Effect of ENSO events on sediment production in a large coastal basin in northern Peru

Abstract

Although the importance of ENSO on hydrological anomalies has been recognized, variations in sediment fluxes caused by these extreme events are poorly documented. The effect of ENSO is not limited to changes in sediment mobilization. Since ENSO events can affect terrestrial ecosystems, they may have important effects on sediment production and transport in river basins over time spans that are longer than the duration of the event itself. The Catamayo-Chira basin is an interesting casestudy for investigating these geomorphic implications. The objectives were: (i) to study the effect of ENSO on stream flow and sediment yields in the basin, (ii) to investigate if ENSO events affect sediment yields in the post-ENSO period and (iii) to understand which factors control the ENSO and post-ENSO basin response. During strong negative ENSO periods, mean annual stream flow discharge at the inlet of the Poechos reservoir in the lower basin was 5.4 times higher than normal annual discharges, while average sediment fluxes exceeded those of normal years by a factor of about 11. In two heavily affected periods, 45.9% of the total sediment yield in the 29years observation period was generated. Sediment fluxes in the post-ENSO period are lower than expected, which proves post-ENSO event dynamics are significantly different from pre-event dynamics. Our analysis indicates the increase of vegetation growth in the lower basin is not the main reason explaining considerable sediment flux decrease in post-ENSO periods. During strong ENSO events, sediment in alluvial stores in the lower part of the basin is removed due to enlarging and deepening of channels. In post-ENSO periods, normal discharges and persisting sediment supplies from the middle/upper basin lead to river aggradation and storage of large amounts of sediment in alluvial plains. The decrease in sediment export will last for several years until the equilibrium is reestablished.

Identification of Priority Areas for Integrated Management of Semiarid Watersheds in the Ecuadorian Andes

“…in the east, where slopes are generally steep (>40%). The Catamayo River is the main river in the catchment with a length of 120 km, and is the main tributary of the Ecuadorian‐Peruvian hydrographic system (17,000 km 2 ), called the Catamayo–Chira, which drains into the Pacific Ocean (Tote et al ). Average annual water flow is 35 m 3 /s, which reduces significantly to 22 m 3 /s during the dry season (June–November) (Ochoa et al ).…”

Pertinent spatio-temporal scale of observation to understand suspended sediment yield control factors in the Andean region: the case of the Santa River (Peru)

“…For Andean catchments similar to the Santa and Tablachaca catchments, there are no published data about bedload yield. More to the north of Peru, in the Catamayo-Chira catchment, total sediment yield has been quantified with bathymetric monitoring of the Poechos reservoir (Tote et al, 2011). Unfortunately, these data cannot be compared to ours because the climate of the Catamayo-Chira catchment is impacted more by El Niño and La Niña events than that of the Santa and Tablachaca catchments, and because differences in the SSY vs. Q rating curves between these catchments reveal different sediment production and transport processes.…”

21st century climate change: where has all the geomorphology gone?

“…For instance, Tote et al (2011) showed for a river basin in northern Peru that El Nino Southern Oscillation (ENSO) was responsible for the flushing of stored sediment, reversed during post-ENSO periods. For instance, Tote et al (2011) showed for a river basin in northern Peru that El Nino Southern Oscillation (ENSO) was responsible for the flushing of stored sediment, reversed during post-ENSO periods.…”

“…Given our ability to quantify variability over shorter timescales, a further trend is emerging: the ability to evaluate, across a range of different environments, geomorphic forcing by climatic variability at the scale of years to decades. For instance, Tote et al (2011) showed for a river basin in northern Peru that El Nino Southern Oscillation (ENSO) was responsible for the flushing of stored sediment, reversed during post-ENSO periods. Brook et al (2011) show that the area of small glaciers fluctuates in relation to the forcing of ablation by regional atmospheric circulation, notably the ENSO but also the Interdecadal Pacific Oscillation.…”