A new practical aid to regional hydrogeologic planning: The runoff coefficient map

Abstract

The principal aim of this research is to solve problems of water-budget estimation in particularly indeterminate conditions, of the kind that are frequently encountered in the field, in which absence or insufficiency of hydrographic instrumentation prevents the adequate evaluation of runoff.To do this we have developed techniques that are based on the method of Kennessey (1930), in which the runoff coefficient of a watershed in estimated using three physiographic variables (slope angle, permeability, and vegetation cover) and a parameter that defines the climatic conditions of the local area. Our comparison of the Kennessey method with instrumental records from a wide variety of instrumented drainage basins in central Italy shows that the method provides reliable estimates of runoff. Our analysis also indicates the best criteria for its application, as shown by the examples and results presented in this article.This research enables us to present a new application of the method, namely the runoff coefficient map, which, in addition to its specific usefulness for the evaluation of runoff, has three advantages. First, it supplies a more realistic vision of the local distribution of runoff/rainfall ratios; second, it allows one to overcome the spatial constraints imposed by the narrow frame of reference represented by the watershed; and third, it makes an important contribution to the solution of other hydrogeological problems, such as the evaluation of the amount of water required for adequate recharge of the intake areas of deep aquifers or the maintenance of geothermal processes.Hence we propose this mapping technique as a valuable practical aid to regional hydrogeologic planning.The calculation of water-budgets usually precedes any form of applied hydrogeological study, as it enables the researcher to obtain a good estimate of the water resources of a particular area. The spatial frame of reference that is normally used in such analyses is the drainage basin, but it is always necessary to ascertain whether the surface water catchment coincides with the underlying groundwater basin if reliable estimates are to be obtained.The various parameters of the water-budget are usually determined from data recorded by suitably located instruments, and, in particular, runoff is calculated by integrating the discharges measured at the basin outflow point. However, even in well-instrumented regions, the density of measuring stations is often very limited, especially that of water-level recorders, which makes it extremely difficult to assess the water resources of an individual catchment accurately and still more difficult to appraise the contribution derived from portions of it, especially regarding the estimation of surface runoff.To overcome these difficulties, various more or less empirical indirect methods have been proposed to calculate the values of runoff. However, such methods have so far yielded only modest results, above all owing to the difficulties of singling out and evaluating, quantitatively and in their just p...

Studying travertines for neotectonics investigations: Middle–Late Pleistocene syn-tectonic travertine deposition at Serre di Rapolano (Northern Apennines, Italy)

“…Pleistocene-Holocene travertine masses (Carrara et al 1998) and active thermal springs are aligned along the Rapolano Fault (Barazzuoli et al 1988;Minissale et al 2002), mainly where this structure has been dissected by Quaternary faults (Brogi 2004). Hydrothermal fluid circulation begun during the Pleistocene and is ongoing, in several places, with a widespread upwelling of hydrothermal fluids (39°C) and CO 2 leakage (Baldi et al 1992;Minissale et al 2002;Brogi 2008a;Brogi and Capezzuoli 2009).…”

“…This area is characterised by a geothermal anomaly (Della Vedova et al 2001) giving rise to widespread low-enthalpy hydrothermal circulation of bicarbonate-supersaturated waters (Minissale et al 2002 and references therein). Thermal springs and gas vents were tectonically controlled by permeable fault zones related to the superimposition of two fault systems with different ages (Brogi 2004), and determined the deposition of extensive Pleistocene-Holocene travertine bodies (Cipriani et al 1972; Barazzuoli et al 1988;Guo and Riding 1992, 1994, 1998Guo et al 1996;Carrara et al 1998;Brogi et al 1999;Brogi and Capezzuoli 2009). The extraordinary extent of travertine exposure at Cava Oliviera quarry (Fig.…”

Using GIS for modelling the impact of current climate trend on the recharge area of the S. Susanna spring (central Apennines, Italy)

“…Barazzuoli et al, 1989;Gazzetti et al, 2005). This estimation is based on the calculation of the Kennessey coefficient, Ck , as a sum of three numerical values calibrated on (1) slope, (2) land use and (3) rock permeability, according to the classes shown in Table V, and compared with the aridity index Ia (De Martonne, 1926, modified by Tardi and Vittorini, 1977) given by:…”

Empirical Determination of the Average Annual Runoff Coefficient in the Mediterranean Area

“…Because of difficulties on modeling spatial variability of topography, geology, soil type and vegetation, as well in climate fluxes such as rainfall, infiltration and evapotranspiration, simple empirical approaches to determine average annual Runoff Coefficient (RC) have been widely applied (Barazzuoli et al, 1988;Santos and Hawkins, 2011). Between the simple empirical models the Kennessey method (Kennessey, 1930) provides RC values by accounting for the main factors wherefrom RC is influenced: Climate characteristic, surface permeability, mean slope and vegetation cover.…”