Stanley W. Trimble

The cow as a geomorphic agent — A critical review

Cows are important agents of geomorphological change. On the uplands, heavy grazing compacts the soil, reduces infiltration, increases runoff, and increases erosion and sediment yield. However, light and moderate grazing have effects that are much less significant. In riparian zones, grazing decreases erosional resistance by reducing vegetation and exposing more vulnerable substrate. Trampling directly erodes banks, thus increasing turbulence and consequent erosion. Future studies should be framed within the hydroclimatological, edaphic and geomorphological dimensions of the areas being studied so that controlling variables may be more readily isolated. We believe that both empirical studies and deterministic modeling can provide insights as to the effects of grazing on geomorphology.

Changes in Sediment Storage in the Coon Creek Basin, Driftless Area, Wisconsin, 1853 to 1975

For any time period, total basin sediment yield can be used to make reliable estimates of upland erosion rates only when no significant change in sediment storage is in progress. In the case of Coon Creek, almost 50 percent of human-induced sediment has historically gone into floodplain storage and less than 7 percent has left the basin. However, some of the stored sediment is becoming mobile, and the present yield per unit area may actually be increasing downstream with the augmentation coming from the storage loss.

Stream channel erosion and change resulting from riparian forests

Forested stream banks, compared to grassed ones, can destabilize stream channels by promoting erosion. Four reaches of Coon Creek, Wisconsin, each with long-term grassed and forested subreaches were examined. Grassed reaches were narrower and had smaller channels (bankfull cross sections) than forested reaches, suggesting that grassed channel reaches stored about 2100 to 8800 m 3 more sediment per kilometre than forested reaches. Available evidence suggests that conversion of riparian forests to grass would allow storage of sediment along channels, possibly decreasing downstream sediment yields. These findings are important as many grassed riparian corridors are rapidly reverting to forest because of economic conditions and governmental policies.

Reclaiming freshwater sustainability in the Cadillac Desert

Increasing human appropriation of freshwater resources presents a tangible limit to the sustainability of cities, agriculture, and ecosystems in the western United States. Marc Reisner tackles this theme in his 1986 classic Cadillac Desert: The American West and Its Disappearing Water. Reisners analysis paints a portrait of region-wide hydrologic dysfunction in the western United States, suggesting that the storage capacity of reservoirs will be impaired by sediment infilling, croplands will be rendered infertile by salt, and water scarcity will pit growing desert cities against agribusiness in the face of dwindling water resources. Here we evaluate these claims using the best available data and scientific tools. Our analysis provides strong scientific support for many of Reisners claims, except the notion that reservoir storage is imminently threatened by sediment. More broadly, we estimate that the equivalent of nearly 76% of streamflow in the Cadillac Desert region is currently appropriated by humans, and this figure could rise to nearly 86% under a doubling of the regions population. Thus, Reisners incisive journalism led him to the same conclusions as those rendered by copious data, modern scientific tools, and the application of a more genuine scientific method. We close with a prospectus for reclaiming freshwater sustainability in the Cadillac Desert, including a suite of recommendations for reducing region-wide human appropriation of streamflow to a target level of 60%.

THE DISTRIBUTED SEDIMENT BUDGET MODEL AND WATERSHED MANAGEMENT IN THE PALEOZOIC PLATEAU OF THE UPPER MIDWESTERN UNITED STATES

The distributed sediment budget model describes the complex sediment storage fluxes of three basin zones—tributaries, upper main valley and lower main valley—in the Paleozoic Plateau of the Midwest and is therefore useful for purposes of watershed management, especially for sediment-yield control. Tributary zones, an important sediment source of the past, are increasingly stable and now are often minor sediment sinks. They require little additional management. The upper main valley is the most problematic zone because high banks of historical sediment are being eroded, increasing downstream sediment yield. A variety of management alternatives are available, but all have some negative consequences. Simply permitting this zone to evolve naturally will eventually reduce both sediment loss and flooding in the reach, but this process will require several decades. Although upland erosion has been curtailed, the lower main valley continues to aggrade, causing backswamp areas to increase and local groundwater to ...

Dating fluvial processes from historical data and artifacts

Abstract Geographers have long used historical data and artifacts to reconstruct past landscapes. Many of the same data can provide powerful tools for dating stream processes over the past century or so but applications can range from months to millennia. Historical techniques are important not only to mainstream geomorphological investigations but also to fluvial applications in environmental management. The approach is useful for human-induced fluvial changes as well as for those occurring naturally. This paper is intended as an introduction to several of the primary techniques.

The use of historical data and artifacts in geomorphology

Historical data and artifacts, as commonly used in historical geography, can provide powerful tools for dating geomorphological processes over the past century or more and applications can range from months to millennia. Investigations in geomorphology and environmental management can be greatly enhanced by the use of historical techniques. The approach is useful for tracing human-induced changes as well as for those occurring naturally. Several primary techniques are introduced in this essay.

Historical sources and watershed evolution

Historical data, including structures, documents, photographs and eyewitness reports, allow changes in some drainage basins to be documented in fine detail over time periods ranging from a few days to several decades. The USA is rich in data sources that are freely available. Rates of bank erosion, meander migration, channel width, riparian vegetation and watershed land use and cover conditions can be assessed, which are especially valuable where there is controversy over the human contribution to erosion and deposition. Studies of Coon Creek and the southern Piedmont of the USA have yielded results that sometimes contradict established views.

Book Review: The human impact on the natural environment (5th edn)

like flow path analysis are generally more difficult to derive. Other chapters show that for some applications standard GIS functions can be used to derive relatively complex models at a range of spatial scales. Clear illustrations are the chapters on snowmelt runoff from a 400 ́ 200 m rock glacier in Switzerland and computation of the spatial variation in long-term denudation rates, estimated to be between 0 and 100 m/Ma, across a 700 km2 area of the Central Kenyan Rift. The other main objective of the book was to identify the limitations of current GIS and to identify future directions for GIS in physical geography and related disciplines. These are dealt with to different degrees in each chapter but the call for ÔinteroperableÕ open distributed GIS is a common theme. Not surprising given the overarching theme of the IOGIS project, but there is no real attempt to define even a conceptual model of how such systems should operate in order to meet the needs of the researchers. Overall this book provides a valuable insight into work undertaken by German geographers on applications of GIS, some of which has not yet been published in English. However, it lacks real coherence, which may be inevitable with a book like this, and it would have benefited from a final chapter to bring together the key ideas from the book. Some of the chapters provide good overviews of GIS applications in very specific areas of physical geography and together form a useful reference for those considering implementing GIS in their research.