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4. 38 Variable cross sections and curvil inear alignment desirable. 5. Channel layout must be capable of carrying discharges for a range of roughness, bed materials, and bed slope. a. Roughness coefficient for new condition, unmaintained conditions, and future landscaping. b. Variable sediment loads and aggradation. c. Varying slopes due to erosion and aggradation. 6. Provide positive controls to limit range of horizontal and vertical movement and section configuration. CROSSINGS 1. Provide stablt sections. 2. Bridges to be designed to minimize debris hangup with smooth rounded sectional profile. 3. Freeboard 1.0 feet above energy gradel ine for Q100 for low chord. 4. Maximum mean velocity of 12 fps. HYDRAULIC CONTINUITY 1. Analyze flow routine for Q100' with consideration given for lesser and greater events. 2. Provide for the safe conveyance and acceptance of tributary flows. I I I I I I I I I I I I I I I I I I I 3. Identify sediment deposition zones for various flow frequencies. 4. Identify areas of contingency planning to accommodate flood dis- charges larger than the lOa-year event or operational failure of the designed improvements. LOW FLOW CHANNEL 1. Provide controls to insure self cleaning within range of normal flows. 2. Limit horizontal and vertical cutting of low flow channel, but try to allow natural type deposition, cutting, overhanging banks, and sand bars within controls. 3. Establish satisfactory meander ratio. 4. Estab] ish satisfactory pool-riffle ratio, and pools with satisfactory depth and self cutting provisions. 5. Provide for overhanging vegetation and bottom vegetation. 6. Provide high degree of variability in low flow channel. MAINTENANCE ASPECTS 1. AI] mowed slopes to have slope of 4:1 or flatter. 2. Continuous access to or through all structures and channel.