Sand Wars coming to a county near us - soon
It will be interesting to see how good science fares against partisan politics in what seems to be shaping up to become the Big Pass sand wars.
Big Sarasota Pass separates Lido and Siesta keys in Sarasota County. The inlet has never been dredged, and tends to migrate north and south at the whim of winds and waves.
Although the pass generally is somewhat deep and historically has usually been navigable to boaters, shoals have begun to clog the inlet in recent years. Last year, in fact, the shoaling was happening so fast that the U.S. Coast Guard pulled up all the channel markers and classed the pass to a "use-at-your-own-risk" inlet.
The pass shoaling at its Gulf of Mexico mouth had also created a huge sandbar. Ironically, the creation of the sandbar seemed to spur erosion at the north end of Siesta Key, threatening a score or more of beachfront trophy-style houses.
It was, in short, a mess.
So after a few months of debate, Sarasota County commissioners commissioned a team of coastal geologists to look at the pass, look at the shoal, look at the erosion, and bring some hard science into the equation of what to do with the whole matter.
Regarding Big Sarasota Pass, the report by Dr. Richard A. Davis and Dr. Ping Wang of the University of South Florida's geology department states:
"The large ebb-tidal delta [the sandbar outside the pass in the Gulf] bypasses considerable sediment across the inlet to Siesta Key. The nourishment of Lido Key has increased the volume of bypassing sand and has added sediment to the ebb delta. This bypassing has provided sand for the beaches of northern Siesta Key, but now the ebb delta is so large that this sand is moving onto the barrier island several hundred meters south of the end of the island. Erosion is extensive and severe on the north end of Siesta Key at the present time.
"Tidal currents in the main channel of Big Sarasota Pass exceed a meter per second. As a consequence, it is expected to stay open and to maintain a channel similar to the present one. The mouth of the channel as it exists toward the south into the Gulf is shoaling and provides navigational problems. Under the present circumstances this condition is expected to persist and perhaps become worse.
"Sediments that comprise the ebb-tidal delta at Big Sarasota Pass are dominated by fine quartz sand with varying amounts of carbonate sand and gravel. The volume of this type of quartz sand-dominated sediment in the ebb delta is at least 10 million cubic yards. At least this amount of nourishment-quality sediment is available in this sediment body.
"Utilization of a portion of the ebb-tidal delta as a borrow site for nourishment will not cause problems for the inlet or for the northern portion of Siesta Key beaches. In fact it will enhance beach development in this part of the barrier island."
The pair of scientists were asked to address five specific questions by the county commission.
What is the likelihood of Big Pass closing?
Under the present circumstances there is little likelihood that Big Pass will close in the sense that there will no longer be tidal flux through the inlet. It is likely that the mouth of the main channel will continue to shoal as has been the case over the past several years.
Does the Big Pass shoal benefit directly from updrift restoration projects [Lido Beach renourishment efforts]?
Is the sand in the Big Pass shoal suitable for beach renourishment projects?
Are there any portions of the shoal that can be removed without having a detrimental impact to the adjacent shorelines?
Yes. In fact, the removal of this portion of the sand body would benefit the northern end of Siesta Key by enabling bypassed sediment to reach this critically eroding area whereas now it is carried several hundred meters to the south.
Would dredging in and around the inlet affect the stability of the channel, especially in the more seaward areas?
It is not recommended to dredge the main channel of Big Pass, which is stabilized and maintains a depth of 5-8 meters. Dredging of the distal portion of the inlet channel in combination with removal of sediment for nourishment purposes would enhance tidal flux in this area and would provide for a deeper distal portion of the main channel. It is unlikely that the channel would remain in this state for very long, but would continue to shoal and migrate to the south in response to the longshore sediment transport from the north. A possible solution would be the regular dredging and use of this sediment for nourishment purposes.
There's the science. Now for the politics.
About 15 years ago, Venice beaches were suffering from severe erosion. Venice has a wastewater treatment plant that's right on the Gulf - OK, so they may not be all that bright down there - and the plant was threatened with inundation due to the lack of sand on the beach.
Venice officials started looking around for a sand source and, low and behold, found one in the huge sandbar off the north end of Siesta Key. Beach-quality sand, not too far from where it needed to go, all within Sarasota County - it seemed too good to be true, and the Venice gang started quiet negotiations with the county gang to get the sand.
The negotiations became anything but quiet when Siesta Key residents learned of the sand exchange. Siesta thought that the sand in the shoal protected the key from storm threats, pointed out that Siesta beaches weren't suffering from any erosion, and basically said to leave our damn sand alone.
It got ugly quick. In fact, one county commissioner whose district encompassed Siesta Key lost his re-election bid in part because of the sand wars. Venice dropped the fight, found another offshore sand source that cost more, but got its beaches renourished.
... and now, by the numbers
Drs. Davis and Wang have estimated that there is about 10 million cubic meters of sand available for renourishment at the Big Pass shoal, out of a total of better than 14 million cubic meters.
When Venice made its proposal all those years ago, it wanted about 450,000 cubic meters of sand, and proposed to "feather" the sand from the outer edges of the shoal. According to my math, that works out to about 3.5 percent.
Now, the numbers get a little more interesting.
Anna Maria Island underwent its second beach renourishment project April-June 2002. We got our sand from an offshore borrow site off the north end of the Island, and about 1.5 million cubic meters of sand was used to add a beach about 250 feet wide on approximately eight miles of shoreline on the Island.
Now, rounding things off dramatically, we might assume there is enough sand at the Big Pass shoal to renourish all the beaches from Anna Maria's north end to Ft. Myers with some to spare. Roughly 70 miles of beach renourishment, all benefiting from that one really big sandbar.
It will be interesting to watch the politics in Sarasota as the Sand Wars pick up this summer.
Ever noticed how some barrier islands look alike? Anna Maria, Siesta Key, Gasparilla Island and North Captiva are what Drs. Davis and Wang call "drumstick" islands because they have a fat end that tapers to something of a point, because they look like the leg of a piece of fried chicken.
The shape is probably due in part to the large inlets at the northern ends of the keys and all the energy that takes place in the change of tides and the strong currents.