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Thread: Shoreline protection structures and erosion

  1. #1
    Cyburbian TerraSapient's avatar
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    Shoreline protection structures and erosion

    I searched the forums first to see if there was already a post about whether seawalls contribute to or exacerbate shoreline erosion and loss of beach habitat; however, I did not find anything, so I have decided to start a new thread on the subject. If there is already a thread on the subject, perhaps someone will provide me the link.

    Those of us who live in coastal regions may already be aware of a debate about whether or not seawalls and other shoreline hardening measures are contributing to beach loss and coastal erosion. The academic and professional discussions on the matter seems to be divided—strong belief that shoreline hardening exacerbates erosion and contributes to beach loss, and strong belief that seawalls, rip rap, bulkheads, revetments, etc. do not exacerbate the problem or contribute to beach loss.

    The point of shoreline protection features being to prevent or reduce erosion and to prevent property loss, this seems an important matter to investigate. The State of Hawaii, and The City and County of Honolulu, Department of Planning and Permitting has seemingly taken a strong position against permitting the development of more shoreline protection structures or even repair of some existing seawalls in certain highly sensitive areas. They appear to be making this decision operating under the philosophy that shoreline hardening does contribute to beach loss and erosion. This, of course, effects hundreds or thousands of property owners in the coastal zone of the state.

    There is not, however, any regulation that explicitly prohibits them, except seaward of the shoreline, unless other conditions are met.

    To this extent, one then has to argue what is more important 1) an individual property owner's rights to preserve an investment and take whatever precautions are necessary to reduce loss of their property, 2) the right of the public to enjoy a communal good - the beach and access to it - particularly assuming that if shoreline hardening does contribute to beach loss, that any hardened shorelines will experience permanent loss of beach.

    These are the arguments as I understand them. Shoreline hardening either 1) Contributes to beach loss and exacerbates erosion, therefore we need to develop better tools to protect private property - ones that do not come with permanent loss of a communal good and the right of current and future generations to enjoy the beach, or 2) shoreline hardening does not contribute to beach loss, does not exacerbate erosion, and the erosion and beach loss we do witness at hardened shorelines is a natural phenomenon that would have occurred regardless of the installation of a seawall.

    Those that support the latter argument tend to state that the reason shorelines are hardened in the first place is precisely because erosion is occurring, and that the protection structure is a necessary means to prevent or reduce erosion. Also, that sea level rising is the cause of beach loss, not the shoreline protection structure.

    Those that support the former argument tend to state that (in reference to the natural features of Hawaii in particular) erosion is a natural process, and that yes sea level rising is contributing to beach loss; however, that wherever erosion of a sandy shoreline has occurred in the past, wave action against the sandy shoreline has enabled the beach to remain in tact despite the eroding shoreline because the beach is able to move inland along with erosion. Supporters of this argument state that hardened shorelines prevent this natural phenomenon.

    I am curious how other planners who may have to deal with this issue on a regular feel about this dilemma.
    How do your local governing and regulatory bodies handle this apparent conflict?

    I am also interested to hear what the environmental planners have to offer on the subject, based on professional experience.

  2. #2
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    shoreline ordinances

    Have you read Maui and Kauai County shoreline ordinances?

  3. #3
    Cyburbian ColoGI's avatar
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    Quote Originally posted by TerraSapient View post

    Those of us who live in coastal regions may already be aware of a debate about whether or not seawalls and other shoreline hardening measures are contributing to beach loss and coastal erosion. The academic and professional discussions on the matter seems to be divided—strong belief that shoreline hardening exacerbates erosion and contributes to beach loss, and strong belief that seawalls, rip rap, bulkheads, revetments, etc. do not exacerbate the problem or contribute to beach loss.
    Seems madam? Nay, it is - I know not seems.

    I wasn't aware there were any modern studies that disputed the findings that hardening exacerbates erosion.

  4. #4
    Cyburbian TerraSapient's avatar
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    The evidence, in my opinion, points to what most researchers have been saying for years - that shoreline hardening does promote beach erosion; however, there are a handful of very vocal property owners on Oahu who argue that they have had seawalls on their properties for 50+ years with no beach loss. Based on the research I did last year, there are very few academic publications disputing that hardening promotes beach loss and coastal erosion, but I did find a few. In an study published earlier this decade (2001 maybe?), Coastal Engineering concluded that the alignment of the seawall with local longshore currents played an important role in whether or not erosion would be exacerbated. However, collecting data about how current direction changes throughout the year in a specific location would be required before you could model local conditions. I haven't followed up on this topic in quite sometime however, so I could be misquoting.

    LE Smith I have read the shoreline ordinances for other Hawaii counties. As I recall they were relatively similar to Honolulu's.
    Is the topic of hardening shorelines as controversial on Kauai? It seems that the debate is resurfaced in Honolulu rather frequently since there are so many homes built right up to the shoreline, many of which are within the shoreline setback area and require a SSV and EA before seawall repairs can be permitted.

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