Abstract: Laguna La Torrecilla, Laguna de Pinones, Laguna San Jose, and Laguna del Condado, in the San Juan, Puerto Rico area, are located within a metropolitan area of more than 1 million people. Bathymetric maps made during the study, in 1973, showed that Lagunas La Torrecilla, San Jose, and del Condado have been modified by dredging and filling; whereas, Laguna de Pinones has remained in a near natural state. Laguna La Torrecilla has been dredged to a depth, in places, of about 18 metres, and Lagunas San Jose and del Condado, in places to about 11 meters. Dredging in the San Juan lagoons has been harmful, beneficial, and in a few instances has had little or no noticeable effect on the water quality. Usually, dredging in the connecting canals has been beneficial if the water entering the lagoons through the canals was of better quality than the water in the lagoon. Dredging in the mouths of lagoons has been beneficial; whereas, filling or blocking the mouths has been harmful.

This report used "annual peak-discharge records at fifty sites with five or more years of record" to determine individual site frequency curves. It includes several maps.

From introduction: The purpose of this report is to summarize available information concerning iron-ore resources in the United States in order to provide a general background for understanding and appraising the present status of this basic commodity.

Abstract: Lajas Valley is plagued with problems of salinity and waterlogging the soils. Use of brackish (500 milligrams per liter) irrigation compounded ground water for the problem until an irrigation-drainage system was constructed in 1955. Lajas is an alluvium-filled limestone highlands. The alluvium, mostly clay and as much 300 feet (90 meters) thick, contains brackish ground water except in the recharge areas located along the foothills...Results from a digital model show that a network of discharge wells could alleviate waterlogging of the soils in the artesian area.

Report summarizing results of research conducted by the U.S. Geological Survey during fiscal year 1965. It provides an overview of the economic and scientific work of the organization.

Abstract: The principal chemical, physical and biological characteristics, as well as the hydrology of Laguna Tortuguero, Puerto Rico, were studied from 1974-75. The lagoon, with and area of 2.24 square kilometers and a volume of about 2.68 million cubic meters, contains about 5 percent of seawater. Drainage through a canal on the north side averages 0.64 cubic meters per second per day, flushing the lagoon about 7.5 times per year. Chloride and sodium are the principal ions in the water, ranging from 300 to 700 mg/L and 150 to 400 mg/L, respectively. Among the nutrients, nitrogen averages about 1.7 milligrams per liter, exceeding phosphorus in a weight ratio of 170:1. About 10 percent of the nitrogen and 40 percent of the phosphorus entering the lagoon is retained. The bottom sediments, with a volume of about 4.5 million cubic meters, average 0.8 and 0.014 percent nitrogen and phosphorus, respectively.

A bibliography that lists about 1,300 U.S. Geological Survey publications related to coal and published prior to January 1, 1971.