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I I I I I I I I I I I I I I I I I I I V-4 Another important criterion is that the urban drainage system cannot be separated from the total urban envi ronment. Therefore, maj or drai nageway improvements should realize benefits arising from multiple uses, and not limit itself narrowly to those uses associated with the reduction of flood damages. Among the other types of uses to be considered are those arlslng from recreation, parks, open space, improved transportation access and the reestablishment of riparian habitat. The criteria for box culverts and bridges are as follows: o The maximum velocities to be 7.0 fps. o Froude numbers may not exceed 0.8. o Max i mum des i gn depths are to be kept at or 1 ess than 5.0 feet, unless circumstances dictate greater depths. o Slopes should be kept in the range of 0.2 to 0.6 percent along the channel. o Channels should have radii of curvature of 100 feet or twice the design top width, whichever is greater. o Freeboard requirements should generally be a minimum of 1 velocity head or 1 foot. o The maximum allowable side slope is 4:1. o Trickle channels which simulate the existing low flow channel are to be designed. o Whenever possible, box culverts are to be designed for free flow conditions, or without large pressurization. o When tailwater conditions dictate pressurized flow, the hydraulic grade line shall remain beneath the surface of the ground. o Cross sectional areas should not decrease in the downstream direc- tion. o The opening height for box culverts and bridges should be a minimum of 8 feet to allow for maintenance vehicles to pass through the opening. o When practical, the height should be 10 feet to allow equestrian traffic. o The hydraulic analysis of bridges and box culverts assumes no debris blockage. Design Criteri a The design criteria for grass lined channels are as follows: UNIT COSTS AND COST ESTIMATES Unit Construction Costs Unit costs were derived from an analysis of recent construction bids and adj usted to refl ect current costs. These unit costs were ori gi na lly pre- sented in the Phase A report and revised or modified as deemed appropriate. Unit costs used in the preparation of the cost estimates for this study are shown on Table V-I. o The maximum depth of flow will be 9.0 feet. o The maximum velocity will be 10.0 fps. o The Mannings roughness coefficient shall be "n" is equal to 0.030. Right-of-Way Costs Estimates of the required right-of-way costs have been prepared as part of thi s study. Ri ght-of -way i ncl udes property acqui s iti on required for the improvements, construction easements required for constructi on, permanent easements necessary to provide access to the improvements, and easements requi red for underground condui ts. Table V-2 presents the ri ght-of-way acquisition costs used in this study. The criteria for European type channels are as follows: