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on August 28, 2025, 3:34 pm, in reply to "Re: Arroyo meeting tomorrow, Aug 23, Saturday "
CONCLUSIONS
The study of the Characterization and Diagnosis of the Arroyo La Manzanilla del Mar Basin, in the Municipality of La Huerta, Jalisco, shows the basin's sensitivity to erosive processes that cause the dragging and disposal of sediments (gravel) on the beach.
It is concluded that the basin's relief is fragile due to the presence of soils with little gravel structure, influenced by steep slopes with long peaks and ridges. When impacted by heavy rainfall, these soils cause high drainage densities due to high surface runoff, which increases the detachment of soil particles deposited in streams with high flow activity, where gravel particles are transported by the channels until they are deposited in the basin's outlet area.
Structural fragility is determined to exist primarily in the middle zone of the basin, as indicated by the bulk density data found and the sinuosity of the main stream. This, combined with the dominant presence of Regosol soils with low moisture retention capacity, generates the buildup and transport of unconsolidated material such as gravel. The drag of these materials toward the lower parts of the basin results in gravel deposits, mainly on the beach.
Regarding land use and vegetation, the basin is 83% forested. This is a favorable percentage for maintaining stable hydrological conditions within the basin.
These areas are not suitable for annual crops, but are suitable for natural vegetation with very steep slopes and thin soils that offer minimal resistance to the erosive action of water and wind. It is important to emphasize that the most significant change trends continue to be for forests in all categories, with 4.56% shifting toward induced grasslands and urban areas. Just as the deforestation rate within the basin, at 3.76%, shows a very high value, these negative effects are observed in the upper reaches due to land use changes toward grasslands and in the lower reaches due to population growth.
It is concluded that current erosion within the basin is a key factor in sediment drag.
48.63% of the surface area is found in the strong to extremely strong erosion range, making it a basin highly sensitive to rainfall and extreme return periods, thus causing a loss of soil substance and generating gravel deposits at the basin outlet.
To control and carry over sediment within the basin, it is important to develop a proposal for runoff control works. This document analyzes the available information from weather stations in the basin's area of influence using the CONAGUA manual. Design flow rates (m3 s-1) for the basin were defined for return periods of 25, 50, and 100 years. In addition, the locations for the installation of gabion dams (silt retention dams) within the basin were defined, following the steps established in the National Forestry Commission's Manual of Works and Practices for the Protection, Restoration, and Conservation of Forest Soils (2023). It is important to emphasize the need to develop a bathymetric and tidal movement study, the latter of which produces gravel beaches. Tides, along with waves and currents, play a crucial role in the formation and transport of sediments along coasts.
The modification of tides, combined with waves and currents, has a significant impact on beach dynamics, including the formation and transport of sediments. Gravel beaches can form in areas where tides are broad and where waves and longshore currents transport and deposit gravel and rocks.
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Arroyo meeting - SpencerC August 7, 2025, 5:20 pm
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