Makowski, C.; Finkl, C.W., and Vollmer, H.M., 2017. Geoform and landform classification of continental shelves using geospatially integrated IKONOS satellite imagery.

Geomorphological characterization of coastal environments along continental shelves depends on accurate interpretation of mesoscale lithic and clastic benthic geoforms and landforms. Using the Geospatially Integrated Seafloor Classification Scheme (G-ISCS), cognitive visual interpretations of seafloor geoforms and their associated landforms were conducted along a diverse segment of the southeast (SE) Florida continental shelf. GeoEye IKONOS-2 satellite imagery provided the remotely sensed visual medium on which interpretations were based. With ESRI ArcGIS^® ArcMap software, classification maps were created from the cognitive interpretations to show spatial distribution results of geoform and landform features throughout the study area. Additionally, smaller-scale “call-out figures” documented specific geomorphological associations among the classified units. Analysis attribute tables compared and contrasted the abundance (i.e. number of classifying vector polygons) and calculated areas for each geoform and landform classified. It was determined that classification of geoform and landform benthic features along continental shelves can be achieved where water clarity conditions allow for the cognitive visual interpretation of such seafloor formations. Future studies may build upon the classification of continental shelf geoforms and landforms to integrate more transient biogeomorphological features of the marine environment (e.g., sediment distribution, biological species identification, density of flora and fauna present), thus creating a more detailed and inclusive classification of a selected coastal region.

Watson, P.J., 2017. Acceleration in European mean sea-level? A new insight using improved tools.

Research into sea-level rise has taken on particular prominence in more recent times owing to the global threat posed by climate change and the fact that mean sea level and temperature remain the key proxies by which we can measure changes to the climate system. Under various climate change scenarios, it has been estimated that the threat posed by the effects of sea-level rise might lead to annual damage costs across Europe on the order of €25 billion by the 2080s. European mean sea-level records are among the best time series data available globally by which to detect the presence of necessary accelerations forecast by physics-based projection models to elevate current rates of global sea-level rise (≈3 mm/y) to anywhere in the vicinity of 10–20 mm/y by 2100. The analysis in this paper is based on a recently developed analytical package titled “msltrend,” specifically designed to enhance estimates of trend, real-time velocity, and acceleration in the relative mean sea-level signal derived from long annual average ocean water level time series. Key findings are that at the 95% confidence level, no consistent or compelling evidence (yet) exists that recent rates of rise are higher or abnormal in the context of the historical records available across Europe, nor is there any evidence that geocentric rates of rise are above the global average. It is likely a further 20 years of data will distinguish whether recent increases are evidence of the onset of climate change–induced acceleration.

Warrick, J.A.; Ritchie, A.C.; Adelman, G.; Adelman, K., and Limber, P.W., 2017. New techniques to measure cliff change from historical oblique aerial photographs and Structure-from-Motion photogrammetry.

Oblique aerial photograph surveys are commonly used to document coastal landscapes. Here it is shown that adequate overlap may exist in these photographic records to develop topographic models with Structure-from-Motion (SfM) photogrammetric techniques. Using photographs of Fort Funston, California, from the California Coastal Records Project, imagery were combined with ground control points in a four-dimensional analysis that produced topographic point clouds of the study area's cliffs for 5 years spanning 2002 to 2010. Uncertainty was assessed by comparing point clouds with airborne LIDAR data, and these uncertainties were related to the number and spatial distribution of ground control points used in the SfM analyses. With six or more ground control points, the root mean squared errors between the SfM and LIDAR data were less than 0.30 m (minimum = 0.18 m), and the mean systematic error was less than 0.10 m. The SfM results had several benefits over traditional airborne LIDAR in that they included point coverage on vertical-to-overhanging sections of the cliff and resulted in 10–100 times greater point densities. Time series of the SfM results revealed topographic changes, including landslides, rock falls, and the erosion of landslide talus along the Fort Funston beach. Thus, it was concluded that SfM photogrammetric techniques with historical oblique photographs allow for the extraction of useful quantitative information for mapping coastal topography and measuring coastal change. The new techniques presented here are likely applicable to many photograph collections and problems in the earth sciences.

Wegner, C.E. and Ellis, J.T., 2017. The influence of sea-level rise on wave-energy dissipation and wave-driven currents at Buck Island Reef National Monument.

Modern Caribbean reefs have undergone significant degradation in the past century because of various anthropogenic stressors, which include climate-change-related impacts, hurricanes, and, potentially, sea-level rise. Degraded reefs will be unable to maintain sufficient vertical accretion with substantial increases in sea level, which will alter the hydrodynamics of these systems. A reduction in wave dissipation by reefs has the potential to shift the shorelines behind the reefs, potentially resulting in economic and habitat losses for tropical shorelines. This study focused on a barrier reef with low, live coral cover (<10%) and accretion rates comparable to current rates of sea-level rise in the region (∼1.7 mm/y). Tides served as a proxy for sea-level rise, with the spring high tide representing a future low tide. These findings indicate that at low tide, infragravity wave frequencies (0.004–0.04 Hz) dominate in the lagoon and are a function of wave breaking on the reef. At high tide, the infragravity waves are less prominent. Current velocities were higher at high tide, averaging 0.14 m s⁻¹ vs. 0.11 m s⁻¹ at low tide. The spectral current characteristics correlate with the infragravity wave frequencies and suggest that these waves are a driving force in lagoon circulation. Wave-energy transmission increased at high tide by 20–30% throughout the sampling period. These results suggest that with sea-level rise, infragravity band waves will be reduced and affect the stresses on the sea bed and sediment-transport processes, also allowing larger and more energetic waves to reach the shoreline.

Cho, A.; Cheong, D.; Kim, J.C.; Shin, S.; Park, Y.-H., and Katsuki, K., 2017. Delta formation in the Nakdong River, Korea, during the Holocene as inferred from the diatom assemblage.

The causes and succession of the Nakdong River delta formation related to sea-level change and precipitation in the early–middle Holocene were discussed based on diatom analysis. On the basis of ecology, stratigraphic changes of diatom flora were divided into five divisions, labeled zones I–V. According to the diatom assemblage, the first marine transgression occurred at about 10.5 ka at this research site. At that time, marine species gradually increased, and freshwater species had their highest values. This site was an estuary influenced by inputs of fresh and marine water until 9.8 ka (zone I). Zone II is dominated by bay and offshore species, meaning that sea level rose continuously after about 9.8 ka (zone II) when the Nakdong River mouth region was an inner bay. Then, the environment of this site changed to an outer bay after 8 ka (zone III) because of sea-level rise, which is supported by increasing numbers of oceanic species. At the end of this zone, at 6–7 ka, sea level highstand occurred. A prodelta began forming just after the highstand under slow sea-level rise (zone IV), and the delta front arrived at its present location at 5 ka by voluminous sediment input from the Nakdong River related to high precipitation during the Holocene Climate Optimum (zone V). After 5 ka, the delta front remained around its present site because of stable or decreasing sea level. Compared with other Asia deltas (Yangtze and Mekong), the initiation of the Nakdong River delta was delayed by about 1000–2000 years because of differences in relative sea-level changes.

Zarranz Elso, M.; Manent, P.; Luque, A.; Ramdani, M., and Robaina, R.R., 2017. Genetic description and remote sensing techniques as management tools for Zostera noltii seagrass populations along the Atlantic Moroccan coast.

Seagrass meadows provide an essential ecological service in coastal ecosystems worldwide, although they are sensitive to many human factors, as a serious global regression has been documented. During sampling along the Atlantic Moroccan coast, five coastal lagoons were found characterized by the presence of intertidal monospecific seagrass Zostera noltii meadows (from south to north, Nayla, Oualidia, Sidi Moussa, Moulay Bousselham, and Larache). Two descriptive methods used to characterize Z. noltii populations could be used as management tools for future monitoring implementations: (1) the estimation of surface area covered by Z. noltii meadows using remote sensing techniques and in situ field surveys, and (2) the genetic characterisation of Z. noltii populations using simple sequence repeats (microsatellites) as molecular markers. Results revealed that the Nayla lagoon showed the largest area covered by Z. noltii (269,868 m²) and the highest coverage rate (5.19%), while presenting the lowest genetic/genotypic diversity values (T = 36, Â = 3.58, G = 50; R = 0.544; H_e = 0.43). On the other hand, northern populations displayed lower rates of seagrass coverage (∼1%) and higher values of genetic/genotypic diversity. Further genetic characterization also revealed that Z. noltii populations seem to be highly isolated in three geographically independent regions: northern Morocco (R1, Larache and Moulay Bousselham), central Morocco (R2, Oualidia and Sidi Moussa), and southern Morocco (R3, Nayla), which should be considered independent management units. Both seagrass coverage rate and the genetic description of seagrass populations along the Atlantic Moroccan coast seem to be useful management tools that could be used to evaluate changes in seagrass meadows over time to further establish appropriate conservation strategies.

Niu, L.; van Gelder, P.H.A.J.M., and Vrijling, J.K., 2017. Physical limitation of phytoplankton dynamics in coastal waters.

Research on phytoplankton dynamics in coastal waters has frequently been proposed, motivated by environmental factors. The present study aims to develop a vertical phytoplankton model to investigate the phytoplankton variability in a case of the Jiangsu coastal waters, driven by physical limitation. The quality of the parameter estimation largely determines the reliability of the model output. Skill assessment results reveal that the vertical phytoplankton model is able to reproduce reliable predictions of phytoplankton biomass in this case. Significant correlations are established between phytoplankton biomass and chlorophyll a. The phytoplankton biomass is significantly correlated with the variables of temperature, light attenuation coefficient, and euphotic depth. A decrease of phytoplankton biomass corresponds to deeper water, excluding the case of Yangkou station. Particular attention has been paid to the depth-averaged phytoplankton biomass. In the presence of uncertainty, the bootstrap method is used to derive a 95% confidence interval of the estimate, as well as mean value, standard deviation, and skewness. The findings of this study contribute to understanding of the coastal ecosystem and coastal management.

Kawanisi, K.; Zhu, X.-H.; Fan, X., and Nistor, I., 2017. Monitoring tidal bores using acoustic tomography system.

Continuous measurements of flow velocities and suspended sediments were carried out in the Qiantang River (China) with extreme tidal bore conditions. Fluvial and coastal acoustic tomography systems (FATS/CATS) were used in the field studies simultaneously with acoustic Doppler current profilers (ADCPs) and optical backscatter (OBS) equipment. A couple of broadband transducers were installed diagonally across the river around 90 km upstream of the mouth. The length of the sound transmission line was 3050 m. Cross-sectional averaged velocities (V) collected by FATS/CATS enabled the authors to estimate important characteristics of the tidal bores (bore height and celerity). The changes in V recorded during the upstream movement of the bore ranged from 1.35 to 1.76 ms⁻¹. The height and celerity of the bore varied from 1.0 to 1.32 m and 7.59 to 8.29 ms⁻¹, respectively. Since a point/vertical measurement cannot represent a river's cross section, the ADCP data for velocity and water level (pressure) near the riverbank underestimated the bore height by 22% and 16%, respectively. The maximum suspended sediment concentration (SSC) was observed to have occurred approximately 1 h after the bore's arrival; the time lag between the maximum SSC and the bore front is considerably larger than the time lags in previous works. In the case of larger bores, the section mean SSCs, which were deduced from the sound attenuation of FATS/CATS due to suspended sediment, appeared to be appropriate. The time history of the velocity, measured by ADCPs, during the passage of the bore deviated from the normal velocity profile, i.e. the velocity magnitude decreased with an increasing height above the bed for the relaxation time of a few minutes following the arrival of the bore.

Kuang, C.; Liang, H.; Mao, X.; Karney, B.; Gu, J.; Huang, H.; Chen, W., and Song, H., 2017. Influence of potential future sea-level rise on tides in the China Sea.

This study investigates the diurnal and semidiurnal tidal responses of the entire China Sea to a potential rise in sea level of 0.5–2 m. A modified two-dimensional tidal model based on MIKE21 is primarily configured and validated for the present situation; then, three (0.5, 1, 2 m) sea-level rise (SLR) scenarios are simulated with this model. The predicted results show that the principal lunar semidiurnal (M₂) and diurnal (K₁) tidal constituents respond to SLR in a spatially nonuniform manner. Generally, changes of M₂ and K₁ amplitudes in shallow waters are larger than those in the deep sea, and significant tidal alterations mainly occur in the Bohai and Yellow seas, Jianghua Bay, Hangzhou Bay, Taiwan Strait, Yangtze River estuary, Pearl River estuary, and Beibu Bay. Possible mechanisms further discussed for these changes mainly relate to bottom friction decreasing, amphidromic point migration, and resonant effect change. Additionally, simulated changes in M₂ and K₁ amplitudes in response to three SLR scenarios imply that M₂ amplitude changes are proportional to the magnitude of SLR, whereas this proportionality does not hold for K₁ amplitudes. Identifying the response of tides in the China Sea to SLR not only increases our knowledge of tidal systems, but also assists in setting conservation requirements and management plans in coastal areas.

Flores-Cárdenas, F.; Hurtado-Oliva, M.A.; Doyle, T.W.; Nieves-Soto, M.; Díaz-Castro, S., and Manzano-Sarabia, M., 2017. Litterfall production of mangroves in Huizache-Caimanero lagoon system, México.

The ecological legacy of the Huizache-Caimanero lagoon system has long been known as a trophically rich and productive ecosystem that supported artisanal fisheries of local and regional importance; however, a decline in fisheries' yields has been observed in recent decades. Mangroves are a fundamental component of this ecosystem, though data records and field studies are lacking in describing their structure and seasonal characteristics. Mangrove litterfall production was monitored during 2012–13 and described for the dominant species, Avicennia germinans (L.) Stearn and Laguncularia racemosa (L.) C.F. Gaertn. Forest surveys and monthly litter collections were obtained along a latitudinal gradient within the larger lagoon system to characterize the forest structure, leaf biomass, and related biological indicators (chlorophyll a concentration and Normalized Difference Vegetation Index [NDVI] estimated on leaf tissues). Results showed that structural characteristics (diameter at breast height, basal area, height, and crown diameter) were greater in Huizache, corresponding to patches with a dominance of A. germinans, while higher stem density was recorded for L. racemosa in Caimanero, comparatively similar to other mangrove habitat in NW Mexico. Litterfall was highest from May to October for both species. Litterfall production was also higher overall in 2012 in comparison to 2013, possibly corresponding with meteorological differences, most notably wind conditions. Annual litterfall production was similar by species across northern and southern Sinaloa. A contrast of the NDVI by site and species showed a wide interval, including low values for A. germinans, suggesting stress conditions for this species.

Xu, Q.; Zhang, S.; Cheng, Y., and Zuo, J., 2017. Interannual feature of summer upwelling around the Zhoushan Islands in the East China Sea.

The interannual feature of summer upwelling around the Zhoushan Islands off the Zhejiang coast over the East China Sea (ECS) shelf has been investigated using multiscale ultrahigh resolution (∼1 km) sea surface temperature (SST) data during the period from 2003 to 2014 and an auxiliary Pathfinder SST data set with a relatively low resolution of 0.05° × 0.05° during 1985–2002. Coastal upwelling usually occurs during April to June, reaches its peak intensity in July and August, and starts to decay in September. It has not strengthened or weakened obviously during the past 30 years. The influence of sea winds on the interannual variation of the summer upwelling is analyzed using the National Oceanic and Atmospheric Administration/National Climatic Data Center blended sea surface wind data. Results demonstrate that the sea wind over the ECS, which is part of the East Asian summer monsoon (EASM) system, plays a dominant role in determining the changes in upwelling intensity, and the southeasterly wind is favorable for the formation of the summer upwelling around the Zhoushan Islands. The El Niño–Southern Oscillation (ENSO) modulation of the interannual variability of the upwelling intensity is complex because of the unstable correlation between the EASM and the ENSO cycle.

Restrepo, J.C.; Escobar, J.; Otero, L.; Franco, D.; Pierini, J., and Correa, I., 2017. Factors influencing the distribution and characteristics of surface sediment in the Bay of Cartagena, Colombia.

This study evaluated patterns of coastal sediment movement and deposition under different seasonal conditions (warm and cold phases of the El Niño–Southern Oscillation [ENSO] and normal conditions) in Cartagena Bay, Colombia. A calibrated numerical model (MOHID modeling system) was applied to assess the spatial distribution of sediments transported by the Canal del Dique to the bay and studied the spatial distribution and major textural characteristics of 234 surface sediment samples. Currents in the Bay of Cartagena are controlled primarily by the strength and direction of the wind. Model results show major sediment deposition in the southern sector of the bay during the dry season. More homogenous spatial distribution of sediments throughout the Bay of Cartagena occurs with an increase in river inputs from the Canal del Dique. These patterns were enhanced or weakened, respectively, by cold and warm phases of the ENSO. Predominant sediments were medium size (ϕ = 5.35 ± 1.2), poorly sorted (σ = 1.63 ± 0.8), with notable asymmetry (Sk = −0.052 ± 0.2) and kurtosis (k = 0.84 ± 0.4). Sediments with lower sand content (<5%) are located along a latitudinal axis from the Canal del Dique delta to the western end of the island of Tierrabomba. CaCO₃ content of the sediments is <10%. Water and sediment flow, controlled by the Canal del Dique, has favored the transport and deposition of poorly sorted, symmetric, and mesokurtic mud in most of the Bay of Cartagena. As a result, autogenous calcareous sediments have been covered by fine terrigenous sediments that were delivered via the Canal del Dique. Thus, the channel plays a more prominent role in sediment transport and deposition in the Bay of Cartagena than thought previously.

Dai, P.; Zhang, J., and Zheng, J., 2017. Predictions for dynamic tidal power and associated local hydrodynamic impact in the Taiwan Strait, China.

Dynamic tidal power systems are a new alternative to tidal barrage systems for extracting tidal potential energy. In these systems, a dike perpendicular to the coast is used to create a water head, which is then converted into electricity. In this study, a mathematical model was developed using Delft3D FLOW to evaluate the power output and hydrodynamic consequences of a dynamic tidal power system in the Taiwan Strait. The model is composed of a coarse-resolution subdomain and a fine-resolution subdomain, and a domain decomposition technique was adopted to simulate flow through the interfaces of these subdomains. In the simulation, the mean power reached its maximum (0.89 GW) at a dike open ratio of 8%. The power system strongly affected the M₂ tide in the local region. Overall, the amplitude of the M₂ tide increased on the NE side of the system and decreased on the SW side; specifically, at an open ratio of 8%, the amplitude increased (decreased) by 0.25 m on the NE (SW) side. The variations in the tidal system decreased with increase in the open ratio. The effect of the system on the K₁ tide was weaker than that on the M₂ tide.

Zhang, Y.; Liang, S., and Sun, Z., 2017. Measurement and numerical study of vertical mixing microstructure in the Bohai Strait.

Vertical mixing plays an important role in three-dimensional hydrodynamic and water quality models. The purpose of this study is to analyze the characteristics of vertical mixing in strong tidal waters and the simulation capability of turbulence closure models under the influence of flow velocity variations and temperature distribution. The distribution characteristics of thermocline and vertical mixing in the Bohai Strait is analyzed through field observations conducted using the Turbulence Ocean Microstructure Acquisition Profiler in summer. Based on the measured temperature and mixing data, three-dimensional numerical models are established with various temperature distribution and turbulence closure schemes. It is concluded that the vertical eddy viscosity K_m and the thermal-diffusion coefficient K_h, using the Mellor and Yamada level 2.5 (MY-2.5) and the k-ϵ turbulence closure models, exhibit a significant change with change in flow velocity and a time delay compared with the flow velocity process disregarding the effect of wind. The vertical mixing coefficients due to changing flow velocity under isothermality or temperature stratification could vary by one or two orders of magnitude, respectively. Simulated mixing coefficients using two different turbulence closure models exhibit different variations under isothermality and temperature stratification and have a significant discrepancy with the measurement data. Thermocline evolution is compared using three different methods for K_m and K_h. It is found that the temperature mixes gradually using constant mixing coefficients in the vertical direction. When the mixing coefficients are computed with the MY-2.5 and k-ϵ models, the temperature mixes rapidly in the shallow-water zone. The mixing of temperature is even faster in the lower layer than in the upper layer in the deepwater zone, leading to the thermocline moving toward the upper layer. Moreover, the temperature mixes faster in the k-ϵ model than in the MY-2.5 model.

Alfredini, P.; Arasaki, E., and de Melo Bernardino, J.C., 2017. Santos sea outfall wastewater dispersion process: Physical modeling evaluation.

To be environmentally sustainable, the ocean disposal of domestic sewage via a sea outfall must be carefully studied, such as previous modeling of waste-plume dispersion processes, for environmental impact assessments. A scale model, reproducing the Santos Bay and Estuary was calibrated at the Hydraulic Laboratory of Polytechnic School, University of São Paulo, Brazil. The complete modeling of this large estuarine system used numerical and scale models, which were all related to each other. Such an overall model, composed of individual hydraulic and numerical components, is called a hybrid model. It combines the advantages of both model components and adequate field survey measurements and is particularly important for simulating the plume dispersion process in Santos Bay. The goal hereby is to present a performance comparison of the outfall plume dispersion for improvement in the length of the Santos outfall. The study required preliminary numerical simulations in the near-field mixing processes to define the boundary conditions in the beginning of the far field. In addition, numerical simulations in the far field were required to reproduce the wind effect for calibrating the scale model of the air-tunnel hydro-aerodynamics. Scale model runs, using an advanced methodology for dye-plume monitoring, were calibrated with a numerical model of the plume dispersion and validated with independent runs of another numerical model of plume dispersion and comparison with satellite images of the plume. The conclusion was that an enlargement of 1 km of the outfall would reduce the risk of the plume returning.

Lonard, R.I.; Judd, F.W.; Summy, K.R.; DeYoe, H., and Stalter, R., 2017. The biological flora of coastal dunes and wetlands: Avicennia germinans (L.) L.

Avicennia germinans (L.) L. is a pantropical, subtropical, and occasionally warm-temperate mangrove species that occurs on shorelines that have a broad horizontal tidal range. Also known as black mangrove, stands typically develop under anoxic, water-logged conditions in substrates of silt or clay. Black mangrove can tolerate salinity values ranging from 0 to 90 parts per thousand. Salt is excreted from salt glands on both leaf epidermal surfaces, and aerosol salt spray and salt crystals are frequently observed on the upper leaf epidermis. Avicennia germinans is viviparous. The embryos have no dormancy requirements, and there is no seed bank. This mangrove species has the northernmost distributional range of any mangrove species in North America. It occurs in Louisiana and northern Florida. Color-infrared photography and airborne video imagery techniques have been used successfully to map stands of black mangrove on subtropical coastal shorelines. Reforestation efforts using seedlings and saplings have been successful in several areas of the tropics and subtropics. Avicennia germinans stands play an important role in ecosystem functions as a natural barrier to coastal erosion caused by tropical storms, as habitat for a wide range of organisms in intertidal food chains, and as a carbon repository.

Knight, J.; Eslami-Andargoli, L.; Dale, P., and Fry, B., 2017. State changes in tropical intertidal systems: A palaeo-ecological approach.

The aim was to review ecosystem state changes and the role of palaeo-ecological tools with application to intertidal subtropical and tropical intertidal wetlands. These systems are especially vulnerable to stress from sea-level change, climate change, and development activities. Responses to stress can lead to significant state changes with the system passing thresholds, potentially beyond recovery. Indicators of state changes and approaching tipping points include a critical slowing down following perturbation signalled by, for example, slowing recovery rates, increased attribute variance, and changed skewness. To identify such changes, data are needed for the relevant variables such as vegetation, sea level, and sediment processes so as to observe the indicative changes and their timing. Because changes may be relatively slow in ecological terms, very long-term data are needed to inform management about future likely states or thresholds so that mitigation or adaptation can be planned. One approach is to use palaeo-ecological data. These data are relatively scarce in tropical intertidal systems. This paper reviews a range of palaeo-indicators. These include state indicators (pollen, foraminifera, and diatoms), stable isotope analysis, and stratigraphy and temporal indicators involving sediment dating. Each is potentially useful, although there are uncertainties related to, for example, the redistribution organic matter in sediment cores. In conclusion, it is recommended that integrating or combining several indicators can assist in triangulating results, thereby increasing confidence in their interpretation. It is also suggested that data, if available, can be retrofitted to assess at least some of the state change indicators, such as data variance and skewness.

Xu, C. and Dong, P., 2017. A dynamic model for coastal mud flocs with distributed fractal dimension.

Suspended sediments entrained from muddy estuarine and coastal areas usually contain a large amount of mud flocs of various sizes and densities. The size and settling velocity of these mud flocs are unsteady and may vary over a large range. In most theoretical descriptions the mud flocs are treated as self-similar fractal entities with the fractal dimension being considered as either a constant or a simple function of the mean floc size. This deterministic description of fractal dimension has recently been found to be inadequate as for a given size class; fractal dimension of the mud flocs is not a single value but is distributed over a certain range. To address this problem this paper proposes a new flocculation model for the temporal evolution of floc size by considering the fractal dimensions for a given floc size class D to be normally distributed and validates the model with available experimental data. The proposed model is found to perform better in predicting the temporal evolution of floc size than that based on a single fixed floc-size-dependent fractal dimension, especially under high shear conditions and with large equilibrium floc size.