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HomeMy WebLinkAboutSS3 - Morning Canyon Restoration Project - C-3517CITY OF NEWPORT BEACH CITY COUNCIL STAFF REPORT Study Session Item No. SS3 March 22, 2005 TO: HONORABLE MAYOR AND MEMBERS OF THE CITY COUNCIL FROM: Public Works Department Robert Stein, P.E. 949 - 644 -3311 rstein @city.newport- beach.ca.us SUBJECT: MORNING CANYON RESTORATION PROJECT, C -3517 Introduction The Morning Canyon Stream Stabilization and Channel Restoration Study prepared by RBF Consulting (RBF) that you are receiving this evening, states that the erosion and slope failures in Morning Canyon have progressed to the point where damage to private improvements is a threat. This study recommends installation of engineered rock stabilization blankets (gabion) at strategic locations along the canyon bottom to forestall further erosion of the canyon bed which undermines the canyon slopes. If these measures are implemented before the next rain season, further erosion of the canyon bed will be prevented. Property owners on the canyon have turned to the City for help. As a practical matter, the City stands as the most reliable entity to act in the best interest of the community and it is appropriate for the City to guide the corrective process and to prepare a master plan for drainage, restoration, and water quality for this channel. Project History The stability of Morning Canyon has been affected by actions in the canyon that have occurred over the past fifty years. The following timeline highlights major events in the canyon's history as based on information obtained from staff, property owners, consultants, and canyon reports. A more detailed recount of events follows. 1950-1980 Cattle grazing activities occur in hills of Newport Coast resulting in increase in canyon bed elevation 1959 Substantial grading activities for Cameo Highlands Development occur 1960 City incorporates Cameo Highlands 1980's Arundo donax invades canyon streambed disrupting flow pattern 1990 Construction begins on Pelican Hills Golf Course and housing developments 1992 Significant increase in dry- weather flows entering canyon SUBJECT: MORNING CANYON RESTORATION PROJECT, C -3517 March 22, 2005 Page 2 1997 Massive failure of canyon slope at 607 Rockford Road (Wynkoop Slope) 2000 City staff identifies severe scour hole at 615 Rockford Road 2002 Rivertech completes concept -level stability analysis of canyon 2004 RBF hired to prepare Stream Stabilization and Canyon Restoration Study Prior to construction of the Cameo Highland tract, this area was drained by two canyons, Surrey Canyon flowing into Morning Canyon from the east, and Morning Canyon flowing to the ocean. At the confluence of two canyons, 2/3 of the flow was carried by Surrey Canyon and the remainder by Morning Canyon. Over a thirty -year period beginning in the 1950's, grazing activities and removal of natural vegetation in the upper watershed disrupted the soil and a surplus of material was washed into the canyon by storm water runoff. This surplus of material allowed several feet of sediment to accumulate in the canyon bottom and created a broadly rounded channel in the 1980's. The fill slopes (Cameo Highlands) have experienced failures on various occasions on several properties, including a report of a slope failure as early as 1977 (Lockwood -Singh & Associates, 1999). In the late 1950's, with the grading of the Cameo Highlands tract, the canyon that crossed the tract, Surrey Canyon, was filled and a 51 -inch storm drain was installed across the tract with the outlet about 250 feet north of the mouth of the now filled Surrey Canyon. Two 18 -inch storm drain lines, one from Rockford Road and one from the Rockford Place cul -de -sac, were constructed and drain to Morning Canyon. A high slope on the east bank of Morning Canyon was created which partially intruded into the natural flowline of Morning Canyon. Slope grading and compaction would have been inspected by the County and would have been performed in accordance with the standards in force at that time. After completion of construction of the tract, the City accepted the tract in 1960. The tract map includes a 22 -foot easement along the western boundary of the tract for storm drain purposes. This easement is largely located on the fill slope. It is anticipated that this easement was required and granted to allow for the construction of a future storm drain facility in the event that the upstream properties were developed. The giant reed, Arundo donax, invaded the canyon bottom in the 1980's. Arundo and other dense vegetation in the channel bottom are contributing factors to the degradation of the channel. The heavy vegetation in the center of the canyon forces flood flows to run along the banks of the canyon. Erosive scour areas form along the toe of slope that will eventually undermine the slope and cause it to fail. Dramatic changes occurred when grading for the Pelican Hill Golf Course and housing developments commenced. Pictures of flood flows coming off the denuded slopes in 1990 show large amounts of muddy water flowing down the channel, a dramatic change from previous years. Two detention basins at the northern boundary of Cameo Highlands (one on Morning Canyon and one at 'Surrey Canyon') became operational in 1991. The detention basins, designed per approved regulatory standards, reduced the peak flows from large storms while increasing the duration of storm flows through the canyon. More importantly from the standpoint of canyon stability, the beneficial transport of upstream sediment into the canyon was reduced by approximately 50 SUBJECT: MORNING CANYON RESTORATION PROJECT, C-3517 March 22, 2005 Page 3 percent as estimated by Moffatt & Nichol Engineers. As a result, the clearer water entering the canyon within Cameo Highlands picks up sediment from the canyon bottom accelerating the natural canyon erosion process. The reduction of sediment supply to Morning Canyon is especially significant as this canyon is steep enough to force storm water runoff to move at a sufficiently high velocity to erode the channel bottom. Over time, this erosion creates deep incisions in the channel bottom. Prior to the construction of the golf course and detention basins, this naturally occurring erosive condition was counteracted in Morning Canyon by sediment washing into the canyon from the upstream grazing areas. With the construction of the golf course, the replenishing supply of sediment was reduced and erosive forces created an incision in the canyon bottom. With the formation of the incision, the erosive process accelerated because flood flows were now concentrated within the incised channel. The deepening incision is what motivated many property owners to act by reinforcing slopes with rock and concrete structures. These activities were ineffective. The rapid destabilization of the canyon became evident in the winter of 1997 -1998 when this area experienced above average rainfall and significant individual storm events. These storms and the resultant storm water runoff accelerated erosion and entrenchment, and general degradation of the canyon particularly in the portion of the channel adjacent to the Wynkoop and Walton properties (601 Rockford Road and 507 Rockford Place respectively). Canyon downcutting and undercutting processes, along with surface failures associated with heavy rainfall directly on the slope, caused the Wynkoop /Walton slope to fail. In 2000, Staff discovered a deep scour hole approximately 120 -feet upstream of the Wynkoop property. Prior to the 2004/05 winter storms, continued downcutting has caused additional erosion pushing the drop in the canyon bed approximately 30 feet upstream to the outlet structure of the 51 -inch storm drain. The unusually high rainfall this season has caused the downcutting to progress another 50 feet and has now reached the stormdrain outlet structure. While it appears the 51 -inch storm drain outlet structure will not be undermined this season, this severe erosion has resulted in surface erosion (sloughing) of the Patterson slope (621 Rockford Road) including the loss of a mature tree. Additionally, the McCabe slope (615 Rockford Road) appears on the verge of sloughing. Finally, many people have noted that there is now a continuous flow of water coming down Morning Canyon due to upstream irrigation and wash -down activities. With the upstream development of the golf course and houses, there has been an increase of dry- weather flows into Morning Canyon. While the velocities are too low to cause any significant erosion, these flows do maintain a saturated condition in the canyon bottom that potentially facilitates erosion during storm flows due to the reduction of interparticle cohesion. Additionally, this nuisance runoff transports pollutants, fertilizer and pesticide residues into the channel. The fertilizer and pesticide residues have most likely accelerated the vegetative growth in the canyon. The City on at least two occasions has cleared the bottom of the canyon of foliage and debris to prevent materials from being washed down to Coast Highway and potentially blocking the culvert under the highway. SUBJECT: MORNING CANYON RESTORATION PROJECT, C -3517 March 22, 2005 Page 4 Of the actions that occurred over the past 50 years which finally resulted in altering stream stability in a negative manner for residents along the canyon, the most important factors were: 1. Loss of sediment re- supply due to upstream housing and golf course development including detention facilities. 2. Grading steep slopes that encroached into the canyon during the development of Cameo Shores 3. Diversion of Surrey Canyon flow upstream to a 51 -inch storm drain constructed as part of the Cameo Highlands development Less important, but contributing factors include: • Invasion of the Arundo • Certain property owner encroachments including fencing, weir, and rip -rap • Year -round low flow which saturates the canyon bottom • Clearing activities in the canyon bottom • The design of certain storm drain and detention basin outlet structures were based upon older design standards that have since been updated due to advances in drainage science. • Climatic changes in rainfall intensity and durations (record rainfalls and storm events in 1982/83, 1992/93, 1997/98 and this year) Issue at Hand On March 9, 2004, Council approved a Professional Services Agreement for RBF to prepare 1) a stream stabilization and canyon restoration study and 2) final construction documents, environmental documents, permits and easements for the stabilization project. Council approved proceeding with Phase 1 and reporting back to Council at the completion of this task with recommendations. The City has reviewed RBF's report and recommendations composed of the following key components: • Clearing non - native vegetation from the canyon bottom; • Importing soil to fill scour areas of the canyon; SUBJECT: MORNING CANYON RESTORATION PROJECT, C -3517 March 22, 2005 Page 5 • Installing seven gabions at strategic locations along the streambed designed to protect the canyon from dangerous erosion from storms up to the 100 -year storm event; and • Planting drought tolerant, Fire Department approved landscaping in the canyon bottom. The preliminary cost estimate prepared by RBF is $825,000 which includes a 25% contingency. Maintenance of the stabilization and erosion control structures and the native landscaping is estimated at $5000 per annum. Staff is recommending approval of a professional services amendment with RBF at tonight's meeting for Phase 2 so the final construction document, environmental documents, permits and easements can be prepared. The schedule calls for these documents to be completed by July 2005 such that construction can proceed in the Fall of 2005. Prepared by: Robert Stein, P.E: Principal Civil Engineer Submitted by: Steph,eh G. Badum Pub}(c Works Director 1-rN rb Ln � S§ O S§ i i M u p' 0 Ct 4J U1 4J P1 V1 Ct 0 a� U iii=_.. ^�•- - ' ;� \• � .,may_ � a .�•.',�..i •._ � -_. ,�i.r . .., , �r ; 4r; SIA 1 � f1 ♦P �; / ,r i y' A." P '.i ; i. 44 a !� `t' w �� _ �., Y, ���1. � .. \. ..- � ♦1. r� � � ; . .. •,�..r.! .''x`11, 1'� T -.� • f _ .. � i \'ti �:• : =L! fit. �' �`. Y,. •� -''�.' -`"• ::' �1• 1. If �' f i.•.. ' \. � '�� '• •! � � � � .. SAC`' p•. i•l - TZ kv NL �.��. . \a . 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