Rock Ramp Design Guidelines David Mooney MS Chris Holmquist-Johnson MS Drew Baird Ph.D. P.E. Kent Collins P.E.
Rock Ramp Design Guidelines OUTLINE Local and System Interactions with Rock Ramps Ramp Geometry and Hydraulics Riprap Design Fish Swimming Capabilities and Passage Criteria Design Event and Lifecycle Costs Boulder Clusters and Isolated Rocks Step Pools Future Guidelines Work Appendix A Basic Ramp Design Example
Ramp Geometry and Hydraulics Full Spanning Ramp High Flow Channel Low Flow Channel
Partial Spanning Ramp
Rock Ramp Geometry Design Procedure Evaluate the appropriateness of a rock ramp including local and system interactions. Determine the biological fish passage criteria Estimate ramp geometric parameters and generate low flow hydraulics to meet fish passage requirements and project constraints. Includes iterating the slope and roughness. Determine the high flow design discharge. Iterate high flow geometry to provide adequate flood flow passage. Design entrance and exit transitions Biologic review to validate fish passage characteristics Add special features such as boulder clusters or step pools. Review the impact from special features on the basic design.
Local and System Interactions Degradation Local supply limited cases such as downstream of a dam Downstream base level lowering Aggradation rising sediment levels such as from changes in land use or debris flows Channel Migration Past temporal and spatial rates of meander migration River bends move laterally as well as translate downstream Evaluate the effects of potentially altering channel migration patterns Place structures in reaches where the potential channel migration is a minimum River migration may cause local flanking of a structure, determine countermeasures if necessary Structures can impede or accelerate migration processes. Construction Disturbances Geomorphic Thresholds (i.e. alter the water sediment relationship)
Steep Slope Roughness Abt et al. (1987) texted angular rock on steep slopes from 0.01 to 0.20. Rice et al. (1998) performed additional tests (slopes from 0.167, and 0.333). Rice et al. (1998) combined Apt et al. (1987) with their data to develop 0. Where, n = n = Manning s n-value; 0.029 D50 = median grain diameter of the riprap (mm); and S o = slope of the rock ramp. ( ) 147 D 50 S 0 Individual stones extending above the rock ramp surface will increase the potential of rock dislodgement
Depth Based Roughness (Darcy-Weisbach) Depth = 1.25 Depth = 1.50 Depth = 2.00 Depth = 3.00 0.12 0.10 Roughness N-Value 0.08 0.06 0.04 0.02 Typical Boulder Bed Streams 0.00 0 2 4 6 8 10 12 14 Relative Protrusion = Depth/(0.5* D 50 )
Low Flow Geometry and Hydraulics 0.005 0.015 0.025 0.035 0.045 0.055 Profile Slope (ft/ft) 5.5 4.5 3.5 2.5 1.0 Low Flow Side Slope (H:V) 0.005 Depth (ft) 3.5-4 3-3.5 2.5-3 2-2.5 1.5-2 1-1.5 0.015 0.025 0.035 0.045 Profile Slope (ft/ft) 0.055 5.5 4.5 3.5 2.5 1.0 Velocity (ft/s) Low Flow Side Slope (H:V) Velocity 7-7.5 (ft/s) 6.5-7 6-6.5 5.5-6 5-5.5 4.5-5 4-4.5 3.5-4 3-3.5 2.5-3 2-2.5 1.5-2
Riprap Design Methods Sizing Methods Account for Overtopping Flow Abt and Johnson (1991), Ullman (2000), Ferro (1999), Robinson et al. (1998), USACE (1991), Whittaker and Jaggi (1986), Stevenson (1979), and more. Gradation D 100 < 2 * D 50 1.25 < D 60 / D 10 < 2.4 Filter Criteria Upstream and Downstream Transitions Cutoff Wall Downstream Scour Protection
Design Flow and Lifecycle Costs Selection of a design event balances the cost of initial construction versus the cost, effort, and probability of replacing or repairing weaker structures if larger flow event occurs. Design Flow s Determined by Regulatory Requirements Land owner Requirements Stake holder Requirements Economics Management Decision The methods do not account for lost delivery opportunities and assume all structures are maintained when required.
Fish Swimming Capabilities Literature review of fish capabilities swimming speeds including sustained, prolonged, and burst Leaping capabilities Life stage specific criteria State and Federal fish passage criteria Example installations of nature-like fishways Biological criteria planning processes
Replacement and Maintenance Frequency 1 Probability of Maintenance or Replacement 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 1 2 3 4 5 6 7 8 9 10 Number of Events Requiring Maintenance or Replacement in 50 years Less than a 95% chance we must replace a structure more than 4 times Less than a 50% chance (less certain) that we must repair a structure more than 4 times Cumulative Probability of Maintenance Cumulative Probability of Replacement Frequencies indicate the likelihood of no more than a given amount.
Design Flow Event 50% Chance of Equal or Lesser Cost 60% Chance of Equal or Lesser Cost 80% Chance of Equal or Lesser Cost 90% Chance of Equal or Lesser Cost 25 20 Lifetime Cost 15 10 5 0 5 10 25 50 100 Design Event Site specific lifecycle costs for different design events
Boulder Cluster Additions Depth = 2 ft Continuity Velocity = 2.8 ft/s Normal Depth = 1.75 ft Velocity = 3.7 ft/s Cluster sizing, layout, and spacing Hydraulic Impacts Ramp Interactions Construction concerns
Step-Pool Additions Range of applicability Hydraulics Parameters Step height Step frequency Design Parameters Rock size Scour pool dimension Rock ramp interaction
Guidelines Software An analysis software package can facilitate detailed computations Low flow hydraulics require iterative computations Riprap design uses multiple equations Lifecycle costs requires iterative calculations Charts and graphical displays assist in conveying information to support decision making Validated software standardizes methods