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WDFW Water Crossings County Road Administration Board October 9, 2009

WDFW Water Crossings County Road Administration Board October 9, 2009. 2003 edition Habitat considerations No slope culvert design Hydraulic culvert design Stream simulation culvert design Profile adjustment 2010 edition Bridge design Temporary culverts Culvert removal/abandonment

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WDFW Water Crossings County Road Administration Board October 9, 2009

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  1. WDFW Water Crossings County Road Administration Board October 9, 2009

  2. 2003 edition • Habitat considerations • No slope culvert design • Hydraulic culvert design • Stream simulation culvert design • Profile adjustment • 2010 edition • Bridge design • Temporary culverts • Culvert removal/abandonment • Fords • End treatments • Tide gates • Tidally influenced crossings

  3. Hydraulic Code Rules • WAC 220-110-070 • Water crossing structures. • Bridge construction • Temporary culvert installation • Permanent culvert installation • No-net-loss of productive capacity • Shall not to impede fish passage • Resist flood forces • Avoid or mitigate construction impacts

  4. 17 general “impacts” associated with water crossings. Most can be “mitigated” through proper design. “Proper design” considers risk, design standards, stream processes, construction impacts, and permit requirements. How you design and build this part is important. But how you design and build this part is VITALLY important for fish passage (why we do these projects).

  5. Road crossing design process Habitat considerations Culvert Bridge No slope design Stream Simulation design Hydraulic design (Draft Guidance) Road Crossing design process Crossing Siting BFW<15 ft BFW>15 ft Design Lower gradient Smaller streams Temp. retrofits Fishway design Higher gradient Larger streams

  6. Bridges

  7. Bridge sizing WAC … achieve no-net-loss of productive capacity … … placement of the foundation and superstructure shall be outside the ordinary high water line … … pass the 100-year peak flow with consideration of debris likely to be encountered. … not constrict the flow so as to cause any appreciable increase in backwater … or to cause channel wide scour.

  8. USDOT FHWA : “Backwater: the increase in water surface elevation relative to the elevation occurring under natural channel and floodplain conditions, induced by a bridge or other structure that obstructs or constricts the channel.”

  9. Channel Width • Bankfull vs. OHW "Ordinary high water line" • …the presence and action of waters are so common and usual … as to mark upon the soil or vegetation a character distinct from that of the abutting upland • the elevation of the mean annual flood (approx. 2.2 year flood) Appendix H, P. 100

  10. Channel Width • Bankfull vs. OHW “Bankfull width" • The width at the height of incipient flood • Distance between channel width indicators • The width at the 1.25 to 2 year flood Appendix H, P. 100

  11. Channel Width • Bankfull vs. OHW • For “small” streams, they are mostly the same • For “large” streams, OHW is wider than BFW. Appendix H, P. 100

  12. Channel Width Bankfull width Flood Plain

  13. Bankfull flood event Xtrb Salt Ck, Clallam Co.

  14. Bankfull flood event YN Toppenish near bankfull

  15. Channel Width Indicators Indications of minimum bankfull depth Undercuts in the bank Height of depositional features

  16. Channel Width Indicators Change in slope Change in vegetation

  17. BF width = 17 ft Entrenchment ratio = 1.5 Slope = 1.6% QBF = 157 cfs Q2 = 194 cfs

  18. 5 1 4.5 4 Surveyed cross section 3.5 3 2.5 2 1.5 BFD 1 0.5 Stage hydrograph Oct-Feb, 2007 0 0 5 10 15 20 25 30 35

  19. BFW BFW = 6 Entrenchment ratio = 1.2 Slope = 14% QBF = 10 cfs Q2 = 12

  20. Strictly for fish passage, culvert shape does not matter. The differences are in regional preferences, constructability, cost and construction impacts.

  21. Bear Ck. No Slope Method

  22. No Slope Option 1. Culvert at flat gradient 2. Culvert bed width equal to channel bed width 3. Minimum downstream countersink 20% of rise 4. Upstream countersink 40% of rise maximum

  23. No-slope option;Information needed • Bankfull channel width • Natural channel slope outside the influence of the culvert • Evaluation of headcut impacts (for replacements) • Elevation of natural channel bed at the culvert outlet

  24. Stream Simulation Culvert Design Road fill Profile view Countersunk 30-50% of culvert rise. Plan view Channel Width

  25. Stream Simulation Width Criteria Width of bankfull channel 1.2 x Width of bankfull channel + 2 ft Significant inlet contraction or long culvert may require a larger pipe size.

  26. U/S Channel gradient Culvert bed gradient Slope Ratio Culvert bed gradient Slope ratio = U/S Channel gradient Slope ratio must be less than or equal to 1.25. Slope ratios > 1.25 represent a change in channel type, not simulation of the adjoining channel.

  27. Low Slope Stream Simulation Bed Slope < 4.0% Well-graded rock bands (D100 = 1 to 2 times bed D100) to control initial shape Well-graded, not stratified, native streambed sediment mix

  28. Rock Bands Crest of rock bands have a streambed shape

  29. Culvert bed with no stream channel shape. Low slope without bands

  30. Rock bands just after construction

  31. High Slope Stream Simulation • HIGH GRADIENT(greater than 4%) • Rosgen type A, B, some F, G • Cobble-boulder bed • Very stable • Step-pool morphology

  32. WF Stossel Ck. Width ratio = 1.8 Slope = 6.4%

  33. No channel features built into bed. Slope = 7% 10 Mile Ck.

  34. 15% slope culvertStep-pool structure painted on wall

  35. Which is best? • No Slope • short, low slope streams (<75’ , <3%) • simple situations (single lane road, low fill) • confined to moderately confined channels • Stream Simulation • default for channels <15 ft • steeper, longer culverts • improved ecological connectivity required • moderately confined channels • Hydraulic Method • retrofits • exceptional circumstances • Bridge • default for channels >15 ft • wide, steep, or high energy streams • high potential for vertical or • horizontal instability • high debris or sediment load

  36. DOT specs 9-03.11 Streambed Aggregates Streambed Aggregates shall be naturally occurring water rounded aggregates. Aggregates from quarries, ledge rock, and talus slopes are not acceptable for these applications.

  37. DOT specs • 9-03.11(1) Streambed Sediment • Sieve Size Percent Passing • 2 1/2" square 100 • 2" square 65 – 100 • 1" square 50 – 85 • U.S. No. 4 26 – 44 • U.S. No. 40 16 max. • U.S. No. 200 5.0 – 9.0

  38. DOT specs 9-03.11(2) Streambed Cobbles Approximate SizePercent Passing 4" 6" 8" 10" 12“ 12" 100 10" 100 8" 100 70 max. 6" 100 70 max. 5" 70 max. 40 max. 4" 100 70 max. 40 max. 3" 40 max. 2" 40 max. 1 ½" 40 max. ¾" 10 max. 10 max. 10 max. 10 max. 10 max.

  39. DOT specs 9-03.11(3) Habitat Boulders Rock Size One Man 12" - 18" Two Man 18" - 28" Three Man 28" - 36" Four Man 36" - 48" Five Man 48" - 54" Six Man 54" - 60"

  40. Long Profile • Long profile is necessary to understand reach-level behavior of the channel • identify grade breaks • assess regrade potential and effects • average scour depth of pools • determine channel incision • channel characteristics for stream simulation Survey minimum 40 channel widths plus culvert length Chapter 7, P. 40

  41. Outlet drop caused by scour pool vs. incised channel Outlet Scour Original Channel Grade Incised Channel Original Channel Grade Nick point supported by culvert Incised Channel Grade

  42. Channel profileScale of Problem = Scale of Solution Outlet scour – Solution at culvert scale Short Incised channel – Reach solution; regrade Expected regrade Long

  43. Maintain upstream bed elevation to protect current habitat or infrastructure Channel Regrade Options Grade control (or fishway)

  44. Channel Regrade Options Grade control impacts • Required to maintain culvert within design criteria (part of culvert design) • Locks-in channel section in a vertically mobile channel system (often leads to more controls downstream). • Requires maintenance for the life of the culvert (obligation of the landowner). • May reduce habitat value of reach.

  45. Allow upstream bed elevation to lower and establish a new profile. Channel Regrade Options Regrade

  46. Channel Regrade Options Regrade

  47. Channel Regrade Options Regrade impacts • Temporary upstream habitat loss • Possible permanent loss of habitat (exposure of bedrock) • Downstream sediment deposition • Potential lowering of local water table, perching riparian • Undermine infrastructure, initiate landslides

  48. Channel Regrade Options Regrade benefits • Reestablishment of natural stream profile and processes • Rejuvenation of upstream habitat • Elimination of man-made structure in stream

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