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HomeMy WebLinkAbout02/26/1990 Item #F-9aaF -9(a) BY THE CITY COUNCIL !! CITY OF NEWPORT BEACH CITY OF NEWPORT BEACH OFFICE OF THE CITY ATTORNEY FEB 2 61990 1 6 i p L 777-777 .Ll [ -L: ACL jarLam. February 16, 1990 TO: Mayor and Members of the City Council FROM: Robert H. Burnham SABJ: Newport Dunes Settlement Agreement Water Quality Study The Newport Dunes Settlement Agreement requires the owner to prepare a Water Quality Study prior to constructing any improvements in the mouth of the swimming lagoon. This requirement stemmed from a concern that the construction of slips and /or the pedestrian bridge could reduce tidal flushing action. The consultant for Newport Dunes has completed the Water Quality Study and a copy is attached as Exhibit A. The City has, in the past, used this consultant to analyze water quality impacts and staff believes the consultant is qualified to conduct the study. The consultant has concluded that the proposed improvements will have "a minimal impact on tidal flows in and out of the lagoon." In fact, water quality may be slightly improved as a result of the turbulence created by the structures. The dredging of the area north of the improvements may reduce tidal current velocity by 115 to 10 percent" but this reduction will be offset by the slight increase in the depth of the channel through which water flows. Staff also asked the consultant to analyze the impact of the structures on surface debris. As one would expect, the consultant concluded the improvements would "increase the chance of trapping any surface floating material ...." Newport Dunes has agreed to manually remove debris on a regular basis and this should have the effect of reducing surface debris in the Upper and Lower Bay. 0 6 -z - It is recommended the City Council approve the Water Quality Study prepared by Noble Consultants subject to written confirmation from Newport Dunes of their commitment to regularly remove surface debris trapped in and around the improvements. l A, xoAerr x. burnnam City Attorney RHB:jg Attachment NOBLE C O N S U L T A N T S January 16, 1990 Mr. Robert H. Gleason Newport Dunes 1131 Back Bay Drive Newport Beach, CA 92660 Re: Water Quality Study Dear Mr. Gleason: NCI No. 663 -01 This letter report summarizes our results of a water quality study conducted to assess potential impacts associated with the proposed recreational marina improvements at the Newport Dunes Resort. Our scope of services was conducted in accordance with our letter proposal, dated December 22, 1989. The purpose of this investigat- ion was to assess the general water quality concerns as a result of the construction of water - related amenities at the resort. The City of Newport Beach has requested an assessment of water quality impact associated with the above - mentioned improvements. The specific items of interest were listed in a letter from Robert H. Burnham of the City of Newport Beach, dated December 21, 1989. This report was directed to respond to those questions reproduced below: 1. The extent to which construction of the pedestrian bridge and /or slips at the mouth of the lagoon will restrict tidal flows in and out of the swimming lagoon; 2. The extent to which construction in the mouth of the lagoon will trap surface material within the swimming area; 3. Assuming some reduction in tidal flows resulting from construction in the mouth of the lagoon, identification of mitigation measures that would minimize restriction on tidal flows or improve water quality by reducing the extent to which pollutants enter the swimming lagoon; 11111 SITU It LING IIIGIM!AY, 'WITIE 11 -;86, ?II I.L \'A LLG 1', CA 94941 -3610 4151331.3944 �1 2 20 1 DUNONT DItI\'R, SUITE 620, IR \,INR, CALIFORNIA 92715.1515 714/752.1530 14 0 NOBLE CONSULTANTS Robert H. Gleason Newport Dunes January 16, 1990 Page 2 9. Assuming the construction will trap surface pollutants, measures and procedures available to remove these pollutants from the swimming lagoon; and 5. The extent to which dredging for boat slips or other activities in the lagoon will increase the time required for complete tidal turnover of water in the lagoon. Site Description The Newport Dunes study area, as shown in Figure 1, occupies approximately 96 acres located within the southern portion of upper Newport Bay, north of Pacific Coast Highway and west of Jamboree Road. The water - related components of the existing facility consist of a boat - launching ramp, a marina, and a swimming lagoon. The lagoon, with an approximate dimension of 800 feet wide by 1,200 feet long, is connected to the main navigation channel through a 350 feet wide by 300 feet long entrance channel. The master plan proposes construction of 90 additional slips at the mouth of the Newport Dunes Lagoon and approximately 110 additional slips within the existing 211 slip marina. The construction will be performed by extending the length of the existing main walkways and constructing two new piers at the entrance to the swimming lagoon. To accommodate the new wet storage area at the mouth of the lagoon, about 15,500 cubic yards of material will be dredged to establish a controlling depth of -8 feet, MLLW. Access at the resort is proposed for improvement via a pedestrian bridge that will span the lagoon entrance. The timber structure will be supported by two -pile bents spaced at 30 feet intervals. The plan sketch is illustrated in Figure 1. Tidal Flow Pattern Tides in the Newport Bay are characterized as mixed semidiurnal and consist of two unequal high tides and two unequal low tides each day. The typical tidal range for the study area is about six feet with the tidal exchange between the ocean and the bay taking place through the main navigation channel. I NOBLE CONSULTANTS Robert H. Gleason Newport Dunes January 16, 1990 Page 3 The entire upper Newport Bay experiences semidiurnal tides with a tidal prism of about 1,500 acre feet'. Rapid fresh seawater exchanges of the upper bay through the main navigation channel occurs and a complete turnover is estimated to occur within a few tidal cycles. It was estimated that the mean residence time of water in the upper bay is about 1.7 days'. The duration for a complete tidal exchange in the lagoon is slower since it is not located within the course of the main tidal flow which is the primary mechanism for tidal exchange. In order to estimate the circulation patterns within the project site, visual observations were made on December 29, 1989 during peak ebb flow conditions. Preliminary field observations indicate that current velocity of tidal exchange through the entrance of the lagoon is considerably slower than the ebb flow observed in the main navigation channel. Figure 2 illustrates the estimated flow pattern during an ebb tide condition. The current pattern on the east side of the entrance appears to flow toward the area of state ecological reserve peninsula. The water column on the marina side tends to be directed toward the main navigation channel and merge into the main tidal flow. The tidal current at the entrance to the lagoon was estimated to be less than 0.1 feet per second by monitoring floatable traces; and the duration of a complete turn- over of water in the lagoon was estimated to be approximately two days. Although the field observations were not performed in a flood tide condition, it is felt that under a flood tide, a slow tidal current at the mouth of the swimming lagoon is expected as well. Because of the relatively small current velocity, wind - drifted surface flow may be significant in the east side of the entrance. Impacts on Water Quality Given the above - discussed assumption of tidal flow conditions, the following paragraphs summarize development impacts. ' EIR, Newport Dunes Development, 1980 S N0B'I.0 CONSULTANTS • Robert H. Gleason Newport Dunes January 16, 1990 Page 4 `J Marina Expansion The pedestrian bridge will be supported by two parallel 12 -inch diameter piles on a 30 foot span. The timber docks for boat slips will float on the water surface in accordance with the tidal range. The bridge and the docks are estimated to not appreciably reduce seawater exchange since they do not act as a dam and block the tidal flow. The observed low velocity flow pattern within the swimming lagoon suggests that the basin raises and lowers more in response to the tide wave frequency as opposed to direct water discharge. As a consequence, the tidal cycle is not appreciably effected by the proposed structures. There may be some increase in mixing of the water flow exchange due to turbulence which would be beneficial. However, because of the overall low flow velocit- ies, this effect is considered to be minor. Impacts on Trapping the Surface Floating Material Floating debris is estimated to primarily originate from upstream sources or to a lesser extent from within the swimming lagoon area. It was noted during the December 29 field observation that no delivery of debris from upstream areas of Newport Bay is likely to propagate into the swimming lagoon area unless strong, persistent northerly winds exist. This is estimated on the basis of the pre- dominant downstream flow pattern in the main channel that bypasses the Newport Dunes area. In general, a prevailing westerly wind tends to set up a surface flow pattern that would drive debris out of the lagoon. The additional slips and boats would tend to increase the chance of trapping any surface floating material in and out of the lagoon. As a result the slips would tend to provide a means to trap debris for subsequent removal. The regular clean- up of the floating debris in the boat and slip area can be perform- ed to remove trapped debris. No debris comes in during ebb flow conditions. 10 9 0 NOBLE CONSULTANTS Robert H. Gleason Newport Dunes January 16, 1990 Page 5 tion Measures to Minimize Restriction on Tidal Flows or Because the proposed improvements are estimated to have a minimal impact on the existing circulation of the lagoon, the need for mitigation measures to minimize restricted flow conditions is not necessary. Some improvements might be obtained if surface water runoff from the upland areas of the lagoon is directed to points of discharge closer to the main channel. This recommendation has been previously addressed and was implemented during recent construction activity to the maximum extent practical. Alternatives of Removing the Surface Pollutants Based upon the field observation, the surface pollutants and floating debris are likely to be trapped at Areas A and B, as illustrated in Figure 3, after completion of the project. It is believed that the majority of the floating debris will be trapped in Area A. Accumulated debris may simply be removed manually at regular intervals. Impacts of Dredging on the Exchange of Lagoon Water Dredging will be conducted north of the pedestrian bridge, as necessary, to construct 90 boat slips. Approximately 15,500 cubic yards will be dredged at the mouth of the lagoon to accommodate the slip construction. It is estimated that the nominal deepening would not alter the tidal prism inside the swimming lagoon because the circulation is mainly related to long period tide wave propa- gation as opposed to water discharge. The average tidal current velocity would be decreased as a result of deepening the lagoon entrance. However, it is estimated that the velocity would be reduced by about five to ten percent over existing conditions. Therefore, it would have little effect, if any, on the exchange of lagoon water. 1'l N' O VLF C O N S U L T A N T S • • Robert H. Gleason Newport Dunes January 16, 1990 Page 6 This completes our assessment of project impacts on water quality and alternative recommendations to preserve/ improve the water quality in the swimming lagoon. Please contact us should you have any questions regarding the information presented in the report. Sincerely, CONSULTANTS, INC. P. E. :CCL:slh Attachments: Figure 1 Figure 2 Figure 3 E Chia -Chi Lu, Ph.D. Engineer -Z, Z� U R NEW F BAY o Pie ILe all o° r,in0 MarSh Npv \Gp�\ON STA LOGICAU ESERVE • • '. �10wy �04T PROPOSED FD 1.00 SVpS BOAT SLIPS �+ tii F41 9919 • BOAT LAUNCHI Cb+ P IDUSTING 4t4RI , 4�S�e. ((/ �CuD ° FEET POSED QQ SCALE aoo 400 PEDESTRIAN BRIDGE S, m� SWIMMING LAGOON NEWPORT DUNES AQUATIC PARK STUDY SITE REFERENCE: NATIONAL OCEAN SURVEY. NO. InSil, 1900 �T O B LE c 0 M v i T a M To FIGURE , I zl'� L11J 1!'] e X11 t U R NEWF� BAY Pile A. INOB 3 0 \\ V �m0 j e•' e I �NNEL e MP�N NAV`G�� SEA LOGIC. ` ��ROPOSED ESERVE 11101 �qT 4 AT SLIPS = IL Tel fl�Tl�� �. • � � �4f' POSED 1 Cby EXISTING WRIHgC q up a 4� C 4t> FEET SCALE • z 400 N ES BRIDGE SWIMMING • LAGOON EBB FLOW PATTERN REFERENCE: NATIONAL OCEAN SURVEY, 1/O. 19751, 126 0 . Marsh • M 7• �Q f FIGURE 2 to R NEWP1 BAY f ' Pde �n1 a rang Marsh I Npv`GP1\011 ` ` MpsN STA LOGICAL, ESERVE •• mOtL"'00gT PROPOSED`R , ✓ PRO • SED A� ldVpd BOAT SLIPS ^� • � � � 1 :�� i ► v i ,BOAT LAUNdiI Cb MP EXISTING MART �� RE 9 S Cup o '1b FEET PROPOSED SCALE 20o too PEDESTRIAN BRIDGE D SWIMMING LAGOON NEWPORT DUNES AQUATIC PARK SURFACE MATERIAL TRAPPED AREA REFERENCE: NATIONAL OCEAN SURVEY. NO. 19751. 1900 O B LE I cor�vi' *•rsr FIGURE 3