APPLICATION OF MUSLE, FRN AND HEC-RAS TO INVESTIGATE THE SOIL EROSION AND SEDIMENT TRANSPORT OF LA GAVIA RIVER, MÉXICO

TEJEDA SAMUEL; DE LOS SANTOS VILLALOBOS, SERGIO; H. VELASCO

Viena

Simposio; International Symposium on Managing Land and Water for Climate-Smart Agriculture; 2022

International Atomic Energy Agency

Soil erosion is one of the most serious environmental problems caused by changes in land use in the highlands of central Mexico. Therefore, to understand the erosive dynamics in these regions becomes essential.La Gavia river sub-basin (578,87. km2) is located 55 km northwest of the city of Toluca (19°15’ y 19°35’ North latitude and 99°40’ y 100 °00’ West longitude), Mexico. The predominant climate in the region is temperate sub humid, with an average annual temperature between 12ºC and 18ºC, the temperature of the coldest month between -3ºC and 18ºC, and the temperature of the hottest month around 22ºC. With precipitation in the driest month, less than 40 mm. Precipitation varies seasonally, with a dry season from November to April, and a rainy season from May to October. In the sub-basin there are plots where, over a period of 60 years, strata up to 1 m of soil have been lost due to the abandonment of the plots by the peasant owners.This agricultural sub-basin has been investigated to estimate sediment production by using the Modified Universal Soil Loss Equation (MUSLE), the soil erosion rate on the slopes by applying the 137Cs tracer (FRN), and sediment transport through the Gavia river towards the Ignacio Ramírez reservoir applying the HEC-RAS model.The results show that soil erosion varies between 16, 22 and 25, 02 Mg per event according to MUSLE for the return periods of 2 and 5 years. Land cover management is the main factor responsible for soil erosion in the basin.The results of FRN show an interval between – 1,1 and – 54,3 Mg ha-1 y-1. The average annual erosion rate of the four transects exceded the permitted limit of 6,7 Mg ha-1y-1 for this type of soils.The HEC-RAS results show that the sediment discharge mass at the beginning of the river section was 2 Mg, which increased to 8.5, 7.5 and 4.5 Mg in the sections of 4200, 3700 and 2500 m respectively. The sediment load is high in relation to the size of the basin; this is attributed to the soil degradation in the hills and in the inefficient agricultural practices. The river presents erosion of 20 to 30 cm in the bottom layer upstream and deposition of sediments downstream for the maximum flow. The area of the river that is close to the Ignacio Ramírez reservoir presented sediment deposition from 10 to 20 cm.The investigation with the integrated techniques confirmed that the high levels of erosion generally observed on the slopes dedicated to the cultivation of maize in central Mexico, makes it necessary to implement actions in order to reduce erosion and preserve the soil.