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<br />4. Sedioent acc"mulation in barrel - 80~ restricted. <br /> <br />street grading operations, particularly in winter when culverts !:lay not be <br />viaible, cannot avoiding pushing 1I11nd and gravel over the culvert enda. The <br />rellult is that the ends become partially blocked and sediment accumulates in <br />the barrel from trickle flows. Without regular flushing of sediments, the <br />culverts eventually plug. <br /> <br />* NOtES FOR TABLE-9 (CONTINUED) <br /> <br />5. Plugged by sediment. <br /> <br />6. Bridgehu tvo barrels 4' wide with present clear waterway 15"high. <br /> <br />7. Both culverts are clear. <br /> <br />Another cauSe of sedimentation 1S vegetation growth in the channel. AL- <br />though gtass growth is desirable for channel stabilization and aesthetics, <br />it hall caused excessive sediment accumulation in sOme areas. Downstream from <br />the Elm/~lbert Streets intersection, the dense grass and brush vegetation <br />retards flow and traps lIediment. The sediment haa continued to build up until <br />the culvett outlets are being buried. <br /> <br />,. "" storm scwerllize varies from 4' <4' to 21;' , ,. '0 J' d' '0 42" <br /> circular. See Plate '0< approximate lengths of each section. <br />9. Culvert i. clear. <br />10. Plugged >, sediment. <br /> <br />By c~ntrast, the culverts ~n the straight sectionll <br />of the street along Mobile, Paddock, and Tabor Streets are clear of sediment. <br />This is a~parently the result of stable ditches, adequate culvert length, and <br />positive outtet drainage. <br /> <br />Based On the proposed criteria, it ia clear that the culvert capacities should <br />be increased througbout the town. <br /> <br />The key points in preventing culvert sedimentation arc 8S follows: <br /> <br />Sedimentation <br /> <br />L. Provide c"lvert lengths which will terminate several fect beyond the <br />street shoulder to prevent damage and plugging due to street grading. <br /> <br />:>","'~;.ti'm of ccdi",.ent in t'~lve"n and chann..ls is ~ """iO\l1l !,roblem in !o;liza- <br />beth. A number of culverts are partially Or totally restricted by sedi~nt. <br /> <br />2. Culverr slopes should be sli,o;htly steeper than the incoming channel <br />slope to..aintainequivalcnt sediment transport. If the culvert sedi- <br />meot transport capacity i. less than the channel, the barrel will <br />begin to accumulate sediment and eventually pluS. A 2% slope is a <br />desirable minimum. <br /> <br />In Dur o~inion, the majority of the seditlent supply originates from the streets. <br />Each time the streets are graded loose sand and gravel arc bladed to the street <br />shoulders. Subsequent rains and snowmelt runoff ..ash the sediments into the road- <br />side drainage ditche.. Where flow in the ditches is insufficient to move the <br />.ediments, they continue to accumulate and restrict ditch ca~acitie" <br /> <br />3. Provide regular maintenance for channels upstream and downstream of <br />culwrts wh"re sediment tends to accUIIlulate. <br /> <br />Sedimentation in culverts is also partially caused by street grading operations. <br />Restricted culverts are located at County Road 136 and at a number of intersections <br />including the SIlO/Mobile and Elm/Elbert Streets intersections. Most of these <br />culverts hav~ commOn causes for the sedimentation. Fl.rst, the culverts are rela- <br />tively short which placcs the inlets and o"tletB directly at the shoulder of the <br />"treet. A 'lumber of culvert ends hav~ b"en crushed by crr"nt vehicles. Second, <br /> <br />-57- <br /> <br />-'>li- <br />