Suspended‐sediment rating curve response to urbanization and wildfire, Santa Ana River, California

Abstract

[1] River suspended-sediment concentrations provide insights to the erosion and transport of materials from a landscape, and changes in concentrations with time may result from landscape processes or human disturbance. Here we show that suspended-sediment concentrations in the Santa Ana River, California, decreased 20-fold with respect to discharge during a 34-year period (1968À2001). These decreases cannot be attributed to changes in sampling technique or timing, nor to event or seasonal hysteresis. Annual peak and total discharge, however, reveal sixfold increases over the 34-year record, which largely explain the decreases in sediment concentration by a nonlinear dilution process. The hydrological changes were related to the widespread urbanization of the watershed, which resulted in increases in storm water discharge without detectable alteration of sediment discharge, thus reducing suspended-sediment concentrations. Periodic upland wildfire significantly increased water discharge, sediment discharge, and suspendedsediment concentrations and thus further altered the rating curve with time. Our results suggest that previous inventories of southern California sediment flux, which assume time-constant rating curves and extend these curves beyond the sampling history, may have substantially overestimated loads during the most recent decades.

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

“…Early investigations into antecedent hydrologic effects on suspended sediment flux were primarily focused either on the association of regional 4 u n c o r r e c t e d , a c c e p t e d scale patterns in suspended load resulting from long-term precipitation and discharge characteristics (i.e., Langbein and Schumm, 1958) or watershed scale studies of the 'lag effect' during individual hydrologic events, which results from slower moving sediment pulses relative to the transmission of peak water discharge at the event scale (Heidel, 1956;Carson et al, 1973;Shi et al, 1985). Identification of the principal factors affecting suspended sediment behavior has been an active field of study since suspended sediment-discharge rating relationships were found to lack predictive power in smaller catchments (Walling, 1977;Syvitski et al, 2000;Warrick and Rubin, 2007;Sadeghi et al, 2008).…”

Spatial linkages between coral proxies of terrestrial runoff across a large embayment in Madagascar

“…of both sediment and leached dissolved components delivered to the coastal ocean (Warrick and Rubin, 2007). Madagascar is an iconic example of the extreme environmental impacts human deforestation and habitat destruction has on soil runoff and land degradation (Green and Sussman, 1990;Harper et al, 2007).…”

Conversion to drip irrigated agriculture may offset historic anthropogenic and wildfire contributions to sediment production

“…damming) causes declines in basin scale sediment yield by trapping sediment in reservoirs and altering the natural flow regime, particularly through reduction of peak flood discharge magnitudes (Pasternack et al, 2001;Vorosmarty et al, 2003;Willis and Griggs, 2003;Walling and Fang, 2003;Walling, 2006;Warrick andRubin, 2007, Estrany et al, 2009). After an initial spike during construction, urbanization can also lead to sediment load decreases with the increase in the cover of impervious surfaces (Wolman, 1967;Wolman and Schick, 1967;Warrick and Rubin, 2007;Minear, 2010). Conversely, extensive urbanization can act to increase sediment yield by altering basin scale precipitation -discharge characteristics (i.e.…”

“…In this way, wildfire (Florsheim, 1991;Cerdà, 1998;Lavé and Burbank, 2004;Warrick et al, 2012), urbanization (Wolman and Schick, 1967;Trimble, 1997;Warrick and Rubin, 2007), and agriculture (Gao and Pasternack, 2007;Abaci and Papanicolaou, 2009;Estrany et al, 2009;Florsheim et al, 2011) have been found to exert significant control on fluvial sediment flux. However, understanding the fluvial sediment dynamics of most systems over inter-decadal time scales requires the disentanglement of multiple controls, particularly at larger spatial scales.…”

“…Furthermore, factors affecting watershed-scale sediment production operate over a wide range of time scales, with even seemingly discrete events generating legacy effects that may last for years or decades (Warrick et al, 2012;Warrick et al, 2013;Gray et al, 2014). Semi-arid basins in particular have been found to display persistent dependence on climatically driven antecedent basin conditions, such as storm/flood and wildfire histories (Abraham, 1969;Tanji et al, 1980;Lenzi and Marchi, 2000;Lana-Renault et al, 2007;Warrick and Rubin, 2007;López-Tarazón et al, 2011;Gray et al, 2015a). The addition of human influences further complicates sediment flux controls in the highly developed portions of the world that are the most intensively studied (Walling, 2006;Syvitski and Milliman, 2007).…”