CARMEL RIVER LAGOON RESTORATION Scenic Road Protection Options

Prepared Under Contract to Whitson Engineers for:

Monterey County Water Resources Agency 893 Blanco Circle, Salinas, CA 93901-4455

Prepared by:

moffatt & nichol 2185 No California Blvd., Ste. 500 Walnut Creek, CA 94596

February 25, 2013 M&N Job No: 7871 Scenic Road Protection Options

CONTENTS 1. INTRODUCTION ...... 1 2. Data Summary ...... 4 2.1 Topography ...... 4 2.2 Bathymetry ...... 4 2.3 Geotechnical Conditions ...... 4 2.4 Additional Information ...... 5 3. Coastal Processes ...... 6 3.1 Water Levels ...... 6 3.2 Wave Climate ...... 6 3.3 Sea Level Rise ...... 7 3.4 Littoral Transport ...... 8 3.5 Beach Morphology ...... 8 3.6 River Breaching ...... 9 4. Conceptual Protection Options ...... 11 4.1 Alternative 1 - Revetment (Rip Rap) Located at the Toe of Slope ...... 12 4.2 Alternative 2 - Seawall Located at Toe of Slope ...... 12 4.3 Alternative 3 - Reinforced Earth Wall Located at Mid-Slope ...... 13 4.4 Alternative 4 - Pile Wall Located at Top of Slope ...... 14 5. REFERENCES ...... 16

APPENDICES A. County Aerial Photographs

i Scenic Road Protection Options FIGURES 1. Project Site Overview 2. Depths (in fathoms, MLLW) near project site (NOAA Chart) 3. Nearshore Bathymetry (in ft, MLLW) 4. Wave Conditions (Annual Average) for Monterey Bay (~30 Miles Northwest of Project Site) 5. Wave Conditions (Annual Average) for Point Sur (~50 Miles South of Project Site) 6. Winter (left) and Summer (right) Wave Height for Monterey Bay 7. Winter (left) and Summer (right) Wave Peak Period for Monterey Bay 8. Observed Seasonality in Wave Conditions for Monterey Bay (Winter (left) and Summer (right)) 9. Wave Refraction Diagram for WNW, 11-second Swell (Howell, 1972) 10. Example of Nearshore Wave Model Domain (PMS Model) 11. Example of Nearshore PMS Wave Model Results 12. Alternative 1 – Riprap 13. 10+00 Cross Section Alternative 1 – Riprap 14. 14+00 Cross Section Alternative 1 – Riprap 15. 16+00 Cross Section Alternative 1 – Riprap, Alternative 2 – Seawall & Riprap 16. Alternative 2 – Seawall & Riprap 17. 10+00 Cross Section Alternative 2 – Seawall & Riprap 18. 14+00 Cross Section Alternative 2 – Seawall & Riprap 19. Alternative 3 – Reinforced Earth & Riprap 20. 10+00 Cross Section Alternative 3 – Soil Nail Wall & Riprap Grade Control 21. 14+00 Cross Section Alternative 3 – Soil Nail Wall 22. Alternative 4 – Pile Wall at Edge of Road 23. 14+00 Cross Section Alternative 4 – Pile Wall at Edge of Road

ii Scenic Road Protection Options 1. INTRODUCTION

This report presents an overview of the Scenic Road Protection Project, and provides a description of potential bluff protection options for times when Scenic Road is threatened by a northerly meandering Carmel River. The project description below describes the Carmel River history and management drivers. Subsequent sections include a summary of available topography and bathymetry, a description of the coastal processes influencing the beach dynamics along Scenic Road, and potential bluff protection options. The Carmel River drains an approximate 250 square mile watershed. Like many California streams entering the Pacific, there is a very productive estuary at the mouth, called the Carmel River Lagoon, which serves as rearing habitat for juvenile steelhead. The Carmel River Lagoon supports threatened species such as the South-Central California Coast (S-CCC) steelhead, California red-legged frog, Western snowy plover, and Smith’s blue butterfly. The Carmel River was also designated as critical habitat for S-CCC steelhead in September 2005 (County of Monterey et. al, 2012). The lagoon is not connected to the ocean during times of low or no river flow, when waves build a barrier beach across the mouth of the river. When the mouth of the river is closed, lagoon water levels rise between late fall and spring seasons and threaten private properties along the northern edges of the lagoon, as well as a parking lot and restroom facility operated by the State Parks. Therefore, since 1973 the County has mechanically breached the sandbar. Evidence shows that the barrier beach has been breached since at least the early 20th century (Final Study Plan, 2007). Historically, the breaches were created such that the river would flow directly west out to the Pacific Ocean; however, the river meanders north or south along the beach in response to beach build-up from wave action. Often numerous breaches are mechanically and naturally formed over the winter and early spring, depending on variable ocean and river conditions (James, 2005). Beginning in 2005, the sandbar has also been mechanically closed in the spring when the river flows have subsided in order to maintain adequate water levels for steelhead throughout the summer. A larger, deeper lagoon during the summer and fall increases the quality and quantity of fish and wildlife habitat until river flows resume during the winter (County of Monterey et. al, 2012). The rate of the lagoon drawdown after a breach and the post-breach lagoon water surface elevation are dependent on several factors, including breach location, channel length and width, tidal conditions, and the presence or absence of a rock sill along the outflow channel. Breaches which result in the lagoon reaching relatively low elevations reduce the available aquatic habitat area for fish and wildlife. Breaches directly west out to the ocean also have swift stream flows that push juvenile steelheads out to sea prematurely. When the river channel migrates along the northern or southern beach, a longer, meandering path is taken which extends the hydraulic gradient slowing the water exit. Local fisheries groups and agencies have preferred a northern meandering outlet channel alignment because, in the past, when the river channel migrated northwards, it reduced the rate and amount of drawdown (drop in lagoon water levels before and after a breach to the ocean) and subsequent loss of threatened juvenile steelhead that get flushed out to sea, as compared to when the channel flows along the southerly and westerly outlet channel (James, 2005). Scenic Road is located immediately north of the Carmel River mouth in Monterey County. It is a publicly maintained road that is threatened by erosion when the river takes a northerly route along the beach before discharging into the Pacific Ocean. The road runs around the northern headlands of Stewart’s Cove, southwest to intersect with Carmelo Street near the Carmel River State Beach parking lot and restrooms. Scenic Road provides recreational access to the State Beach, sole access to six private homes, and has a sanitary sewer pipe under the

1 Scenic Road Protection Options roadway. Monterey County (County) is investigating bluff stabilization methods to protect the road, sewer infrastructure, and homes. If a northerly river alignment on the beach were to persist over an extended period of time (several months), it is likely that the bluff fronting Scenic Road may also require protection from wave erosion. As a result, although river-induced scour is believed to be the primary mechanism that undermines the sand dune fronting the bluff (Thornton, 2005), the protection options developed for this study take both factors into consideration. Bedrock underlies the northern beach that prevents a deep exit channel from forming. A bedrock sill is also found on the south beach, and often mechanical breaches are directed towards this sill to prevent damage. In 1992, regulatory agencies informed the County that sandbar management did not qualify as an emergency due to the predictability of flooding at Carmel River Lagoon. In response, the County prepared an Interim Management Plan and Breaching Criteria and submitted it to the agencies. The County updated the agencies in the years following; however, a lack of supporting data and analysis was expressed by the agencies. In 2007 a Final Study Plan for Long Term Adaptive Management was released, identifying baseline studies needed to find a long-term solution to managing Carmel River (Final Study Plan, 2007). In November 2011, the County applied for permits from the US Army Corps of Engineers (Corps), Regional Water Quality Control Board (RWQCB), California Coastal Commission (CCC), and the California Department of Fish and Wildlife (CDFW) to manage lagoon water levels and install a sand ramp for public beach access. The Corps consulted with the NMFS and the US Fish and Wildlife Service (USFWS) as part of permit review. In September 2012, the County and the Corps, in consultation with NMFS, drafted a Memorandum of Understanding (MOU) regarding the management of the Carmel River Lagoon. The MOU lays out a long-term plan to balance protection of private property with protection of federally listed species. The MOU parties also recognize that mechanically managing the Carmel River Lagoon over the long run is not in the best interest of the County, Corps, and NMFS (County of Monterey et. al, 2012). So the MOU identified two long-term solutions as alternatives to performing sandbar management: the Ecosystem Protective Barrier (EPB) and the Scenic Road Protection and Preservation Project (this project). The Scenic Road Protection Project is proposed for the purpose of protecting Scenic Road and the State Parks parking lot and restrooms from erosion when the river is allowed to naturally breach along a northern alignment. The purpose of the EPB is to protect nearby residential property by constructing a flood wall around portions of the lagoon, which would allow a higher lagoon water level, significantly reducing, if not eliminating, the need for sandbar management. The EPB and Scenic Road Protection Projects are anticipated to be completed by 2018 or earlier. Meanwhile, the Interim Sandbar Management Plan (County of Monterey et. al, 2012) provides well-established protocols on sandbar management. These include:  The use of sandbags, public outreach, sandbar breaching and closure, and sand relocation for access purposes;  Mobilizing equipment and personnel when the water level in the lagoon reaches +12.77 feet NAVD881, or when the projected water level is expected to reach this elevation within hours, or when the flow in the river reaches 200 cfs;

1 All elevations in this report reference the North American Vertical Datum (NAVD) of 1988, unless specifically stated otherwise. The conversion factor between NAVD and the National Geodetic Vertical

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 Mechanical sandbar breaching when the Lagoon water level reaches +13.27 feet NAVD88, or high river inflows and/or wave overtopping is expected to raise the water level to +12.77 feet in less than 6 hours, or if the predicted tides are unusually high;  Managing the breach in the winter to maintain a minimum lagoon elevation of +6 feet NAVD88, or closing the breach if excessive scouring is observed;  Managing the breach, and conducting beach grooming as required, in the summer with the intent of achieving a +12.77 feet pool elevation in the lagoon. This is a change to the County’s historic practice, which in general, was to mobilize at +10.27 feet and breach at +11.55 feet (James 2005). In reality, the average lagoon elevation at breaching was +11.83 feet for the 1992-1998 period, and +13.57 feet for the 1999-2005 period. This change over time was likely due to the Federal listing of the Carmel River Steelhead as a threatened species in 1997, which increased the involvement of resource agencies such as the National Marine Fisheries Service (NMFS).

Datum (NGVD) of 1929 is 2.77 feet, with the NGVD datum being higher (add 2.77 feet to NGVD elevations to obtain NAVD elevations)

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2. DATA SUMMARY

2.1 Topography The project reach is within a crenulate-shaped bay, anchored by the rocky Carmel Point headland (south of Stewart’s Cove) to the north and a bedrock outcrop to the south. Consistent with typical headland-bay beaches, the shoreline shape is oriented parallel to the wave crests as they refract and diffract around the headland. There is also a wave energy gradient along the beach such that during the winter, when waves are predominantly from the northwest direction, the energy decreases from south to north. The slope of the beach also progressively becomes flatter from the south to the north. Field observations by Prof. Ed Thornton of the Naval Postgraduate School show that the beach slope varies from about 8H:1V (12%) at the north end of the beach, to about 3.6H:1V (28%) at the south end of the beach (Thornton, 2005). Sand grain size, and therefore wave energy, also increases from the north to the south end of the beach. Sand is deposited on the beach berm by wave action, and at high tides, waves overtop the berm depositing sand and debris on the back beach (nearest the lagoon). Prof. Thornton also determined that the beach is relatively stable and has not migrated over the past 130 years (Thornton, 2006). The beach topography is seasonally variable and dependent on numerous factors including river flow, wave height, period and direction, tide, mechanical or natural breaching, wind direction and strength, and river sediment deposition. After reviewing the available surveys of the Carmel River mouth and beach along Scenic Drive, it is evident that the beach is heavily managed and mechanical breaching significantly alters the beach topography. By mechanically breaching in different locations each year, the beach to the north, south and middle of the river mouth are unnaturally modified, eliminating the ability to decipher the “natural” beach topography and breaching process. If natural breaching predictability is desired, cross sections for multiple years would have to be surveyed along the beach at specific locations to maintain congruency in the data. Surveys would have to be completed prior to, and after, sand management on the beach (after final closure and before first breaching) over several years to remove inter-annual variability to decipher a natural signal. 2.2 Bathymetry The sea floor offshore of the Carmel River Beach is relatively steep, quickly dropping off to depths greater than 100 ft in the Carmel Canyon; however, very little detailed information exists on the nearshore bathymetry within the surf zone. Figure 2 below gives a detail from the NOAA navigation chart of the area, but survey dates are unknown and there is still a lack of detail in the direct project vicinity. A bathymetric survey performed in the early 1970’s, with the locations of 20 to 100 feet depth contours, is provided in Figure 3 (Howell, 1972). Rock outcroppings at the northern and southern headlands are evident in the figure, with the sea floor between the two headlands reported to be mantled by over 5 feet of fine to coarse sand. In 2007 RMC performed a stage-volume analysis for Carmel River Lagoon. They performed bathymetric surveys in 2006 and 2007 of the lagoon and utilized a 2003 LIDAR survey to build the stage-volume curve (RMC, 2007). 2.3 Geotechnical Conditions As part of this SRPS Project, a feasibility-level geotechnical investigation was performed by Pacific Geotechnical Engineering. The draft report presents recommendations for the various

4 Scenic Road Protection Options conceptual design options based on a subsurface geotechnical investigation of the project area and review of past investigations. In addition to geologic cross-sections in the project area, the report includes information on topography, bathymetry, and anecdotal records of recent changes in beach character. 2.4 Additional Information Additional information on the basic hydrologic and oceanographic processes at Carmel River including lagoon levels, streamflows, wave heights, and rainfall, along with an analysis on open and closed lagoon dynamics including natural and mechanical breaching practices is also available (Monterey Peninsula Water Management District, MPWMD, 2005).

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3. COASTAL PROCESSES

3.1 Water Levels Typical tidal water levels at the site can be characterized using measurements from the Monterey, CA tide gage, located approximately 7 miles north of the project site on the opposite side of the Monterey Peninsula. The lag time between water levels over this distance is less than 5 minutes, and differences in water levels are negligible (Laudier, 2009). Table 1 below gives the tidal datums at the project site referenced to Mean Lower Low Water (MLLW), NGVD29, and NAVD88 datums. Table 1: Tidal Datums at Monterey, CA (NOAA CO-OPS #9413450)

Elevation (ft) Tidal Plane MLLW NGVD29 NAVD88 Datum Datum Datum Mean Higher High Water (MHHW) 5.34 2.74 5.48 Mean High Water (MHW) 4.64 2.04 4.78 Mean Tide Level (MTL) 2.87 0.27 3.01 National Geodetic Vertical Datum 1929 (NGVD29) 2.6 0 2.74 Mean Low Water (MLW) 1.1 -1.5 1.24 Mean Lower Low Water (MLLW) 0 -2.6 0.14 National Geodetic Vertical Datum 1988 (NAVD88) -0.14 -2.74 0

Note that the difference between NAVD88 and NGVD29 datums of 2.74 ft is provided at the Monterey tide gage and is used in this report. At the project site, the County uses a conversion of 2.77 ft (County of Monterey et. al, 2012). 3.2 Wave Climate The wave climate offshore of the project site is characterized by long-period, energetic swell that typically approaches from the west through northwest (clockwise) directions. Figure 4 and Figure 5 show wave height roses for the two closest wave measurement buoys located approximately 30 miles NW and 50 miles south of the project site, which show the predominance of the west through northwesterly swells. The wave climate varies seasonally to a high degree. During the fall and winter seasons, North Pacific storms generate long period swells that propagate from the west though northwest directions, though infrequent southerly swells can occur as well (James, 2005). During the summer months, shorter period (local seas) waves predominate from the northwest; infrequent southern hemisphere swells are also present. Figure 6 and Figure 7 give summer and winter wave height and peak period roses for the Monterey Bay gage, where the seasonal shift is evident. Figure 8 plots a measured time series of sea and swell conditions at a Coastal Data Information Buoy during a recent winter storm season and the subsequent summer. Carmel River Beach is largely protected from the predominant wave directions by both the southern end of the Monterey Peninsula and the rocky headland directly north of the beach. As long period NW waves propagate towards shore, they undergo refraction due to changes in bathymetry and diffract to a large degree by the protecting headlands, filtering out higher- frequency wave energy so that mostly low-frequency swell impacts the beach. The beach is exposed to the rare, westerly storms, where wave focusing can amplify approaching waves

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(Thornton, 2005). At the northern portion of the beach, diffraction of wave energy from the sheltering headland results in further diminished waves that approach the curved portion of the beach at a northerly direction. Figure 9 below gives a computed wave refraction diagram for WNW swell of 11 seconds, where the refraction and diffraction of waves along the northern section is evident (Howell, 1972). Overlaid on the figure are schematic wave rays (direction of wave travel) and sediment transport directions that are typical of a headland-bay system in California. While the reduction in wave heights towards the northern section of the beach can only be calculated using site-specific, quantitative methods, calculated wave refraction/diffraction patterns at similarly-shaped crenulate beaches can offer a good indication of the expected patterns at the Carmel River State Beach. Figure 10 and Figure 11 from a similar crenulate shaped headland-bay system (Shelter Cove in Mendocino County) show the results of a detailed numerical modeling effort to determine refracted and diffracted waves. Waves approaching Shelter Cove from the southwest (240o) to south (180o) direction are similar to north to northwest waves approaching Carmel River State Beach because Shelter Cove is a south-facing beach, while Carmel is a west-facing beach. The Shelter Cove model results show the gradient in wave heights moving from south to north that results from the headland- induced wave transformation processes. 3.3 Sea Level Rise Sea level rise (SLR) projections for the project vicinity were taken from the October 2010 State of California Sea-Level Rise Interim Guidance Document and are given below in Table 2. While some estimates of historical rates of global sea level rise indicate an accelerating trend, the current rate of increase along the San Francisco coast is less certain, and analysis of the most recent 19 year tidal record from the San Francisco gauge does not support the global trend. The October 2010 State of California Sea-Level Rise Interim Guidance Document recommends the use of global mean sea level rise predictions based on present and future greenhouse gas emission scenarios which give future SLR values from the year 2000 baseline (CO-CAT, 2010). The absence of sea level rise over the last 10 years in SF Bay indicates that the 0 ft. sea level rise baseline can be shifted ahead to 2010. With the 2010 baseline, M&N recommends that the high estimate of 1.4 feet (16 inches) in the Interim Guidance Document be shifted to 2060 instead of 2050. Table 2: Sea Level Rise Projections (CO-CAT, 2010) Baseline Modified* Range Range of Models (feet) Year Baseline Year Low Average High 2000 2010 N/A 0 (baseline) 2030 2040 All 0.4 0.6 0.7 2050 2060 All 0.9 1.2 1.4 2070 2080 Low 1.4 1.9 2.3 Medium 1.5 2.0 2.4 High 1.7 2.3 2.7 2100 2110 Low 2.6 3.3 4.2 Medium 3.1 4.0 5.0 High 3.6 4.6 5.8 * 2000 baseline year shifted to 2010 due to lack of observed sea level rise at the San Francisco Presidio gage over the last 10 years. Sea level rise could be expected to increase wave heights in locations where wave height is limited by water depths and the beach response to higher water levels is limited by sand

7 Scenic Road Protection Options supply. The shore along Scenic Road is depth-limited; therefore, sea level rise should influence a shore protection design. 3.4 Littoral Transport

Cross-Shore Transport The periodic, orbital motion of water under waves is important in transporting sediment up and down the beach profile (cross-shore direction). Seasonal changes in wave climate, especially in locations that have a distinct winter storm season, induce corresponding changes in the state of a beach, where sediment is transported offshore during storm events and the beach slowly recovers during less-energetic events (Bosboom & Stive, 2010). Because the Carmel River Beach is sheltered from the predominant wave direction, very little wave energy in the form of large, storm waves reaches the northern portions of the beach; instead, swell impacts the beach for most of the year, transporting sediment shoreward and building up the beach berm (Thornton, 2005). The high seasonal variability in shoreline position common for other area beaches is not observed here, with an estimated position variation of only +/- 10 m (Thornton, 2006).

Long-Shore Transport Waves approaching a beach at some angle away from perpendicular induce a small mean current parallel to the shoreline as they break across the surf zone. This current drives the corresponding transport of suspended sediment parallel to the beach, and gradients in this transport rate due to differences in nearshore wave height or wave incidence angle promote erosion or accretion of the beach face in different areas (Bosboom & Stive, 2010). The incident-angle driven transport gradients often alter the shoreline so that it tends to align with the predominant incident wave angle, diminishing transport rates so that an equilibrium condition exists. Due to the shape of the Carmel River Beach system, long-shore transport is most likely northward in the north portion of the beach and southward in the south portion of the beach, serving to distribute sediment brought to the coast by the river along the length of the beach. This hypothesis was also verified in studies performed for Carmel Beach (Howell 1972). The concave shape of the beach is largely aligned with the crests of the refracted and diffracted breaking waves, suggesting the beach is close to an equilibrium shape and transport magnitudes are relatively low (Thornton, 2005). An additional mechanism other than oblique wave incidence may drive long-shore transport northwards toward the anchoring headland. Waves breaking across the surf zone induce a heightening of the mean water level known as wave setup, and larger waves produce setup of greater magnitude. Because of the sheltering effect of the northern headland, wave heights decrease northward along the beach resulting in a water level gradient that drives a northward flowing current (Thornton, 2005). While the magnitude of the transport due to this gradient is unknown, research at the more-exposed Ocean Beach in San Francisco shows that a setup- gradient induced longshore current can greatly exceed that produced by oblique incidence or tide (Barnard, Hansen, & Erikson, 2012). 3.5 Beach Morphology The Carmel River Beach is steep, reflective, and composed of fairly coarse sand delivered to the beach by the river (Rich & Keller, 2013). Beach face slopes typically vary along the length of the beach, ranging from as low as 8% at the north to 28% to the south (Laudier, 2009;

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Thornton, 2005). The mean grain sizes also increase to the south, corresponding to the increased wave energy along the less-sheltered portion (Thornton, 2005). The shape of the beach shoreline is typical of crenulate or headland-bay beaches where the equilibrium condition can be described by one of several mathematical shape functions, usually log-spiral in form. These equilibrium beach shapes are typically present where a headland fixes the shape at one beach end and waves approach from a predominant direction (Moreno & Kraus, 1999). Waves approaching the beach both refract and diffract into the sheltered zone behind the upcoast headland, and differential long-shore transport shapes the beach so that it is perpendicular to the resulting wave rays at equilibrium (Silvester & Ho, 1972). While littoral transport is limited at the beach, the differences in wave energy reaching the different beach sections has resulted in alongshore variation in beach berm heights with lower berm elevations to the north (Rich & Keller, 2013). 3.6 River Breaching The Carmel River Beach forms a barrier between the Pacific Ocean and the adjacent Carmel River Lagoon that is seasonally breached (either naturally or artificially) when high rainfall events increase the water level in the lagoon (Kraus, Patsch, & Munger, 2008). Because the Carmel river is ephemeral and the beach is subjected to swell for most of the year, wave run- up rebuilds the berm and closes off the barrier beach when river outflows are low or absent (Laudier, 2009). During the early fall, the lagoon mouth usually remains closed to the sea, but occasional overtopping of the beach berm by long period ocean swell can raise the lagoon water level over the typical low, summer levels. Major fall overtopping-induced water level increases have usually been associated with high waves in conjunction with higher tide levels (James, 2005). During late fall/early winter, rainfall in the Carmel river watershed is usually sufficient to advance the flowing river to the lagoon and fill up the available storage. At this point, the beach berm has historically been mechanically breached to prevent flooding of roads and homes along the northern edge of the lagoon. Lagoon outflow through the breach quickly scours a channel sufficient to release most of the stored lagoon water into the ocean. Based on 13 years of observations, the berm breach remains open approximately 85% of the time, with river inflows of 100 cubic feet per second, usually ensuring that the breach will not be closed by predominant wave-transported sand. Because lower flows or large waves encourage breach closure (and then an increase in water level as the lagoon fills), the water level in the lagoon is not directly correlated to river inflow (James, 2005). Historically, the initial artificial breach channel has been excavated straight offshore near the southern end of the beach, though the breach management strategy has varied considerably over the past decade, and has included northerly and southerly managed breaches. Bedrock sills underlie the beach along both the north and south edges, so scour by migrating channels or channels intentionally opened in these sections is less than that when channels are excavated through the central beach portion. With the relatively long channel alignments, further limited by the sills north and south of the river mouth, river outflow is extending over a longer period (drawdown), which is beneficial for threatened species (County of Monterey et. al, 2012; Thornton, 2005). In 2005, the berm was breached toward the north with the unintended consequence of severe erosion along the backing bluff which supports road and wastewater infrastructure (Thornton, 2005). An elongated channel forms to the north along the beach in half of the years of observation (James, 2005) and either natural breaching or channel migration is expected to tend towards the northern alignment since the antecedent, lowered beach alignment has not recovered to typical berm heights and widths (Thornton, 2005). The lower berm elevations, due to milder

9 Scenic Road Protection Options beach slope and finer sediment, also favor natural breaching or channel migration towards the northern portion of the beach; however, this varies greatly on a year to year basis and depends on wave energy arriving over the winter/spring seasons. A preliminary analysis of beach berm elevations from the County provided surveys for the 2003 to 2012 period indicates the following:  The low point of the beach berm is generally about +14 feet and is to the south of the river mouth in most of the surveys (5 out of 7 surveys reviewed). The highest elevation of this low point was about 15.5 feet in Dec 2004.  The high point is generally in the middle of the beach, and ranges from +16 to +17 feet (5 of the 7 surveys reviewed).  The beach immediately north of the entrance is generally between the above two range of elevations and was as low as the southern portion in 2 of the 7 surveys reviewed, and actually was the high point in 2 of the 7 surveys. The above observations indicate that the low point in the beach berm is about 1 to 2 feet higher than the +13.3 feet elevation which is the current trigger for breaching the sandbar by the County under the Interim Management Plan.

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4. CONCEPTUAL PROTECTION OPTIONS

Bluff erosion along the project site has been attributed to northward-flowing, river-induced scour along the bluff toe. To prevent this from occurring while the river seeks a northern breach, some form of slope protection along the bluff toe is necessary. The primary objective of the slope protection is to limit the landward migration of the bluff toe, so it must be a non- erodible feature capable of resisting anticipated waves and currents. Typically, bluff slope protection will fall into one of the following categories: Engineered Revetment – a thick layer of armor rock sized to withstand wave and current forces, often underlain by a thinner layer of smaller rock and/or a geotextile fabric to prevent fine aggregate from being eroded through the revetment. The revetment does not support the bluff slope above the revetment, but prevents landward migration of the bluff toe. Seawall Structure – a retaining wall constructed vertically (or near vertically). The wall height depends on the retained height and the embedded depth, which in turn is dependent on whether the wall is cantilevered or tied back with earth anchors. Reinforced Earth Structure – this type of structure will have soil nails or tiebacks inserted into the slope and a facing to prevent the retained soil from erosion. The facing can be solid (shotcrete, precast concrete panels) or partially open (gabions). Pile Wall - this type of structure would be a tangent or secant type of pile wall. The piles are driven in at the top of slope, likely along the County right-of-way and would be exposed after the dune and portions of bluff fronting the pile wall are eroded. At that time, the exposed pile wall could be given a shotcrete facing for a natural bluff appearance. The alignment of the slope protection will be roughly parallel to Scenic Drive and will be either along the existing toe of the bluff slope (Alternatives 1 and 2); or at some location landward of the toe of slope (Alternatives 3 and 4). The alignments which follow the existing toe of slope allow for a natural dune above the structure and would provide the minimum visual impact, as the structure would be naturally reburied by wave action. The alignments which are located at some point mid slope (Alternative 3), or at the top of the slope (Alternative 4), would provide a wider beach over which the river could meander. (Note that an evaluation of the likelihood for the river to go in a northerly or southerly direction is beyond the scope of this Study). Also, Alternative 4 would be significantly more expensive but is included because it is within (or very near to) existing County right of way, which could be important for project feasibility as the other three alignments presented would need to be constructed on State Parks property or the property would need to be acquired by the County. The existing toe of the bluff slope is typically at an elevation of approximately +20 feet. The alignment will extend from the southern tip of the public parking lot toward the northwest for a total length of about 900-ft. The northern terminus was selected to match the general topography of the beach during non-breach periods; this currently shows a wave-built sand berm running west-east and connecting with the bluff at around station 10+00. The slope protection will thus be aligned to direct the riverine flow to turn west and breach at approximately station 10+00, which would be the northern limit of river migration. The reasoning for having a northern limit of migration is to ensure that the river does not swing all the way into the cove where Scenic Road turns to the west, where beach erosion could cause significant damage to the unprotected bluff and habitat that has established there. It

11 Scenic Road Protection Options would also reduce the extent of the bluff toe protection proposed herein, reducing impacts to the environment and minimizing costs. 4.1 Alternative 1 - Revetment (Rip Rap) Located at the Toe of Slope For an engineered revetment, the armor rock would be placed to a stable slope and with a thickness designed to resist both wave forces and riverine current forces. Placement of the rock would require extensive excavation of the beach, followed by installation of a geotextile fabric laid on the excavated subgrade. Two layers of armor rock (1/2 to 1 ton size) would be placed over the fabric and the excavated sand would be re-placed over the rock. Plan and section view graphics of the revetment structure are provided in Figures 12 through 15. The rock would remain hidden from view during most of the year and would be exposed only during significant events. The elevations shown on Figures 12 through 15 reflect this desire to keep the rock revetment buried for most of the year unless exposed when the river migrates to the north. Constructing a rock revetment has several significant benefits: Minimized Cost – Installation of the armor rock involves excavation, placement of rock, and backfill. The methods of performing these operations are standard in the marine construction industry, and can be performed by a number of marine contractors, leading to a relatively predictable cost of construction. Flexibility - Rock can be constructed to conform to a varying subgrade. This is especially beneficial when encountering a non-uniform marine terrace formation. The completed revetment can also adjust to localized scour by self-launching rock from the revetment toe into the scoured area. Energy Dissipation - Rock has the ability to dissipate energy due to wave or currents. Reparability – Additional rock can be added to the revetment to rebuild portions that are damaged by large storm events or to restore areas that self-launched rock into scour holes. Visual Appearance – Although large rock is not naturally present at the site, it is a more natural appearing material than standard concrete or steel. Rock also allows local sand to fill the void spaces and have a lesser impact on aesthetics. 4.2 Alternative 2 - Seawall Located at Toe of Slope This engineered structure would act as a retaining wall, supporting the loads on the landside of the wall. Plan and section view graphics of the seawall option are provided in Figures 16 through 18. This wall can be cantilevered or include tiebacks for additional capacity if necessary. The wall would extend to a depth sufficient to support the loads and ensure stability under various load conditions. The wall would be designed and constructed such that it would be completely buried for most of the year, and would only be exposed during large riverine flow events or large wave events. Once the event has passed, normal wave action or mechanical sand movement would re-cover the structure with sand. A structural seawall alternative has many benefits. It provides a permanent solution with the small footprint, leaving the upper bluff untouched and providing a substantial beach width for riverine flow and beach users. However, it will also have one of the highest costs of any alternative, and will create barriers to access and safety when the beach is eroded from the toe; a potentially 10-ft high vertical drop will exist if river flows to the north scour away the bluff toe. Additionally, the visual appearance of a vertical wall may be undesirable to the public and to stakeholders.

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There are numerous types of walls that can be used based on the site-specific conditions, performance criteria, and other constraints such as cost and permitting. At a minimum, the following issues will be addressed during the type-selection process: Geotechnical Conditions: The depth and location of the dense marine terrace material, water table depth, and the properties of the beach sand will have a profound impact on the type of wall that can be constructed. Construction Method – driven piles or drilled piles. This will be largely determined by the geotechnical conditions. o Driven Wall Type: This type of wall consists of steel piles driven by an impact hammer into the subgrade material. Sheet pile walls use interlocking Z- or U- shaped sheets to create a uniform, continuous wall. Soldier pile walls use heavier structural shapes such as H-piles or wide-flange beams/columns driven at specified intervals; the gaps between the soldier piles are subsequently filled with lagging panels or a structural facing such as shotcrete. o Drilled Wall Type: There are many types of drilled wall that can be constructed. Some are standard in the construction industry, while others are proprietary and require specialized equipment and materials. Although not an exhaustive list, below are some examples of the options available for a drilled wall:  Secant/Tangent Pile Wall (cantilever)  Soldier Pile Wall reinforced with steel H-pile (cantilever or tied back);  Jet Grout Piles reinforced with H-piles (cantilever);  Cast-in-Drilled-Hole (CIDH) pile wall with full-length casing (cantilever or tied back);  Continuous Flight Auger Pile Wall, reinforced with steel H-pile (cantilever);  Other options. In each of the drilled wall types above, the wall would be constructed while the beach has a relatively flat surface suitable for staging of drilling equipment. To determine the preferred wall type, an evaluation of each type would include the ability of the wall to be built through an upper layer of loose beach sand, a lower layer of marine terrace material, and a high water table. Material Type: Steel or Concrete – Due to the marine environment, steel H-piles or sheet piles must be coated to prevent corrosion or oversized to allow corrosion to occur without compromising structural integrity. However, coating can be damaged during driving operations; coatings for drilled piles are less likely to be damaged during installation. A concrete wall may be used for drilled-pile walls (too large for driving through hard material). Because the wall will be in bending, steel reinforcement is needed; typically this is done with a wide-flange structural steel member such as an H-pile, but a reinforced steel (rebar) cage can also be used. Cost Considerations – The various types of seawall have significant cost implications and a cost-benefit analysis may be necessary to reach a preferred solution if the seawall alternative is selected. 4.3 Alternative 3 - Reinforced Earth Wall Located at Mid-Slope Rather than supporting the bluff, this type of slope protection improves the ability of the bluff to support itself by inserting hundreds of tiebacks and creating a mass of reinforced in-situ

13 Scenic Road Protection Options material extending beyond the slip-failure plane. The tiebacks work together with a sloped structural facing (typically shotcrete) to provide a stable bluff with a minimum impact on the visual appearance of the improvements. Plan and section view graphics of the reinforced earth option are provided in Figures 19 through 21. A top-down, tiered construction method is utilized. The uppermost portion of the slope is excavated to the desired slope angle and the facing is constructed. Tiebacks – typically soil nails or grouted anchors – are installed, and the excavation continues to the next tier down. Unlike the toe wall alternatives, after river scouring the normal wave action would only partially re-cover the wall with sand leaving the top portion of the wall exposed. As such, an architectural facing would be applied to the wall, to give it a more pleasing and natural appearance. A reinforced earth alternative has several benefits: Low Cost – The facing will extend only a few feet below the anticipated limit of scour, which minimized the overall area of bluff to be stabilized to a vertical height of 15- to 20-ft at minimum (or a maximum of 40-ft if the entire bluff is to be stabilized). Flexibility – The facing can be conformed to a varying surface, and can be easily adjusted in the field. Visual Appearance – The facing can be sculpted to appear similar to naturally-occurring rock formations and greatly improve aesthetics. There are significant issues to resolve for a reinforced earth alternative, including the following:  Bluff material properties – If the bluff consists of running/caving sands and cannot support itself prior to application of the facing, this alternative may be infeasible. Loose bluff material will also make the facing construction and tieback installation challenging.  Changing bluff toe conditions – The duration of construction may also change the toe conditions after the upper slope is complete, creating a change of site conditions (this may be mitigated by a temporary sheet pile wall along the toe).  Utilities – The installation of tiebacks beneath a city street may impact existing underground utilities, and will hinder future underground or utility work. 4.4 Alternative 4 - Pile Wall Located at Top of Slope Similar to the seawall alternative, a high retaining wall could be constructed along the edge of Scenic Road and within (or very near to) the right-of-way. The height of such a wall would be approximately double that of the seawall constructed at the toe of slope and would range from 30 to 40-ft in retained height. This type of wall would be constructed of a secant or tangent pile wall system embedded into the marine terrace layer and tied back with earth anchors attached at the top of the wall; tieback anchors will extend under Scenic Road. Plan and section view graphics of the pile wall are provided in Figures 22 and 23. The wall would be completely buried until large riverine flow events or large wave events scour away the bluff toe. As the bluff toe scours, more of the pile wall becomes visible; eventually the entire retained height could conceivably be exposed. Unlike the seawall toe wall alternatives, after the storm event has passed, normal wave action or mechanical sand movement would only partially re-cover the pile wall with sand, leaving the top portion visible. Because the pile wall may not be re-covered by the sand, it may be desirable to apply an architectural facing on the pile wall after it has been exposed. The facing would require doweling of short anchors into the concrete piles, placement of rebar mats, and shotcrete

14 Scenic Road Protection Options application. Additionally, the shotcrete can be troweled and stained to provide a natural appearance. This alternative provides a permanent solution with the smallest footprint, providing the maximum beach width for riverine flow and beach users. It will also have the highest cost of any alternative, and will create significant barriers to beach access and safety once the beach is eroded from the toe; a potentially 30- to 40-ft high vertical drop will exist if river flows to the north scour away the bluff toe. As with the seawall alternative, the visual appearance of a vertical wall may be undesirable to the public and to stakeholders.

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5. REFERENCES

1. Barnard, P. L., Hansen, J. E., & Erikson, L. H. (2012). Synthesis Study of an Erosion Hot Spot, Ocean Beach, California. Journal of Coastal Research, 283, 903–922. doi:10.2112/JCOASTRES-D-11-00212.1 2. Bosboom, J., & Stive, M. J. F. (2010). Coastal Dynamics 1: Lecture notes CT4305. Delft, the Netherlands: Delft University of Technology, Faculty of Civil Engineering and Geosciences, Section of Hydraulic Engineering. 3. Coastal and Ocean Working Group of the California Climate Action Team (CO-CAT). 2010. State of California Sea-Level Rise Interim Guidance Document. . 4. County of Monterey, U.S. Army Corps of Engineers, & National Marine Fisheries Service. (2012). Memorandum of Understanding regarding Flood Prevention and Habitat Protection at the Carmel Lagoon. 5. Final Study Plan for Long Term Adaptive Management of the Carmel River State Beach and Lagoon. (2007). (Author unknown) 6. Howell, Buford F., Naval Postgraduate School. (1972) Sand Movement Along Carmel River State Beach, Carmel, California. Naval Postgraduate School. September. 7. James, G. W. (2005). Monterey Peninsula Water Management District, Technical Memorandum 05-01: Surface Water Dynamics at the Carmel River Lagoon, Water Years 1991 through 2005. 8. Kraus, N. C., Patsch, K., & Munger, S. (2008). Barrier beach breaching from the lagoon side, with reference to Northern California. Shore and Beach, 76(2), 33–43. 9. Laudier, N. A. (2009). Wave Overtopping of a Barrier Beach. thesis submitted to Naval Postgraduate School, Monterey, CA. 10. Monterey County Public Works (MCPW). (2005). Sand Bar Survey. May 25. 11. MCPW. (2005). Sand Bar Survey. October 4. 12. MCPW. (2006). Sand Bar Survey. April 18. 13. MCPW. (2007). Sand Bar Survey. October 2. 14. MCPW. (2008). Sand Bar Survey. October 30. 15. MCPW. (2010). Sand Bar Survey. January 15. 16. Moreno, L. J., & Kraus, N. C. (1999). Equilibrium Shape of Headland-Bay Beaches for Engineering Design. Coastal Sediments ’99 (pp. 860–875). ASCE. 17. NOAA Navigation Chart #18686, Pfeiffer Point to Cypress Point, 13th edition, July 17, 1999. 18. Pacific Geotechnical Engineering. (2013). Feasibility Geotechnical Investigation Proposed Ecosystem Protection Barrier and Scenic Road Protection Structure, Monterey County, California. DRAFT. January 11. 19. Rich, A., & Keller, E. A. (2013). A Hydrologic and Geomorphic Model of Estuary Breaching and Closure. in review.

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20. RMC Water and Environment. (2007). Hydrographic Survey and Stage-Volume Relationship. November 29. 21. Silvester, R., & Ho, S. K. (1972). Use of crenulate shaped bays to stabilize coasts. 13th Coastal Eng. Conf. (pp. 1347–1365). ASCE. 22. Thornton, E. B. (2005). Littoral Processes and River Breachings at Carmel River Beach. Naval Postgraduate School, Monterey, CA. 23. Thornton, E. B. (2006). Carmel River Beach Shoreline History. Naval Postgraduate School, Monterey, CA. April 9. 24. Whitson Engineers. (2012). Project Aerial Topographic Map for Scenic Road Bluff Stabilization Project. November 27.

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FIGURES