Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena Identifying a reliable method for estimating suspended sediment load in a temporary river system A.M. De Girolamo a, ⁎ , R. Di Pillo b , A. Lo Porto a , M.T. Todisco b , E. Barca a a Water Research Institute, National Research Council, Bari, Italy b DICEAA, Department of Civil, Environmental and Architecture Engineering, University of L'Aquila, Italy ARTICLE INFO Keywords: Temporary stream Suspended sediment load Load estimation techniques Stratification of data Uncertainty ABSTRACT Sampling strategies and methods used for estimating load can lead to large uncertainties in suspended sediment transport quantification, especially in rivers with a high variability in streamflow. The aim of this paper is to evaluate suspended sediment load, using a number of direct estimation techniques, in order to find a suitable method for temporary river systems, and to assess the uncertainty associated with load estimation, due to the specific method applied. One year of continuous measurement of flow, and discrete sampling (n = 216) of suspended sediment concentrations, taken from 2010 to 2011 in the Celone River (SE, Italy), were used to estimate annual load. Averaging, ratio, and regression estimator methods were applied to the entire dataset, and to subsets of data, to calculate load. The results show a wide range of values, from 220 to 1123 t km -2 yr -1 , with respect to the applied suspended sediment load estimation techniques. Averaging methods resulted biased. Sediment rating curves underestimated load, while, if the back-transformation bias correction was used, load was overestimated. The ratio methods generally overestimate load. Increased precision and accuracy was achieved through applying data stratification, based on flow regime and seasonality. After applying three dif- ferent flow regime stratifications, the annual load ranged from 240 to 606 t km -2 yr -1 and, using seasonal stratification, from 258 to 974 t km -2 yr -1 . It seems that ratio estimator methods, and the regression equations applied to the stratification on a flow regime basis, are more suitable for estimating load in temporary, flashy streams. 1. Introduction Most of the river basins influenced by the Mediterranean climate are affected by erosion and soil degradation. During the last few decades, there has been a significant increase in studies of erosion (de Vente et al., 2009), sediment transport dynamics (Gentile et al., 2010; Bisantino et al., 2010; Gallart et al., 2013; Regüés and Nadal-Romero, 2013; García-Rama et al., 2016; López-Tarazón and Estrany, 2017; Kheirfam et al., 2017), and load estimation methodologies (Letcher et al., 2002; Tabatabaei et al., 2014). Several models have been de- veloped for quantifying soil erosion by water and wind, which have been applied on regional (Kirkby et al., 2008; Panagos et al., 2015; Vigiak et al., 2017) and basinal scales (Abouabdillah et al., 2014; Bagarello et al., 2017; Ricci et al., 2018). Sediment load quantification is an important task in river basin management, as it provides the order of magnitude of soil loss. It is also fundamental in evaluating reservoir siltation, and the consequent loss of water reservoir capacity (Vericat and Batalla, 2006), and is necessary for calibrating models used to estimate erosion and sediment load. On the other hand, hydrological and sediment regimes are the basic drivers of water quality (Larned et al., 2010) and river ecosystems (Arthington, 2012; Wohl et al., 2015), and an accurate load estimation allows us to understand the impacts of anthropogenic activity on rivers. Sediment load, transported in a certain time interval through a section of river, is quantified by integration of instantaneous flux, which is the product of suspended sediment concentration (SSC) and discharge (Q). This simple equation, in several cases cannot be applied, due to limited data availability. In a number of basins, at the most, measurements of streamflow are available on a daily time-scale, whereas SSC measurements are generally taken on a weekly or monthly basis (De Girolamo and Lo Porto, 2012). Hence, to calculate sediment load, it is necessary to estimate the concentrations for those days when no measurements are available. This is the so-called “load estimation problem” (Lee et al., 2016). Several direct techniques have been de- veloped for estimating suspended sediment load by using infrequent samples of SSC and continuous measurements of Q (Asselman, 2000). The characteristics of the dataset (i.e. number of samples), the dimen- sions of the river basin, and the flow regime, play an important role in https://doi.org/10.1016/j.catena.2018.02.015 Received 5 December 2017; Received in revised form 8 February 2018; Accepted 12 February 2018 ⁎ Corresponding author. E-mail address: annamaria.degirolamo@ba.irsa.cnr.it (A.M. De Girolamo). Catena 165 (2018) 442–453 0341-8162/ © 2018 Elsevier B.V. All rights reserved. T