Sediment origins in the Catamayo-Chira Transboundary Basin: Impacts on Poechos Reservoir Capacity under ENSO influence

María Sofía Dunin-Borkowski^1,2*Marina Farías de Reyes³Fausto W. Asencio²Jorge Reyes-Salazar²Pablo Ochoa-Cueva^4*

• ¹Faculty of Engineering, Universidad Tecnológica del Perú, Av. Arequipa 265., Lima, Peru
• ²Posgraduate School, Universidad Nacional de Piura, Campus Universitario s/n. Urb. Miraflores,, Piura, Peru
• ³Department of Civil Engineering, Universidad de Piura, Urb. San Eduardo, Piura, Peru
• ⁴Department of Biological & Agricultural Sciences, Universidad Técnica Particular de Loja, Campus San Cayetano alto., Loja, Ecuador

The Poechos Reservoir began operations in 1976 with a water storage capacity of 885 hm3. This indicated a 58.77% reduction in storage capacity after 42 years of operation. The objective of this study is to determine the total mass and annual origin of the sediment by analyzing the annual precipitation and time series of vegetation cover mosaic images in the Transboundary Catamayo-Chira Basin, between 2001 and 2017. The study period was defined based on data availability: MODIS satellite images of vegetation cover (available since February 2000), annual bathymetry of the Poechos Reservoir conducted by PEChP (available until 2018), and gridded PISCOp precipitation data from SENAMHI (available until mid-2018). Sediment supply was estimated using the Sediment Delivery Ratio (SDR) model from the Integrated Valuation of Ecosystems Services and Tradeoffs (InVEST 3.13.0) software. Results show that the basin supplies an annual average of 6.91 x 106 t · yr-1, a value consistent with 6.53 x 106 t · yr-1, estimated from bathymetric measurements for the same period. Based on the median of model outputs, it is inferred that 84.3% of the sediment supplied (SSup) to the reservoir originates from eastern sub-basins: Macará (2.34 x 106 t · yr-1), Quiroz (1.98 x 106 t · yr-1) and Catamayo (1.50 x 106 t · yr-1). In contrast, the western sub-basins Alamor and La Solana contributed significantly less, with 0.65 and 0.18 x 106 t · yr-1, respectively. However, during the 2017 El Niño-Southern Oscillation (ENSO) event, the model revealed strong spatial and temporal variations. That year, the total SSup from the basin reached 34.92 x 106 t. The sediment supply from each of the three eastern sub-basins tripled to 5.60 x 106 t. In the Alamor sub-basin, SSup increased tenfold to 6.68 x 106 t, while in La Solana it increased fifty-seven times, reaching 10.50 x 106 t. In 2017, approximately 52% of the sediment supplied to the Poechos Reservoir originated from the western sub-basins. This study provides valuable information to support decision making related to vegetation cover management and restoration, considering climatic variability and sediment source areas in semiarid Andean basins.