One century of hydrological monitoring in two small catchments with different forest coverage

Abstract

Long-term data on precipitation and runoff are essential to draw firm conclusions about the behavior and trends of hydrological catchments that may be influenced by land use and climate change. Here the longest continuous runoff records from small catchments (<1 km(2)) in Switzerland (and possibly worldwide) are reported. The history of the hydrological monitoring in the Sperbel- and Rappengraben (Emmental) is summarized, and inherent uncertainties in the data arising from the operation of the gauges are described. The runoff stations operated safely for more than 90% of the summer months when most of the major flood events occurred. Nevertheless, the absolute values of peak runoff during the largest flood events are subject to considerable uncertainty. The observed differences in average, base, and peak runoff can only partly be attributed to the substantial differences in forest coverage. This treasure trove of data can be used in various ways, exemplified here with an analysis of the generalized extreme value distributions of the two catchments. These distributions, and hence flood return periods, have varied greatly in the course of one century, influenced by the occurrence of single extreme events. The data will be made publicly available for the further analysis of the mechanisms governing the runoff behavior of small catchments, as well as for testing stochastic and deterministic models.

The relevance of hydrological research in small catchments – A perspective from long-term monitoring sites in Europe

“…The use of small catchments in hydrological research dates to the 1900s and the comparative monitoring of the Sperbelgraben (forest) and Rappengraben (grassland) catchments, in studies of the effect of vegetation cover on the hydrological regime and flood dynamics in Swiss mountain areas (Engler, 1919cited in Keller, 1988Stähli et al, 2011). Several years later the first experimental paired watersheds were established for the Wagon Wheel Gap Experiment in Colorado, USA (Bates andHenry, 1928, cited in Hewlett, 1982).…”

Status and perspectives of hydrological research in small basins in Europe

“…Their contributions focussed on different scales (plot, hillslope, catchment) and aimed the deepening of the process understanding to enhance the concepts and algorithms of runoff modelling. Stähli et al (2011) described an even longer data series based on the long-term observations in Emmental, Switzerland. In particular two small catchments (Sperbelgraben and Rappengraben) were monitored since the year 1903 and form a valuable data base for public access for time series and extreme event analysis.…”

Runoff generation in a pre-alpine catchment: A discussion between a tracer and a shallow groundwater hydrologist

“…Research in the Alptal watershed in central Switzerland began in 1963 and focused on the effects of forestry on floods and water quality. The areas underlain by flysch (which is a geologic formation consisting of a sequence of sedimentary rocks that were deposited in a basin adjacent to a rising mountain belt) had undergone significant reforestation since the 1900s because it was thought that the logging and degradation of the forests could be attributed to the large floods in 1834, 1839, 1860, and 1868(Hegg et al, 2006Stähli et al, 2011). The Alptal is typical for the Swiss pre-alpine region; it is characterized by frequent and high rainfall and low permeability soils, and therefore mostly wet conditions.…”