Long term planning for flood risk management in coastal areas requires timely and reliable information on changes in land and sea levels. A high resolution map of current changes in land levels in the London and Thames estuary area has been generated by satellite-based persistent scatterer interferometry (PSI), aligned to absolute gravity (AG) and global positioning system (GPS) measurements. This map has been qualitatively validated by geological interpretation, which demonstrates a variety of controlling influences on the rates of land level change, ranging from near-surface to deep-seated mechanisms and from less than a decade to more than 100,000 years' duration.During the period 1997 to 2005, most of the region around the Thames estuary subsided between 0.9 and 1.5 mm a -1 on average, with subsidence of thick Holocene deposits being as fast as 2.1 mm a -1 . By contrast, parts of west and north London on the Midlands Microcraton subsided by less than 0.7 mm a -1 , and in places appear to have risen by about 0.3 mm a -1 . These rates of subsidence are close to values determined previously by studies of Quaternary sequences, but the combined GPS, AG and PSI land level change data demonstrate a new level of local geological control that was not previously resolvable.

Journal of Flood Risk Management AbstractLong term planning for flood risk management in coastal and estuarine areas requires timely and reliable information on changes in land and sea levels. In this paper we describe how we have produced a detailed, high resolution map of current changes in land levels for the Thames region, and carried out a new assessment of the changes in sea level relative to the land along the Thames Estuary over the past few decades / past century. We conclude the paper by considering the potential benefits of extended monitoring for the long term planning of flood and coastal defences in that region.

Ground affected by periglacial and glacial processes can be among the most variable formed by nature. Previous chapters have graphically illustrated this variability and explained the topographic and sedimentary associations to be expected within former and present-day cold regions. This chapter shows how that background is needed to design and execute an investigation for predicting either the ground response to engineering change or the volumes of material the ground contains. Such an investigation of the ground is also needed to explain its current and former state of stability on slopes and its natural groundwater flow.The starting point of any such investigation is a conceptual model of the ground which subsequent investigation tests and refines; investigations conducted without such a model can easily become sterile and expensive exercises in collecting data. Such a model starts with knowledge of landscape, cold climate processes and their products, initially refined with the aid of a desk study. This then develops with each phase of the investigation, starting with what is known via desk studies, and progressing through what can be readily seen by walkover surveys and shallow investigations, including surface geophysics and remote sensing, all leading towards a model that can be tested directly by various intrusive investigations. Techniques appropriate for such investigations, including sampling, in glaciated and frost-disturbed ground both onshore and offshore are reviewed.Great care must be taken with the description of coarse materials, glaciotectonic structures and the materials within them; a unique feature of this chapter is the correlation it presents between the engineering descriptions of glacial sediments, as used in ground engineering, and the descriptions used by glacial sedimentologists for the same materials. Water levels are also obtained during these investigations, and in these types of ground they are often misinterpreted by applying thinking more appropriate to aquifer hydrogeology. A surprising feature of glaciated ground is its low permeability overall, and the correct interpretation of heads measured in such environments is often that for aquitards rather than aquifers.The initial conceptual model starts with little more than an idea and a broad outline, and evolves as the investigation progresses. It should continue to evolve throughout construction as more and more of the ground is exposed and its behaviour is better known; in this way, the ground model can be thought of as a living document, especially appropriate in such variable ground. The chapter concludes with a review of how this information can be brought together as three-dimensional models that effectively communicate the knowns and unknowns of a volume of ground and their associated risks, in both deterministic and probabilistic ways.

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