USGS
Tropical cyclones and the flood hydrology of Puerto Rico
Fri, 07/29/2011 - 13:18 — ckassSmith, J. A., P. Sturdevant-Rees, M. L. Baeck, and M. C. Larsen (2005), Tropical cyclones and the flood hydrology of
Puerto Rico, Water Resour. Res., 41, W06020, doi:10.1029/2004WR003530.
Abstract:
Some of the largest unit discharge flood peaks in the stream gaging records of the
U.S. Geological Survey (USGS) have occurred in Puerto Rico. Many of these flood peaks
are associated with tropical cyclones. Hurricane Georges, which passed directly over the
island on 21–22 September 1998, produced record flood peaks at numerous USGS
stations in Puerto Rico. The hydrology and hydrometeorology of extreme flood response
in Puerto Rico are examined through analyses of rainfall, based on Weather Surveillance
Radar–1988 Doppler (WSR-88D) radar reflectivity observations and USGS rain gage
observations and discharge from USGS stream gaging stations. Peak rainfall
accumulations of more than 700 mm occurred in the central mountain region of the island.
The largest unit discharge flood peaks, however, were located in the eastern portion of
the island in areas with smaller storm total rainfall accumulations but markedly larger
rainfall rates at 5–60 min timescale. Orographic precipitation mechanisms played an
important role in rainfall distribution over the island of Puerto Rico. Amplification of
rainfall accumulations was associated with areas of upslope motion. Elevated low-level
cloud water content in regions of upslope motion played an important role in the
maximum rainfall accumulations in the central mountain region of Puerto Rico. The
largest unit discharge flood peaks, however, were produced by a decaying eye wall
mesovortex, which resulted in a 30–45 min period of extreme rainfall rates over the
eastern portion of the island. This storm element was responsible for the record flood peak
of the Rı´o Grande de Lo´iza. The role of terrain in development and evolution of the
eye wall mesovortex is unclear but is of fundamental importance for assessing extreme
flood response from the storm. Hydrologic response is examined through analyses of
rainfall and discharge from five pairs of drainage basins, extending from east to west over
the island. These analyses point to the importance of short-term rainfall rates for extreme
flood response. The hydrologic response of Puerto Rico is compared with two other
extreme flood environments, the central Appalachians and Edwards Plateau of Texas.
These analyses suggest that the high rainfall environment of Puerto Rico is linked to the
development of a hydraulically efficient drainage system.
Research plan for the investigation of water, energy, and biogeochemical budgets in the Luquillo mountains, Puerto Rico
Tue, 07/26/2011 - 16:29 — ckassLarsen, M.C., Collar, P.D., and Stallard, R.F., 1993, Research plan for the investigation of water, energy, and biogeochemical budgets in the Luquillo mountains, Puerto Rico: U.S. Geological Survey Open-file Report 92-150, 19 p.
Abstract:
The Luquillo mountains of eastern Puerto Rico are the site of U. S. Geological Survey (USGS) research into biogeochemical and geomorphic processes that control the movement and transformation of water, energy, bedrock weathering products, and nutrients in the earth-surface environment. This study was begun in 1990 and is scheduled to last three years, with the possibility of being extended for further data collection. The study area for this research effort includes the 113 square kilometers Luquillo Experimental Forest (LEF) that is administered by the U. S. Forest Service. The LEF has been the site of ongoing research since 1988 as part of the National Science Foundation's Long Term Ecological Research program. In addition, comparative studies are being conducted in the RÃo Grande de LoÃza basin (LoÃza basin), an urban and agriculturally developed 600 square kilometers watershed located immediately to the west of the LEF.
The principal elements of the study described in the report are as follows:
Determination of biogeochemical budgets: water, energy, carbon, nutrient, ion, sediment, and gas budgets will be calculated in two LEF watersheds instrumented with meteorologic, soil, hydrologic, and ground-water monitoring equipment. A biweekly time series of samples is being collected. In addition, intensive sampling is undertaken during selected storms.
Study of weathering, erosion, and mass-wasting processes in undeveloped watersheds of contrasting lithology: chemical-weathering, erosion, and mass-wasting processes in watersheds underlain by the two dominant rock types, volcaniclastic and quartz diorite, are being compared. The effects of mass wasting on biogeochemical cycling in each rock type will be evaluated through a compilation of physical, chemical, and mineralogic properties for a chronosequence of landslides. Water and sediment budgets will be used to develop a conceptual model of hillslope hydrology and landform evolution.
Comparison of weathering and gas flux in developed and forested watersheds: paired basins were selected and gaged in the relatively undisturbed LEF and in the agriculturally developed LoÃza basin. Budgets of all aqueous constituents will be compared and contrasted in the developed and forested basins of similar lithology. Gas-flux differences (carbon dioxide, nitrogen dioxide, methane) between developed and undeveloped areas will be evaluated using chamber techniques and the results related to land-use differences.
Measurement of reservoir and agricultural pond gas fluxes: methane production is being measured in selected reservoirs and agricultural ponds in and near the LoÃza basin and LEF. A regional methane budget will be calculated.
CONTINUOUS AUTOMATED SENSING OF STREAMFLOW DENSITY AS A SURROGATE FOR SUSPENDED-SEDIMENT CONCENTRATION SAMPLING
Tue, 07/26/2011 - 16:13 — ckassLarsen, 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-
102–III-109.
Abstract:
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.
Forecasting hurricane-related disasters
Tue, 07/26/2011 - 15:52 — ckassAbstract:
The punch from hurricane-strength winds is quick. In the Caribbean, the storms whip across the
islands tearing out trees and shattering buildings. Monitoring hurricanes is a centuries-long
tradition. But with all hurricanes, and even with less formidable rain storms, comes the threat of
landslides and flooding to the hills and valleys on the islands' mountainous terrain.
To help emergency personnel evacuate regions at high risk to these secondary rain-induced
hazards, a consolidation of technology is needed, says Randall Updike of the U.S. Geological
Survey in Denver. He is working with colleagues at the USGS, along with scientists from the
National Oceanic and Atmospheric Association (NOAA) and NASA, to establish a united front on
forecasting landfall disasters from hurricanes in the Caribbean. UNESCO (United Nations
Educational, Scientific and Cultural Organization) and The World Meteorological Organization also
support the proposed idea, Updike added. Currently these organizations operate independently of
each other. Updike presented his proposal of bringing the groups together at the annual meeting of
the American Association for the Advancement of Science in Denver on Feb. 15.
