The Malibu Creek floodplain has been significantly modified by changes in its hydrogeologic character.¹ The lagoon project, a small part of that floodplain, is the latest such modification. Understanding that project requires investigating both its environmental origins, e.g., as presented in Part II of this review, as well as its physical character, and particularly its relation to the sand bar along the shore that periodically impounds² the creek. During impoundment, the creek mouth takes on the appearance of a coastal lagoon. However, it is questionable whether the creek mouth ever had the character of a true coastal lagoon, i.e., a coastal fresh-water body that receives tidal circulation more or less on a daily basis and as a result develops a habitat especially attuned to a well-circulated brackish condition. Rather, for thousands of years the condition of the Malibu Creek mouth has been one of lengthy periods of total impoundment followed by drainage when the bar is breached. When that occurs, the creek mouth is exposed at least as far upstream as the highway bridge and takes on the character of a mudflat in which low ridges of coarse-grained flood deposits mostly in the range of coarser gravels and smaller cobbles are exposed. Nevertheless, with regard to this condition, such terms as "lagoon" and "estuary" are misleadingly applied. In fact, there seems to be no specific term for the hydrogeomorphic condition in the vicinity of the Malibu Creek mouth. Only for convenience, and with reluctant deference to incorrect local usage, is the periodically impounded area referred to herein as a lagoon.

EARLY HISTORIC FLOODPLAIN CONDITIONS

This figure, modified from Doyle, et al. (2012, p. 61), shows three channel-like lagoonal "arms" as they appeared sometime prior to 1916. Most, if not all, the indicated cultural features probably were added about 1931. The southernmost lagoonal arm extended from the creek mouth to near what later became the eastern side of the initial Malibu Colony subdivision. A indicates the Malibu pier and C the impounded lagoon. At B, the dashed line represents a track later improved as Serra Road, and D is next to the Adamson house site on Vaquero Point. Additions in red added for present purposes include F, the site of a bridge for the original County Road, close to what is now the intersection of Cross Creek Road and Civic Center Way, and just upstream of the encircled original ford across Malibu Creek, MC in the vicinity of what is now the Malibu Country Mart, and K at the present location of the gate kiosk on Malibu Colony Road. Encircled arm areas are discussed in the text. Line segments along the shore connecting encircled points presumably are meant to approximate the mean high tide line. North to top of page; no scale.

It seems likely that during the Keller possession, Malibu Creek was crossed by a wagon ford about 2,500 feet north of the shoreline at a point about 500 feet south-southeast of what is now the intersection of Civic Center Way and Cross Creek Road. At that time, the road led from location B in Figure 1 first north-westerly and then curved westerly to the ford encircled in the figure. Then, the creek mouth - indicated as "Malibu Lagoon" - extended from its present eastern edge at the base of Vaquero Point to its western edge incised by three west-trending lagoonal arms separated by low ridges believed to be remnant shoreline bars.

Grading associated with ranch operations in the floodplain, probably undertaken in the middle to late 1890s, was generally along a lowermost section of what is now Cross Creek Road. Then, what is now Cross Creek Road was just a wagon track leading northward to its end at a ford where the Cross Creek bridge now is located, about 0.8 miles upstream from the shore. East of that ford, the track - along which Mariposa de Oro in the Serra Retreat area now is located - led to the Rindge ranch headquarters close to what is now the intersection of Serra Road and Palm Canyon Lane.

More important for present purposes, the effect of that grading was to relocate the western edge of the creek between the shore and a point roughly 0.6 miles upstream. This eliminated the pronounced curvilinear creek alignment shown in Figure 1 that had passed through the area now occupied by Malibu Country Mart and probably included filling the northernmost two western lagoon arms shown in the figure. It also provided a site for the western side of the trestle crossing the creek for the Rindge's never-to-be completed Hueneme, Malibu & Southern Railway. That location was close to where the west abutment of the present highway bridge now is located.

Thus removed from the normal stream regimen in the late 1890s or early 1900s, the area directly south of the western railway trestle abutment as well as others adjacent to the west crossed later by Pacific Coast Highway and Malibu Road, and north of what now is the Malibu Colony was used as late as the 1920s for limited agricultural development. However, the part of that land that was to become the lagoon project area thereafter became a disposal site related to grading for the initial State highway development in the mid- to late-1920s. As a result, and the remaining lagoonal arm shown in Figure 2 was filled. Probably in the late 1940s, there may have been additional disposal related to grading for Pacific Coast Highway, and for a time in the 1950s partly for two Little League baseball fields and a parking lot.

This figure is taken from the work of Rockhold (1916, Sheets A2 and A6) who surveyed a court-mandated County road through Malibu Rancho. At the time, the creek was crossed by a railroad trestle where the highway bridge now is located. The County road alignment crossed the creek near the original creek ford as shown in Figure 1. Regarding "Malibu Lake," see Part I - Floodplain Development.

Comment

A pronounced easterly littoral drift⁴ - that for thousands of years has helped to define the geomorphic character of the Malibu coast - affected both the earlier and later floodplain Malibu Creek stream regimes discussed in Part I of this review. Periodically, it causes the mouths of streams at the shore to be closed by barrier bars. Certainly, in latest pre-historic time, the stream regimen at the mouth of Malibu Creek functioned the same as today, i.e., with alternating periods of total impoundment and open flow to the sea.

The indentations encircled in Figure 1 in the northern side of the southernmost lagoonal arm are remnants of distributary deltaic floodplain stream channels resulting from late Holocene lateral stream planation. The linear ridges along the seaward sides of the two northern arms in Figure 1 are remnants of earlier bars formed as deltaic deposition that has progressed seaward during latest prehistoric time.⁵ The behavior of the bar at the mouth of Malibu Creek has been modified since the 1920s by bulkheads installed to protect Malibu Colony residences. The specific manner in which those structures now affect the barrier bar as to its formation and its semi-static condition is uncertain.

As mentioned earlier, the area that was to become the site of the lagoon project was completely filled by 1929. Reportedly, it was used as a waste disposal site presumably related to grading operations for the original Pacific Coast Highway⁶ - also referred to as the "Coast Highway," "Roosevelt Highway," and "State Highway" - probably constructed through Malibu Rancho during the period 1925 - 1929. In any event, from 1929 onward, the eastern edge of the future lagoon project site remained roughly along a line drawn from the western highway bridge abutment southward to the western side of the barrier bar or, when it was absent, the shoreline at the eastern side of the Malibu Colony.

For the more historically interested, the road alignment shown in Figure 2, officially "Malibu Road"⁷ but commonly referred to simply as the "County road," is part of the condemnation awarded the County of Los Angeles by the Superior Court⁸ in 1916. Most of the County road was never constructed. A few unpaved graded sections remain, but it appears there was never any serious intent to construct the original alignment. Rather, during a poorly recorded period in the mid- to late-1920s, the first state highway was constructed through Malibu crossing Malibu Creek along the abandoned alignment of the Rindge railway trestle. However, the section of the County road that crossed Malibu Creek at F in Figure 1 by way of what appears to have been a low two-lane bridge just upstream from the original wagon ford was still in existence in 1929. Probably, was no longer used except possibly for ranch operations. Subsequently, it was either physically removed or perhaps destroyed during a flood. However, the County road section across much of the floodplain west of that bridge remained in use and was renamed "Civic Center Way," probably in the 1940s.

ECO-CHANNEL DEVELOPMENT AND DECLINE

"... initiated a salt marsh restoration project ..." in the 16-acre project site "... to reintroduce tidal flow to the area..." by construction of "tidal channels" in what later would be the project area..."

Reportedly, those channels were to be one to two meters deep. Since their purpose was to introduce ecological conditions unrelated to drainage or stream flow, it is appropriate to refer to them as "eco-channels."

Based on the only data immediately available,⁹ elevations in the project area at the time ranged from about 2 - 8 feet, presumably mean sea level (msl), with average elevations of about 5 feet msl and an arithmetic mean of about that value. Consequently, eco-channel invert elevations probably would have ranged from about +2 to -1 feet, msl. Three channels were constructed "... (U)nder the direction of a group of biologists and landscape architects ... and seeded with salt marsh plants in 1983" (op. cit., p. 8-3). They had a total length of about 3,500 - 4,000 feet (see Photo 1, below).

During the following twenty years, environmental conditions in the eco-channels declined. Sutula, et al., (2004), although concerned primarily with sources of nutrients in the lagoon, offer certain insight regarding the extent to which adverse physical conditions in the eco-channels had developed by 2002. In particular, they note that the channels then supported growths of Ruppia maritima, a salt-tolerant fresh-water plant - commonly called "widgeon grass" - and occasionally "... green mat-forming mats such as that of the alga Rhizoclonium hookeri... which in excessive abundance can reduce habitat quality ..." (op. cit., pp. vi., 1, 3). It was observed by one of these co-workers, K. Kramer, that the widgeon grass was so dense in September 2002, that it impeded circulation (op. cit., p. 18). Since conditions in the absence of the widgeon grass apparently were not observed during that study, this seems simply speculative insofar as suggesting at any time there was significant eco-channel circulation.

Comment

Flow from the impounded creek mouth into the eco-channels of course resulted in a certain kind of ecological development in response to the induced artificial conditions. But the concept of restoration so extensively relied by the eco-channelers and all the lagoon project proponents since is clearly baseless because: [i] there is specific record of the natural biota at the time the Rindges took title, and [ii] the dredged channels in no way could replicate the actual hydrodynamic conditions under which the natural lagoon arms of Figure 1 had been formed. Attempting to "restore" an artificially modified coastal site such as the mouth of Malibu Creek without understanding either its original or existing hydrodynamic character seems rather like applying sun-tan lotion to cure leprosy.

HYDRODYNAMIC OBSERVATIONS

"In 1983, approximately 36 acres (sic) of the lagoon were restored. This included most of the study area where channels were dredged with U-shaped cross section and steep sloping banks. In the five year period since restoration the Lagoon has changed only slightly in morphologic features, with partial to complete infilling of the channels."

Further, and more important for present purposes, they took note of conditions during outflow from the eco-channels (see Fig. 4, below) as follows (ibid.):

"Observations made during a 24 hour survey in June 1988 indicate that when the entrance to the Lagoon is opened by the bulldozer, water flows faster out of Channel C than from Channel B. Flow out of both channels have [sic] been clocked at a 1 inch drop in water level in slightly less than 2 minutes. It is only when levels in the Lagoon drop below 2.75 ft. that circulation patterns in the inlet channels change. At that point the sand bar at the mouth of Channel C is exposed, and water from all the inlets must flow out of Channel B."

Artificially breaching the barrier bar, as previously noted, had been "mandated" by DPR based on the 1978 report. At the time, concern had developed regarding whether treated Tapia reclamation plant effluent disposed in Malibu Creek represented a health hazard¹¹ per se, or somehow was rendered so by lengthy impoundment. This, like a similar issue regarding septic-system effluent in the creek from floodplain developments, remains to be clarified. In any event, it was determined to shorten the period of impoundment presumably to reduce possible bacterial or other harmful organism gestation. As noted by Dillingham and Sloan (op. cit., p. 69), in order to limit the impounded water level to an elevation no higher than a "... mandated 3.5 ft ...,"¹² the plan was to have a bulldozer cut a channel in the bar. The informality of this procedure is indicated by the "... difficulty of getting the one bulldozer to the Lagoon to open the entrance..." when the level reached that elevation so that on occasion the level would reach as high as 5.2 feet (ibid.).

Conditions noted by Dillingham and Sloan (op. cit.) concerning bar breaching are illustrated in Figure 4. In this regard, they state (ibid.):

"Water circulation patterns in the Lagoon remain to be studied if the sediment patterns are to be fully understood. For instance, the building of a sand bar at the entrance of C channel has significantly altered water flow patterns in the B and C inlets, directing all flow through channel B when water levels are below 2.75 feet. The result is that water often stagnates at Station D .... Management of an ocean entrance to maintain water quality in the Lagoon throughout the year has surely increased the rate of deposition of both sand and organic material (drift algae) near this managed entrance. "

This figure, from Dillingham and Sloan (op. cit., Ch. 4, p. 64) is relabeled to show north to the top of the page; no scale.

It is especially relevant to note the sand bar that developed just downstream of location D at the outlet of Channel C. Such a deposit is due to aggradation.¹³ Although the sketch shows aggradation at the outlet of Channel C, similar deposits occur at the inlet of the channel breaching the bar as drainage reduces the gradient in the inundated area, and at the outlet when tides raise the ocean base level.

The part of the UCLA study most relevant in this regard is that by Orme, et al. (2000, Ch. 2, pp. 2-1 - 2-112), and particularly Section 2.5.1 titled, "Tidal Channel Hydrodynamics" (ibid., pp. 2-71 - 2-97). During the period of late September 1997 to late October 1998, their observations were concerned primarily with breached channel flow rates and changes in lagoon water volumes. Their description of the thalweg of a bar channel soon after its breaching at an elevation of -1.7 meters rising in a few weeks to 0.0 meters¹⁴, and also their observation that the "...0.0 elevation, routinely observed throughout the water year, appears to represent a quasi-equilibrium for the throat of the tidal channel ..." (op. cit., p. 2-77) are especially germane to the issue of breaching channel behavior in relation to that of nearby lagoon tributaries such as the eco-channels. It is instructive to compare Figure 4 with Photo 1. Although aggradation at the outlet of channel C shows no aggradation there, it is occurring just downstream of the breaching channel inlet.

This photo is presented rather than Figure 1.4 from the study by Dillingham and Sloan (op. cit.) showing the eco-channels which is unsuitable for reproduction. Lighter hues in the breaching channel as well as along the landward shore of the bar compared to those upstream both in the lagoon and the eco-channels are a result of aggradation. Photo: M&N staff (2005b, p. 2, Fig. 1).

The initial study by M&N staff (2005a) was concerned with both the lagoon, referred to as the "main channel," and area of the eco-channels referred to as the "west arms" (op. cit., Sec. 3.2, p. 18). Its focus was an analysis of physical characteristics - primarily those of the west arms - in order to determine means of increasing tidal flushing, circulation, and holding capacity (op. cit., p. 6). M&N's approach to the problem of maintaining "restored" lagoonal conditions despite periodic creek flooding involved a berm as an integral part of Alternative #1.5 described as follows (op. cit. p, 44):

This alternative proposes to install a naturalized berm along the western side of the main lagoon from the PCH bridge to the new channel opening on the south. The proposed naturalized berm will be at an elevation of approximately +2 feet msl (or 1 feet above the existing cobble berm or "speed bump") to physically separate the western arms from the path of the bed sediment load in the creek during storms, yet low enough to be inundated during closed conditions to provide for wind fetch. The naturalized berm will be constructed in a manner similar to that of the existing "speed bump," utilizing stone materials found within the lagoon. The design of the naturalized berm needs to be confirmed with additional analysis at a later stage to specify the appropriate effective crest elevation. The elevation may range from the +2 feet shown here by 1 to 2 feet vertically. The significance of constructing the berm to the appropriate elevation is that a berm that is too low may result in damage to the newly-restored marsh from sedimentation during certain flood events that may render the restoration ineffective or even reverse restoration benefits. A berm that is too high may impede the circulation of surface waters during closed conditions reducing benefits of water turnover and oxygenation.

Except to note differences during lagoon open and closed conditions, no attention was given to the manner in which a bar-breaching channel behaves. However, the study does provide the only useful data in the entire record thus far reviewed regarding elevations of the barrier bar which at the time were 5.8 feet at the west end, 6.7 feet near the center, and 8.2 feet at the east end (op. cit., Fig. 16, p. 24). Presumably, these data refer to the National Geodetic Vertical Datum of 1929 (NGVD1988).

Aside from the questionable efficacy of the proposed "speed bump" barrier, the results of a numerical model employed by M&N staff (2005a, App. 3) are of special interest. That model, based on a version of the well known Hjulstrom-Sunborg curve, was used to produce theoretical distributions of deposits under a variety of conditions including both deposition and flushing "potentials" for existing average and 5-year maximums for both Alternatives #1.5 and #1.75. Essentially, the model predicts grain-size materials to be deposited or left undisturbed under both ebb-tide and flood-tide conditions. All the modeled conditions resulted in either pebbles or very coarse sand deposited at the outlet of the Alternative #1.5 C channel which is essentially a modification of channel C in Photo 1. Reproduced Figures 6a and 6b show the results most relevant for present purposes. Apparently, the model assumes the DPR's "mandated" procedure of artificially breaching the channel at the southernmost edge of the inundated lagoonal area according to a planned resource objective announced by Tjaden, et al., (1978, p. 10, § 6).

These results of the numerical model applied by M&N staff (2005a, App. 3) demonstrate the tendency for deposits to develop at the mouth of Channel C close to the inlet of the breaching channel at the southernmost point of the inundated area. The ebb-tide depositional regime of Fig. 6b predicts deposits there of grain sizes of silt to coarse sand.

M&N conclusions significant for present purposes are those assuming the open condition as discussed by M&N staff (2005a, Sec. 5.1.2, p. 61). There, it is clear that their hydrodynamic analysis is limited to flow velocities expected to develop in either the Alternative #1.5- or #1.75-modified eco-channel systems in response to flood- and ebb-tides, the former tending to close them and the latter tending to keep them open.

Comment

The preoccupation of planners with the geometry and storage in the lagoon proper - i.e., the periodically impounded creek mouth - is difficult to understand, because that cannot be controlled by any feasible means. Consequently, such data have little if any predictive value. Whether regarded as a lagoon or a periodically impounded deltaic mudflat, natural deposits at the mouth of Malibu Creek to the shoreline will always be above mean sea level. Similarly, bar development at the creek mouth presents a natural condition that in the absence of artificial modification will persist with a depositional regime entirely independent of stream flow except for periods when it is removed due to flooding. Whether or not artificially breached from time to time, its mechanical response is to reform itself as a total barrier according to a well defined physical regime. In the absence of artificial channel breaching, the closed condition period is inversely proportional to the level of inundation, in turn primarily a function of surface inflow and subsurface outflow. As an observable consequence, it commonly persists for months during the dry season when the creek does not receive Tapia plant effluent and therefore belies any interpretation of the creek mouth as a true tidal lagoon. Nor can it properly be regarded as a wetland as commonly defined.

The over-all purpose of the UCLA study was to develop data in support of strategies for managing the long-term development of the Malibu Creek lower watershed, by which seems to have been meant the creek floodplain - a rather daunting task - especially in the absence of local basic data.¹⁵ Regarding the creek's behavior, attention necessarily focused on the open and closed conditions. It is regrettable that in observing a breaching channel's lateral development more attention could not be given to effects induced by its aggradation, but at the time, lagoon project planning was still in early formulation stages, and the study period was limited, essentially, to a single year of observation.

REVISED PLANNNING

"The other invalid premise is that hydrologic conditions in Malibu Creek permit creation of a sort of laboratory lagoon in a new channel. Now proposed is a problematical "naturalized berm" allowing entry of low-flow stream water but not sediment-laden flood water at the channel head and a permanent opening in the bar opposite the channel mouth, about 300 feet east of the Colony. Theoretically, the bar would stay open by flow in a dredged feeder channel from the main lagoon, but at flood cessation, that channel would fill with debris when the stream velocity reduces. All streams do that."

In any event, and presumably sometime thereafter, Jones & Stokes was hired to produce a new design for the lagoon project entirely different from Alternative #1.5. Hence, the Jones & Stokes plan by civil engineer Steven R. Seville - begun sometime prior to October 5, 2007 and completed, presumably sometime in November 2010 - thereafter became the ICF Int. (ICF) plan submitted in support of the application for a coastal development permit (CDP).¹⁶ In was in its near-final stage of design that the ICF plan was submitted to CCCom and assigned CDP number 4-07-098.

A protracted period of CCCom review due to local opposition based on biological concerns is not relevant for present purposes, but it did require two extensive CCCom staff reviews, both of which recommended issuance of CDP 4-07-098. It seems clear that CCCom staff, apparently lacking any training in hydrodynamics, simply assumed that the project would function satisfactorily. Nevertheless, CCCom staff hedged its bet, as indicated by Tysor (2010a, Sec. 5, B2), by requiring that if monitoring the project subsequent to construction does not indicate that circulation "...within the lagoon ..." - and presumably the lagoon project as well - revised plans will be issued indicating "... additional or supplemental measures to modify those portions of the original plan .... not in conformance with the original approve lagoon restoration plan."

Comment

In the closed condition, it is noted (M&N staff, 2005 a, Sec. 5.1.1, p. 55) that "... the only feasible forcing mechanism to move the water in the lagoon during closed conditions is to increase the circulation effects of the wind ...," and this clearly is meant to apply to either Alternative #1.5 or #1.75. Further, it is concluded that the effect of such circulation can only be determined by a system of careful and detailed observations while recognizing that until unspecified "... source reduction efforts are implemented ..." reduction in eutrophic conditions would be limited (Moffatt and Nichol staff, 2005b, Sec. 2.3.2, pp. 20-21). In other words, during the closed condition, circulation due to wind alone probably would not be sufficient to prevent algae development and induced hypoxia unless nutrients from either the Tapia plant or local septic systems are reduced.

Apparently, it was assumed that such analysis also applied to the ICF design. In the absence of criteria other than those upon which the M&N designs were based, it seems clear that the ICF design took into account the fact that - as earlier observed and as the model predicted - aggradation such as that illustrated in Figures 4, 5, 6a, 6b, and in Photo 1, was to be expected. To better understand matters, the hydrodynamic character of the breaching channel should have been carefully considered. However, insofar as the record reflects, it was not.

So far as the record discloses, planning has entirely ignored the possible effects of sea-water intrusion in lagoon project channels. This process, initially referred to as the Ghyben-Herzberg principle in recognition of its early investigators in the late 1880s, given a rigorous interpretation by Hubbert (1940, pp. 924-926), and extensively quantified by Cooper, et al. (1964), need not be elaborated here. It suffices for present purposes to note that because of the relatively higher density of saline water, its occurrence inland in an adjacent terrestrial mass saturated with fresh ground water is a function of the fresh-water head above sea level and the local hydraulic conductivity which affects the rate of diffusion, and hence the thickness, of a saline-intruded zone and its proximity to the surface landward of the shoreline. In practical terms, this raises, first, the extent to which saline-diffused water may enter project channels, second, whether in such a diffusion process, algae also are introduced, and third, if so, the extent of any related algae bloom.

BARRIER-BAR HYDRODYNAMIC REGIME

Once breaching outflow begins, the loose bar sands are easily entrained so that a relatively deep channel immediately develops. If at the beginning of a breach the impoundment level is very high and there is a low enough tide level, the breaching channel probably is eroded deeply enough to expose underlying deltaic deposits of gravels and cobbles and in the bottom of the impounded area exposed trains of gravels and cobbles - low ridges of the most recently released flood-stream load deposits - separated by intervening sand- and silt-filled scours giving the entire area much the character of a mudflat. During the normal breaching process, the drainage velocity is so low that only finer-grained materials from the inundated area are incorporated in the flow. Consequently, much of the mudflat material, silts and finer-grained sands are left exposed in the drained area. Only in the breach itself is the drainage velocity great enough to entrain the bar sands.

Although not so far described in the record, it is obvious from direct observations that the barrier sand bar at the mouth of Malibu Creek functions according to - for want of a better term - a "master" hydrodynamic regime which, arbitrarily, consists of a single bar-forming mechanism and three well defined, and interdependent cyclical bar-breaching channel sub-regimes. The bar-forming mechanism operates at all times essentially by a combination of surf and tidal conditions that causes beach sand to be deposited above the littoral zone, and it is independent of both the breaching channel mechanism as well as creek flow except during flooding so great as to entirely erode away the bar.

Beginning when the bar has been completely formed, the following sub-regimes of the bar-breaching channel mechanism can be regarded as developing sequentially:

Sub-regime [i] - Beginning with total impoundment: rates of impounded volume increase and surface elevation rise are functions of precipitation, surface runoff, Tapia-plant effluent inflow, and bank-storage inflow, the total of which is reduced by rates of evaporation, transpiration, and ground-water outflow through the bar.

Sub-regime [ii] - Barrier-bar breaching: after sufficient rise in the impoundment, and probably on occasion in combination with higher tides and surf, a breaching channel forms generally transverse to the bar length and normal to the shoreline, initially with a high flow rate and velocity that gradually decreases as the impounded surface elevation decreases.

Sub-regime [iii] - Barrier-bar redevelopment: easterly longshore current entrainment and deposition of bar and beach sands at the channel outlet causing it to shift laterally eastward thus lengthening the channel, and causing it to develop the classic concave-bank and associated convex-bar manner of low-energy streams so as to transform the initial deep, southerly draining channel stream to one aggraded and draining east-southeasterly diagonally through the bar with a broadly meandering course until its outlet reaches the easternmost side of creek mouth where reduced channel flow enables littoral drift deposits to close the outlet thus reinitiating total impoundment.

Certain aspects of this master regime have been reported by Dillingham and Sloan (op. cit.), Schwarz (1999), and Orme, et al. (2000), but none with regard to its effects in the impounded area. Apparently the previously announced objective of the 1978 study of periodically artificially breaching the bar had been accomplished to some extent up to the time of the work of Dillingham and Sloan (op. cit.), and presumably thereafter perhaps as late as 1998-1999, the period of the UCLA study.

In one way or another, mandated bar breaching has been accomplished at least since 1989. In recent years, this has involved - to use one County lifeguard's term - cutting a "notch" in the inner edge of the bar at the southernmost edge of the lagoon. Presumably, when the impounded level rises high enough, it first flows into the notch so that is the place where overflow and hence breaching occurs. Ostensibly, the purpose of this is to keep the drainage as far as possible from the more populated surfing area. However, this also considerably lengthens the period during which there can be lagoon-like tidal entry.

Comment

Deposits in the mudflat of the lagoon or "main channel" as described by M&N staff are a result of aggradation as the stream load is deposited on reaching ocean base level and also locally that of the inundated area. The sand bar shown in Figure 4 at the mouth of Channel C is the earliest recorded example of an aggraded deposit specifically associated with a bar-breaching episode. To explain the "sand bar" of Figure 4, it is to be inferred that it formed as a result of stream load deposition upon reaching the local base level at the outlet of Channel C adjacent to the inlet of an artificially induced breaching channel.

During field work for the UCLA study, Orme, et al. (op. cit., Sec. 2.5.1, pp. 2-75 - 2-76) observed an irregular increase in the elevation of a breaching channel thalweg of approximately one meter (3.281 feet) during the period of late April to July 29, 1998. Since their attention was limited to the specific behavior of the bar at the time, little attention was given to breaching channel hydraulics. However, their observations have a certain serendipitous value in that they describe barrier-bar behavior during a wet period which is to be compared with that now prevailing in response to the continuing drought. At the time of the UCLA study, breaching channels behaved in response to streamflow that included increments of surface runoff, relatively high bank-storage effluent,¹⁸ and Tapia-plant effluent, whereas today because of drought conditions streamflow is almost entirely due to Tapia-plant effluent with a somewhat lesser increment of bank storage. The result is simply a focus on two distinct patterns of barrier-bar behavior, the importance of which is the longer period of impoundment and hence lack of circulation when drought conditions prevail.¹⁹

For present purposes, tidal data at Santa Monica, California may be taken as that representative of elevations used by M&N staff (2005a). According to Reid, et al. (2012, App. C, p. 5) the current tidal datums (sic) in feet for Santa Monica are:

Highest observed water level (11/30/1982) = 8.63
Mean higher high water MHHW = 5.49
Mean high water MHW = 4.73
Mean tide level MTL = 2.84
Mean low water MLW = 0.95
Mean lower low water MLLW = 0.00
Lowest observed water level (12/17/1933) = -2.70.

These are close to the "MLLW" data used by Orme, et al. (op. cit., Table 2-6, p. 2-57) converted from meters to feet. Consequently, their observations have relevance for certain observations during the open condition in relation to project water levels with respect to observations at the WOP of Figure 7 where the level of the deck is approximately 6.5 feet msl, based on inscribed decorative tiles installed along the walkway leading to the WOP.

Aggradation of the breaching channel at its inlet as well as along its axis is extremely important in considering the character of circulation and drainage from both the lagoon and the project area as well as the extent to which they can occur during both the open and closed conditions. The littoral drift mechanism includes the manner in which the barrier bar forms as well as the process by which the outlet of the breaching channel is closed. Mechanical analyses of grab sand samples along the entire stretch of the bar show 90 percent of the gain sizes of six individual samples between 0.35 and 0.12 millimeters. Curves shown by Pettijohn (1975, Fig. 15-1) from the work of Hjulstrom (1935, Fig. 18) indicate such materials are transported either by traction or suspension in streams with velocities of 1-3 centimeters per second (cm/s).

Further, on February 20, 2014, velocities observed in a well developed meandering breaching channel commonly ranged from near zero up to about 30 cm/s along the central channel axis for a period of about an hour during which the volumetric flow rate was seemed essentially constant at about 6.6 cubic feet per second, equivalent to 4.3 million gallons per day (mgd). According to Dingman (2014), Tapia effluent disposal on that day was 3.01 million gallons. Considering probable release only during part of the day, this suggests a fairly direct relation between plant effluent release flow and breaching channel flow. Such observations appear to be a reliable basis upon which to predict the manner in which the lagoon project can be expected to perform during the open condition. Observations of flow over the Rindge dam spillway should be similarly instructive.

References

Cooper, Hilton H., Jr., Francis A. Kohout, Harold R. Henry, and Robert E. Glover, 1964, Sea water in coastal aquifers: U.S. Geol. Survey WSP 1613-C.

Dagit, Rosi, 1989, Ch. 2, Physical and chemical parameters of Malibu Lagoon in Malibu Lagoon: a baseline ecological survey, B. Sean Manion and Jean H. Dillingham, eds.: Topanga-Las Virgenes Resource Conservation District rpt. for Los Angeles County Dept. Beaches and Harbors and California State Dept. Parks and Recreation under Grant #4-400-7171, pp. 17-42.

Dillingham, Jean H., and Katherine M. Sloan, 1989, Ch. 4, Sediment Survey in Malibu Lagoon: a baseline ecological survey, B. Sean Manion and Jean H. Dillingham, eds.: Topanga-Las Virgenes Resource Conservation District rpt. for Los Angeles County Dept. Beaches and Harbors and California State Dept. Parks and Recreation under Grant #4-400-7171, pp. 63-72.

Dingman, Brett, 2014, Tapia plant discharge schedule: e-mail, courtesy David Llippman.

Doyle, Tomas W., and Ronald L. Rindge, with William R. Clarke and Glen Howell, 2012, Malibu Rails and Roads: Malibu Adamson House Foundation, 100 pp.

Hjulström, F., 1935, Studies of the morphological activities of rivers as illustrated by the River Fyris: Bull. Geol. Inst. Uppsala, v. 25, pp. 221-527.

Hubbert, M.K., 1940, The theory of ground-water motion: Jour. Geol., vol. 48, no. 8, November-December.

Jones & Stokes staff, 2006a, Malibu Lagoon Restoration and Enhancement Draft EIR: Jones & Stokes in cooperation with Terry A. Hayes Assoc. rpt. for DPR, RCDSMM and CCCon, January.

Jones & Stokes staff, 2006b, Malibu Lagoon Restoration and Enhancement Final Environmental Impact Report (EIR): Jones & Stokes in cooperation with Terry A. Hayes Assoc. rpt. for DPR, RCDSMM and CCCon, March.

M&N staff, 2005a, Malibu Lagoon restoration feasibility study final alternatives analysis: M&N in association with Heal the Bay rpt. for California State Coastal Conservancy & California State Parks, March.

M&N staff, 2005b, Final Malibu Lagoon restoration and enhancement plan: M&N in association with Heal the Bay rpt. for California State Coastal Conservancy & California State Department for Parks and Recreation, July 17.

Michael, Don, 2006, Ltr. to Malibu times, March 17.

Orme, Antony, Kenneth Schwarz, Priya Finnemore, Mark Khulman, and Johannes Feddema, 2000, Ch. 2, Hydrology and Morphodynamics in Lower Malibu Creek and lagoon resource enhancement and management, Richard F Ambrose and Antony Orme, principal investigators: Dept. Geography, Univ. Calif. Los Angeles, final report to Coastal Conservancy, pp. 2-1 - 2-223, May.

Pettijohn, F.J., 1975, Sedimentary Rocks, 3^rd ed.: Harper & Row, Pubs., Inc.

Reid, Gregory S., Trans Systems staff, and exeltech staff, 2012, Dan Blocker Beach parking lot wave run-up and coastal analysis report rpt. for Mr. Ed Andrews, L.A. Co. Dept. Public Works, September 10.

Rockhold, J.E., 1916, Map showing land to be condemned for the opening of the new "Malibu Road, Pacific Coast Hy." through Rancho Topanga Malibu Sequit: County Surveyor, Sheets A2 and A3, March - July.

Schwarz, Kenneth Michael, 1999, Hydrogeomorphology of Malibu estuarine lagoon: Univ. Calif. Los Angeles, Dept. Geography PhD dissertation (Call no. LD 791.9 G2 S411).

Sutula, Martha, Krista Kramer, and Jaye Cable, 2004, Sediments as a non-point source of nutrients to Malibu Lagoon, California: Southern California Coastal Water Research Project Tech. Rpt. #441, Final report to LARWQB, November 1.

Tjaden, Albert, Jean Roberts, and Ken Pierce, 1978, Malibu State Beach, resources management plan, general plan, and environmental impact report: California Res. Agency, Dept. Parks and Recreation spec. rpt., April.

Troxell, Harold C., and Walter Hoffman, 1954, Hydrology of the Los Angeles region, Ch. VI, Cont. No. 1, Geology of Southern California: Calif. Div. Mines Bull. 170.

Tysor, A., 2010a, California Coastal Commission Staff Report Regular Calendar, Item Th19a re Application 4-07-098, July 29.

Yerkes, R.F., and R.H. Campbell, 1980, Geologic map of the east-central Santa Monica Mountains, Los Angles, County, California; U.S. Geol. Survey Misc. Inv. Series Map I-1146.

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End Part III