A Method to Extract Measurable Indicators of Coastal Cliff Erosion from Topographical Cliff and Beach Profiles: Application to North Norfolk and Suffolk, East England, UK

Recession of coastal cliffs (bluffs) is a significant problem globally, as around 80% of Earth’s coastlines are classified as sea cliffs. It has long been recognised that beaches control wave energy dissipation on the foreshore and, as a result, can provide protection from shoreline and cliff erosion. However, there have been few studies that have quantified the relationship between beach levels and cliff recession rates. One of the few quantitative studies has shown that there is a measurable relationship between the beach thickness (or beach wedge area (BWA) as a proxy for beach thickness) and the annual cliff top recession rate along the undefended coast of North Norfolk and Suffolk in eastern England, United Kingdom (UK). Additionally, previous studies also found that for profiles with low BWA, the annual cliff top recession rate frequency distribution follows a bimodal distribution. This observation suggests that as BWA increases, not only does cliff top recession rate become lower, but also more predictable, which has important implications for coastal stakeholders particularly for planning purposes at decadal and longer time scales. In this study, we have addressed some of the limitations of the previous analysis to make it more transferable to other study sites and applicable to longer time scales. In particular, we have automatised the extraction of cliff tops, toe locations, and BWA from elevation profiles. Most importantly, we have verified the basic assumption of space-for-time substitution in three different ways: (1) Extending the number or years analysed in a previous study from 11 to 24 years, (2) extending the number of locations at which cliff top recession rate and BWA are calculated, and (3) exploring the assumption of surface material remaining unchanged over time by using innovative 3D subsurface modelling. The present study contributes to our understanding of a poorly known aspect of cliff–beach interaction and outlines a quantitative approach that allows for simple analysis of widely available topographical elevation profiles, enabling the extraction of measurable indicators of coastal erosion.

Glacier changes between 1971 and 2016 in the Jankar Chhu Watershed, Lahaul Himalaya, India

ABSTRACTGlacier changes in the Jankar Chhu Watershed (JCW) of Chandrabhaga (Chenab) basin, Lahaul Himalaya were worked out based on Corona and Sentinel 2A images between 1971 and 2016. The JCW consists of 153 glaciers (>0.02 km2) with a total area of 185.6 ± 3.8 km2that include 82 glaciers with debris-covered ablation zone, comprising 10.9% of the total glacierized area as in 2016. Change analysis based on Corona (1971), Landsat (2000) and Sentinel 2A (2016) was restricted to 127 glaciers owing to the presence of cloud cover on 26 glaciers in 1971. A subset of glaciers was also mapped using Landsat Thematic Mapper (TM; 1989) image. The total glacier area decreased by 14.7 ± 4.3 km2(0.3 ± 0.1 km2a−¹). The number of glaciers in the JCW increased by four between 1971 and 2016 due to fragmentation. More recently (2000–16), recession rate has increased. Clean-ice area decreased by 21.8 ± 3.8 km2(0.5 ± 0.1 km2a−¹) while debris-covered ice increased by 7.2 ± 0.4 km2(0.2 ± 0.01 km2a−¹). Field observations of select glaciers also support derived recession trend in the JCW. Retreat rates in the JCW have been observed to be much lower than previously reported.

EVOLUTION FORECAST OF THE GULF OF GDANSK SAND SPITS IN 21 CENTURY

The forecasting algorithm consists of three main steps. They are estimating of sediment fluxes and sediment budget for the coast under investigation, consideration of possible sea level changes and the model SPELT for a longterm modeling of coastal profile evolution. It is shown that the total sediment budgets at the main part of the Vistula Spit and at the Hel spit are nearly balanced. The only exception is the end part of the Vistula spit where the budget deficit is about 13 m3m-1year-1. According to the most plausible scenario the recession rate of the stable coasts of two spits would be about 0,3 m/y in 2010‒2050 and 0,4 m/y in 2050‒2100. For the end part of the Vistula spit the controlling factor is the sediment deficit, whereas the changes in sea level are of secondary importance. In the period 2010‒2100, the coast is expected to retreat up to 160‒200 m.