Water, Sediment, and Nutrient Discharge Characteristics of Rivers in Puerto Rico, andtheir Potential Influence on Coral Reefs

Warne, A.G., Webb, R.M.T., and Larsen, M.C., 2005, Water, Sediment, and Nutrient Discharge Characteristics of Rivers in Puerto Rico, and their Potential Influence on Coral Reefs: U.S. Geological Survey Scientific Investigations Report
2005-5206, 58 p.

Data from 29 streamflow-gaging stations, including 9 stations with daily suspended-sediment concentration, and data from 24 water-quality stations were compiled and analyzed to investigate the potential effects of river sediment and nutrient discharges on the coral reefs of Puerto Rico. The largely mountainous watersheds of the 8,711-square-kilometer island of Puerto Rico are small, channel gradients are steep, stream valleys tend to be well-incised and narrow, and major storms tend to be intense but brief; hence flooding is rapid with peak discharges several orders of magnitude above base discharge, and flood waters recede quickly. Storm runoff transports a substantial part of fluvial suspended sediment from uplands to the coast, as indicated by sediment data from a set of nine streamflow-gaging stations representative of runoff from watersheds considered typical of conditions in Puerto Rico. For example, the highest recorded daily sediment discharge is 1 to 3.6 times the annual suspended-sediment discharge, and runoff from major storms induces sediment transport 1 to 32 times the median annual sediment load. Precipitation associated with Hurricane Georges in September 1998 is estimated to have averaged 300 millimeters across the island, which is equivalent to a volume of about 2.6 billion cubic meters. Analysis of runoff and sediment yield from Hurricane Georges indicates that more than 1.0 billion cubic meters of water and at least 2.4 million metric tonnes of sediment (and as much as 5 to 10 million metric tonnes), were discharged to the coast and shelf as a result of this major storm. Because of their relatively small size, dams and reservoirs of Puerto Rico have relatively little effect on total discharge of water and sediment to the coastal marine waters during major storms. The presence of reservoirs, however, may be detrimental to coral reefs for two reasons: (1) coarse sediments deposited in the reservoir can be replaced by finer sediments scoured, if available, from the river channels and flood plains below the dam; and (2) the loads of phosphorus and ammonia reaching the coastal waters may increase as organic matter decomposes in the anoxic bottom waters of the reservoir. Rainfall, water discharge, sediment discharge, and sediment yield vary across the island. Mean annual runoff for the island is estimated to be 910 millimeters, about 57 percent of mean annual precipitation (1,600 millimeters). Mean annual suspended-sediment discharge from Puerto Rico into surrounding coastal waters is estimated to range from 2.7 to 9.0 million metric tonnes. Hydrologic and sediment data associated with Hurricane Georges indicate that sediment yield is generally proportional to the depth of storm runoff. Discharge and sediment-concentration data indicate that during this storm, river water and sediment that discharged into the marine environment generally formed hypopycnal plumes (buoyant suspension layers). Generally, hyperpycnal (density) plumes can develop in areas with high discharges and sediment concentrations. Both hypopycnal and hyperpycnal plumes distribute suspended sediment over broad areas of the Puerto Rico shelf and shelf slope. Comparison of long-term suspended-sediment discharge and watershed characteristics for Puerto Rico with those of other river systems around the world indicates that Puerto Rico rivers are similar to temperate and tropical upland river systems.


Minimum streamflow information is commonly used to determine the water available for extraction and to analyze instream environmental parameters. Minimum streamflow estimates are frequently desired at ungaged locations, either on a stream having gages at other locations, or a stream without any gages. This study presents regional regression equations to estimate minimum streamflow using two parameters: watershed area and mean annual rainfall. These equations are based on a revised rainfall map which incorporates the available rainfall data from 127 raingage stations and also considers geographic parameters.

Luquillo Mountains Puerto Rico A water energy and biogeochemical budgets program site

Larsen MC, Stallard RF. Luquillo Mountains, Puerto Rico–a water,
energy, and biogeochemical budgets program site. US geological
survey fact sheet. Washington, D.C.7 U.S. Geological
Survey; 2000. p. 163– 99.

The Puerto Rico research site consists of the 113 square-kilometer Luquillo Experimental Forest (LEF), administered by the U.S. Forest Service, and the nearby Río Grande de Loíza drainage basin, an urbanized and agriculturally- developed watershed. This combined region serves as a terrestrial laboratory for the study of issues related to the global loss of tropical forest, and the associated changes in land-use practices. Findings from the WEBB research help scientists understand how vegetation, landscape, and people interact to affect the quantity and quality of water and the erosion of the landscape. The results of this work can be applied not only to Puerto Rico, but also to many other regions, where deforestation and rapid land-use change are issues.


Larsen, M. C., Alamo, C. F., Gray, J. R., and Fletcher, W. (2001).
„Continuous automated sensing of streamflow density as a
surrogate for suspended-sediment concentration sampling.‰
Proceedings of the 7th Federal Interagency Sedimentation
Conference, March 25–29, 2001, Reno, Nevada, Vol. I, pp. III-

A newly refined technique for continuously and automatically sensing the density of a water-sediment mixture is being tested at a U.S. Geological Survey streamflow-gaging station in Puerto Rico. Originally developed to measure crude oil density, the double bubbler instrument measures fluid density by means of pressure transducers at two elevations in a vertical water column. By subtracting the density of water from the value measured for the density of the water-sediment mixture, the concentration of suspended sediment can be estimated. Preliminary tests of the double bubbler instrument show promise but are not yet conclusive.

Fluvial Processes in Geomorphology and Environmental Management: The 2006 Benjamin Franklin Medal in Earth and Environmental Science awarded to Luna B. Leopold and M. Gordon Wolman

Frederick N. Scatenaa, and Robert D. Varrin
Fluvial Processes in Geomorphology and Environmental Management: The 2006 Benjamin Franklin Medal in Earth and Environmental Science awarded to Luna B. Leopold and M. Gordon Wolman
Journal of the Franklin Institute
Volume 347, Issue 4, May 2010, Pages 688-697
The 2006 Franklin Institute Awards

Starting in the 1950s Luna B. Leopold and M. Gordon Wolman transformed the field of geomorphology with quantitative and process-orientated studies designed to understand landscape adjustments to temporal and spatial changes in sediment supply and streamflow. By integrating fundamental science with keen observations they developed the first comprehensive and mechanistic understanding of rivers and floodplains. Their research has not only provided a quantitative framework for understanding landscape evolution, it is a cornerstone of modern water resource management and environmental impact analysis. Specific research areas included quantifying: (1) the “hydraulic geometry” of rivers; (2) the morphology and processes of rivers; (3) channel networks and the longitudinal profiles of rivers; (4) processes controlling floodplain formation; (5) the magnitude and frequency of geomorphic processes; and (6) the cycle of sedimentation in response to urban development. Much of this research was published in seven co-authored articles and in a widely used 1964 book that they co-authored with John Miller, Fluvial Processes in Geomorphology. While their contributions are synergistically linked and stem from their co-authored papers, their individual contributions are distinct and extend over 50 years. For these accomplishments, Luna Leopold and M. Gordon Wolman were awarded the 2006 Benjamin Franklin Medal in Earth and Environmental Science.

Linking habitat stability to floods and droughts: effects on shrimp in montane streams, Puerto Rico

Covich A.P., Crowl T.A. & Scatena F.N. (2000) Linking
habitat stability to floods and droughts: effects on
shrimp in montane streams, Puerto Rico. Verhandlungen
der Internationalen Vereinigung fu¨r Theoretische und
Angewandte Limnologie, 27, 2430–2434.

Most previous studies on Caribbean flood and drought frequency have examined hydrological (e.g. MORRIS & VAZQUEZ 1990, GARCIA et al. 1996) rather than ecological effects (COVICH et al. 1998). We analyzed temporal and spatial distributions of rainfall, stream flow, and mean maximum pool depth over an 8-year period (1990–1997) to evaluate effects of variable flows. We examined the response of a biotic variable (the coefficient of variation in shrimp densities) to changes in water depth (coefficient of variation of maximum pool depth) along an elevational gradient.

Unusual Hydrograph Characteristics, Upper Río Chagres, Panamá

Justin M Niedzialek, "Unusual hydrograph characteristics, upper Rio Chagres, Panama" (January 1, 2007). Dissertations Collection for University of Connecticut. Paper AAI3265788.

Inaccessible locations and inhospitable working conditions have resulted in a lack of detailed hydrological knowledge in the tropics. I have established a new field observatory located near the town of Gamboa, Panama, adjacent to the mid-point of the Panama Canal. This observatory allowed detailed measurements of the hydrologic cycle at the first-order catchment scale. My investigations reveal that competing runoff production mechanisms are responsible for the observed streamflow. Both of these mechanisms are strongly dependent upon rainfall rate and secondarily upon cumulative rainfall volume. I have identified a small but hydrologically significant riparian zone that is decoupled from the hillslope. In contrast to the remainder of the catchment this riparian zone shows signs of frequent overland flow. Upslope regions occasionally produce overland flow during high-intensity rainfall. Parallel to the small scale studies in Gamboa, sub-watersheds of the 414 km2 upper Rio Chagres were instrumented. These gages showed that the Rio Chagres rarely reacts uniformly; instead, the observed runoff is usually the result of a limited portion of the watershed. Based on inspiration from field research a new conceptual model, Sac3, was developed. Sac3 was successfully calibrated and verified on several study watersheds. Sac3 was also used to explore the relationship deep groundwater storages had on seasonal changes in baseflow runoff behavior.

Hydrologic regimes of forested, mountainous, headwater basins in New Hampshire, North Carolina, Oregon, and Puerto Rico

Post, David A.; Jones, Julia A. 2001. Hydrologic regimes of forested, mountainous, headwater basins in New Hampshire, North Carolina, Oregon, and Puerto Rico. Advances in Water Resources, Vol. 24: 1195-1210.

This study characterized the hydrologic regimes at four forested, mountainous long-term ecological research (LTER) sites: H.J. Andrews (Oregon), Coweeta (North Carolina), Hubbard Brook (New Hampshire), and Luquillo (Puerto Rico). Over 600 basinyears of daily streadow records were examined from 18 basins that have not experienced human disturbances since at least the 1930s and in some cases much longer periods. This study used statistical methods to systematically evaluate the relationship between precipitation and streamflow at a range of spatial and temporal scales, and draw inferences from these relationships about the hydrologic behavior of the basins. Basins in this study had fundamentally different abilities to store and release moisture at a range of time and space scales. These different hydrologic regimes are the result of different types of forest canopies, snow, and soils in the study basins. Through their influences on interception and transpiration, forest canopies appear to play a very important role in the hydrologic regimes at Andrews and Luquillo, but at Coweeta and Hubbard Brook, the current deciduous forest plays a more limited although seasonally important role. Because of the timing of melt and its interaction with soils, seasonal snowpacks at Hubbard Brook and Andrews have quite different effects upon streamflow and vegetation water use. A variety of water flowpath types in soil, from macropore flow to long flowpaths in deep soils or fractured bedrock, appear to operate at the four sites. Hydrologic regimes may help predict the temporal scales of biogeochemical cycling and stream ecological processes, as well as the magnitude and timing of hydrologic response to disturbance and climate change in headwater basins.
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