Overall Question for Science Advisors

Questions from the Working Group

    General Questions

    Natural Resources

    Sand Movement, Retention & Nourishment

    Revetments and Other Physical Solutions

    Management and Maintenance

Additional Questions Provided on January 16, 2004

Further Research/Information Needs and Questions - Identified by participants in Community Visioning Sessions (Sep and Oct, 2003)

Overall Question for Science Advisors:

Q:

Is there consensus on the issue areas and impact to Goleta Beach?

A:

Jeremey Lowe:  We need to clearly define what are the goals and objectives of the project. We need to identify all the different uses and functions of the beach/park. These functions include manmade ones such as car parking, lawn areas, restaurant facilities, utility corridors as well as natural ones such as habitat, wave energy dissipation, position within the littoral transport system. These need to be accommodated in a limited area within certain constraints. Some of the constraints are natural (e.g. location of the beach), some are manmade (e.g. location of the utilities). We need to understand the nature of these constraints and determine to what degree they shape our vision of the future and to what degree they can be mitigated. Once we have clear goals, in particular a long-term vision of the future, then we can start to think about solutions.

Essential to this process is the development of a conceptual model of how we think the natural system is behaving and how it has been modified over time and how it is likely to evolve into the future. At the moment I think our focus is too narrow, centered on the beach. We need to step back and look at the park in its true context as a coastal spit lying at the mouth of Goleta Slough and being subject to both wave and tidal forces. Once we understand how the whole system works we can start to understand what the impacts of changes we make will be on its future evolution. We cannot reverse what has been done already nor can we hold everything static - the natural environment is changing regardless of what we do (e.g. sea level rise, sediment supply). We need to ‘design’ a new shoreline that is sustainable in the future and that accommodates both the natural and manmade functions of Goleta Beach.

I do not know to what degree there is consensus on the issue areas, but I don’t think all the issues and impacts have been identified in a systematic way. Until we do so then any solutions will tend to be sectoral in nature.

Questions from the Working Group:

  General Questions

Q:

Which actions could save the beach?

A:

Susan Tonkin:  Nourishment and sand retention (including breakwaters or groins). Managed retreat will not necessarily lead to a wide beach – if the beach continues to lose sediment then it will remain narrow.

Jeremy Lowe:  I would not differentiate between beach and park – I would try to manage the two together. The coast is a dynamic environment and has no fixed boundaries; the management of the park has to acknowledge this. I don’t think it is a question of saving one or the other but rather had you mange both together in the future.

Q:

Which actions could save the park?

A:

Susan Tonkin:  Revetment or seawalls, which may be buried with a nourishment project.

Q:

What is the feasibility of creating dunes and using dune plantings to minimize sand loss? How would this impact downcoast sand transport?

A:

Susan Tonkin:  Dune plantings would not be a complete solution. Vegetation on the sand would provide minor benefits in trapping sand (and, of course, there could be ecological benefits). However, the vegetation would not withstand direct wave action and should not be considered as a soft “equivalent” to rock revetments or seawalls. Remember that the site does not naturally support a high dune system.

Jeremy Lowe:  Dunes are a natural feature of some beaches, depending a lot on the availability of fine sand, a high drying beach and suitable winds. They are not static features as they are essentially temporary reservoirs of sand for the beaches. During storms, sand moves offshore to form bars that dissipate wave energy by causing them to break, some of that sand is from the dunes. During quieter periods sand is moved onshore, the beaches get higher and wider and some is blown in to the dunes. Manmade dunes can be located at the top of the beach but they will be subject to erosion during the winter. How much erosion will depend on how big the dunes are and how far up the beach they are located. If the dunes are small, they may be eroded away before the end of winter. Whether they accrete in the summer is dependent upon the local wind conditions and a supply of sand. Stabilizing the dunes with vegetation is usually associated with some control of access to prevent trampling.

In the context of Goleta Beach I don’t know if there is sufficient space to have large enough dunes between the top of the beach and the edge of the existing parking lots. It may be possible by rearranging the layout of the park to give the dunes and beach more space. The other concern would be the long-term maintenance of the dunes, essentially renourishing each year as the area seems to have a deficit of sand. An alternative would be to create dunes much further back and used as a backstop during flood events, this would allow the dunes to last longer but would not allow them to act as a reservoir of sand for the beaches on a regular basis and so erosion would still occur.

Creating dunes does not address the fundamental problem of an eroding shoreline and would still require renourishment.
 

Q:

 What are the impacts of current activities on the park/environment?

A:

Jeremy Lowe:  I’m not sure if the current activities have an impact rather their location. Parking lots, restrooms, utilities, restaurant aren’t particularly mobile but the beach and the shoreline areas they respond to environmental change. Inevitably, there will be problems as shorelines move and encroach on fixed infrastructure. Dynamic systems need space, not just to accommodate annual variations but also long term (decadal) change.

Q:

In consideration of reducing slough dredging by the county Flood Control Dept., is it more beneficial to have the slough entrance to the ocean periodically open or closed as is the current situation or to have it open year-round?

A:

Jeremy Lowe:  I don’t know enough about the slough ecology to say what the closure behaviour should be. My guess is that the inlet is smaller and closed more often due to the larger reduction in tidal prism of Goleta Slough over the last century. Opening the inlet by dredging may help stabilize the eastern end of Goleta Beach, but a bigger impact, and perhaps more sustainable would be to consider restoring tidal prism.

Q:

In consideration of pathogenic bacteria in the Goleta Beach nearshore waters, is it more beneficial to have the slough entrance to the ocean periodically open or closed as is the current situation or to have it open year-round?

A:

Jeremy Lowe:  I have no knowledge of this subject.

  Natural Resources

Q:

Looking at the area East of the Goleta Slough Mouth,

Q:

What are the known or suspected ecological effects of nourishment done from the Mean High Tide Line seawards?

Q:

What are the ecological effects of beach grooming? Can ceasing beach grooming enhance beach habitats and mitigate impacts to beach habitats?

Q:

What species were previously at GB but have been extirpated?

Q:

To Dugan / Hubbard: What are the ecological effects of revetments on sandy beach and intertidal habitats, and species such as shorebirds, invertebrates and grunion. If these are not known, what could they be? Could reducing the sandy beach size (i.e. through enhanced beach erosion caused by revetments) reduce the biodiversity, abundance or organisms and biological productivity of these habitats? Have you studied the ecology of beaches with rock revetments of other seawalls or do you avoid these areas. Please explain.

Q:

In consideration of wildlife habitat, is it more beneficial to have the slough entrance to the ocean periodically open or closed as is the current situation or to have it open year-round?

Q:

How are species that feed on the wrack affected by revetments? Also could we have explanation of terms used by Jenny Dugan in her article?

Q:

If the rocks are used at GB and high tides wash against the rocks leaving no sandy beach, what does this do to grunion spawning? To the beach habitat, ecology and species?

Sand Movement, Retention, and Nourishment

Q:

· What did the beach look like 30, 40, 50 – 100 years ago?

A:

Susan Tonkin:  It was wider than now 30 to 40 years ago, and similar to the present situation 50 years ago

Jeremy Lowe:  I think beyond the question ‘what did the beach look like’, which I think is being put together by others using maps, photographs and anecdotal evidence, is the question why did the beach look like it did and why does it change. This is where we need a conceptual model of the beach and slough to try to explain why the beach looked like it did and to understand how the beach behaves over decades and centuries. What the photos do show is large-scale long-term variability in the beaches, which any future management plan for the park needs to be able to accommodate.

Q:

How is the erosion and other factors at Goleta Beach different than that at other local or west facing beaches? (i.e. artificial fill material, south facing bay, islands off-shore).

A

Jeremy Lowe:  Every beach has a different exposure to waves, a different position on the sediment transport pathway along the coast, a different location with respect to tidal inlets, a different history of human impacts. There may be common symptoms of loss of beach but the cause may be different, the goals of the local community may be different and so the solutions should be tailored to the particular place.

Q:

Where does the sand come from and where does it go? Has there been a sediment transport study or analysis?

A:

Jeremy Lowe:  I would defer to the work of Gary Griggs’s group from Santa Cruz on this subject.

Q:

What are the reasons for the reduction of the wide beach area beginning in the 1980’s? Why did this not occur during the prior 4 decades?

A:

Susan Tonkin:  This is, to me, the big unknown. Generally speaking, the sediment is transported from west and north of GB, travels east and south, is significantly impeded by Santa Barbara Harbor; to the extent that it passes by Santa Barbara Harbor, much of the sand deposits in Mugu Canyon.

While the main sources are probably fluvial, the reasons for the change in behavior over the past century is very unclear. Possible reasons include the following:

Presumably there was even less sediment generally available at the GB site during the 19^th century, in that Goleta Slough was navigable until the 1860s.

Jeremy Lowe:  I would defer to the work of Gary Griggs’s group from Santa Cruz on this subject.

Q:

Is the Santa Barbara Harbor area a good long-term source of sand for Goleta Beach replenishment?

A:

Susan Tomkin:  Yes, to the extent that can be transported cost-effectively.

Jeremy Lowe:  I think this presupposes the solution. We need to be sure of our long-term vision before we suggest a solution. Replenishment on its own will only hide the symptom – it is not a cure for erosion. Replenishment is a long-term commitment unless other measures are taken to stabilize the beach. In addition, it can be a case of robbing Peter to pay Paul, the down drift impacts of extracting sand must be considered.

Q:

Where are other viable sources of sand for beach replenishment?

A:

Susan Tomkin:  Dredging from offshore, opportunistic sand, slough dredging.

Jeremy Lowe:  Again this presupposes the solution.

A:

Jeremy Lowe:  There has been a beach at Goleta for at least several centuries – as shown in a number of maps. The interplay of wave driven sand transport from the west and the tidal flow due to Goleta Slough caused a spit to form, the seaward side of which is now called Goleta Beach. It was not always in exactly the same position nor was it exactly the same size – it responded in the past to climate and sea level change just as it does now. More recently, however, the sediment supply has been altered, the Slough has been diked, the spit has been fixed in position with fill. Changes in the beach position and shape (as shown by beach erosion) show that it is responding to these alterations in the system. The key here is to try to determine what future changes in beach position shape are needed to bring it to a new equilibrium position and how that can be accommodated along with the other functions of the park

Q:

What is causing the erosion at Goleta Beach? Is it the bluffs?

A:

Susan Tomkin:  The cause is a long-term deficit in the sediment supply; we are far from sure as to what the sources of sediment are and have been (i.e., the sediment budget is known only very approximately). Recent work by Griggs suggests that bluff erosion supplies a very small part of the sediment budget, so the bluffs probably are not responsible for the erosion. The bluff at the West end of the park may have a localized effect on erosion, due to wave reflection off the bluff towards the beach.

Jeremy Lowe:  The movement of the beach that has been observed over the last few decades is probably a combination of natural variability due to stormy periods, El Nino etc and long-term trend. The long-term trend is I think a combination of factors – changes in sediment supply from the watersheds, changes in tidal prism of the slough, changes in sea level and wave climate due to climate change. All of these have resulted in the changes in the form and location of the beach to some new equilibrium with its environment – the symptom of change in this case is erosion. This movement and change of the beach only becomes recognized as a problem when it reaches some fixed structure such as a parking lot.

Q:

How sure are we that Goleta Beach loses 80,000 cu. yd. of sand each year? (Moffatt and Nichol Report page 2-6 – “the long-term average sediment deficit at Goleta Beach, and the UCSB East Beach, is approximately 80,000 cu. yd./year from a net longshore transport of 260,000 cu. yd./year”)

A:

Susan Tomkin:  This is a 25-year average, and a very approximate calculation. However, the order of magnitude is likely to be correct (so – a “medium” confidence level).

Jeremy Lowe:  I understand that 80,000 cubic yards is a long-term average rate. It would be interesting to estimate the change in rate over time. Usually as a landform gets closer to an equilibrium and stable position the rate at which it evolves (in this case erodes) slows. If we are getting a slowing then it may help indicate how much further the beach has to adjust before it is naturally stable for the present configuration of the coast.

Q:

We lump a variety of approaches to sand replenishment under a single label of nourishment. Mostly it has been conceived and implemented as dumping sand on the beach mostly below high tide line. Would it not work as well in some parts of the beach to:

Would this avoid impacts yet still provide a quality, large, and perhaps even a varied GB experience?

A:

Susan Tomkin:  A big issue here would be the potential for an erosional scarp. Beaches form naturally in a slope from offshore upwards toward the extreme wave runup elevation, in such a way as to dissipate wave energy. If the beach were built up over the lawn, the wave energy would not be dissipated; waves would still reach the lower part of the beach slope and would cut back the bottom of the slope. The result, in the medium term, would be a vertical cliff about 10 feet tall at the edge of the upper beach.

Eventually the lawn would be cut back to an area such that a beach would form

It could be feasible to remove the east parking lot and to allow this portion of the park to return to the condition of a seasonal sand spit.
 

Jeremy Lowe:  Again this presupposes the solution. If you were doing a replenishment then maybe a combination of all of the above (a-d). But first, you need to understand how the beach behaves now and how it will behave with the additional sand. If nothing else, this will avoid false expectations of replenishement ‘solving’ an erosion problem.

Q:

We know that the sand still comes in the spring/summer to GB and is lost in the winter perhaps as it has done for a long time. Is it not likely, however, that the extent of that seasonal deposition and scour is now modulated by the turf wall and revetment? The purpose of this question is twofold. First, to explore the idea that those deflection devices (revetment and parking lot) at the W end have contributed to the erosion we have seen recently at Goleta Beach? Second, while we still have loss and gain of beach, is the balance shifted in favor of loss and does that have an effect on the level of support this beach provides for grunion, inverts, and shorebirds?

A:

Susan Tomkin:  The revetment at the West end is almost certainly not a significant factor in increasing erosion at the West end compared to elsewhere in the Park, except through passive erosion (passive erosion is discussed further below – basically, the term describes the narrowing of a beach as the shoreline moves inwards towards a fixed point).

The sheer bluff face at the West end of the park now extends well beyond the MHW line and is essentially vertical. This acts much more strongly as a deflection device than does the revetment, which is only subject to direct wave action at high tide and which is not vertical. (The bluff also acts somewhat as a groin). Revetment dissipates wave energy in voids between rocks, while a wall reflects it.

When the West parking lot was constructed in the 1980s, the seaward edge was raised relative to the natural sand level – in other words, the parking lot already extended relatively far seaward; the revetment was constructed shortly after the parking lot. The revetment has caused passive erosion, in that the shoreline would have retreated past the currently location of the revetment in the absence of any structures. However, except at the far West end – where the revetment meets the bluff, and there are clear wave-structure interactions – there is no real evidence of increased erosion due to the revetment. For example, there is no change in beach width at the eastern end of the West revetment.

If the revetment and the turf wall were a significant factor in causing erosion then we would expect to have seen the rate of erosion increase in the past 5 years, during which period the turf wall has been exposed to the waves during winter. The erosion rate has remained more or less constant since the early 1980s. The erosion is due to less sediment entering the system, not to more sediment leaving it.
 

Jeremy Lowe:  The beach is trying to develop a new equilibrium profile and planshape. The interaction with the turf wall and revetment are due to the fact that these lie seaward of the equilibrium beach and are preventing it from moving landward. However, vertical walls and rock structures do reflect which promote scour of the beach so their presence on the beach may be exacerbating the situation. Ultimately, however, it is the fact that they prevent the beach from extending land ward that is the main concern and the drop in beach levels in front of them is probably inevitable regardless of their form (vertical, rock or otherwise).

Q:

If left unprotected, how far inland could the shoreline move?

A:

Susan Tompkin:  The shoreline would probably move quite a way through the Park. The fact that the erosion rate in the past 10-15 years has remained similar to that in the 1980s suggests that the shoreline is not close to equilibrium.

Jeremy Lowe:  This is the key question to answer before determining a solution as it shows how much more space the beach needs. This is why a conceptual model of the beach is so important as it will help answer this question. It may be that the stable position of the beach is not much further inland in which case rearranging some of the layout of the park is all that is required to give the beach more space. If it requires too much space then other solution may need to be considered – for instance moving the stable position offshore using headland control and/or the ebb delta of the tidal inlet.

Q:

Considering beach advancement in the last 10 years, when would the beach be at the Highway 217 embankment if beach advancement is not deterred?

A:

Susan Tomkin:  If the rate of retreat did not change, it would take about 20 years for the beach to reach the Highway 217 embankment. The rate of retreat probably will decrease over time, since as the beach retreats it is more protected by the bluff at the West end of the park. Also, the soil underlying the lawn is probably more resistant than beach sand, so it would retreat more slowly. A guess would be 20 to 50 years.

Jeremy Lowe:  It appears that the beach was a long way from its stable position, eroded quickly and is now slowing down, back to an alignment that it has had for several centuries. The slough and the western bluff should have more influence on the beach and the erosion should slow. I do not know the exact location of the embankment but the natural position of the spit has always been somewhere in the vicinity of the parking lot (which is why the parking lot is there!!).

Q:

How long will replenishment sand remain on the beach in significant storm events?

A:

Susan Tomkin:  Small replenishments (a few 10,000’s of cubic yards) could be moved from the placement site in a single storm event. It may, however, not leave the system but move temporarily offshore to be brought back onshore the following summer.

Jeremy Lowe:  Replenishment will not reduce the erosion rate. The length of time the sand remains is simply dependent upon how much sand is placed. In managing replenishments, the technique is to monitor the beach profile until it has eroded to some level where it no longer provides adequate protection and the beach is then replenished again. The time for this to occur is usually pretty consistent and replenishment schedule can be set pretty accurately in advance.

Q:

What is the travel path of sand in storm events and in the course of normal seasonal wave action?

A:

Susan Tomkin:  Under high wave energy conditions, the sand tends to travel offshore and down the coast; this occurs during normal winter seasons and during storms. The sand tends to move onshore (towards the beach) under low wave energy conditions, including the summer. During severe storms, the sand can be moved so far offshore that it does not return to the beach during the following summer.

This short-term offshore-onshore movement is superimposed on the long-term motion of sand towards the east.

Jeremy Lowe:  In general, during storm events sand moves offshore to form dissipating bars, in quieter periods the sand moves back onshore.

Q:

If natural sources of sand were re-established, would this prevent beach erosion during storm events? Would there be any mitigating effects of these natural sources of sand during storm events?

Susan Tomkin:  Beach erosion during storm events would not be prevented. However, if a significant source of sand were re-established and a wide beach were regained then beach erosion during storm events would be less (or not at all) damaging – the wide beach, rather than upland areas and structures, would be washed away.
Recall, however, that the area has not supported a stable wide beach over most of its history. The 1970s did not necessarily represent the typical, natural state of the beach.
 

Jeremy Lowe:  This is a much bigger question than Goleta Beach since the source of sand is primarily updrift watersheds and is dependent upon their management. The transport paths are so long that it may take years/decades to have positive impacts; just as it takes similar periods of time to have negative impacts.

Q:

Does taking sand from West Beach Santa Barbara to Goleta Beach adversely affect sand movement to or along the coast below SB City (i.e., Montecito)?

Susan Tomkin:  No, because dredging does not move it far enough out of the wave shadow to move to Montecito. The City paid more money for the sand to be pumped farther last year, but the USACE does not move it far enough to widen downcoast beaches. It remains at East Beach and returns over time.

Jeremy Lowe:  Probably, it depends upon how much sand is recycled westward and where that sand was going.

Q:

Is there a sediment budget for this region / littoral cell?

Susan Tomkin:  Budgets have been developed in the past; they are currently being updated.

Jeremy Lowe:  Gary Griggs’s group at UC Santa Cruz has/is working on one.

Q:

What are the cumulative effects of all revetments, scraping and berm building, nourishment and beach grooming?

Jeremy Lowe:  The cumulative impact is simply covering the symptom without addressing the cause. None of the above addresses the causes for the movement of the beach nor allows it to achieve a stable position. They in fact all attempt to hold the beach in an unstable position and so erosion continues.

Q:

Is there enough sand to conduct beach nourishment as a long term solution, and is it a cost effective solution?

Susan Tomkin:  If the beach is not retained then this would be a very expensive solution. Traditional sand retention structures such as breakwaters would make this a cost-effective solution. Dunes will not significantly retain the sand.

Jeremy Lowe:  If the sand can be recycled efficiently, you may renourish the beach indefinitely however problems down drift will start to accumulate. Whether it is cost-effective depends on what value you place on the beach.

Q:

Do the cement structures at Campus Point reduce sand passage to Goleta Bay beaches below the UCSB bluffs and Goleta Beach?  Would alteration of Goleta Point put the S-facing bluffs (W of Campus Point) in greater jeopardy?

Jeremy Lowe:  I do not know these structures. Again modification of part of the coast can have unforeseen impacts on other parts of the coast and it may not have immediate discernable impacts at the beach.

Q:

Does creating a berm and increasing the grade of the beach profile through beach scraping destabilize the sand and/or increase sand erosion? 

Susan Tomkin:  No, these activities have been at too small a scale to make an effect. Ocean conditions dwarf anything man has done there.

Jeremy Lowe:  Wave energy is dissipated through friction and breaking as it travels up the beach profile. Scraping the beach will remove sand from the profile, lowering it and making it less efficient at dissipating wave energy. Large waves will reach the shore and tend to draw sand down leading to erosion at the shoreline.

Q:

Does creating a berm and increasing the grade of the beach profile through beach scraping damage the beach ecosystem?  How?

Jeremy Lowe:  Not my area of expertise.

Q:

What are the known or suspected ecological effects of beach nourishment?

Jeremy Lowe:  Not my area of expertise.

Q:

What are the ecological effects of beach grooming.  Can ceasing beach grooming enhance beach habitats and mitigate impacts to beach habitats?

Jeremy Lowe:  Not my area of expertise.

Q:

Are there alternatives to rock revetments and armoring that can protect recreational uses at GB?

Jeremy Lowe:  Not my area of expertise.

  Revetments and Other Physical Solutions:

Q:

Do the UCSB rock revetments at campus point reduce sand contribution to GB? Could the concrete ramp which plugs a gap between rocks comprising campus point reduce sand flow around the point and toward GB? There often appears to be more sand upcoast of this plug than downcoast. Could it be making the point act more like a jetty or breakwater and deprive down coast beaches of sand?

Susan Tomkin:  It is unlikely that rock revetments at Campus Point have more than a marginal effect on the sand contribution to GB. Recent work by Griggs and his co-workers suggests that a very small part of the sediment budget in the Santa Barbara littoral cell is due to bluff erosion. I have attached a recent abstract at the end of this document that summarizes the current state of understanding relating to the effects of seawalls on the beaches in front of them.

Jeremy Lowe:  I do not know these structures but it is a possibility, particularly in the long term as sea levels rise, bluffs erode and concrete headlands stand more prominent. I do not know if sediment transport around Campus Point has been studied in any detail. This is also where the coast abruptly changes orientation and that may be a factor as well.

Q:

Are geotubes feasible – do they cause less damage than revetments?

Susan Tomkin:  Geotubes do not cause less damage than revetments. If they are exposed to waves they reflect the waves just as much as revetments; if they successfully hold the line of the shore against the waves they cause passive erosion in exactly the same way as revetments do. Geotubes should not be considered intrinsically “softer” than rock.

Geotubes have a reputation for being a relatively “soft” solution because they have been used as dune cores in the Gulf Coast and other areas with natural dune systems and relatively low energy waves. They have not been successfully tested in areas where they will be exposed directly to high energy waves typical of the West Coast.

Jeremy Lowe:  Any fixed structure (concrete wall, rock revetment, geotube) will prevent erosion behind the structure however if the beach is not in a stable position then there will be lowering of the beach in front of the structure. A fixed structure will not remove the cause of erosion. Some structures reflect wave energy less than others but that is only a major consideration when there is already a low beach and waves regularly reach the structure; no concrete wall, rock revetment or geotube revetment will promote the accretion of a beach.

Q:

Are there alternatives to rock revetments and armoring that can protect recreational uses at GB?

Susan Tomkin:  Sand retention structures combined with beach nourishment (although breakwaters are sometimes considered “armoring” their functioning and impacts are very different from revetments).

Jeremy Lowe:  There are lots of alternatives – some management, some structures, some renourishment, - it depends what you want to do. The important things are to have an understanding of the system that you are trying to manage and to have a clear vision of what you want to achieve (see remarks in relation to the first question).

Q:

Is there consensus amongst experts about the general effects of revetments and other seawalls on adjacent sandy beaches and shoreline sand supply and transport? On downcoast sandy beaches and sand supply?  What is the consensus, or if none, the majority opinion?

A:

Susan Tomkin:  Consensus is that there are four possible erosional impacts of a revetment or other shoreline hardening structure:

1.  Passive Erosion

It is important to recognize the distinction between the possibility of enhanced beach erosion caused by a seawall or revetment – which has not been proven – and the very real reduction in beach width that will occur when a seawall is constructed on a recessional coast.

Passive erosion is used in this letter to describe the latter effect. Because the revetments at Goleta Beach hold the line of the upland edge of the beach, the beach narrows at a rate equal to the natural rate of shoreline retreat – approximately 20 feet per year.

2.  Encroachment

This is a one-time loss of beach resulting from a revetment being constructed on top of the beach. The current encroachment of the revetments at Goleta Beach is about 20 feet.

3. Denial of Sediment

Erosion resulting from denial of sediment is normally considered a downdrift effect. As a bluff erodes, it feeds sediment into the littoral cell. If a revetment or other shoreline hardening stops this erosion from occurring, a corresponding quantity of sediment would be missing from the littoral cell. GB revetments do not deny sand to the downcoast areas – the lawn area is largely fine fill that would not feed downcoast beaches.

4. Wave-Current Interactions

This is the area of most controversy concerning the impacts of revetments and seawalls: what are the changes in the beach and changes in the neighboring back-beach line (end effects) that occur when waves hit the seawall? The most recent studies suggest that the net erosion rate generally does not increase in the presence of a seawall. Storm-induced erosion is greater, and the seasonal retreat of the beach at the start of the winter season is more rapid, in the presence of a seawall. However, the beach recovers to the same position whether a seawall is present or not.

The abstract attached to the end of this document summarizes the current state of knowledge regarding this issue.

Earlier scale model studies suggested that there was an increase in the net erosion rate in the presence of a seawall, and this result is often quoted with more certainty than is supported by more recent results.

Jeremy Lowe:  I think there is consensus on the impacts of structures. The differences are in terms of how much significance you attach to these impacts which in turn depends on the length scales and time scales you consider. In many cases the problem lies with the specification of the project – people will say ‘I want to stop my property eroding’ which you can do for a limited amount of time by covering it in concrete however if the client said ‘I want a sustainable solution that continues to provide the natural and manmade functions of the coast in a dynamic environment’ then you may think of a different solution.

  Management and Maintenance

Q:

How can we frame the discussion regarding cumulative effects of revetments on beach functions? Include revetments, scraping and berm building, nourishment, maintenance, and beach grooming?

Jeremy Lowe:  I’m not sure what this question is asking – if you could expand I’d be happy to have a go.

Additional Questions Provided on January 16, 2004

Q:

What is the cause of the erosion?

A:

Jeremy Lowe:  The movement of the beach that has been observed over the last few decades is probably a combination of natural variability due to stormy periods, El Nino etc and long-term trend. The recent erosion is the beach reestablishing a stable position following large changes to the shoreline over the last century or so.

Q:

How can sand bypassing of hard structures be accomplished?

Jeremy Lowe:  This depends on the form of the structure and how far offshore it extends. Structures may push the sand further offshore and affect its down drift movement. As part of the design of a hard structure, there should be an assessment of how much sand it will trap, the new beach profile that will evolve and the impact on down drift transport.

Q:

Is the volume erosion rate higher in front of the hard structures.

Susan Tomkin:  Not in the long term. There are short-term effects during storms, but these do not contribute to cumulative erosion.

Jeremy Lowe:  The erosion rate is not necessarily higher but a hard structure will not necessarily stop erosion of the beach in front of it.

Q:

What is the recovery rate of armoured beaches compared to non-armoured beaches?

Susan Tomkin:  The rates are similar.

Jeremy Lowe:  The recovery rate may be the same if the structure is set a long way back, if it is lower on the beach then it may reduce the recovery rate due to the reflection of wave energy from the structure.

Q:

How wide of a beach is desired?

Jeremy Lowe:  The width of the beach is a function of the ability of the beach to dissipate wave energy. The primary factors determining the width of the beach will be the limit of wave run up(giving the height of the beach) and the beach slope. These will be determined by the incident wave energy and the grain size of the sand. The other factor to consider in addition to width is the position of the beach with relation to the rest of the coast. The question should be where and how wide should the beach be?

Q:

Has the long-shore and cross-shore transport of sand been quantified at the West End?

Jeremy Lowe:  I don’t know

Q:

Has the Army Corp of Engineers wave study regarding an artificial reef at the oil piers in Ventura County started yet?

Susan Tomkin:  Yes, it is in final engineering design for construction.

Jeremy Lowe:  I don’t know.

Q:

What modular artificial reefs are available and how effective are they?

Jeremy Lowe:  This presupposes the solution. Reefs effectiveness in reducing wave energy depends upon the depth of water over the top of them and on their width – they can be tall and narrow or short and wide (short and narrow won’t work). They need to be constructed to provide protection at high water when the largest waves are most likely. Structures will therefore likely to be visible at low water or much larger if in deeper water.

Q:

Is Beacon monitoring beach nourishment?

Susan Tomkin:  Yes

Jeremy Lowe:  I don't know.

Q:

What are reasonable and cost-effective alternatives to hard protective solutions?

Susan Tomkin:  Nourishment with sand retention structures.

Jeremy Lowe:  In the long term, designing a coast that accommodates both the natural and manmade functions of the beach. This does not have to be done immediately but is more a long-term plan that would need to be implemented incrementally.

Q:

What are the effects on the slough ecosystem of a West End outlet?

Susan Tomkin:  With a second entrance the inlets would have trouble remaining open.

Jeremy Lowe:  The West End outlet would probably have to be held open by a larger tidal prism. The tidal exchange would therefore be greater and on a more regular basis. The salinity distribution and the inundation regime of the slough may therefore change.

Jeremy Lowe:  There are methods to estimate the amount of sand deposition for a given tidal inlet. This is based on observation of similar inlets. The amount depends upon the tidal prism of the inlet (the amount of water that flows out of the slough on each tide) and on the ocean wave energy.