ABSTRACT Houston, J.R., 2021. Sea-level acceleration: Analysis of the world's high-quality tide gauges. Journal of Coastal Research, 37(2), 272–279. Coconut Creek (Florida), ISSN 0749-0208. Coastal sea-level acceleration is analyzed using all of the world's high-quality tide gauge recordings with lengths of at least 75 years that extend through 2017–19. Earlier studies have demonstrated that tide gauge recordings of at least 75 years in length are required to reduce the effects of multidecadal variations on acceleration. There are 149 tide gauge records that meet the criteria. Mean and median sea-level accelerations based on these gauges were 0.0128 ± 0.0064 mm/y 2 and 0.0126 ± 0.0080 mm/y 2 , respectively, both at the statistically significant 95% confidence level. The mean acceleration is larger than that of earlier studies that analyzed fewer gauges or considered record lengths shorter than 75 years.

ABSTRACT Houston, J.R., 2017. Shoreline change in response to sea-level rise on Florida's west coast. Shoreline position measurements about 300 m apart have been made along the Florida shoreline from the 1800s. There has been net shoreline advance during this time on the Florida E and SW coasts, but the Florida W coast has had net recession. Information is available on factors causing shoreline change on the Florida W coast, including sea-level rise, beach nourishment, loss of sediment to inlets, offshore dredged-sediment disposal, longshore sediment transport, and long-term, onshore sediment transport. Estimates are presented on the contributions these factors have made to shoreline change since the 1800s along 334 km of shoreline in seven west Florida counties. Summing the contributions results in net shoreline recession that agrees with measured recession within standard deviation confidence intervals in each of the counties and for the total shoreline. Sea-level rise is shown to have accounted for less than 20% of the magnitude of all shoreline change (including shoreline advance produced by beach nourishment). Projections of future shoreline change are made using sea-level rise projections of the Intergovernmental Panel for Climate Change (IPCC), along with projections of shoreline change that would be produced by each of the factors. It is shown that beach nourishment quantities at past rates can offset the recessional effects of sea-level rise for most IPCC sea-level rise projections from 2016 to 2065 and 2016 to 2100. A modest increase in nourishment can offset shoreline recession from sea-level rise based on the worst-case IPCC sea-level rise scenario.

ABSTRACT Houston, J.R., 2016. Discussion of: Boon, J.D. and Mitchell, M., 2015. Nonlinear change in sea level observed at North American tide stations. Journal of Coastal Research , 31(6), 1295–1305. Boon and Mitchell determined sea-level acceleration using monthly averaged relative mean sea-level data from 45 U.S. tide stations and 1 Canadian station for 1969–2014. Their methods of analyzing tide gauge data are interesting and useful. However, they then projected sea-level change for 58 years from 1992–2050 based on constant accelerations calculated from these 46-year records. Calculations of acceleration based on records as short as 40–50 years are well known to be heavily corrupted by decadal variations in sea level. For example, Boon and Mitchell showed that 3–6 year variations in record length or time period resulted in what they said were “dramatic change” in calculated acceleration. Therefore, the accelerations they calculated did not even remain constant for a few years, making long-term projections based on them untenable. Boon and Mitchell projected significant sea-level falls from 1992 to 2050 on the coasts of California, Oregon, and Washington, in stark contrast with projections of significant rises by the National Research Council. Similarly, their projections on the U.S. Atlantic and Pacific coasts differ remarkably from projections of the Intergovernmental Panel on Climate Change. Acceleration calculated from 46-year records varies significantly through time, and it is not valid to fix an acceleration value and project it into the future as if it were a constant.

ABSTRACT Houston, J.R. and Dean, R.G., 2016. Erosional impacts of modified inlets, beach encroachment, and beach nourishment on the east coast of Florida. Most of the 21 inlets along the 588 km of sandy shoreline on the Florida east coast have been modified, primarily to improve navigation efficiency and safety. These modifications have usually caused significant downdrift shoreline erosion. Shoreline change data for the Florida east coast during the period from about 1869 to 1971, which was before widespread beach nourishment, are analyzed. Modified inlets during this period impacted about 25% of the shoreline and conservatively caused about 70% of the shoreline area recession and about 75–85% if counties are excluded that did not have modified inlets that caused net downdrift recession. During this same period of about 100 years, the remaining 75% of the shoreline advanced on average 46 m seaward. However, before Florida began regulating coastal construction, development often encroached on accreting shorelines, effectively masking much of the accretion. From about 1971 to 2007, a period of widespread beach nourishment, only about half of the nourishment sand was placed on eroding shorelines. About half was placed on shorelines that accreted or were stable from about 1869 to 1971 but where encroachment by development made the nourishment necessary. Over half of the recession caused by modified inlets still exists. The criteria used by the Florida Department of Environmental Protection to designate the erosional state of Florida east coast beaches was found to be problematic, since it currently designates 65% of this shoreline as eroding when only 20% eroded during the period of widespread beach nourishment from about 1971 to 2007.

ABSTRACT Houston, J.R., 2015. Shoreline response to sea-level rise on the southwest coast of Florida. The state of Florida has a unique database of shoreline position measured about every 300 m and dating back to the mid-1800s that presents an opportunity to determine the effects of sea-level rise on shoreline position. In addition to sea-level rise (Bruun rule initially assumed), data are available on the southwest coast of Florida for other factors contributing to shoreline change, including beach nourishment, inlet shoal change, and longshore sediment transport. The sum of these factors should have caused significant shoreline recession, but instead the average shoreline position of this coast was stable during the early period from the 1800s to the 1970s (prior to beach nourishment) and strongly accretive from the 1800s to the 2000s. When the Bruun rule is used, shoreline change predicted by the sum of the factors compares poorly with measured data, but it compares quite well when the Dean equilibrium concept is used. The Dean equilibrium concept says that under wave action and with sufficient available offshore sand, shorelines will advance with sea-level rise due to onshore sand transport. Long-term shoreline change data for most of the Florida east coast and the Dutch central coast also support the Dean equilibrium concept. The source of the onshore sand transport in southwest Florida is identified. Sea-level rise results in long-term shoreline advance rather than recession for shorelines with sufficient onshore sand movement from beyond closure depth to the active profile, probably during episodic storms.

ABSTRACT Houston, J.R. and Dean, R.G., 2014. Shoreline change on the east coast of Florida. A shoreline change data base for Florida dating back to the mid-1800s is unique in the United States, and perhaps the world, with thousands of shoreline change measurements at a nominal spacing of 300 m. Moreover, data are available on factors contributing to shoreline change, including beach nourishment, disposal of dredged sand outside the littoral zone, cutting of new inlets and subsequent growth of ebb shoals, and longshore sediment transport into and along the east coast of Florida. Effects of relative sea level rise can be estimated using the Bruun Rule. These factors should have caused significant shoreline recession since the mid-1800s, but instead, the east coast of Florida has experienced significant average shoreline advance. The formation of carbonate sand is shown not to account for this difference. Onshore transport of sand from beyond closure depth, probably during episodic storm events, is the only possible source of the large quantity of sand that has advanced on average the shoreline of Florida's east coast. For shorelines with significant offshore deposits of sand, it is possible that sea level rise in conjunction with wave action contributes to onshore transport and shoreline accretion.

ABSTRACT Houston, J.R., and Dean, R.G. 2013. Effects of sea-level decadal variability on acceleration and trend difference. Previous research has shown that sea-level acceleration determined from individual tide gauge records has remarkably large scatter as record lengths decrease due to decadal variations in sea level. We extend previous data sets to the present time and find even greater acceleration scatter. Using analytic solutions, sinusoidal oscillations with amplitudes and periods of typical decadal variations are shown to basically account for the relationship between record length and both acceleration and trend difference. Data show that decadal variations will obscure estimates of underlying accelerations if record lengths of individual gauges are not greater than at least 75 years. Although worldwide data are less affected by decadal variations than individual gauge data, decadal variations still significantly affect estimates of underlying accelerations, in particular for record lengths less than about 60 years. We give two examples of recent studies that use record lengths of about 30 to 60 years to determine acceleration or related trend difference. Previous authors dismissed the importance of decadal variations on their results and, as a result, reached invalid conclusions.