12-Acre
Closure Book
1:FFDW Org
2:Enabling
3:Survey
6:Erosion
Editor: fortfunston@hotmail.com
Webmaster: Wedosites@mail.com
Examining The Land:
 |
A Rebuttal To The Claims Regarding The Geology And Topography Made In The National Park Service Proposal To Close Twelve Acres At Fort Funston
Landslide
at Fort Funston (Photograph by members of the San Francisco Bay Region Project">
12-Acre Closure
Book 1:FFDW
Org 2:Enabling 3:Survey 6:Erosion Editor:
fortfunston@hotmail.com Webmaster:
Wedosites@mail.com
Examining
The Land:
Landslide
at Fort Funston (Photograph by members of the San Francisco Bay Region Project,
USGS) Introduction The four reasons the National Park Service gives
for closing off twelve-acres of land to all public access at Fort Funston can be
summarized as follows: (I) protection of the bank swallow, (II) protection of a
unique geological resource, (III) conservation and protection of dune habitat,
and (IV) concerns about public safety.
The
following section addresses some of the claims made by the Park Service
throughout their proposal about the geology and topology at Fort Funston.
Specifically, this section will consider the following questions
concerning the claims made in the NPS proposal: 1. To
what extent, if any, has the park service demonstrated conclusively that human
recreation on the cliffs within the proposed closure area disturbs the bank
swallow nesting colony? Are these disturbances prevented with the proposed
closure? 2.
To
what extent are the cliffs at Fort Funston a “fragile” and “unique
resource,” as described in the NPS proposal?
If so, does human recreation within the proposed closure area threaten
the geology at Fort Funston? The
focus of this section is on the accuracy
and strength of the basic science underlying the NPS arguments.
Each claim regarding the cliffs made in the National Park Service
proposal for the closure of the land was examined, published scientific
literature and the basic science relevant to the argument was reviewed, and
experts in the field in question was contacted, when appropriate.
1.
NPS Claim: Closures Required To Prevent Harassment Of Bank Swallows One
of the primary reasons cited by the National Park Service for this twelve-acre
closure is the protection of the bank swallow nesting sites.
Informational signs posted along the fences surrounding the current
ten-acre closure explain that visitors are no longer allowed in the area for the
protection of bank swallows, a state-threatened species.
The NPS
proposal acknowledges that “bank swallows are tolerant to some disturbance,”
but goes on to claim ,“few colonies are subjected to the intense recreational
pressure at Fort Funston.” An
article describing bank swallows in California (Garrison, 1999a) includes
descriptions of a number of successful colonies that co-exist side-by-side with
intense human activities. Successful
colonies have been observed within active rock quarries, along busy interstate
highways, near pasture used for commercial agriculture, and on the banks of
lakes and rivers used for recreational boating.
As Garrison (1999a) states: “Adjacent land uses that retain nesting
bank integrity, allow bank erosion to occur, and provide insect food resources
are unlikely to have substantive adverse impacts to Bank Swallows.”
Therefore,
to justify the proposed closure at Fort Funston, the NPS needs to demonstrate
that this colony of bank swallows is either (1) less
tolerant of human disturbances than other nesting colonies studied around the
country or (2) subjected to frequent
and egregious interference originating from human activities occurring above
their burrows. Nowhere does the
proposal suggest the former. The
proposal, however, does describes six “documented” ways in which the colony
is being disturbed: “Documented
disturbance events at Fort Funston include: cliff-climbing by people and dogs;
rescue operations of people and dogs stuck on the cliff face; people and dogs on
the bluff edge or in close proximity to active burrows; graffiti carving in the
cliff face; aircraft and hang-glider over-flights; and discharge of fireworks
within the colony.” How
serious are these disturbances and do they merit the permanent closure of the
area? Of these six disturbances listed, four
originate outside the proposed area and would continue even if the bluffs were
declared permanently off-limits to all recreation. These include: cliff climbing
(in which people climb up the cliffs from
the beach), graffiti carving (in which people climb up
the cliffs and carve the bluffs), aircraft and hang-glider overflights
(which occurs in the air), and discharge of fireworks (which occurs on the beach
under the colony of swallows). Only two
“documented” disturbances to the nests listed in the proposal potentially
are prevented by barring recreation on the tops of the bluffs.
These are disturbances caused by: (1) people and dogs on the bluff edges
and (2) rescue operations on the cliffs. Yet
while these disturbances are described as “documented,” the proposal does
not provide any data on the frequency of these events within
the proposed, closure area. To
assess the seriousness of problem and the appropriateness of the solution, it is
incumbent on the park service to provide such frequency data.
For example, how many people are actually
sighted on the bluffs above the burrows during bank swallow nesting season
and what are they doing to disturb the otherwise tolerant bank swallow?
How many cliff rescues occur within
the proposed closure area each year?
The NPS
proposal additionally describes “potential impacts” on the bank swallow
nests due to recreation and rescues, including the “crushing of burrows” and
“active sloughing and landslides.” Again,
the document does not include data on the actual
number of incidents that have occurred. For example, how many burrows are
crushed each year during rescue operations within the proposed closure area?
How many instances of collapsed or damaged burrows can the park service
directly attribute to people or pets engaging in recreational activities on top
of the bluff tops in question?
The
National Park Service also maintains that people and pets on the bluffs may
disturb the colony by the “casting[of]
shadows that may be perceived as predators” (emphasis added). The
proposal states that “The institution
of the proposed 12-acre closure area …will protect the bank swallow colony by
preventing most of these disturbances. There will be no visitor access to the
bluff edges above the nesting sites, thus preventing… casting of shadows”
(emphasis
added). The claim that visitors can cast shadows on the
nests is completely erroneous because doing so would violate some basic laws of
physics, specifically the way in which light behaves and shadows are formed. Light travels in straight lines and shadows happen
when light is blocked. Let’s
consider a rare, “fog-free” day at Fort Funston during summer bank swallow
nesting season. From sunrise to
noon, the sun is in the east and objects on the cliff will cast shadows westward
over the ocean (see Figure 1). From
noon to sunset, the sun is in the west and the shadows cast by objects on the
bluff tops will go east -- away from the cliffs (see Figure 2).
At noon during the summer months in San Francisco, the sun is about 70°
above the southern horizon. Shadows cast at that time will also be cast on the
bluff tops, but will be directed to the north. At
no time can an object on top of the west-facing cliffs cast a shadow on the bank
swallow nests below. Figure
1: Cliffs And Shadows In The
Morning
Ocean Figure
2: Cliffs And Shadows In The Afternoon
2.
NPS Claim: Closures Are Needed To Protect A Unique Geological Resource The
proposal justifies the closure on the basis of the need to protect the unique
geology of the area. The document states: “The
bluffs at Fort Funston provide one of the best continuous exposures of the last
2 million years or more of geologic history in California, covering the late
Pliocene and Pleistocene eras. This exposure of the Merced Formation is unique
within both the Golden Gate National Recreation Area and the region. It is a
fragile, nonrenewable geologic resource. NPS regulations, policies and
guidelines mandate preservation of such resources by preventing forces (other
than natural erosion) that accelerate the loss or obscure the natural features
of this resource.” To assess the
validity of this claim, it is important to understand what the Merced Formation
is and what portions of the formation will be protected by the proposed closure.
The Merced Formation is a large geological feature that lies along the
San Andreas Fault and extends from Ocean Beach to Coyote Point in San Mateo
county (see Figure 3). The cliffs along Ocean Beach, starting at Sloat Boulevard
and ending a few miles south of Fort Funston, represent the exposed portions of
the formation. The cliffs within the proposed closure are a portion (but
not all) of this exposed section of the Merced Formation.
Dr. James Hengesh, a geologist contracted by the
United States Geological Survey (USGS) to study the deformation of the Merced
Formation from Ocean Beach to Coyote Point, was asked to comment on the accuracy
of statements made in the NPS proposal. Dr. Hengesh’s research included a detailed survey of the
sea cliffs below Fort Funston (Hengesh and Wakabayashi, 1994).
Specifically, Dr. Hengesh was asked to confirm (1) whether the bluffs at
Fort Funston date to the Pleistocene era, (2) in what way, if any, these bluffs
are unique, and (3) whether human recreation on the bluffs might damage the
formation it in any way. This was Dr. Hengesh’s response: “…
In response to your questions I would say that (1) yes this area does
have one of the most complete Pleistocene stratigraphic sections in the Bay
Area. The Section extends from
Ocean Beach (approx. Sloat Ave.) south forming the seacliffs along the beach to
the San Andreas fault (several km). I do believe it is an important stratigraphic record,
however, (2) I do not believe that non-motorized
recreational use of this area would have any impact. This area
experiences very high rates of natural cliff retreat, and there are numerous large
landslides that effect(sic) extensive reaches of the exposures along the
coastline. The amount of material
lost through cliff retreat and land sliding
dwarfs any impact I can imagine from people walking along the cliffs and beach”
(emphasis
added).
(Hengesh, 2000) An
examination of USGS data on landslides and cliff failures at Fort Funston
supports Hengesh’s argument. Figures
4 and 5 show a photograph of a typical landslide that occurred at Fort Funston. In that landslide 3700 cubic yards of material fell from the
cliffs, or an amount of material equal to over 100,000 large buckets of sand.
This report is a rebuttal to some of the National
Park Service’s justifications for the need to permanently close 12-acres of
coastal land at Fort Funston to recreation.
Specifically, this document examined the scientific validity of
statements made about the cliffs within the proposed closure. Two questions were
asked and formed the basis of the assessment: 1. To
what extent, if any, has the park service demonstrated conclusively that human
recreation on the cliffs within the proposed closure area disturbs the bank
swallow nesting colony? Are these disturbances prevented with the proposed
closure? 2.
To
what extent are the cliffs at Fort Funston a “fragile” and “unique
resource,” as described in the NPS proposal?
If so, does human recreation within the proposed closure area threaten
the geology at Fort Funston? To summarize, we found the following: • In describing ways bank swallows are disturbed by human
recreation, the NPS lists a number of activities that originate on the beach or
in the air, and would not be prevented at all by restricting access to the
bluffs. • Of those activities that potentially disturb nesting bank
swallows and might be prevented by restricting recreation on the bluffs, the NPS
does not provide any data on the number of incidents they have documented.
To demonstrate the need to permanently close recreational space to the
public, it is incumbent on the NPS to provide this information. • The NPS claims that recreation on the bluff tops must be
restricted to prevent the “casting of shadows on the nests.”
But it is impossible for an object on the bluffs to cast a shadow on the
west facing cliff face below. • The NPS claims that the closures would protect the
geological record contained in the Merced Formation and exposed at Fort Funston.
Yet the NPS proposal neglects to mention that this closure would
represent a small section of the approximately five kilometer stretch of coastal
cliffs that contains this stratagraphic record. • Recreational activities will not harm this small exposed
section of the Merced Formation. Compared to the amount of material lost through
natural processes of erosion and landsliding, the damage done by non-vehicular
recreation is negligible. Garrison,
B.A. (1999a). Bank
Swallow: In California Partners
in Flight: Bird Conservation Plan. Philadelphia, PA Garrison,
B.A. (1999b). Bank
Swallow (Riparia riparia). In
Birds of North America, No 414 (A. Poole and F. Gill, eds.). The Birds of North
America, Inc. Philadelphia, PA. Hengesh,
J. (2000). Private e-mail
correspondence. Hengesh
J. and Wakabayashi, J. (1994). Quarternary
Deformation Between Coyote Point And Lake Merced On The San Francisco Peninsula:
Implications For Evolution Of The San Andreas Fault.
Report to the United States Geological Survey, National Earthquake Hazard
Reduction Program. Wallace,
R.E. ed. (1990) The San Andreas Fault
System, United States Government Printing Office, Washington, DC.
A
Rebuttal To The Claims Regarding The Geology And Topography
Made In The National Park Service Proposal To Close Twelve Acres At Fort
Funston
Figure
3: A map of the geology of the San
Francisco Bay Area as it relates to the major fault systems. Section A in this
map is the outcrop belt of the marine Merced Formation. [From The
San Andreas Fault System, California
edited by Dr. Robert E. Wallace and published by United States Government
Printing Office, Washington in 1990 and 1991.]
Figure 4: Landslide
at Fort Funston. Slide mass contains approximately 2,830 cubic meters (3,700
cubic yards) and is 30 m (100 ft) high. Figure 5 provides an aerial view of this
slide. [D.M. Peterson, U.S. Geological Survey]
Figure
5: Aerial view of a large slide
north of the Fort Funston parking lot. A ground perspective of this slide is
shown in Figure 4. [S.D. Ellen, U.S. Geological Survey]
3.
Summary
4.
References