6414 HARDESON RD 2018-01-02 MF Import

IN 04'96 10:30 FR W a H PRCIFIC I ;�KLOHN LEONOFF CONSULTING ENGINEERS I � Oecember 4, 1990 Wilsey 6 Ham Pacific 2731 Netmore Avenue Everett, WA. 98201-3526 ATTN: GENE WRIGMT, P.E. RE: MERRILL 6 RING CREEK Dear Gene: 206 E2Z 5�41 TO E21�aE1 We have completed the hydraulic analyses rehabilitatton fo� Merrill 8 Ring Creek. Our model runs with the proposQd channel and bridge of the site of material required to resist bed P.03�14 Our File: PW0255 0101 ,� 1 �, , rt�'i �� y�'C � �.¢ �; e�� r �'�' ; . (H �`,:, �� �0!� I�C �) ,y. 1 � �ri I A of the proposed channel analyses consisted of HEC-2 configuration, and analyses erosion in the new channel. Summaries af the hydraulic analyses are attached for your review. The final i�� • channel configuration we used in our analyses was a 5-foot wide, 2-foot deep I,� �• channel With 2:1 (horizontal:vertical) side slopes. 7he bridge opentngs used ,,•.' were 15 feet. The channel slopes used in the HEC-2 model was ranged from;`:: 0.006 to 0.009 for the downstream reach of the channel (Stations 120t10 te' 140+80), and Station 120+10 upstream to the edge of the site, a slope of ;;, approximately 0.02 was used in the HEC-2 model. We understand that the ''� slopes of the upstream reach may change, however 6ecause of the steepness ',�: '� ' of the channel, capacity should not be an issue. A Manning's "n" value of •• ..�;�' 0.04 was used to describe the channel roughness, and a"n" value of 0.04 was - � used to describe the overbank roughness. A roughness value of 0.04 for � overbank conditions is required to give sufficient channel capacity for the� creek. The lindstaping or,revegetatian requirements to meet the "n" value requtreme'nt�s'-i�n ffie overbank areas can be discussed in fur�her detail�after revi�N'of'tii� report. The design flowrates used in the model were obtained frofi'your firm, and were approxSmately 64 cfs for a 2-year flood event, and 200 cfs for a 100-year flood event, although they varied with location along the creek depending on stormwater discharges from the development site. The chan�el used in our analysis would have sufficient capacity to convey the design flows without overtopping the adjacent street. 7he primary channel is also predicted to have adequate capacity to contain the 2-year flood. The required material siie to ii'mor the bed of the channel was calculated using a stable channel design program based on Corps of Engineers design criteria. The channel stability program was wrStten for angular riprap, and a� appropriate safety factor was used to account for the less stable rounded gravel and cobbles which are proposed for the new channel. The recommended material sizes were also checked for stability us•ing the Meyer-Peter Muller bedioad transport program. .... i�.a.^.�• u,r i�txk . Min n., vr i�,ae PM. K�••��a�n .}�...�.•;�:n 9,-:::.N • Te'e:tVro 1.'Qi1 B25;i529. F;.. 'JJ6i P:q fFS.^