Sediment generation in Panama.
This page summarizes research on long-term sediment generation in the upper Rio Chagres basin.
For a more detailed explanation please read a preprint of our manuscript in The Rio Chagres: : A Multidisciplinary Profile of a Tropical Watershed
For ongoing and future research scroll to the bottom of the page.
The Rio Chagres supplies a significant portion of the water for operation of the Panama Canal. Water from the upper basin (>400 km2, and outlined by the black box) drains into Lago Alhajuela where it is stored and used for water supply, power generation, and canal usage. We quantified the long-term sediment generation of the upper Rio Chagres basin using cosmogenic 10Be.
Suspended sediment yield data collected from 1981 shows that the forested Chagres basin has a lower sediment yield that the adjacent and partly deforested Pequeni and Boqueron basins. The present day sediment yield results of the Chagres compared to the adjacent basins differ significantly, by factors of ~2.5 and 3.
In order to determine the long-term sediment generation rates in the upper Rio Chagres basin, we collected samples from small tributary basins (<5 km2), at the confluence of the the Rio Chagres and major tributaries (~20 to ~90 km2), and from the last sand bar before Lago Alhajuela (CLA).
Sediment storage with in the upper Rio Chagres is limited. Much of the basin is bedrock controlled and sediment is flushed out the system "quickly". Thus, our sediment generation results are good approximations of long-term sediment yield.
The suite of three samples for large tributary confluences (Rio Chagres on the left [CHAG-17] and Rio Piedras on the right [PIED]) were collected more than one hundred meters above the confluence and more than one hundred meters below the confluence [CPC].
Basin-wide erosion rates were variable for small tributary basins. However, the spatially weighted average of the small basins is similar to the basin-wide erosion rate for the larger tributaries and the entire basin. Thus, all basins in the upper Rio Chagres are producing sediment, on average, at similar rates over the millennial scale and at similar rates to the present day suspended sediment data, ~270 tons km-2 y-1, equivalent to ~100 mm ky-1 of erosion.
We are presently working on two more projects in Panama. 1) We are analyzing samples from the Boqueron basin (light blue) and the Pequeni basins (green) to quantify their long-term sediment generation rates. We expect to see long-term sediment generation rates similar to the Chagres basin and thus will be able to determine the impact of moderate deforestation. 2) We are analyzing samples from the rivers that drain down the opposite side of the Chagres, Boqueron, and Pequeni rivers (to the north). These rivers have the same elevation drop but are only 1/5 as long or less.