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Black, K.P.; Baba, M.; Mathew, J.; Kurian, N.P., and Ilic, A., 2021. Guidelines to prepare India's coast for climate change. Journal of Coastal Research, 37(6), 1117–1129. Coconut Creek (Florida), ISSN 0749-0208. India's first coastal protection guidelines for climate-change adaptation are described. The guidelines are holistic, recognizing the links between engineering, economic, physical, legal, social, environmental, and governmental intricacies. Robust protection solutions under climate change for millions of coastal residents may occur only when all these facets are improved within the complex regulatory, budgetary, and practical circumstances in India. Fifty-seven specific guidelines are presented in nine categories ranging from administrative to best-practice coastal protection. An "environmental softness ladder" that ranks coastal protection methods was developed as a scientific tool to guide policy development and project implementation. "Minimum floor level" for safe building was defined for each Indian coastal state using climate-change data produced for the study by Indian and international institutes. Beaches are more stable when the net sediment transport fluxes are close to neutral. "Grand schemes," which make large-scale changes to the coast rather than continuing with piecemeal localised works, are recommended. With diverse dynamics over a long coastline in India, the 4-year study engaged an exceptionally large number of experts, agencies, government bodies, development partners, and other stakeholders. [ABSTRACT FROM AUTHOR]

Black, K.P.; Kulkarni, K.B.; Naik, G.B.; Naik, M., and Mathew, J., 2021. Improving training wall orientation at river and estuary entrances. Journal of Coastal Research, 37(3), 484–493. Coconut Creek (Florida), ISSN 0749-0208. Natural river and estuary entrances adjust in response to the prevailing sedimentary and hydrodynamic environment. In India, during the monsoon rains, the ebb jet can be very large, firing water and sediments along a variable orientation to create the associated ebb deltas. However, once the entrance is trained onto a fixed alignment, this powerful jet "pump" can have adverse impacts. Due to downdrift erosion caused by the entrance training walls at the Old Mangalore Port (Karnataka, west coast of India), the breakwater was modified to reorient the ebb jet in the direction of the longshore drift. The goal was to beneficially use the natural pumping action to drive sand across the entrance without mechanical assistance. Three years of monitoring revealed improvements in downdrift beaches and navigational safety, while maintenance dredging has ceased. The entrance region has deepened by 854,166 m3 after reorienting the ebb jet over the period from October 2017 to February 2020. In contrast, the entrance shoaled by 160,305 m3 over the period from September 2008 to October 2017. The results are relevant to river and estuary entrances with moderate to strong river flows and/or tidal prism. [ABSTRACT FROM AUTHOR]

Black, K.P.; Reddy, K.S.K.; Kulkarni, K.B.; Naik, G.B.; Shreekantha, P., and Mathew, J., 2020. Salient evolution and coastal protection effectiveness of two large artificial reefs. Journal of Coastal Research, 36(4), 709–719. Coconut Creek (Florida), ISSN 0749-0208. Two offshore reefs constructed at Ullal, Karnataka, on India's west coast, are exhibiting coastal protection benefits. The reefs are large (275 m and 325 m long) and uniquely placed well offshore (600 m and 760 m) in intermediate depths (6 and 7 m below chart datum). Their crests are between low-tide and midtide level. Bathymetric and beach surveys show that sand has accumulated to form two evolving shoreline salients, which are currently 2–3 times the length of the reefs. The salients have grown underwater on the inner shelf to create a large sand-retention zone up to 1 m thick and stretching from the beach to the distant lee of the reefs. The reefs are the first protection structures that have restored the beaches and enhanced sand storage over this broad, severely eroded region, both inshore and on the inner shelf. Prior rubble-mound rock revetments (seawalls) and 50–70-m-long groynes failed to restore the beach in stormy monsoon conditions, while the inner shelf continued to erode. The reefs were designed using a combination of computer simulations, measurements of natural salients in India, and empirical relationships. The methodology that led to the reef shapes/sizes and their position offshore is discussed, along with monitoring results. [ABSTRACT FROM AUTHOR]

Existing cross-shore sediment transport models for two-dimensional surf zone bathymetries almost invariably predict offshore-directed sand transports and bar migrations during storm conditions. However, onshore-directed suspended sediment fluxes and associated nearshore bar migration were observed during recent field experiments on a gently sloping beach on the Danish North Sea coast. Field measurements of suspended sediment flux obtained during three experiments on two different beaches are used to parameterize the observed fluxes. This parameterization predicts suspended sediment transport due to incident waves and undertow across bars in two-dimensional surf zones. First, a non-dimensional sediment flux index is formulated which describes the tendency towards net onshore or offshore transport and the strength of that tendency. The non-dimensional formulation circumvents the problem of measurement inconsistencies due to varying elevations of sediment concentration sensors relative to the bed. The index is found to depend upon the undertow velocity, the incident wave skewness and the cross-correlation between orbital velocity and sediment concentration. However, some of these parameters are difficult to predict, particularly in barred surf zones and therefore, the independent variables are recast in terms of a set of more easily obtainable parameters. The sediment flux index depends on a combination of the following: non-dimensional bed shear stress (the Shields parameter), relative water depth, wave orbital velocity, relative wave height and bed slope. Finally, a formulation of suspended sediment transport across bars is obtained by linking the flux index with a parameterization of the sediment concentration/distribution in the water column. These concentrations are found to depend on non-dimensional bed shear stress, relative wave height and water depth. The formulation predicts a tendency for onshore-directed sediment transport due to incident waves on gently sloping beaches and/or with large bed shear stresses. On steeply sloping beaches and/or in the inner part of the surf zone there is a tendency towards offshore sediment transports due to the undertow. [Copyright &y& Elsevier]

A placement mound of 47,000 m³ dredged-sand was constructed at a nearshore site in water depths of 5- 10 m on a predominantly rocky seabed down-drift of Port Taranaki, New Zealand. Empirical information on the manner and rate of sediment flux from the mound was gained through repetitive hydrographic and side-scan sonar surveys over an 18-month period, and directional wave/current measurements over a 12- month period. The results of the monitoring show a spatially uniform pattern of erosion from the mound, with rates of erosion that are reasonably well correlated (R²=0.42) to the wave height (raised to the 3rd power). Measured volumes at the mound show a highly correlated (R²=0.83) linear decrease with time, and after 18-months some 29% of the placed volume had been eroded. Side-scan sonar images reveal that rocky areas adjacent to the mound did not become inundated with sand, nor did the placed material migrate as a contiguous body. The data suggest that littoral transport to and from the placement region is primarily by sediment suspension, rather than bedload. An energetic wave climate was observed, with significant wave heights of up to 4.47 m and persistent long-period (12-14 second) swells. A 100° range in wave directions was recorded, although 72% of data were within a 40° directional window. Near-bed currents had a broad directional distribution and reached a maximum velocity of 29.24 cms-1, with a mean value of 5.72 cms-1. No direct relationship between mound erosion and the current regimen was found. The relatively slow erosion of the mound, despite high sediment entrainment potentials, is attributed to the gradual re-establishment of the pre-placement sedimentary equilibrium under a dynamic and multi-directional sediment flux. Numerical simulations of the nearshore circulation concur with measured currents and further indicate the placement region is in a zone of moderate and variable flow. This ultimately attenuates the facility of the region to disburse the placed sediments, even though prior refraction modelling had shown the site to be in a zone of relatively high wave energy. [ABSTRACT FROM AUTHOR]