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,. <br />,, <br />III IIIIIIIIIIIII III <br />sss <br />h E M O <br />R~C~IYED <br />SEP 17 1~ <br />N 7drc~ <br />MMIED W~ AE6iJ-MATION <br />Colo. Dept. a Netwef tieeowces <br />T0: JIM MILLER ,,~,n DATE: <br />FROM: MIRE MCDERMID ~i/y~"' JOB NO.: <br />SEPTEMBER 10, 1986 <br />043-001 <br />SUBJECT: RESPONSE TO PORTION OF SEPTEMBER 4, 1986 COMMENTS BY TOM <br />SCHREINER OF CMLRD STAFF - "C, EAST ROATCAP CREEK DRAINAGE <br />CULVERTS" <br />1. Reference attached set of culvert construction drawings and specifica- <br />tionsand set of Design Calculations. <br />2. (C-1) <br />We agree with this comment and the attached drawings show the culvert <br />on a uniform slope. <br />3. (C-2) <br />We do not agree with the necessity for constructing cutoff collars <br />along the pipe for the following reasons: <br />a) There will be no head on the upstream face of the fill to create <br />seepage along the pipe. Even the 500-year event has a head of only <br />3.6 feet over the pipe for a short duration. <br />b) The permeability of the in-situ colluvium materials is very low <br />(see Golder Associates' calculations and logs of test borings). <br />The ccmpacted embankment may also be expected to have low permea- <br />bilities. The most permeable material may be the bedding material <br />(see bedding detail, drawings sheet 1). Even assuming a <br />permeability of 10-y cm/sec for this material and a four-hour <br />duration of any head on the evbankment, a seepage front would have <br />moved only about five feet through the material. <br />c) There is a cutoff wall at the upstream end as shown on sheet 2. <br />This concrete wall will connect to natural ground below the pipe <br />and extend three feet CUr more, as required by site conditions) to <br />the sides. <br />4. (C-3) <br />*. <br />., <br />This comment has been covered as shown in the drawings. The inlet <br />length ie fifteen feet, in excess of the ten feet noted in the <br />comments. The outlet length is twenty feet, again in excess of the <br />fifteen feet noted in the comments. Riprap is expected to be hard, <br />durable igneous boulders generated from the bench excavation. The <br />drawings show the inlet and outlet geometry and construction specifica- <br />tions. Calculations showing the riprap size criteria are given in [he <br />attached design calculation. <br />a:%, s"~ <br />