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'One foot of freeboard from t:he desi9n water surface 1:0 th,~ top of all channels was provided as a sa fe.tO' fact:or for local abnormal blockages" !Jnderground Condui t:s Underground conduits were used for drainage improvements for reaches where open channels were not. practical. For solving local draina.ge problems, circula r condui t:s were chosen because the pipe sizes were noi: too large to conflict: with existing underground utilities, especially sanitary sewer pipes. (The 5-year frequency was used :Eor design:'.ng local drainaqe improve-' ments). For major waterway improvements. box culverts were desi'lned because they can j1ave thE~ followinq advantaqes: (1) less cha.nce to conflict with existing utilities because of thei I:' smaller vertical dimension, and (2) a bet.ter transi t.ion betw'~en street crossing and chan:nel. However, pipe is also a feasible alternative for major drainage improvements.. A de- tailed study should be made in the final design to determine t:he feasibility bet:ween box culv'~rt and pipe. Box cuI vert:s were desi'lned to have free-flow conditiom; with the water surface for the design storm approxima1:ely 6 inches below the roof .to prevent surc:larging the culvert:, which would decrease the conveying capa-' city. Manning's n value used for box culvert:s was 0.015 based on t:he assumption that: they would lXl cas1:-in-place. Winq walls were provided at box culver1: enl:rances and exj. st too ensure smooth t:ran:5i tions. Pipe:3 were desiqned for less than flowinq full condi t:ion. Manning's n value of 0..013 was uSE,d for precast concrE,te pipes wi th ordinary joint: alignments.. Detention S1:orage. Storm detention storage facilities were designed to contain the future runoff volume from the tribut:a.ry drainaqe an,a for a 100-yr storm event witch no embankm'~nt or spillway overflow. ~Che emerqency spillway sElct:ions were designed to [ass a dE~sign flood selected in accordance with the hazard leve1. Outlet ',vorks capaci l:i.ss a:ce dependent on the storage volume available at the detention site arid the capacities of dovmstream draina(),~ structures. Because the soil conditions at the proposed DayLon detention pond were not fully inv'~stigated,. a typical embankment section \'lith an impE~rvious core was designed. 'rhe exact material for the embankment should be, selecbl:'l du:cing final design -17..