Blind Pass Research Articles

Morphodynamics of barrier-inlet systems in the context of regional sediment management, with case studies from west-central Florida, USA

The temporal and spatial scales controlling the morphodynamics of barrier-inlet systems are critical components of regional sediment management practice. This paper discusses regional sediment management methods employed at multiple barrier-inlet systems, with case studies from West-Central Florida. A decision-support tool is proposed for regional sediment management with discussion of its application to barrier-inlet systems. Connecting multiple barrier islands and inlets at appropriate spatio-temporal scales is critical in developing an appropriately scoped sediment management plan for a barrier-inlet system. Evaluating sediment bypassing capacity and overall inlet morphodynamics can better inform regional sand sharing along barrier-inlet coastlines; particularly where sediment resources are scarce and a close coupling between inlet dredging and beach placement is vital to long-term sustainable management. Continued sea-level rise and anthropogenic activities may intensify the need for investigating longer-term processes and expanding regional planning at a centennial timescale, and are acknowledged as challenging tasks for RSM studies. Specifically, we suggested that a regionally focused, multi-inlet study were necessary for management plan of individual inlet for the west-central Florida case studies. Key recommendations based on the case studies include: 1) allow the natural sediment bypassing to be re-established at Blind Pass inlet through reduced ebb-tidal delta mining, 2) reduce the interruption to sediment bypassing at John's Pass and Pass-a-Grille inlets through an improved design of the dredged mining areas located along sediment bypassing pathways, 3) allow for continued natural sediment bypassing at Bunces Pass, and, 4) incorporate the cyclic swash-bar attachment sediment bypassing into the management plan at Bunces Pass and adjacent barrier-islands.

Local and regional effects of reopening a tidal inlet on estuarine water quality, seagrass habitat, and fish assemblages

Blind Pass is an inlet that separates Sanibel and Captiva Islands in southwest Florida but has historically closed and opened by both anthropogenic and natural processes. In July 2010, a dredging project to open the small inlet between the two barrier islands was completed. The objective of this study was to use and supplement ongoing estuary-monitoring programs to examine the responses of water quality, seagrass habitat metrics, and fish assemblages both in the immediate vicinity of the inlet and at broader scales (up to 40km2). As far as we are aware, there are no previous studies with this intensity of sampling, both before and after an inlet opening. Significant increases in salinity and turbidity were observed inside Blind Pass, with significant decreases in CDOM and chlorophyll a, however, the effects were not far-reaching and limited to less than 1.7km from the inlet within Pine Island Sound. Seagrass habitat metrics were expected to respond rapidly after the inlet was opened given the reduced light attenuation. However, there were no changes in shoot densities, species composition, and epiphytic algae within the approximately one-year duration of the study. The reopening of the pass did not substantially change fish assemblage structure, except for those from deeper habitats. Although immediate increases in the abundances of estuarine-dependent species were predicted in shallow habitats post opening, this did not occur. In conclusion, the effects of reopening a relatively small ocean inlet on water quality were apparent in the immediate vicinity of the inlet (within 1.7km), but far-reaching effects on water quality, seagrass metrics, and fish assemblages were not immediately apparent in this well-flushed estuary. If subtle changes in tidal exchange and circulation affect productivity of seagrasses or its fish assemblages at broad scales, it may take several years to reach a steady state.

Morphodynamics of an anthropogenically altered dual-inlet system: John's Pass and Blind Pass, west-central Florida, USA

The morphodynamics of the John's Pass–Blind Pass dual inlet system were investigated based on hydrodynamic and morphology measurements, and numerical modeling. The co-existence of the dual inlets is realized by the dominance of mixed-energy John's Pass in terms of tidal prism and size of the ebb delta and the artificial maintenance of the wave-dominated migratory Blind Pass. Due to the secondary role of Blind Pass, the aggressive anthropogenic activities there do not seem to have a significant influence on the morphodynamics of John's Pass. On the other hand, the opening (in 1848) and subsequent evolution of John's Pass had substantial influence on Blind Pass, causing it to migrate rapidly to the south. In addition, anthropogenic activities had much more influence on the morphodynamics of the secondary Blind Pass than that of the dominating John's Pass.Results from numerical modeling provide a semi-quantitative understanding of the hydrodynamics and morphodynamics of John's Pass and Blind Pass in association with cold front passages, which have substantial influences on inlet morphology. Two large eddies are modeled from the interactions between the southward longshore current and John's Pass ebb and flood flow, respectively. These eddies are closely related to the morphodynamics of the channel margin linear bar and longshore transport divergence at the downdrift side. Both are key features of a mixed-energy inlet. The shallow water and wave-breaking-induced longshore current and elevated sediment suspension along the ebb delta terminal lobe provide the pathway for sediment bypassing. The morphodynamics of Blind Pass are dominated by wave forcing. The weak ebb jet is not capable of forming a sizable ebb delta and tends to be deflected by the strong longshore current, causing elevated longshore transport along the downdrift beach. The 90-degree turn of the inlet, which is common for wave-dominated migratory inlets, results in weak ebb flushing along the updrift (north) side of the inlet, and is responsible for the alongshore migration of the inlet before the artificial stabilization and sedimentation along the northern side of the inlet following stabilization.

Modeling Regional-Scale Sediment Transport and Medium-Term Morphology Change at a Dual-Inlet System Examined with the Coastal Modeling System (CMS): A Case Study at Johns Pass and Blind Pass, West-Central Florida

The Coastal Modeling System (CMS), developed by the US Army Engineer Research and Development Center's (ERDC) Coastal Inlets Research Program (CIRP), is applied to model morphology change at a dual-inlet system, the Johns Pass and Blind Pass system in West-Central Florida. The CMS combines computation of current, wave, and sediment transport, leading to the prediction of morphology change at tidal inlets and the surrounding beaches. Medium-term CMS runs, with simulated times of 1.2 to 1.6 years, were completed and compared with extensive field data. Stronger tidal flow through the dominating Johns Pass and weaker flow through the secondary Blind Pass were calculated, indicating that the model reproduced an essential aspect of this interactive two-inlet system. The complicated wave refraction and breaking over the ebb tidal deltas and along the adjacent shorelines were accurately modeled, leading to a realistic representation of the wave-current interaction. Wave-breaking induced elevated sediment suspension and transport were described by the model. The predicted morphology change agreed well with field data. The CMS captured several key spatial trends of morphology change, e.g., erosion along the downdrift beach and accretion at the attachment point. The computed 32,000 m3/yr sedimentation volume in the dredge pit at the updrift side of Blind Pass matched the measured value of 35,000 m3/yr with a similar spatial distribution pattern, suggesting that the calculated net longshore sediment transport rates are accurate. The computed sedimentation rate of 60,000 m3/yr at a designed dredge pit on Johns Pass ebb-delta agrees with the generally accepted gross longshore transport rate. Rapid and large morphology change in response to high wave-energy events is predicted and is consistent with field observations.

Design of a mechanical clutch-based needle-insertion device

Insertion of trocars, needles, and catheters into unintended tissues or tissue compartments results in hundreds of thousands of complications annually. Current methods for blood vessel cannulation or epidural, chest tube, and initial trocar placement often involve the blind pass of a needle through several layers of tissue and generally rely on distinguishable anatomic landmarks and a high degree of clinical skill. To address this simply and without the use of electronics, a purely mechanical clutch system was developed for use in medical devices that access tissue and tissue compartments. This clutch utilizes the surface contact of a buckled filament inside an S-shaped tube to transmit force from the filament (catheter/guide wire) to the tube (needle). Upon encountering sufficient resistance at the tip, such as dense tissue, the catheter buckles and locks within the tube, causing the filament and needle to advance as one. When the needle reaches the target tissue or fluid-filled cavity, the filament unlocks and slides freely into the target region while the needle remains stationary. A similar locking phenomenon has long been observed in drill strings inside drill shafts used by the oil-drilling industry, and oil industry models were adapted to describe the motion of this clutch system. A predictive analytical model was generated and validated with empirical data and used to develop prototypes of a complete device then tested in vitro on muscle tissue and in vivo on a porcine laparoscopic model with promising results.

Anterior Tonsillar Pillar Perforation During Glidescope® Video Laryngoscopy

To the Editor: The Glidescope® video laryngoscope is an effective and well-established device for facilitating tracheal tube placement (1,2) Here we report an unusual complication of Glidescope® assisted intubation. A 72-yr-old man presented for resection of a thoracic spinal cord arteriovenous malformation. The patient had a past medical history significant for myotonia congenita and hiatal hernia with mild acid reflux. On physical examination he was found to have a Mallampati Class II view of the oropharynx with mouth opening slightly <4 cm and normal range of motion of the cervical spine. In addition, review of his previous records revealed that during a prior anesthetic he had a Cormack–Lehane Grade 3 laryngeal view necessitating three direct laryngoscopy attempts and the use of an intubating stylet to secure the airway. Anesthesia was induced with lidocaine, fentanyl, propofol, and cisatracurium. After 3 min of ventilation via mask, we easily inserted a Glidescope® video laryngoscopy blade and obtained a Grade I view of the vocal cords. An 8.0 mm internal diameter tracheal tube with the manufacturer recommended Rigid Stylet™ was passed through the vocal cords under Glidescope® visualization. The cuff was inflated and positive pressure ventilation through the tube produced a normal end tidal CO2 tracing and bilateral breath sounds. At this point a small amount of blood was noted in the retropharynx on the Glidescope® monitor. Upon withdrawal of the Glidescope® blade the tracheal tube was seen perforating the right anterior tonsillar pillar. After consulting with an otolaryngologist, we removed the tracheal tube and reintubated the trachea using a fiberoptic laryngoscope without difficulty. The trachea was extubated in the operating room following the procedure, and minimal throat soreness was reported on postoperative day one. We postulate several mechanisms for this unusual complication: After obtaining an adequate view of the vocal cords with the Glidescope®, we blindly passed the tracheal tube through the oropharynx until visualizing the tip of the tube adjacent to the glottic opening on the Glidescope® monitor. It was during this blind pass of the tube that the anterior tonsillar pillar was perforated. We used a standard tracheal tube and the manufacturer recommended Rigid Stylet™. The combination of the stylet and the sharp edge of the tracheal tube may have contributed to perforation of the anterior tonsillar pillar. Patients with myotonia congenita can be resistant to the effects of nondepolarizing muscle relaxants in the setting of direct stimulation (3). Inadequate relaxation of the palatoglosseus muscle may predispose to anterior tonsillar pillar perforation. The already thin tonsillar pillar membrane may have been pulled taut by palatoglosseus muscle contraction, making it more susceptible to perforation. To avoid similar complications when using the Glidescope® video laryngoscope we suggest the following: Use of a soft-edged endotracheal tube (such as the Parker Flex-Tip™) to avoid damage to pharyngeal structures, especially in conjunction with the Rigid Stylet™. Verathon Medical has recently introduced such a tube for use with the Glidescope® system (GVL® GlideRite™). Directly visualize the tracheal tube as it is inserted into the mouth along the curvature of the Glidescope® laryngoscope blade. Only after the tip of the tube has passed out of view should the Glidescope® video monitor be viewed. Asif M. Malik, MD Jonathan K. Frogel, MD Department of Anesthesiology Henry Ford Hospital 2799 West Grand Blvd. Detroit, MI 48202 [email protected]

Morphodynamics of the barrier-inlet system, west-central Florida

The barrier-inlet system along the Gulf Coast of peninsular Florida has one of the most diverse morphologies of any barrier system in the world. The delicate balance between tidal- and wave-generated processes on this low-energy coast permits only slight changes in either of these processes to result in significant and rapidly developing morphologic responses. Some of these responses are the result of natural phenomena such as hurricanes opening tidal inlets, closure of inlets due to longshore transport of sediment, and changes in the availability of sediment. Tidal prism is the primary factor in controlling inlet morphology and is greatly influenced by anthropogenic activities in the backbarrier area. Human activity has also modified the coast in many ways over the past several decades, beginning with the construction of the first causeways in the 1920s. The various modifications by development have resulted in important morphodynamic changes in the barrier-inlet system. These include hardening the coast on the beach and at inlets, dredging and filling in backbarrier environments, and construction of fill-type causeways connecting the islands to the mainland. Construction of seawalls and jetties has inhibited normal coastal processes. Examples include the downdrift erosion at Blind Pass and Big Sarasota Pass. Construction of fill-type causeways between the barriers and the mainland has created artificial tidal divides that reduce the tidal prism at some inlets, thereby resulting in instability or closure such as Blind Pass and Dunedin Pass. This is further exacerbated by dredge and fill construction that reduces tidal prism by reducing the area of open water in the backbarrier. Dredging of the Intracoastal Waterway also results in a negative impact on selected inlets by channeling tidal flux away from some inlets. Impacts of these changes inhibit the barrier/inlet environments from responding to open coast processes.

How anthropogenic factors in the back-barrier area influence tidal inlet stability: examples from the Gulf Coast of Florida, USA

Abstract Human development along the coast of the world has caused important changes to coastal morphodynamics. The barrier-inlet system of Florida, especially the tidal inlets, has been severely impacted by this development. Beginning in the 1920s and continuing through the 1960s there was: (1) extensive construction of fill-type causeways connecting the mainland to the barrier islands, (2) widespread dredge-and-fill construction along the backbarrier and mainland, and (3) dredging of the Intracoastal Waterway (ICW) in the back-barrier area. The primary effect of these various types of construction and development was to cause instability of many inlets by diminishing the tidal flux through them. In some cases there was a combination of human and natural causes that resulted in the inlet degradation or closure such as at Dunedin Pass and Blind Pass, whereas at others this instability was almost exclusively the result of human activity such as at Midnight Pass. Although these detrimental development practices have been stopped, a large amount of irreparable damage has been done.

MEASUREMENT OF BED FRICTION IN TIDAL INLETS

The flow characteristics and the stability of a tidal inlet are governed, among other factors, by the channel bed friction. In order to determine the bed shear stress regime and the frictional characteristics, near-bed velocity profiles were obtained at the throat sections of two inlets, John's Pass and Blind Pass, on the Gulf Coast of Florida. A specially designed steel cage with five current meters in a vertical array was used to obtain the profiles in the bottom one meter of the flow. The profiles were found to be logarithmic but it is noted that, especially near the times of slack water, the effect of inertia becomes significant. However, during the major part of the flood or ebb flow period, frictional effects are dominant. In the fully rough regime of flow, the bed-shear stress - velocity relationship is found to follow the square law, with a constant, characteristic friction factor and Manning's n for each inlet. This friction factor is used in hydraulic formulas, based on uniform, steady open channel flow relationships, to obtain the tidal prism - throat cross-sectional area ratio, which is then compared with that obtained from flow discharge measurements. Agreements and discrepancies in the comparison are discussed. The relationship between the bed shear stress at incipient motion and the grain size at the bed is reviewed, and it is noted that the observed relationship at the two inlets does not agree with the well-known correlation of Shields for uniform sandy beds.

Discharge of a plane air jet into a blind pass

The existence of two discharge regimes of a plane jet into a blind pass was established experimentally. It is shown that the initial section is absent in such a jet and the range of the jet is commensurable with its width.