Temporal variability in the relationships between precipitation, discharge and suspended sediment concentration in a small Mediterranean mountain catchment

Abstract

Relationships between discharge and suspended sediment are very complex in most Mediterranean catchments. In the case of the Arnas catchment (Central Spanish Pyrenees), with a long history of human activity, the main factors that explain the variability of suspended sediment concentration (SCO during floods are the peak flow and the intensity of precipitation. A cluster analysis distinguishes four types of floods according to different characteristics of precipitation, discharge, suspended sediment transport and antecedent moisture conditions. G1 and G2 floods occur under dry conditions (which prevail most of the year), with moderate rainfall and low precipitation intensity; the discharge and suspended sediment response are very fast but limited in intensity. This suggests that the origin of water and sediment is restricted to areas located very close to the channel. G3 floods also occur under dry conditions, although during Intense rainfall events; then the response in both discharge and suspended sediment is very high, showing an enlargement of the contributing areas. Under very wet conditions (G4 floods) relatively moderate precipitation produces a very high response in discharge, but suspended sediment concentration records moderate values due to the effect of dilution when the entire catchment is contributing. IntroductionMedilemiiiean water resources mainly depend on the hydromorphological functioning of the watersheds in mountainous areas (Thornes 1999). The strategic impoitance of the latter has spurred the development of research projects which try to understand runoff generation and sediment yield, along with the temporal variability of runoff and sediment contributing areas in a changing scenario. Mediterranean areas are subject to large-scale land-use changes like farmland abandonment of steep cultivated slopes (Lasanta-Marti'nez et al, 2005), plant colonisation of the old field.s (Molinillo et at. 1997), reforestation (Ortigosa et at. 1990, and enlargement of .ski resorts. How these complex proces.ses affect the quality and quantity of waier resources, reservoir siltation and the dynamics of fluvial channels is a key question for understanding the characteristics and temporal trends of water resources in Mediterranean basins.

Reliability of sediment rating curves for a deciduous forest watershed in Iran

“…These results shown in Table 1 Table 1 that the high relative variance of suspended sediment data in comparison with discharge, demonstrates the significant and complex effects of changeful factors such as discharge on SSC, as reported by Lana-Renault et al (2007). The analysis of grouped data sets, as shown in Table 1, resulted in a meaningful change in CV of the order of 13.1-94.8% and 28.6-414.8% for discharge and SSC, respectively.…”

“…Comprehensive studies aim at a better understanding of the rainfall-soil erosion-runoff-sediment system as a whole, by integrating both natural and anthropogenic aspects at different temporal and spatial scales. This finally leads to a proper estimate of sediment yield needed for water management and erosion control structures, and river morphological and evaluation studies (Kothyari et al, 1997;Lana-Renault et al, 2007;Sadeghi et al, 2008b;Wilkinson et al, 2009).…”

Suspended sediment behavior in a coastal dry-summer subtropical catchment: Effects of hydrologic preconditions

“…Sediment dynamics in systems with high discharge variability are further impacted by the deposition and/or reorganization of sediment in the channel by flow recession and ephemeral flows that terminate in the channel as well as sediment supply augmentation or suppression associated with large precipitation/hydrologic events and prolonged periods of no precipitation (Lana-Renault et al, 2007). Basin preconditioning -the sequence and temporal proximity of events that impact hillslope and channel sediment supply -and the long-term implications of these events as well as slower, extensive alteration of the land surface and vegetation also play significant roles in altering fluvial sediment production, particularly in episodic systems (Lenzi and Marchi, 2000;Pasternack et al, 2001;Chakrapani, 2005;Gao and Josefson, 2012;Warrick et al, 2013).…”

“…Sediment and water supply to the channel are controlled by the same major factors, namely precipitation distribution and intensity, basin structure (relief, substrate composition), and basin preconditions (moisture levels, vegetation states, disturbance states) (Wischmeier and Smith, 1978;Syvitski et al, 2000;Lana-Renault et al, 2007;Mano et al, 2009). Increased shear stress during floods can erode channel margins, scour away stabilizing structures such as vegetation, and activate landslide snouts adjacent to the channel in upper basin areas, all of which can lead to increased channel bank and hillslope sediment delivery (Kelsey, 1980;Benda and Dunne, 1997;Poesen and Hooke, 1997;Korup, 2012).…”

“…Previous studies have shown that precipitation-driven storm flows often display dramatically different suspended sediment behavior in comparison to flows attributed to interflow, ground water discharge, or recharge-oriented dam releases (winter recessional or summer base flow), due primarily to the increased contribution of hillslope and channel margin sediment from precipitation events (Lana-Renault et al, 2007;López-Tarazón et al, 2010;Oeurng et al, 2010;Tena et al, 2011;Gao and Josefson, 2012). Lack of sensitivity in the lower Salinas further supports the idea that the channel plays a significant role in moderating In-channel storage has been found to play a significant role in fine sediment dynamics in other rivers, with fine sediment content of 0.04-8.0 g/cm 2 reported for a wide range of rivers using a method that involved the agitation of the top 5-10 cm of bed material (Lambert and Walling, 1988;Walling and Quine, 1993;Droppo and Stone, 1994;Walling et al, 1998.…”