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ENVIRONMENTAL LESSONS
of the
MALIBU LAGOON PROJECT
PART IV - LAGOON PROJECT HYDROLOGIC CONSIDERATIONS
E.D. Michael
October 25, 2014

INTRODUCTION

Construction of the Malibu lagoon project began about June 1, 2012. The project's ribbon-cutting ceremony on May 3, 2013 may be taken as the official date of project completion, although the parking area, i.e., Phase I of the project, remains unpaved. Phase II, including grading, construction of walkways and other peripheral elements, and landscaping, all were close to completion by early March, 2013. A certain amount of grounds-keeping and irrigation in support of the "natural" vegetation continues; otherwise, the lagoon project now appears complete. However, although the design of project in terms of recreational use appears adequate, the record to date shows that insofar as its hydrologic purpose is concerned, it fails to function properly. As a basis for this assertion, it first is desirable to describe the method of hydrologic equilibrium.

HYDROLOGIC EQUILIBRIUM

The science of hydrology concerns the physical relationships of water to the earth. An important approach to such study is the method of hydrologic equilibrium which considers the manner in which water occurs within a volume - essentially a vertical column - that includes both the atmosphere to some arbitrary elevation and the subsurface to some arbitrary depth. Generally, the horizontal cross-section of such a column conforms to an area of the earth's surface that is of economic interest, and it is applied for a given period during which gains and losses of water to and from the volume are balanced much like book-keeping balances assets and liabilities.

Commonly, the period of observation is a year so as to include seasonal change. Applied to the study area of this review - i.e., the Department of Parks and Recreation (DPR) lagoon project and the creek mouth seaward of the highway bridge to the shoreline - the gains due to inflows of surface waters, ground waters, imported volumes, and rainfall, must equal losses due to outflows of surface waters, ground waters, exported volumes, evaporation, and transpiration, with due regard to storage changes.1

To date, only surface inflow is measured sufficiently accurately to be used in a hydrologic equilibrium analysis of the study area. Annual surface outflow, i.e., bar-breaching channel flows, although simple enough to estimate from rudimentary observations, is part of the record so far reviewed only for short periods. As to subsurface outflow through the bar sands and underlying stream alluvium, nothing has been considered, although it should be reasonably easy to estimate. Rainfall could be better measured than it is, and with care, evaporation and transpiration could be satisfactorily estimated. Least well understood, and in fact to some extent seriously misunderstood, is subsurface inflow, i.e., ground-water inflow to the creek from the adjacent floodplain alluviums.2

Comment

Considering hydrologic equilibrium with regard to the study area is useful for present purposes to illustrate, conceptually, conditions when the barrier bar at the creek mouth is either fully formed, or when it has been breached so as to develop a through-flowing stream. Henceforth, the term "bar" refers to that at the mouth of Malibu Creek unless the context indicates otherwise.

Drought currently affects the hydrologic equilibrium of the study area significantly. Generally, a drought is defined as a period during which there has been insufficient rain to support some sort of human activity. Diminished runoff to local reservoirs and reduced surface infiltration by which aquifers are recharged are together the basis for considering the drought now in progress to be area-wide in southern California as well as elsewhere. Locally, the reduced volume of Tapia-plant effluent creek discharge in order to support local irrigation requirements has strongly affected the hydrologic equilibrium of the study area.3 It is clear that at the present time, an investigation of the study area's hydrologic equilibrium would have results strongly skewed in terms of those determined under more normal climatic circumstances.

In passing, it seems fair to say that the interest, not to mention zeal, for development in and adjacent to the Malibu Creek floodplain far exceeds acquisition of the hydrologic data needed for such activities to be adequately approached scientifically. The hydrologic character of the floodplain, per se, has never been investigated. The UCLA study by Ambrose and Orme (2000) was a step in the right direction, but certainly it is insufficient as a basis for planning a hydrologic facility such as the lagoon project. In fact, planning for projects to date proposed or actually undertaken in the floodplain - whether for development or ostensibly improving the environment - have been approached in virtual ignorance of the necessary data, viz., climate, aquifer characteristics, sea-water intrusion, local runoff, and water quality.4 Furthermore, this also is true of similar planning apparently is in the offing for other creek-mouth areas along the Malibu coast.

OPEN AND CLOSED CONDITIONS

Periodically, flooding washes away the bar. Otherwise, it persists at the mouth of Malibu Creek. With flood-flow cessation, the bar begins to reform in response to the local littoral drift.5 As reformation proceeds, an impoundment6 develops that some regard as a coastal lagoon. Once fully reformed, the bar is subject to breaching in response to one or more natural processes, acting singly or in concert, that include impoundment overflow, possibly the headward erosion of a foreshore spring induced by impoundment hydraulic head, or simply foreshore erosion by waves in combination with an especially high tide. However, breaching can easily be induced artificially by trenching and, reportedly, that has been initiated at times either in accordance with DPR management policy or possibly by individuals, unauthorized breaching bandits, whose environmental concerns far exceed their intellectual grasp of the problem.

When the bar is breached, flow begins to erode a channel. Initially, its axis is normal to the shoreline, and the flow probably is highly turbulent. Soon, however, in response to a reduced hydraulic gradient as the elevation in the impoundment declines, the flow stabilizes at a rate so low that the outflow becomes nearly laminar.7 To a first approximation, it may be assumed that upon the development of laminar flow, littoral drift begins forcing the channel outlet eastward - a process that commonly continues over a period of at least several months - until the channel outlet closes at the bar's eastern end.

It is convenient to refer to the period during which there is a functioning bar channel as an "open condition" and that when the bar is fully formed as a "closed condition." Photos 1(a) and 1(b) show typical appearances of the creek mouth under these conditions.

Malibu Creek Mouth Open and Closed Conditions

Photo 1. Photo 2.

In the open condition, Photo 1, trains of gravels and cobbles, lower right and left middle-ground, were deposited as stream velocity was reduced. At still lower velocities, broad expanses of silts and sands were deposited thereby giving the area the character of a mudflat. Bar channel inlet and outlet are shown by arrows, right and left. Essentially the same view, Photo 2, shows the closed condition giving the site its lagoonal appearance. In it, a well developed strip of algae is exposed along the stream shore, left. Views: south. Photos: EDM, 03/12/06 and 08/08/14, respectively.

Local hydrologic regimes of special interest for present purposes are those concerning surface and subsurface gains and losses - not their quantities for a given period - but rather their different behaviors during open and closed conditions. During the period of this study, which initially included about the latter four months of an open condition followed, so far, by about six months of a closed condition, the level in the lagoon project has fluctuated between about 2.4 and 7.4 feet, NAVD888, while maintaining near-constant elevations for periods of several days or more. Such behavior implies incremental periods of closely approximating hydrologic equilibrium when the sum of evaporation and subsurface outflow is nearly balanced by subsurface inflow.

Comment

Generally, open and closed conditions reflect different stages in the flow regime of Malibu Creek that in turn responds to the hydrologic-equilibrium variables which themselves function as regimes. In terms of biological concerns, the effect of the existing closed condition that has persisted since about the middle of April, 2014, is essentially disadvantageous, because as it progresses, the water quality deteriorates. With reference to the closed condition, Moffatt & Nichols staff (2005a, Sec. 3.1.1, p. 12) state:

"However, lagoon waters do not effectively circulate when the mouth is closed, occurring roughly from May through October every year (with variations depending on climate) (Sutula et. al, 2004) (Figure 7). Low dry season flows entering from upstream are unable to promote any perceptible lagoon circulation because the lagoon is configured with the main body as a broad basin that receives and dissipates any imparted current. Also, vegetative growth within the lagoon reduces potential circulation, and shades lower levels of the water column enhancing stratification ..."

Further, they conclude (op. cit., p. 15):

"... This lack of lagoon circulation throughout the warmest, high sun season can result in water stagnation leading to heating and stratification (layering), retention of nutrients, and hypoxia (low oxygen levels) or anoxia (no oxygen) in the water column (Sutula et. al, 2004; field data collection by M&N and Heal the Bay as part of this study, 2004) ..."

These observations, made without specific reference to the Tapia plant's restricted period of creek discharge, and prior to the current drought, demonstrate the extent to which the current closed condition is environmentally adverse.9

Regardless of such effects however, it is the combined regimes of the bar formation and its breaching channel that is most important for present purposes, because they determine the character of the open condition and hence the extent to which tidal flushing and circulation occurs in the study area. Tidal flushing and circulation, along with holding capacity, were the three main goals of the lagoon project projected by Moffatt & Nichol staff (2005a, p. 6),10 and thereafter specifically addressed by Moffatt & Nichol staff (2005b, Sec. 2.3, pp. 19-21) as part of the planned implementation. As noted by Tysor (2010, III, 5A, p. 16), these objectives were to be incorporated in the final plan prior to issuance of the project's coastal development permit according to a detailed list of specific requirements (op. cit., III, 5A2, pp. 17-19).

In addressing the implemented project design by Seville (2012) - which is entirely different from Alternative 1.5 of Moffatt & Nichol - the Coastal Commission, according to Tysor (2010, IV. A., p. 29) found that:

"... The goal of the proposed restoration project is to increase circulation of water in the lagoon during both open mouth and closed mouth conditions in order to improve water quality and decrease eutrophication ..."

In support of this, the Coastal Commission's issuance of the project's coastal development permit required a "Final Hydrological Monitoring Plan" specifically incorporating all the Moffatt & Nichol recommendations concerning a map of sampling locations and nutrient sampling submitted on an annual basis in a report with appropriate conclusions and recommendations regarding the level of success of the project, all updated by bi-annual monitoring reports for a period 5 years following project completion (op. cit., III, 5.A., pp. 16-19). Further (op cit., p. 29):

"...If the monitoring reports indicate that circulation within the lagoon has not improved or has failed to meet the requirements specified above in B.1., the applicant, or successors in interest, shall submit to the Executive Director, within 180 days of the date of the relevant monitoring report, a revised or supplemental plan, certified by a registered engineer and a qualified Resource Specialist, that specifies additional or supplemental measures to modify those portions of the original plan that have failed or are not in conformance with the original approved lagoon restoration plan..."

BAR SANDS MECHANICAL CHARACTERISTICS

Littoral drift along the Malibu coast for thousands of years has resulted in the formation of sand bars at the outlets of mountain streams. The largest of these - that at the outlet of Malibu Creek - now attains a length of about 1,500 feet immediately east of the Malibu Colony. At the time of the Rindge acquisition, it extended across the entire shore of the creek floodplain, i.e., from Vaquero Hill west to what is now the western end of the Colony. However, seawalls protecting Colony homes now limit its function as a coastal bar.

It is unnecessary for present purposes to dwell on the complex subject of coastal dynamics in order to describe certain mechanical characteristics of the bar in detail. It suffices here to note that despite the fact that beach sands along the Malibu coast commonly recede offshore during winter months, such behavior is not characteristic of the Malibu Creek barrier bar. During winter months when beaches, even as close to the bar as that along Malibu Colony shore, may be almost completely denuded of sands, the bar remains in place.

Such anomalous behavior apparently is due to the manner in which ocean waves, both seas and swells, are refracted as they approach the coast. As shown in a study prepared under the direction of Peacock (1963, App. 1), the bar shore from Malibu Point11 to the Malibu Pier receives less wave energy than sections anywhere else along the coast to the east. In theory at least, this appears to account for the resistance of bar sands to offshore migration during winter months.

The transverse width of the bar changes according to the effects of wave erosion as well as tidal changes and shifting of the bar channel outlet. As a matter of speculation, once fully formed, the bar width between the ocean and the impounded creek mouth shores probably varies between 100 and 150 feet. In well developed cross-section, it is lenticular with a crest close to horizontal and a base sloping seaward at a low gradient. The maximum thickness along its crest probably is about five feet.

It is obvious from casual observations over many years that the bar crest never exceeds a certain elevation and probably develops a slight gradient downward to the east. As noted by Orme, (2000, Sec. 2.4.1.1, p. 2-50), during October and November, 1997, the bar elevation ranged from 2.5 meters in the west to 2.0 meters in the east, i.e., between elevations 8.20 - 6.56 feet, NGVD2912 which they note is 0.8 meters above mean lower low water (MLLW). According to NOAA's web edition of "Tides and Currents," mean sea level (MSL) and MLLW are plus 6.652 feet and 3.827 feet (NAVD88), respectively, for Station 9410660, Los Angeles, giving a difference in elevation of 0.86 meters in close agreement with that noted by Ambrose and Orme, et al. (ibid.).

Comment

The local littoral drift is a very effective sorting mechanism.13 Seven grab samples collected from the bar on February 26, 2014 at depths of about 1 foot and at intervals of 50 to 150 feet along its entire length were found to be sub-angular to sub-rounded fine- to medium-grained sands. Close to 100 percent of each sample was in the range of 0.124 - 0.350 mm, fairly consistent with the findings of Handin (1951, pp. 82 - 83) who found arithmetic mean diameters for beach sands from Corral beach west of Malibu Creek of 0.320 mm and 0.5 mile east of Malibu Pier of 0.368 mm.

The strength of the bar sands is a matter of some interest. The angle of internal friction of loose sand can be approximated as its angle of repose, i.e., the angle the surface of a carefully deposited conical pile of loose sand makes with horizontal. Generally, it is found to be about 27 - 28 degrees. However, eroded banks of the Malibu Creek bar-breaching channels can be as much as 2 - 3 feet high and stand close to vertical. To investigate this, a dried 100-gram bar sand sample thoroughly mixed with 100 milliliters of distilled water produced a decanted solution having a sodium chloride (NaCl) concentration of 1,052 parts per million using the standard Hach kit. This strongly suggests that the stability of the bar sands in steep slopes along channel banks must be due to a certain degree of cohesion apparently derived from NaCl, probably in combination with capillarity. Whether the NaCl acts as a precipitated cement-like binder or induces cohesion due to some sort of molecular attraction is uncertain.

Aside from being the most well developed of some eight similar features14 along the Malibu coast, the bar at the mouth of Malibu Creek is important, because it directly affects the manner in which the lagoon project can perform. Most significant in this regard is the behavior of the breaching channel, and particularly the elevation of its bed, because that directly controls the impounded water surface elevation. In this regard, it is useful to consider a Hjulström diagram that demonstrates, in theory extensively supported by experiment, whether grains of a certain size will, as a function of stream velocity, either be carried in suspension or deposited as stream-bed material. Figure 1, one of many found on the web, is one form of this type of diagram.

The gray area in Figure 1 represents combinations of grain size and velocity where flow is more or less turbulent because of local bed irregularities rather than higher in the stream where it is essentially laminar. Along the beds of streams under such conditions, it is common to observe "ripples," i.e., sequential ridge-like structures with crests normal to the direction of flow and having gentler slopes upstream and steeper slopes downstream.15 The red dotted lines added for present purposes in Figure 1 indicate the range of bar-breaching channel velocities that cause the ripples commonly observed in the beds of both active and abandoned channels.

Figure 1. Malibu Creek Barrier-bar Texture in Relation to the Hjulström Curve.

The Hjulström curve is the "Fall velocity" line that separates grain sizes either carried in the flow or dropped from it as a function of stream velocity. The area above the curve is separated into a lower one in which grains are transported in suspension, in effect floating, and above it, an area where grains are entrained in the flow by erosion. The gray area represents a transitional zone where grains move along the stream bed. It is in this zone that ripples develop in the bed sands.

By way of further explanation, the samples collected for this review were from the crest of the bar. If such samples were fed loosely in a bar channel stream, they would drop to the bed where, as suggested by the gray zone in Figure 1, they would become part pof the ripple mechanism.

BAR CHANNEL FLOW REGIME

Of the bar hydrodynamic regime and its sub-regimes discussed in Part III of this review, it is sub-regime [iii] concerning the manner in which the bar-breaching channel develops that is especially relevant for present purposes. Prior to DPR acquisition, the initial position of the channel inlet could develop naturally anywhere along the inner bar shore. Breaching could be induced simply by impoundment overflow due to stream inflow alone, or as a result of localized erosion of the bar crest from the effects of high surf and tide, or perhaps by headward erosion in the seaward bar face. Following DPR's acquisition, there was an uncertain period during which artificial breaching was authorized by DPR management. Whether this was accomplished simply by "notching" - i.e., grading a narrow section of the bar at its western end16 lower than anywhere else along it so that overflow would begin there - or actually physically excavating a channel across the bar, is uncertain. Once flow began however, it would rapidly erode a channel through the bar to its base, thereby exposing underlying cobbles and boulders previously deposited during flooding.

The manner in which a stream moves its bed material is of some interest for present purposes. As indicated by Figure 1, the mode of transport of clasts of various sizes is directly dependent on the stream's volume and velocity, the latter dependent on the bed gradient. The classical description of such transport recognizes three stages: "suspension" in the flow involving sands and finer-grained material, "saltation," essentially bouncing along the bed involving mostly coarser sands, gravels and smaller cobbles, and "traction," essentially pushing and rolling, involving larger cobbles and boulders. During flooding, all these modes of transport occur. However, the evidence indicates that once the channel comes into essentially equilibrium with drainage from the impounded area, bar channel flow is clear of suspended load and the bed sands move essentially in traction with little or no saltation.

Photos 3 - 8 show various stages of bar channel development during an open condition with approximate tide and project levels. Channels breaching the bar eventually develop a meandering pattern. In form, a meander is a set of paired features resulting from the tendency of a stream to erode laterally. In this process, a curved channel develops which at its outermost side the flow is deepest and its rate greatest. At its periphery, a relatively steep bank is formed, while on the channel side opposite the flow is shallowest and slowest so that bed materials are deposited there. These features are referred to as a "concave bank" and a "convex bar," respectively.

Stream meandering is the subject of a broad field of geologic investigation involving numerous combinations of variables associated with the process generally. In the case of channels that breach the bar at the mouth of Malibu Creek, however, the uniform texture and virtual looseness of the bar materials, the fairly constant flow rate, and the limited gradient between the impoundment and tide levels, reduce the process to near-laboratory conditions. Under such conditions, as Friedkin (1945, p. 242) has observed, "... the only requirement for meandering is bank erosion."

Consequently, although for extended periods the flow rate17 remains essentially constant, the velocity varies according to the channel's local cross-sectional geometry. Photos 3 - 6 show conditions prior to and soon after breaching at the western end of the bar in November, 2013. Photo 6 shows conditions when the channel is still almost directly normal to the shoreline with its outlet just beginning to shift eastward. Photo 7, taken eighty-three days later shows the channel passing in an easterly direction along the length of the bar somewhat east of the bar mid-point. As shown in Photo 8, forty days later, the channel had narrowed considerably with its outlet at the eastern end of the bar, estimated to be about a week before actually closing.

Malibu Creek Bar Channel Inlet Site.

Photo 3. Photo 4.

The west end of the bar during a closed condition is shown in Photo 3 where a previous breaching channel has been filled by shoreline processes, project water elevation, 5.04 ft., NAVD88. Photo 4 shows the inlet of a breaching channel believed to have developed about 11/15/13 showing exposures of creek flood-plain alluvium, foreground, project water level, 2.72 ft., tide, 0.5 ft. Views: north and north-northeast; photos: EDM, 10/24/13; 11/29/13, respectively.

Malibu Creek Bar Channel Inlet Conditions.

Photo5. Photo6.

Photo 5 is a view upstream on the western side of the bar-breaching that probably developed about November 15, 2013, when the Tapia plant began creek disposal. Erosion has exposed darker fill over lighter bar sands. Photo 6, taken from the same location as that of Photo 5 shows the outlet of the channel at the shoreline beginning to shift eastward. Approximate project water level 2.72 ft.; tide, 0.5 ft. Views: north and south, respectively; photos: EDM, 11/29/13.

Intermediate and Late-stage Bar Channel Conditions.

Photo 7. Photo 8.

Photo 7 shows a section of a broad meander about midway along the length of the bar with the characteristic couple of a concave bank about 2 - 3 feet high, right background, and a convex bar, left middle ground. Note ripple marks, center middle and foregrounds. Photo 8 shows the channel outlet within about a week of closing at the shore opposite the former Adamson estate on Vaqueros Hill. The foaming, right middle-ground, is the result of a standing wave created where the creek outflow and the tide inflow meet; project water level elevation, 4.12 ft. NAVD88. Views: northwest and northeast, photos: EDM, 02/20/14, tide, 2.9 ft.; 04/01/14, tide 4.3, respectively.

Comment

Development of the first open condition affecting both the lagoon project and the impounded creek mouth to which it is directly tributary was close to, if not actually coincident with, the period of Tapia's permitted creek disposal period that began on November 15, 2013. The initial breaching channel inlet was at the western end of the bar where a notch earlier had been graded. Once the initial energy due to the relatively high impoundment elevation was eliminated, it appears that there developed a bar channel flow rate that was essentially a function of the Tapia plant creek disposal flow rate. As an example of this condition, according to data provided by Dingman (2014b) for the period of January 1 - April 15, 2014, discharge ranged between 0.13 - 10.45 million gallons per day (mgd) with and average of 3.19 mgd and a median of 2.68 mgd. Assuming, simply for purposes of discussion, that losses due to evaporation and subsurface outflow were equal to subsurface inflow for the period in question, the range in the bar channel flow rate would be 0.2 - 4.9 cfs. Bar channel flow rates observed during the period of this review were well within this range.

Preliminary research suggests that sequentially over time it is common for the bar to develop two or more channel inlets. In such a process, if a new inlet develops east of an earlier one, they will become confluent. An example of such a condition is shown in Photo 9.

Prior to breaching, area a was the aggraded bed of the impoundment. The encircled area is evidence of the irregular manner in which breaching can occur to wit: [1] development of an earlier breaching channel inlet to the west, not shown, having a well developed bed of aggraded sand bar deposits, b; [2] initiation of breaching by channel s stream carving banks c and d, initiating convex bar e deposits, and reaching confluence with the bed b stream; [3] temporary renewed flow of bed b stream eroding a section of bank c (encircled); [4] termination of the flow of the bed b stream apparently due to aggradation at its inlet; [5] continued but diminished flow of the channel s stream taking into suspension b deposits and carving a lower concave section of bank d coincident with enlargement of convex bar, e; [5] high tide encroachment bringing upstream strands of Macrocystis pyriphera, "giant kelp," common along shores in Malibu, the channel islands, and elsewhere in southern California.

Photo 9. Bar Channel Inlet, Advanced Stage of Breaching Process.

Earlier aggraded areas include: a - the aggraded bottom of the impounded area prior to breaching; b - the channel bed of an earlier breaching stream. Later channel features include: c - initial concave bank of s channel, d - concave bank of s channel; e - convex bar associated with d. Note ripples in the active channel around patch of kelp lower right, washed in from previous high tide. See text regarding the encircled area; project water elevation, 4.09 ft., tide: 2.7 ft. View: northwest. Photo: EDM, 02/20/14.

The late-stage open condition indicated by the position of the bar channel outlet as observed on April 1 and shown in Photo 8, had ended well before May 8, and probably on or very soon after April 16. Since according to Dingman (op. cit.) Tapia plant creek disposal ended on April 15, it seems certain that the closure occurred more or less in direct response. Also, initiation of the forthcoming open condition in direct response to plant creek disposal scheduled to begin on November 15 seems likely. In any event, the extent to which these relationships are drought-related is yet to be determined.

BAR CHANNEL AGGRADATION

"Aggradation" is the process by which the bed of a stream rises in response to receiving deposits in accordance with the mechanism illustrated in the Hjulström diagram. The expanse at a in Photo 9 is the aggraded bottom of the impounded area that became exposed when the bar was breached. Aggradation can occur along the reach of any stream due to a local reduction in gradient or when it reaches a base level such as a lake or the ocean. Generally, floodplains such as that at the mouth of Malibu Creek are a result of aggradation along streams that feed them.

Observations over a period of months indicate that flows in channels through the bar at the mouth of Malibu Creek soon after breaching are free of suspended load. The flow is great enough to move the bar sands in traction sufficient to for bed ripples and this combination of flow rate and bed sand texture is characteristic of the bar's breaching channels. Because of meandering and bar sand weakness, caving of the concave bank results in widening and reducing the depth of the channel. However, at the bar's eastern end, massive rip-rap along the shore at Vaquero Hill restricts further shifting of the bar outlet in that direction while the littoral drift mechanism continues to operate eventually closing the bar outlet.

Comment

It is useful to consider the relationship of physical equilibrium in relation to aggradation. Generally, equilibrium implies some sort of balancing. Unlike hydrologic equilibrium which implies balancing volumes of water under various conditions, physical equilibrium involves a balance of forces. If the masses are stable, static equilibrium prevails, and if they are in motion, dynamic equilibrium tends to develop. In the case of a bar channel stream, a condition of limited dynamic equilibrium occurs along the bed itself where the motion of the water is resisted by the bed sands. The pervasive trains of ripples common along channels breaching the bar at the mouth of Malibu Creek represent, within the limits of velocity and grain size, a condition of dynamic equilibrium.

For present purposes, it is especially relevant to note that this condition of limited dynamic equilibrium requires that at its inlet the aggraded channel bed remains essentially stable at a particular elevation. In other words, most of the time during the open condition, the inlet of the bar channel has a close to constant elevation subject to, and only slightly less than, elevation changes in the surface of the creek mouth impoundment which, in the absence of excessive rainstorm runoff, occur only gradually. The extent to which aggradation of the bar channel is affected by tides is uncertain, but the elevation to which the impoundment surface is raised by incoming tides cannot be great considering the limited width of the channel and the relatively large impoundment.

References

Abramson, Mark, Rosi Dagit, Dan Cooper, Jaime King, Ivan Medel, and Charles Piechowski, 2013, Malibu Lagoon restoration and enhancement project comprehensive monitoring report: Santa Monica Bay Restoration Foundation rpt. for State of California, Department of Parks and Recreation, March 19.

Ambrose, Richard F., and Anthony R. Orme, 2000, Lower Malibu Creek and lagoon resource enhancement and management: Univ. Calif. Los Angeles, special study for California Coastal Conservancy.

Dingman, Brett, 2014a, Tapia plant discharge schedule: e-mail communication, April 29.

____________, 2014b, Attachment re Tapia plant discharge, fish flow; 2007 guidelines to maintain minimum flow: e-mail communication, September 12.

Friedkin, J.F., 1945, A laboratory study of the meandering of alluvial rivers: rpt. of U,S. Waterways Experiment Station, Vicksburg, Miss., U.S. Army Crops of Engineers, May 1.

Handin, John W., 1951, The source, transportation and deposition of beach sediment in southern California: PhD thesis, Dept. Geology, Univ. Calif. , Los Angeles, published as Technical Memorandum No. 23, Beach Erosion Board, U.S. Army Corps of Engineers, March.

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

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

Orme, Antony, Kenneth Schwarz, Priya Fennemore, Mark Khulman, and Johannes Feddema, 2000, Hydrology and morphodynamics, Ch. 2 in Ambrose and Orme (2000), pp. 2-1 - 2-112.

Peacock, Earl G., Col., Dist. Engineer, 1963, Cooperative beach-erosion investigation, Malibu-Santa Monica area, California: U.A. Army Corps of Engineers feasibility study of proposed marine locations for State Highway Route 60 and their shoreline effects for California Water Resources and Dept. Public Works, Div. Highways, August.

Seville, Steven R., 2012, Malibu Lagoon State Beach Restoration and Enhancement - Phase 2: ICF International, 51 sheets, June 30.

Stone Environmental, Inc. staff, 2004, Risk assessment of decentralized wastewater treatment systems in high priority areas in the city of Malibu: Stone Environmental, Inc. study, Stone Proj. No. 011269-W, for Santa Monica Bay Restoration Commission and California State Coastal Conservancy.

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.

Tysor, A., 2010, Summary of staff recommendation: California Coastal Commission Staff Report: Regular Calendar, Item W6a re App. No. 4-07-098, September 29 (Hearing Date: 10/13/10).

Valor, Scott, Director, 2014, E-mail response to E.D. Michael re SMB Restoration Foundation activities: Santa Monica Bay Restoration Commission, September 26.

END PART IV.


1 Hydrologic equilibrium requires that during any specified period, gains less storage losses must equal losses plus storage gains - a simple algebraic equation.

2 A hydrologic balance performed by a subcontractor to Stone Environmental, Inc. staff (2004) for the City of Malibu, incorrectly postulated Malibu Creek as an influent stream and hence a loss in creek inflow, rather than the effluent stream where it crosses the creek floodplain, and hence actually an inflow gain.

3It is to be noted, according to Dingman (2014b) that when creek flow is less than 2.5 cfs, policy imposed by the Los Angeles RWQCB requires Tapia enough discharge to the creek during the period of April 15 - November 15 when discharge is otherwise prohibited to maintain that flow rate.

4In such circumstances, Malibu's current desperate plan to dispose of effluent from a local treatment plant now in the planning stage - currently deemed necessary due to the RWQCB's questionable edict limiting further approval of septic systems in the floodplain - is preposterous.

5 "Littoral drift," occasionally "longshore drift," is a graded and reworked deposit of sands and gravels - i.e., clasts from about 0.1 - 2.0 inches in longest dimension - that moves along a shore in response to the induced currents of breaking waves. Along the Malibu coast, littoral drift is eastward. For present purposes, it is unnecessary to discuss a common ancillary movement of the drift locally off Malibu shores during winter months.

6 In this context, "impoundment" refers to a creek mouth water level higher than that which would occur if there were no barrier bar.

7 The manner in which fluids flow is considered theoretically to be either laminar in which fluid particles follow discrete, parallel paths, or turbulent in which the paths of particles cross each other in swirls and eddies.

8 Henceforth, where reported, project water elevations are for the North American Vertical Datum of 1988 (NAVD88), as inscribed on a survey monument set in the top of the curb at the WOP (see Part III, Fig. 7) reading "El. 6.87 NAVD88," and hereinafter taken as fiducial.

9 An astonishing concentration of fish - presumably steelhead trout - frenetically splashing at the westernmost 100-200 feet of the bar inner shore where wave-break overflow occurred during the high surf conditions of August 27-29, 2014, and also when observed on October 6 prior to which surf overflow had become much more extensive along the bar inner shore, all strongly suggesting that unusually prolonged closed conditions seriously interfere with the species life cycle.

10 See Part III of this review re section, "Hydrodynamic Observations."

11 Malibu Point - "Malibu Pt." on the U.S. Geological Survey Malibu Beach 7.5-minute quadrangle - is a coastal minor salient due to the combined effects of deltaic creek deposits and a reef of volcanics(?) which locally limit the effects of coastal erosion by forcing waves to break farther offshore.

12 The National Geodetic Vertical Datum of 1929 (NGVD29) which is mean sea level (MSL) has been placed with the North American Vertical Datum of 1988 (NAVD88) which is Mean Lower low Water (MLLW).

13 It is worth noting for the benefit of those unfamiliar with coastal dynamics that the materials of coastal bars are derived from littoral drift rather than the loads of streams at the mouths of which they form.

14 Beach deposits at the mouths of streams landward of which a certain degree of wetland tends to develop.

15 The analogy of ripples formed when the energy of flowing water is transferred to a stream bed, with water waves when wind energy is transferred to the surface of a water body, or with secondary seismic waves when seismic energy is transferred to the earth's surface, is impossible to ignore, particularly because the invariable development of periodicity demonstrates a mechanism that has never been rigorously determined, i.e, how the initiating randomly distributed energy becomes uniformly distributed in the medium to which it is transferred.

16It is understood that notching the western end of the bar was for the purpose of keeping drainage as far as possible from the area just east of the point where most surfers wait to take off.

17 Volume per unit time, e.g., cubic feet per second (cfs).