University of Massachusetts - Amherst ScholarWorks@UMass Amherst International Conference on Engineering and Ecohydrology for Fish Passage International Conference on Engineering and Ecohydrology for Fish Passage 2011 Jun 28th, 3:25 PM - 3:45 PM Session A6- Mannings "n" roughness characteristic occurring in semi-smooth turbulent flow of nature- Iike fishways Douglas Laiho Consultant Follow this and additional works at: http://scholarworks.umass.edu/fishpassage_conference Laiho, Douglas, "Session A6- Mannings "n" roughness characteristic occurring in semi-smooth turbulent flow of nature-iike fishways" (2011). International Conference on Engineering and Ecohydrology for Fish Passage. 28. http://scholarworks.umass.edu/fishpassage_conference/2011/june28/28 This Event is brought to you for free and open access by the The Fish Passage Community at UMass Amherst at ScholarWorks@UMass Amherst. It has been accepted for inclusion in International Conference on Engineering and Ecohydrology for Fish Passage by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact scholarworks@library.umass.edu.
Manning s n Roughness Characteristic Occurring in Semi-Smooth Turbulent Flow of Nature-like Fishways Douglas R. Laiho, P.E. ASCE and AFS
Fish Passage is all about Velocity Used with permission
Source: USBR
Basic Hydraulic Design Criteria - Fish Passage (for fish with a total length of 50mm 300mm) Depth 100mm 250mm Velocity 35 cm/sec -150 cm/sec Roughness 0.08 -.12 Flows 0.15 cm3/sec 0.25 cm3/sec Provides a small, shallow, rough channel
Manning s Formula V 149. n R 2 3 h S 1 2 f V = average flow velocity, ft/s n = Manning s coefficient of roughness R h = channel hydraulic radius, ft (ratio of water area to wetted perimeter) S f = slope of the energy grade line
Components of Roughness n ( n n n n n ) m 0 1 2 3 4 5 n 0 is a function of bed material, n 1 is a function of channel cross-section irregularity, n 2 is a function of variation in channel cross-section, n 3 is a function of degree of large-scale obstructions, n 4 is a function of aquatic vegetation within the channel and, m 5 is a function of degree of channel meander.
Basic n
Addition for Irregularities n 1
Addition for Channel Variation n 2
Addition for Obstructions n 3
Manning's n Reclamation Style Boulder Fishway 0.100 0.090 0.080 0.070 0.060 0.050 0.040 0.030 0.020 0.010 Manning's "n" vs Submergence 4 ft wide bottom, 2:1 side slopes, 3 boulders spaced 1 ft apart 0.000 90 100 110 120 Percent Boulder Submergence Source: Mefford (undated)
USBR River Gradient Facility Source: Mefford (undated)
Empirical Relationships 0. 38 01. 6 f n 039. S R Jarrett n g f (F r ) d f a 1 6 (REG) f (CD) Bathurst
Shallow Flow Roughness Overland Flow and Sheet Flow Smooth asphalt 0.011 Smooth concrete 0.012 Cement rubble surface 0.024 Natural range 0.13 Dense grass 0.24 Bermuda grass 0.41 Light underbrush 0.40 Heavy underbrush 0.80 Source: FHWA (2001)
Small Streams Roughness Mountain Streams, no Vegetation in Channel, Banks Usually Steep, Trees and Brush Along Banks Submerged at High Stages 1. Bottom: gavels, cobbles and few boulders 0.030-0.050 2. Bottom: cobbles with large boulders 0.040-0.070 Source: FHWA (2001)
Shallow Flow Ditch Roughness Lining Category Gravel Riprap Rock Riprap Lining Type n-value Depth Ranges 0-0.15 m 0.15-0.60 m >0.60 m (0 -.5 ft) (0.5 2.0 ft) >(2.0 ft) 25 mm (1 in) D 50 0.044 0.033 0.030 50 mm (2 in) D50 0.066 0.041 0.034 150 mm (6 in) D 50 0.104 0.069 0.035 300 mm (12 in) D 50 -- 0.078 0.040 * Some temporary linings become permanent when buried. Note: Values listed are representative values for the respective depth ranges. Manning s roughness coefficients n vary with the flow depth. Source: FHWA (2001)
Comparative Roughness Roughness Values Table Site Design n Theoretic n 1 Field n Jarrett n 2 Bathurst n 3 McGinn Ditch Fishway (0.44 0.95) 5 Clear Springs Ranch Fishway (0.33 0.51) 5 1 Per Cowan (1956) 2 Per Jarrett (1985) 3 Per FHWA (1988) 4 Determined using true area, hydraulic radius, wetted perimeter 5 Fr 6 Prototype testing based 0.070 0.085 0.048 4 0.140 0.076 -- -- 0.079 0.087 6 0.111 -- El Pomar Fishway 0.120 0.080-0.101 -- 0.078 0.118 Sam Howe s Pond Fishway 0.100 0.110 -- -- -- DM Fishway 0.100 0.110 -- -- --
Conclusions: Shallow Flow Roughness Values Sculpted concrete channels with embedded rock 0.07 0.09 Riprap rock channels with grouted rock 0.08 0.10 Riprap rock channels with grouted rock and grout texturing 0.09 0.11 Riprap rock channels without grout 0.09 0.11