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2013 12-05 challenging sites-rvss
 

2013 12-05 challenging sites-rvss

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Stormwater management for challenging sites. This slide show was used for a class presented on Dec 5, 2013 at the Rogue Valley Sewer Services in Central Point, OR.

Stormwater management for challenging sites. This slide show was used for a class presented on Dec 5, 2013 at the Rogue Valley Sewer Services in Central Point, OR.

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  • Non-Structural: <br /> Preventative <br /> Restorative <br /> Early planning <br /> Structural: <br /> Mitigative <br /> Engineered/Designed <br /> After the fact <br />
  • “Low impact development is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, small-scale hydrologic controls to more closely mimic predevelopment hydrologic functions.” <br />
  • 0-10% Coverage: Streams are structurally sound with good biodiversity and habitat <br /> 11-25% Coverage: Streambanks become unstable, biodiversity is lost, & water quality is degraded <br /> >25% Coverage: Stream life is lost & water quality is poor <br />
  • Non-Structural: <br /> Preventative <br /> Restorative <br /> Early planning <br /> Structural: <br /> Mitigative <br /> Engineered/Designed <br /> After the fact <br />
  • Reminder: Let’s talk about cost savings <br />
  • Many people think that you can just add some storage rock below the infiltration rain garden, but this just adds depth and won’t be empty in time for the next storm. <br />
  • Wattles are cheap and versatile; they can be used to prevent erosion from concentrated flows down the middle of this facility, for sheet flows, or encircling an inlet or outlet. To be effective, they must be staked into the ground, and overlapped a few inches at the ends. <br />
  • Construction of assembly – explain how and why. <br />
  • Construction of assembly – explain how and why. <br />

2013 12-05 challenging sites-rvss 2013 12-05 challenging sites-rvss Presentation Transcript

  • Stormwater Management on Challenging Sites Sustainable design isn’t about doing something neat, it’s about doing something right.
  • About Me
  • About You
  • Agenda • • • • • • • Introductions/Housekeeping Challenging Sites & Low Impact Development Defined Water Balance Model Managing Rainfall Anywhere Managing Rainfall in (Very) Slowly Draining Soils: Porous Pavement Managing Rainfall in Slow Draining Soils: Bioretention Managing Rainfall on Water Quality & Quantity Constrained Sites
  • Challenging Sites • • • • Steep slopes/landslides High seasonal groundwater High bedrock Inadequate setbacks (ex. Buildings too close together) • Clay soils
  • Types of Site Constraints Real: Water Quality & Quantity • Water Quality: When ground or surface waters may be degraded • Water Quantity: When infiltrating water may cause a problem (i.e. landslides, flooded basements) or cannot be infiltrated (high water table, high bedrock or other shallow impermeable layer)
  • Types of Site Constraints Perceived: Slowly Draining Soils …but, I have tight clay soils with no infiltration!
  • LID takes many forms in each phase of the project (and still incorporates some gray infrastructure) Planning Construction Design Maintenance Sustainability for all the places between the buildings
  • Best Management Practices (aka BMPs) Non-structural vs. Structural
  • Low Impact Development: A Definition “Low impact development is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, smallscale hydrologic controls to more closely mimic predevelopment hydrologic functions.”
  • Water Quality AFTER Development Sediment (air particulates) Nutrients Feces Other debris Runoff volumes Sediment/turbidity Hydrocarbons Heavy metals (particles & soluble) Other chemicals Runoff volume Sediment/turbidity fertilizers pesticides herbicides Runoff volume 11
  • flow base tration) 25% infil ow (shall 25% groundwater (deep infiltration) 0.5% runoff 50% evaporation 100% XX” average annual rainfall Water Balance BEFORE Development Example: WESTERN OREGON
  • Water Balance BEFORE: Simplified
  • No infiltration Reduced infiltration 98% runoff 2% evaporation reduced evaporation 100% average annual rainfall Water Balance AFTER Development Example: EVERYWHERE
  • Water Balance AFTER: Simplified
  • Runoff Volume & Duration from a Watershed Perspective • Additional volumes over pre-developed rates scour stream banks. • Additional durations of flow impact habitat further.
  • Detention
  • Best Management Practices (aka BMPs) Manage Rainfall vs. Runoff Porous asphalt at the Port of Portland manages RAINFALL Bioretention manages RUNOFF from a much larger area than itself
  • Managing Rainfall Anywhere Doesn’t necessarily depend on: • Soils types • Setbacks
  • Minimize Impervious Pavement
  • Green Roofs
  • Ecoroof/Green Roof
  • Contained Planters (Over Impervious Area)
  • Contained Planters (Over Impervious Area)
  • Restored Soils
  • Restore the Soil: Lawn Areas
  • Restore the Soil: Garden Areas
  • Compost Amended Slopes Washington DOT • Great for keeping soil in place on steep slopes, too! http://www.wsdot.wa.gov/Design/Roadside/SoilBioengineering.htm
  • Lots of great information at soilsforsalmon.org
  • Tree Canopy
  • Tree Canopy
  • Managing Rainfall in Slowly Draining Soils • Porous pavements are effective in soils draining as slow as 0.1 inches/hour
  • Porous Pavement Definition • An engineered stormwater facility that you can drive or walk on, which preserves permeability to reduce environmental and social impacts of conventional impervious pavements.
  • Porous Pavement
  • Types Porous asphalt Pervious concrete Grass-crete Courtesy of MGH Associates Courtesy of Fortis Construction Manufactured Permeable Pavers Poured-in-place Permeable Pavers Grid pavements
  • Porous Pavement Generalized Cross Section Detail for Types on Previous Slide • A similar cross section applies to all the types on the previous slide Pervious pavement surface Open-graded crushed aggregate Non-woven geotextile fabric Uncompacted native subgrade
  • OSU Extension Fact Sheet • http://extension.oregonstate.edu Click here
  • OSU Extension’s Stormwater Solutions Additional Resources • Standard Details LID 5.XX • http://extension.oregonstate.edu/stormwater/swamp-lid-details Click here
  • Siting Criteria for Porous Pavements • Porous Pavement Siting Criteria: http://extension.oregonstate.edu/stormwater/porous-pavement-1 • NOT on expansive soils
  • POROUS PAVEMENT DESIGN
  • Design Criteria 1. 2. 3. 1. 2. Manage stormwater = hydrologic design Support traffic loads = structural design Prevent clogging • Siting • Pavement mix design/specifications • Construction • Maintenance Figure out how to get Criteria 1 & 2, even if we can’t prevent clogging = Belt & suspenders approach Avoid UICs
  • Prevent Clogging – Siting Hydraulic Isolation of the Surface Oops! Clogging (Construction) Ridge Impe rviou s Asph alt • Must be “hydraulically isolated”. A source control term that means runoff from some other area should not flow onto porous pavement.
  • Prevent Clogging – Siting Hydraulic Isolation of the Surface Impervious Asphalt Courtesy of Cahill Associates P o r u s P a v e m e n t
  • Prevent Clogging – Siting Hydraulic Isolation of the Surface s rviou Impe te re Conc
  • Water Quantity Hydraulic Isolation of the Surface Impervious Concrete P o r u s P a v e m e n t
  • Prevent Clogging – Siting Hydraulic Isolation of the Surface
  • Relationship of water quality storm and sediment transport/scouring • The most frequent storm (predicted as the 6-month frequency storm, but probably happens more often) • small to very small sized storm, • expected to scour pollutants off a runoff generating surface. • Conclusion: Hydraulic isolation is KEY to low maintenance porous pavements!
  • More Clogging Design Considerations • Pavements should still be sloped at a minimum of 1% (1/8” drop per horizontal foot) in case they clog • Belt and suspenders approach to clogging Not a UIC • This configuration was used at Pringle Creek without being considered a UIC, should it clog.
  • Design Considerations • When porous pavement is installed next to impervious pavement, install a liner the depth of the porous pavement to block flows that could undermine the structural stability of the impervious pavement.
  • Design Considerations Soil Animals • Pringle Creek had gophers digging holes through the base rock of their pervious concrete! • Consider durable, nonpolluting screen or raised or flushed curbs on edges
  • Extra rock storage • Some projects infiltrate roof runoff below the pavement.
  • You MAY have created a UIC if… • • The facility infiltrates & You’re using a perforated pipe underground UIC Not a UIC
  • Porous Pavement Hydrologic Model • http://extension.oregonstate.edu/stormwater/porous-pavement-calculator • Excel model good to determine depth of base rock needed to store desired storm depth until it can infiltrate • MUST compare this against depth of base rock needed for structural stability (from your geotechnical engineer) • Rock needed = greater of these two criteria
  • Simple Hydrologic Design Case Study Assume: • City of Turner • All stormwater must be kept on site • Protection from stream scouring desired = infiltrate the 2-year design storm • Hydraulic isolation • Not in a flooded area
  • Hydrologic Design in Excel Calculator Post-developed Model
  • Step 1: Enter rainfall depth. • Infiltrating the 2-year, 24-hour storm is predicted to meet detention requirements (attenuate flows) and protect streams. • This is a rule of thumb only and varies by watershed from between 18month and 2.5-year frequency interval.
  • Working on Post-developed Worksheet Step 1: Enter rainfall depth. • NOOA Isopluvial Map • 2-year frequency rainfall in tenths of an inch
  • Step 2. Enter pavement area [sf].
  • Step 3: Enter storage rock area. • For now, we’ll assume a simple configuration where we’re only managing rainfall, so the default setting is OK. • Storage rock area will fill in automatically by default.
  • Step 4. Enter runoff coefficient. • There's no runoff from porous pavement usually, but for modeling, we assume that an area of impervious pavement is draining to the same size area of native soil underlying it, so we enter 0.9 - 0.98 for imp surface (the C in Q=CIA rational method of predicting runoff) • You don’t need to change this, but it’s here for those designers who may want to.
  • Step 5. Enter native soil design infiltration rate • Enter after performing infiltration testing in the soil and at the depth where the porous pavement will be installed.
  • Porous Pavement Infiltration Testing
  • Infiltration Testing Proposed Conditions
  • Infiltration Testing Existing Conditions (with Proposed Shown)
  • Infiltration Testing Prepare the Hole 1. 2. Use a post hole digger to the proposed facility bottom elevation. Stick a pencil, pin, or nail in the side of the hole at a height from the bottom that will equal the maximum ponding depth (as predicted by the model, which we’ll see later)
  • Infiltration Testing Prepare the Hole 3. 4. 5. If in clay soils, scrape the sides of the hole a little Clean out any loose material in bottom Set up your field log on a piece of paper. Time [min] 0.00 [sec] 0.00 Dist between pencil and top of water [in] 0.00
  • Infiltration Testing Measuring Water Drop 6. 7. 8. If in clay soils, place a few inches of clean rock in the bottom Fill the hole gently with water up to the bottom of the pin Start a stopwatch right away!
  • Infiltration Testing Measuring Water Drop 9. Wait until the water drops a little bit. If it's dropping fast, then you'll want to make measurements more often than if it's dropping slow. 10. Log the time in min and seconds on a piece of paper and right away… 11. measure the drop in water & log it
  • Infiltration Testing Logging Data Time [min] 0.00 10 [sec] 0.00 52 Dist between pencil and top of water [in] 0.00 1/4”
  • Infiltration Testing Measuring Water Drop 12. Log the time & water drop a few times before the hole empties.
  • Infiltration Testing Logging Data Time [min] 0.00 10 19 32 [sec] 0.00 52 15 34 Dist between pencil and top of water [in] 0.00 3” 5-1/4” 7-1/2”
  • Infiltration Testing Measuring Water Drop 13. Before hole empties, repeat steps 7 – 12 two more times (i.e. refill hole again and measure water drop).
  • Infiltration Testing Measuring Water Drop 14. Use the slowest rate you tested. (It should be somewhere in the last round of refilling.)
  • Yellow cells are what you collected in the field Infiltration Testing Calculate Your Infiltration Rate Use this rate. (Factor of Safety optional.)
  • Infiltration Testing Confirm Vertical Separation 15. When you’re all done and you have your field tested infiltration rate… dig another 3’ down to look for your seasonal high water table. If you don’t hit fragipan or bedrock in 2’ below, this location will work if it actually infiltrated water. This whole process can take around 4 - 8 hours from start to finish, not counting presoaking.
  • Infiltration Testing What About Presoaking? • Presoaking is a holdover from EPA guidance on soil infiltration testing for septic systems, which are constantly wet because we’re constantly adding liquids to the field. • Probably not necessary, especially if you’re testing during the wet season and/or following our guidance to fill the hole 3 times and take the lowest rate. • Regardless, presoaking is often required by jurisdictions and will only make the design more conservative/safe. (In clay soils, presoaking can really drive up costs!)
  • Step 5. Enter native soil design infiltration rate • Enter after performing infiltration testing in the soil and at the depth where the porous pavement will be installed.
  • Step 6: Enter Storage Rock (i.e. Base Rock) Depth • Ask your geotechnical engineer for a porous pavement section recommendation on wet, uncompacted native subgrade for your traffic loading (usually H-20, 16,000 lb/wheel) • Most of the porous asphalt projects I’ve worked on in clay soils in Oregon only needed 12” of rock for structural stability, so try that out as a first guess. • Many pervious concrete projects in clay soils are 6” of concrete on 6” of base rock.
  • Step 7: Enter void ratio of storage rock (i.e. base rock) • Most open-graded rock has a 40% void ratio. You should be able to get this from your rock supplier.
  • How to Test Void Ratio Yourself
  • Step 8: Enter overflow elevation above bottom of storage rock • Enter the depth of water allowed to pond by whatever overflow control structure you employ. • If there is no large storm overflow control structure, this value equals the depth of the storage rock that can pond. • Let’s try the simplest design first – no overflow.
  • Determining Ponding Depth Level Sites
  • Determining Ponding Depth Sloped Sites • Facility bottom must be flat. • Yep, on sloped sites the cost of rock and excavation would make this prohibitive, but many cost effective projects step these flat beds up the hill, carving them into the existing contours to reduced excavation, and use underground check dams to hold back the water.
  • Determining Ponding Depth Using Overflow Control • Pipes need cover, so designers are inclined to put the perforated pipe at the bottom of the facility. • With no controls, ponding depth = 0! Nothing! Nada! • Big waste of your money and will not help meet TMDLs.
  • Determining Ponding Depth Using Overflow Control • Add a control structure with a raised outlet pipe to get ponding. • Use an internal weir when the outlet pipe (shown on the right of the catch basin) cannot meet cover requirements. • CAUTION USING WEIRS: Make sure maintenance staff can still fit their cleaning equipment into both sides of the weir!
  • Step 9: Check that Outflow Elevation doesn’t exceed Storage Rock Depth • Is this is FALSE, you’ve created a physically impossible situation. Increase Depth of Storage Rock or decrease the Overflow Elevation Above Bottom of Storage Rock. • Design pavement so water doesn't overflow out the pavement surface.
  • Step 10: Analyze Calculated Values -- Ponding • From the first test, we see that during the 2-year design storm the highest level in the rock (even with only 40% void ratio) that the water reaches is 1.36 inches. • The base rock empties out in 30 hours and is ready for the next storm. • Another storm dropping 4.8 inches tomorrow could be stored in the base rock voids remaining without infiltration.
  • Conclusion For • City of Turner • All stormwater must be kept on site • Protection from stream scouring desired = infiltrate the 2-year design storm • Hydraulic isolation • Not in a flooded area Porous pavement IS SUITABLE for this site.
  • Construction Stabilize uphill areas • Put erosion control measures into place, especially uphill from pavement area. • Soils must be hydraulically isolated during construction! No run on from other areas or soil could clog!
  • Construction Protect infiltration area from compaction Photo credit: Rob Emanual • Protect infiltration area from compaction throughout the construction process. • Excavate from the side
  • Construction Protect infiltration area from compaction Porous Pavement Parking Lot 18” deep haul road was installed at start of project Building • Lay down a haul road of 3 – 6” diameter rock to drive over. This significantly reduces (spreads out) the wheel load on the native soil. • 18” deep should work, but check with your geotechnical engineer.
  • Great Construction Guidance especially in clay soils • Much more detailed info is here: http://www.psp.wa.gov/LID_manual.php
  • Construction Install geotextile • • • • Lay down geotextile fabric. Keep it clean. Overlap it at least 12”. Run it up the sides of the excavation.
  • Construction Prepare rock Base rock Choker course • Get the rock delivered clean, usually 2% wash loss. • Then, hose off rock on-site to a very clean standard (0.5% wash loss). A little rock dust if OK. • This will prevent clogging at the geotextile/rock interface.
  • Construction Place rock • Place the rock in lifts compacting lightly. • Do NOT use vibratory equipment. • Keep construction equipment off the bare soil by backing over area. Dump first lift that you will then back over, dumping as you go.
  • Construction A note about the choker course • If installing porous asphalt, choker course will be a smaller, opengraded rock that chokes the larger rock below it, allowing you to roll the asphalt out without getting waves in the pavement. • This rock must be clean, too. • Don’t make this deeper than it needs to be to lock larger rock in place or this layer could start to roll, too. • This course is not needed for porous concrete, which is not installed with a roller.
  • Construction Place surface and cut geotextile • Place surface as directed by specifications. • Cut geotextile from sides of trench.
  • Construction Delineate parking • Striping is OK. A small area of surface can be impervious. Use ODOT Standard Spec water based paint. • Different color pavers • Wheel stops • Plastic dots
  • Maintenance • Vacuum trucks: hard to get suction on a pavement that’s open to the air. Works when pavement is clogged. • Leaf blowers: blow air across pavement, not down • Pressure washer: direct water across pavement, not down
  • Maintenance • Here’s a cool product: Storm-crete.com • If it gets clogged, pick it up, flip it over, pressure wash directly through the pours and put it back.
  • Maintenance Will tree leaves clog my pavement? • In 25-years of porous asphalt at the Morris Arboretum, they’ve have had no clogging problem! Courtesy of Cahill Associates
  • Cultural Practices Clogging Prevention
  • Cultural Practices Clogging Prevention
  • Relative costs for Porous Pavements $$$ Commercial pavers $$$ Flexible Pavements $$$ Grass-crete (GrassPave ) Courtesy of MGH Associates $$ Pervious concrete $$ Porous asphalt $-$$ Homemade pavers $ Gravel
  • Cost Comparison to Conventional Impervious Pavements Regardless of type, porous pavement cost is offset by: • Infrastructure typically needed for impervious pavements that’s not needed for porous pavement: pipes, detention ponds, water quality facilities, catch basins, manholes, and excavation • Value added amenity • Lower stormwater fees
  • Managing Runoff in Slowly Draining Soils Bioretention • Rain Gardens • Stormwater Planters • Green Streets or Private Property
  • Types of Challenging Sites Perceived I have tight clay soils with no infiltration!
  • 50% infiltration 50% evaporation 100% rainfall yearly avg 0.5% runoff In Nature (in Western Oregon) Clay Soils Infiltrate A Lot!
  • Siting Criteria for Infiltration with Bioretention • Choose the Right Rain Garden Decision Tree: http://extension.oregonstate.edu/stormwater/choose-right-rain-garden • Rain Garden & Stormwater Planter fact sheets: http://extension.oregonstate.edu/stormwater/lid-fact-sheets
  • Clay Soils That Infiltrate Slowly Design Solutions If water is actually draining, you can: • Make the rain garden bigger. • Don’t make the rain garden deeper.
  • “Infiltration Rain Garden with Planting Soil” • May be compost amended soils OR • Bioretention soil mix 33
  • Rain Garden & Stormwater Planter Excel Models • http://extension.oregonstate.edu/stormwater/lid-infiltration-facilitycalculator-aka-rain-garden-calculator
  • Common Mistakes “The Rock Burrito” • Also, don’t try deepening with a rock trench below. 38
  • Infiltration Testing Choose the Right Testing Depth • Depth depends on difference between existing and final grades as well as type of rain garden!
  • Common Mistake for “Rain Gardens with Planting Soil” • Replacing or amending soil alone will not increase the infiltration rate of the rain garden… Amended soil Native soil
  • Common Mistake for “Rain Gardens with Planting Soil” …unless you’re able to reach a different soil horizon.
  • Construction in Clay Soils Porous Pavement & Infiltration Bioretention 31
  • Constructing Infiltration Facilities in Clay Soils Protect Against Clogging  Don’t let clay soils get exposed to rain 24
  • Construction in Clay Soils Protect Against Compaction  Compost amend soils if built with “shovels and friends” 24
  • Sediment Control for Sheet & Concentrated Flow Wattles (are your friends!)
  • Managing Runoff Without Infiltration
  • Types of Constraints Water Quality & Quantity Constraints • Water Quality: When ground or surface waters may be degraded • Water Quantity: When infiltrating water may cause a problem (i.e. landslides, flooded basements) or cannot be infiltrated (high water table, high bedrock or other shallow impermeable layer)
  • The “Go Anywhere” Lined Filtration Rain Garden Lined on all sides with an impermeable liner = “FlowThrough” 43
  • Lined/Filtration/Flow-Through Stormwater Planters are Also Common
  • Use a Lined Filtration Facility when: • Infiltration siting criteria cannot be met. • Examples: • Too close to structure • Near sensitive area • At the top of a steep slope • Over an area with high seasonal groundwater, bedrock, or fragipan (i.e. buried ash layer)
  • If at all possible, AVOID the Lined Filtration Rain Garden because • If you don’t significantly reduce runoff volume leaving the site, you’re not really protecting water quality. • Only delay runoff by 13 minutes*, so not sufficient to meet flow control requirements. * Study on Portland’s standard of managing the 10-year storm.
  • And, also because they’re EXPENSIVE! 43
  • …and prone to clogging Don’t substitute a geotextile fabric for this. It will probably clog. 43
  • Additional Construction Steps for Lined Rain Gardens: Amend & Place Soils  Place at a depth of 6” then  Boot compact/light tamp or water compact  Repeat until your soil is at the elevation you want
  • Stormwater Planter Excel Model for No Infiltration ENTER RAINFALL DEPTH • Rainfall depth = 1 inch = Pollution reduction standard
  • Stormwater Planter Excel Model for No Infiltration ENTER INFILTRATION RATE • Enter infiltration rate of Bioretention Soil Mix instead of “Native Soil Infiltration Rate” • Can test with ASTM D1557 Method B (85% compaction with boot compaction) & ASTM D2434 (permeability testing) (More Info at: http://www.ecy.wa.gov/programs/wq/stormwater/bsmresultsguidelines.pdf ) OR • Can assume to be 2 inch/hour (minimum) if using Portland’s standard mixes
  • Stormwater Planter Excel Model for No Infiltration ENTER ROCK TRENCH DEPTH • May be anything that will keep the pipe covered.
  • LID Implementation Template DRAFT
  • LID Implementation Template DRAFT • Download: http://greengirlpdx.com/Publications.htm#ImpGuide • To become not a DRAFT someday when we get funding to facilitate a Technical Advisory Committee.
  • Thank You! Sustainable design isn’t about doing something neat, it’s about doing something right.
  • Detention ponds are not LID or… why you must reduce runoff volume to restore water quality Postdeveloped flow rate Post-developed =< Pre-developed Remember: Hydrologic models used by engineers grossly overestimate this. Predeveloped flow rate
  • Detention ponds are not low impact development Post-developed > Pre-developed Ponding begins
  • Detention ponds are not low impact development Post-developed > Pre-developed Ponding continues
  • Detention ponds are not low impact development Post-developed > Pre-developed Ponding continues
  • Detention ponds are not low impact development Rain stops Ponding begins to empty
  • Detention ponds are not low impact development Pre-developed flow out of pond continues
  • Detention ponds are not low impact development …and continues
  • Detention ponds are not low impact development …and continues
  • Detention ponds are not low impact development …and continues
  • Detention ponds are not low impact development 30 hours later, it’s ready for the next storm.