<br />
Rip-Rap<br />
Articulating<br />
Concrete Block<br />
Slope<br />
Paving<br />
Geoweb<br />
Max Permissible<br />
Velocity (fps)<br />
3.5 to 8 (1) 25 21 fps 20 5 to 18 (1) >18 fps (1) >18 (1) 10 to 26.5<br />
<strong>Design</strong> Life<br />
Very Long<br />
Short<br />
(3 yr)<br />
Medium to<br />
Medium to<br />
Medium to Long<br />
Long<br />
long<br />
Long<br />
long (50+ yr) (50+ yr)<br />
(25+ yr)<br />
(25+ yr)<br />
Long<br />
(50+ yr)<br />
Maintenance<br />
Considerations<br />
Mowing<br />
Mowing<br />
No mowing,<br />
must spray<br />
Mowing<br />
Crack<br />
sealing<br />
No Mowing<br />
Mowing<br />
Constructability Easy Easy Medium Medium Difficult Medium/ Difficult<br />
Material Availability High High<br />
Depends on<br />
Area<br />
High<br />
High<br />
High (2 Iowa<br />
Distributors)<br />
Construction Cost<br />
Low to<br />
Medium (2)<br />
Medium<br />
Medium ($9-<br />
10/sf)<br />
Medium High (2) High High<br />
Medium (2) to<br />
High<br />
Maintenance Cost Low (2) May require periodic reseeding. Low (2) Low Low Low (2)<br />
Notes:<br />
• Reference (Fischenich, 2001)<br />
• Reference (IDNR, 2006)
<strong>Embankment</strong> <strong>Protection</strong> Concepts –<br />
Conclusions<br />
• The most practical embankment slope protection alternative -<br />
maximum protection/lowest life cycle cost for long stretches of<br />
existing roadway pavements <strong>and</strong> embankment<br />
• Required maintenance comparable to that of the existing grass<br />
cover<br />
• Reinforced Vegetation/Hard Armor alternative (Geoweb ® ) is<br />
recommended for areas with estimated velocities in excess of<br />
10 fps (I-680)<br />
• For areas with estimated flow velocities between 5 <strong>and</strong> 10 fps<br />
the Reinforced Vegetation alternative is recommended.<br />
• For areas with estimated velocities below 5 fps, a typical<br />
vegetated (grass) cover is recommended
Overview<br />
• Damage Inspection at I-680<br />
• Study approach<br />
• <strong>Hydraulic</strong> analysis <strong>and</strong> results<br />
• <strong>Embankment</strong> protection ti concepts<br />
• Next steps – site specific design
Next Steps-challenges <strong>and</strong> direction at I-680<br />
• Interstate 680 already reconstructed<br />
• Construction of hard armor/reinforced vegetation<br />
very challenging<br />
g<br />
• How to positively connect geoweb <strong>and</strong> navigate<br />
subdrain?
Next Steps-challenges <strong>and</strong> direction at I-680<br />
• Construction of hard armor/reinforced vegetation very challenging<br />
• Create structural embankment protection within ROW (levee) to<br />
protect shoulder <strong>and</strong> embankment toe<br />
• Eases construction challenges reduces high velocities at shoulder<br />
• Eases construction challenges, reduces high velocities at shoulder,<br />
riprap could be used for downstream protection, downstream slope<br />
could be shallower (~less velocity)
Next Steps-challenges <strong>and</strong> direction at I-680<br />
• No flow measurements taken at I-<br />
680 during flood – hard to estimate<br />
unit flow rate or overtopping flow<br />
quantity<br />
• Roadway was wet, but where was<br />
the flow concentrated<br />
• Where did flow break out of main<br />
channel, what role did levees <strong>and</strong><br />
road embankments play in<br />
directing the flow?<br />
• Need site specific 2D model
Next Steps-challenges <strong>and</strong> direction at I-680<br />
• Previously thought that<br />
situation didn’t occur<br />
with downstream side of<br />
embankment dry<br />
• IaDOT desires site<br />
IaDOT desires site<br />
specific 2D hydraulic<br />
model capable of<br />
answering the questions<br />
raised
Thank You.<br />
Questions?
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