1. Rock Riffle Design Course

2. Goals of Streambank Restoration
Work With Nature
Reduce Sediment
Protect Cropland
Protect infra-structure
Improve Water Quality
Improve Aquatic Habitat
Make it Affordable

3. Lanes Balance

4. 200+ years of Human Activity on the Landscape
Cleared the Timber
Plowed the Prairie
Drained the Wetlands
Straightened the Streams
Leveed the Floodplains
Built Cities with Large Areas of Concrete, Asphalt and Rooftops

5. Results of Human Activity on Stream dynamics
Increased Runoff
Increased Stream Slope
Reduced Floodplain Width

6. Design Philosophy Work WITH the Natural Processes.
Know Where Nature is Taking the Stream.
Determine the Cause of The Problem
Treat Only the Cause
Let Nature Finish Healing The Banks
Keep the Cost Down

7. Channel Evolution Model (CEM)

8. Stream Stabilization Techniques
4 Major Practices Used in Illinois ===========================
Rock Riffle Grade Control Structures (stage II or III)
Stone Toe Protection (stage III or IV)
Bendway Weirs (stage IV)
Stream Barbs (stage IV)

9. Rock Riffle Grade Control Structures (stage II/ III streams)
Stabilize the Bed
Creates Riffle/Pool Sequence
Dissipates Energy
Aerates Water
Permit Fish Passage
Aesthetically Attractive

16. Determine Stability
Review I & E Data
CEM Stage?
Entrenchment Ratio?

25. McCray Stream Site Valley slope = 0.0028
Surveyed slope ave (slightly lower)
Bed in Riffle ---Clay (exposed in riffle bed)
Width/Depth ratio = 10.3 (just over 10)
Entrenchment Ratio = 1.28 (just under 1.4)
2 elements suggest Grade Control
2 elements outside suggested range (barely)

26. Channel Geometry Considerations
Sine Wave Flow
Anticipated Scour Depth
Radius Curvature/Bankfull Width Ratio (should be more than 1.8)
Existing Riffle Location
Existing Riffle Spacing

29. Scour Depth Assume Scour Depth will equal Max. Bankfull Flow Depth
Assumes bed material allows full Sine Wave Flow to develop over time

31. Radius of Curvature Ave radius = 2.3 times bankfull width (Leopold)
Range generally from 1.6 to 4.5 times bankfull width (natural streams)
2.3 is the optimum for hydraulic efficiency
1.8 is the suggested minimum under guidelines

33. Locating Riffles 5 to 7 Bankfull widths (28 ft)
Expect Spacing--140 to 196 ft.
Located at Cross-over Points

38. Read The Channel Knickzones and Headcuts May be hundreds of feet long
Little or no bedload in crossover pts.
Will not be bedload material (sand wave)
Increasing bank height downstream?
Stable Points? (Bedrock, Culvert, etc)

40. Gather Survey Data Bed Profile Water Surface Profile
Typical Riffles (detailed)
Low Bank Profile
Stream Cross-over Points (Stations) or surveyed planform

41. Plot profile Channel Grade (riffle to riffle) Riffle Spacing
Compare low bank vs. channel grade
Pool Depths
Stable Points

43. Riffles

44. Existing Riffles? Stations: 0+00, 4+25, 5+90, 8+25, 10+20
11+50, 13+20, 13+75, ,16+40, 20+20
12 riffles in 2020 ft. --Ave. Spacing 168 ft.
Max. Spacing ft.
Min. Spacing-- 55 ft.

45. Low Bank
Grade Line
Profile

47. Bank Heights

48. Plot Cross-Section(s)
Bankfull depths
Riffle Crest Elev.

50. Determine New Gradeline
Slope (will be greater than existing slope)
Stable Upstream(flood out headcut/knickzone)
Stable Downstream(Culvert/Stable Grade, etc)
Blend into existing channel bed (generally 1.0 ft. height or last riffle)

52. Locate Riffles and Crest Elev.
Geometrically Correct
Uniform Gradeline
6 Bankfull Width spacing?
Backwater to Toe of Upstream Riffle

55. Planned Riffles

56. Riffle Spacing Existing Riffles range from 55 ft. to 425 ft.
(2 to 15 bankfull widths)
Ave. 168 ft. (6 bankfull widths)
Planned Riffles range from 210 ft. to 370 ft.
(7.5 to 13 bankfull widths)
Ave. 233 ft. (8.3 bankfull widths)
Too Wide?

57. Riffle Spacing (cont.)
Concern is natural flow pattern and siltation problems if spacing is too wide.
Experience has not shown spacing to be as critical as once thought (especially with silt and sand bed streams)
Attempt to locate riffles near existing riffles at cross-over points and put backwater on tail of upstream riffle.

58. Check for increased Flooding (when necessary)
Bankfull Specific Energy Line
Critical Flow Depth
Critical Specific Energy Line
Allowable Riffle Height = Bankfull Specific Energy - Critical Specific Energy

60. Max. Riffle Ht. Calculation Specific Energy Line
Energy Line = Bkf Depth + Velocity squared divided by 2 times gravity
Energy Line = (5.1sq./ 2 x 32.2)
Energy Line = (26.01/64.4)
Energy Line = = 3.1 ft.

61. Max. Riffle Ht. Calculation Critical Flow Depth
Critical Depth = (Q sq. divided by gravity times width sq.) raised to the 1/3 power
Critical Depth = (350 sq./32.2 x 28 sq.) raised to 1/3 power
Critical Depth = (122,500/32.2 x 784) 1/3
Critical Depth = (122,500/28142) 1/3
Critical Depth = (4.35) 1/3power = 1.63 ft.

62. Max. Riffle Ht. Calculation Critical Energy Line
Critical Energy Line = 1.5 times Critical Flow Depth
Critical Energy Line = 1.5 x 1.63
Critical energy Line = 2.45 ft.

63. Max. Riffle Ht. Calculation
Max. Riffle Ht. Allowable without raising water surface profile or creating backwater effect = Energy Line - Critical Energy Line
Max. Riffle Ht =
Max. Riffle Ht. = 0.65 ft.

64. Max. Riffle Ht. Calculation Summary
Specific Energy Line = 3.1 ft.
Critical Flow Depth = 1.63 ft.
Critical Specific Energy Line = 2.45
Max. Allowable Riffle Ht. W/O effecting water surface elev. = Specific Energy Line - Critical Specific Energy Line or
3.1 ft ft. = 0.65 ft. max. ht.

65. Critical Velocity Estimate
Velocity at Critical Flow(Vc) = (gravity x critical flow depth) raised to the 0.5 power
Vc =32.2 x 1.63 (raised to 0.5 power)
Vc = 52.5 (raised to 0.5 power)
Vc = 7.24 ft/sec.

67. What if I Raise Flood Surface Profile?
Will I increase Out of Bank Flooding?
Will I effect instream pipe outlets, tile, etc.
Is the increase in flood surface profile acceptable to all effected parties?

70. Compute Quantities and Cost
Determine Stone Size from CriticalVelocity Calculations (double size for safety)
Quantity Chart
Average County Cost per Ton of Stone

76. Cost of RipRap Statewide Average is about $25 per ton installed
Check with local quarries/truckers for delivered price of A-5 or A-6 stone---Add $3 to $5 per ton for installation
“quarry run” or “shot-rock” CAN be acceptable--Check with designer for O.K. before using and plan on being at site during delivery.

77. ROCK RIFFLE
CONSTRUCTION

78. Construction Layout
Riffles must be located at stream crossover points where flow goes from one side to the other. (riffles)
Riffles should be located slightly upstream of existing riffle so backslope can “blend” into existing riffle--also places maximum water depth closer to apex of bend and dissipates energy in pool.

79. Sequencing Build from Upstream to Downstream
Riffles will not “seal” and pond water until voids are filled with sediment.
Can speed up “pooling” by placing a few inches of fine silt/clay on front face of riffle.

80. Bed Key 4 ft. minimum width 3 ft. minimum depth/or to bedrock
Extends across channel bottom and 3-4 ft. into outer bank.
Doesn’t need to be larger material
Do not over excavate! Easy to “lose” stone in bed key

81. Bank Key 4 ft. minimum width 5 ft. minimum depth
Construct with a 1.5 on 1 slope into bank so that as “vertical banks”stabilize the ”key” is not exposed
No need to “fill” key trench out to original bank.
Top Elev. approx.1 ft. below top bank

82. Riffle Crest Build Crest to elevation before starting on backslope
Use largest material in gradation
Place crest stones individually with “thumb” if possible
Build Crest with slight “V” shape using control elevation as low point in “v”.

83. Backslope Build with 20:1 backslope
Place next largest stone available from gradation immediately downstream of Crest stones.
Flare the backslope up the channel sides slightly (1.5 ft?)
Leave backslope “rough” to aerate flow and provide resting places for fish passage.

84. Blending into Exit Channel
H-4 dimension is depth to place material below existing channel bed at exit.
Most streambeds are “soft” enough that material can be “pressed” into channel bed without excavating

85. Alignment Align Crest so that desired exit is at 90 degrees to Crest.
If channel has a sharp bend near tail of riffle use Stone Toe Protection downstream to protect against increased velocity near riffle exit. (Riffle backslope has a 5% grade)

86. Follow-up and Maintenance
Check each structure after first major storm (near bankfull flow)
Some movement and of smaller stone and sorting of material is expected.
If any crest stone moves it should be repaired immediately