Rainfall, run‐off, and sediment transport dynamics in a humid mountain badland area: Long‐term results from a small catchment

Abstract

In this study, we investigated rainfall, run-off, and sediment transport dynamics (414 runoff events and 231 events with sediment information) of a humid mountain badland area -the Araguás catchment (Central Pyrenees, Spain)-from October 2005 to September 2016. Use of this long-term database allows characterization of the hydrological response, which consist of low-magnitude/high-frequency events and high-magnitude/ low-frequency events, and identification of seasonal dynamics and rainfall-run-off thresholds. Our results indicate that the Araguás catchment, similarly to other humid badlands, had high hydrological responsiveness (mean annual run-off coefficient: 0.52), a non-linear relationship of rainfall with run-off (common in Mediterranean environments), and seasonal hydrological and sedimentological dynamics. We created and validated a multivariate regression model to characterize the hydrological variables (stormflow and peak discharge) and sedimentological variables (mean and maximum suspended sediment concentrations and total suspended sediment load). In summer and at the beginning of autumn, the response was mainly related to rainfall intensity, suggesting a predomination of Hortonian flows. In contrast, in spring and winter, the responses were mainly related to the antecedent conditions (previous rainfall and baseflow), suggesting the occurrence of saturated excess flow processes, and the contribution of neighbouring vegetated areas. The multivariate analysis also showed that total sediment load is better predicted by a multivariate regression model that integrates preevent, rainfall, and run-off variables. In general, our models provided more accurate predictions of small-magnitude/high-frequency events than high-magnitude/low-frequency events. This study highlights the high inter-and intra-annual variability response in humid badland areas and that long-term records are needed to reduce the uncertainty of hydrological and sedimentological responses in Mediterranean badland areas.

Long-Term Suspended Sediment Concentrations and Loads from a Relatively Undisturbed Agroforested Catchment in the Northwest of the Iberian Peninsula

“…This indicates that other factors besides discharge control the SSCs in the study catchment. Other studies have reported similar results in small catchments [10,13,15,21], which are particularly vulnerable to natural and anthropogenic disturbances, such as changes in vegetative cover, debris flow and changes in SS inputs. Daily mean SSCs varied widely during the monitoring period ( Figure 4) and exhibited much more variability than discharge (coefficient of variation 272% vs. 100%).…”

“…This indicates that other factors besides discharge control the SSCs in the study catchment. Other studies have reported similar results in small catchments [10,13,15,21], which are particularly vulnerable to natural and anthropogenic disturbances, such as changes in vegetative cover, debris flow and changes in SS inputs. With regard to instantaneous values, the SSCs oscillated between 1 and 2138 mg L −1 , although they were below 25 mg L −1 threshold of the EU Freshwater Fish Directive (78/659/EEC), replaced by the Water Framework Directive (2000/60/EC) [35] and Directive 75/440/EEC [36], most of the study period (Table 1 and Figure 5).…”

“…The data were classified as "low discharge" and "high discharge", considering low flow 90% of the Water 2018, 10, 1302 7 of 17 exceedance flow, based on sampled discharge values. The study was focused on the analysis of high discharge because SS transport is generally concentrated in runoff events over long time scales [15,17].…”

“…The data were classified as "low discharge" and "high discharge", considering low flow 90% of the exceedance flow, based on sampled discharge values. The study was focused on the analysis of high discharge because SS transport is generally concentrated in runoff events over long time scales [15,17]. The remarkable observed scatter in the SS-Q relationship constitutes a common feature in this type of relationship [13,21,[34][35][36][37][38], which depends on the patterns of supply and transport of SS over multiple timescales [13,15,37].…”

“…The study was focused on the analysis of high discharge because SS transport is generally concentrated in runoff events over long time scales [15,17]. The remarkable observed scatter in the SS-Q relationship constitutes a common feature in this type of relationship [13,21,[34][35][36][37][38], which depends on the patterns of supply and transport of SS over multiple timescales [13,15,37]. Changes in the parameters of the SS-Q relationship (i.e., a and b parameters) have been reported for many streams [37][38][39], highlighting the time dependence of the parameter values [37,39].…”