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2. DESIGN COMPUTATIONS The following data shall be submitted to the Chief Engineer by the Design Engineer: HYDRAULIC DESIGN DATA. 1. Computations for runoff, conduit and channel sizes, slopes, losses, hydraulic gradient and other hydraulic characteristics and informa- tion pertinent to the system. Computations shall be properly arranged and presented in such a manner that they may be readily checked. 2. The following data shall be shown on the construction plans. a. Design flow (Q), watershed area (A), rough- ness coefficient (n), and velocity (v), for all conduits and channels. b. Hydraulic grade lines. c. Water surface elevation at each manhole and catch basin. d. Building setback lines, where required. 0 STRUCTURAL DESIGN DATA. I. Structural design computations for all drain- age structures other than pipes used within the limits of current loading tables and struc- tures shown in the "Standard Details" of the County of Hawaii Department of Public Works. 2. Information pertinent to the design, such as boring data, soils report, etc. 3. Upon the completion of construction of major structures, submit pertinent data such as pile driving logs, pile tip elevations, etc. 3. CLOSED CONDUITS SIZES AND GRADIENTS 1. The size and gradient will be determined by the Manning formula: Q = A 1.486 R2-13 S11'2 n Q = flow, in cfs R = hyd. rad. in ft. A = area, in sq. ft. S = slope, in ft. /ft. n = roughness coefficient (Manning's) A direct solution of this formula for pipes are found on pages 23 to 31. 2. The following limitations apply — a. Minimum size pipe: 18 inches inside diameter b. Minimum velocity: 2% feet per second c. In general, pipe sizes shall not decrease in the direction of the flow. OMATERIALS AND "n" VALUES The following pipes are acceptable for storm drain construction together with the roughness coef- ficient to be used in the solution of the Manning Formula. Materials n Concrete ................... .013 Cast iron ........ ........ .013 *Corrugated metal pipe (CMP) Unpaved ................. .024 25% paved invert ........... .021 Lower 50% paved ........... .018 100% paved ........... .013 *Use of CMP shall be permitted only when specif- ically approved for an installation by the Chief Engineer in writing. ® LOADING 1. Reinforced Concrete Pipes: Reinforced con- crete pipes shall be constructed to ASTM Specifications and currently classified as Class I, Class II, Class III, Class IV, and Class V pipes. a. Minimum pipe cover in roadways, drive - ways and other areas with vehicular traffic (based on the current, "Standard Speci- fications for Highway Bridges," AASHO) shall be as follows: ASTM Pipe Minimum Classification Diameter Pipe Cover Class III Pipe Less than 48" 2' -6" Class III Pipe 48" and above 2' -0" Class IV Pipe All sizes 2' -0" Should there be a need for a pipe cover of less than 2' -011, the design engineer shall submit a structural design for review and approval. The decision to allow such de- sign will be made by the Chief Engineer. 7