ABSTRACT Mount Diablo State Park exemplifies many other conservation areas where managers balance the dual missions of protecting natural resources while providing public access. Roads and trails that crisscross the park are etched into the geomorphic surface, capturing and redirecting storm runoff, and presenting both a challenge for soil conservation and a consequence of construction and maintenance. We used field mapping, remote sensing, and modeling to assess erosion along the roads and trails in Mount Diablo State Park, which encompasses the headwaters of several urbanized watersheds. The field mapping in 2011 determined that 56% of the assessed roads and trails required either repair or reconstruction to control erosion and that ~67% of the culverts in the park required either repair or replacement. Aerial photography and modeling showed that other erosion (unrelated to roads or trails) preferentially occurred during wet periods, in specific lithologies, and on convergent slopes. Although lithology and climate drive slope-forming geomorphic processes, we found that the road and trail system (1) expanded the stream network with a capillary-like system of rills, (2) catalyzed prolonged erosion, and (3) altered the timing and pattern of sediment yield. In addition to water-driven erosion during wet periods, road and trail surfaces were subject to mechanical and wind erosion during dry periods. Spatially, dry erosion and runoff both conformed with and crossed topographic gradients by following the road and trail network. Road- and trail-induced erosion occurred across a wider range of rock properties and slope geometries than is typical for other erosion. Hence, the roads and trails have expanded the spatial and temporal boundary conditions over which geomorphic processes operate and, due to continual soil disturbance, have accelerated erosion rates. Although road density is a commonly used metric to rank road-related impacts at watershed scales, it misses both spatial variability and the opportunity to identify specific road and trail segments for remediation. We developed a spatially explicit scoring scheme based on actual erosion and the potential for sedimentation of discrete waterbodies. The data were incorporated into the park’s road and trail management plan in 2016.

Abstract Swelling and shrinking soils are soils that can experience large changes in volume due to changes in water content. This may be due to seasonal changes in moisture content, local site changes such as leakage from water supply pipes or drains, changes to surface drainage and landscaping, or following the planting, removal or severe pruning of trees or hedges. These soils represent a significant hazard to structural engineers across the world due to their shrink–swell behaviour, with the cost of mitigation alone running into several billion pounds annually. These soils usually contain some form of clay mineral, such as smectite or vermiculite, and can be found in humid and arid/semi-arid environments where their expansive nature can cause significant damage to properties and infrastructure. This chapter discusses the properties and costs associated with shrink–swell soils, their formation and distribution throughout the UK and the rest of the world, and their geological and geotechnical characterization. It also considers the mechanisms of shrink-swell soils and their behaviour, reviewing strategies for managing them in an engineering context, before finally outlining the problem of trees and shrink–swell soils.

No particular division between soil science and geology existed as the two sciences emerged at the end of the Enlightenment. An institutional chasm emerged at the end of the nineteenth century, when soil-related research and mapping were placed within the U.S. Department of Agriculture—despite interesting efforts to combine the two led by Eugene Hilgard of Berkeley and John Wesley Powell of the U.S. Geological Survey. It is likely that the resulting institutional separation contributed to an academic divergence between the fields, an unfortunate division for both sciences as they contend with emerging problems of societal significance. Soil is the derma of the Earth. It has been suggested that the key attributes that define a soil's quality are its texture, mineralogy, and organically derived components. These are in turn controlled by the variables of lithology, climate, biota, topography, and landform age. The Earth is tectonically active, and thus stable, level landscapes are rare. The rates and processes by which soil is eroded from sloping lands, and replaced by the disruption of underlying rock into soil material contribute to the nature of the soil composition. James Hutton long ago recognized that these counteracting processes are largely in balance in many locations, leading to a local quasi-steady state, or in the terms of environmental vernacular: sustainability. Soils on hillslopes also have certain features characteristic of resilience, a feature where changes in the relative rates of either erosion or soil production produce feedbacks that in turn control the rate of the opposing process. The major geological force capable of disrupting the soil and geomorphic resilience is the array of human activities, particularly cultivation. Cultivation removes vegetative cover and changes the mechanisms of soil transport, which can then rapidly accelerate erosion beyond the capability of soil production. Cultivation also greatly changes the rates of organic matter inputs and losses, generally resulting in large reductions in the soil's store of C, N, and other elements associated with humus. Yet much remains to be understood about these and other problems. Multidisciplinary work involving the reconnection of the geosciences and soil science will result in more holistic means of sustainably managing a cultivated planet.