SUSPENDED-SEDIMENT DATABASE
Daily Values of Suspended Sediment and Ancillary Data
Transport of sediment and associated contaminants in streams is a water-quality issue of national concern. Of the nearly 600 x 107 tons of material eroded annually in the United States only about one tenth of the material reaches the coasts. Much of the sediment is stored on hillslopes, floodplains and other parts of stream valleys causing extensive damage to man's works in the river environment. Toxins sorbed to sediment are not only expensive to remediate but can be a large public heath risk. The determination of contaminant flux is an important step in evaluating remediation priorities and assessing progress in solving water quality problems.
The U.S. Geological Survey has operated a number of daily suspended sediment stations throughout the country, paid for through a variety of cooperative and federal programs. These daily gaging stations provide the best information on sediment flux in the Nation's rivers and represent a sizable investment in time and money. Daily sediment stations were established to meet specific objectives in individual studies and do not represent a network. However, the uniform data collection methods provided by the USGS, provide comparable data across the Nation.
Two basic types of sediment records are published by the Geological Survey -- daily and periodic. Daily records are prepared for sites where sufficient determination of sediment concentration and water discharge are obtained to justify computation of daily sediment discharge. The end product is a tabulation of daily streamflow, daily mean concentration of suspended sediment, and daily suspended-sediment discharge. These data reside in the U.S. Geological Survey's database and are reported on an annual basis in data reports from individual states.
The primary audience for this page is intended to be hydrologists and geomorphologists from around the world interested in the magnitude and timing of suspended-sediment flux.
Although certain tools are available to select certain gaging stations, the primary purpose of this internet site is to provide data to the end user and not to provide sophisticated routines for site selection or for data analysis. The intent was to allow users to retrieve the data and use analysis tools on their own computers. Therefore, no statistical or other packages to analyze the data are included with the database.
This database includes gaging station descriptive information including: Station number, station name, drainage basin area, latitude, longitude, start date of record, end date of record, number of days of missing record, and number of days of record. Output from a data retrieval provides station identification number, date, daily mean streamflow discharge in cubic feet per second, daily mean streamflow discharge in cubic meters per second, daily mean suspended-sediment concentration in milligrams per liter, suspended-sediment discharge in english short tons per day, and suspended sediment discharge in metric tons per day (megagrams per day). Each day is written to a separate line and data values are separated by spaces.
For additional information on the way the data were collected and reduced it is well to consult Edwards and Glysson (1988), Guy and Norman (1982), Guy (1969), and Porterfield (1972). It is worth noting that the daily mean concentration is a time-weighted mean value (Porterfield, 1972, p. 39). Thus, calendar days are divided and analyzed in shorter periods of time when water or sediment discharge exceed certain limits (Porterfield, 1972, p. 47). Suspended-sediment discharge is determined by multiplying the water discharge, in cubic feet per second, by the concentration of suspended sediment, in milligrams per liter, and a coefficient which for these english units is 0.0027.
Ancillary data are also included in this database. These data include: Water temperature, bed material size distribution, and suspended-sediment size distribution. These ancillary data were retrieved for each gaging station. These data are periodic in nature and not available for all stations. However, data available in the national database, WATSTORE, were retrieved and are available here.
Missing record has been recorded as -99 rather than left as a blank. It is important to note that days with streamflow and suspended-sediment discharge and missing values of suspended-sediment concentration result because sediment discharge has been estimated but no value of concentration is estimated.
This collection of stations includes all daily stations retained in the national database, WATSTORE in August 1996.
The rounding rules for water discharge, in ft3/s, suspended-sediment concentration, in mg/L, and suspended-sediment discharge, in english short tons per day follow U.S. Geological Survey conventions (Table 1).
Discharge in m3/s were computed from discharge in ft3/s. The rules for rounding discharge in m3/s, deviate slightly from the Geological Survey conventions (see Water Resources Division Data Reports Preparation Guide, 1985 Edition, p. 120-27) as the aim was to be able to reproduce the discharge in ft3/s. Therefore, discharge in m3/s is rounded to four decimal places for discharges less than 0.028 m3/s and is rounded to three significant figures for all values greater or equal to 0.028 m3/s. The constant used to convert discharge from ft3/s to m3/s is 0.02832.
The rule for rounding suspended-sediment discharge in metric tons are the same as for the english short ton (Table 1). Conversion to metric was performed on the properly rounded english units and then the metric values were rounded. The conversion constant used to convert from english short tons to metric tons is 0.907.
Table 1. U.S. Geological Survey Rounding conventions for parameters routinely stored in the database. --------------------------------------------------------------------------------------------------------------------- parameter 0 to < 1.0 >= 1.0 to < 10 >= 10 to<100 >=100 to 1,000 >= 1,000 --------------------------------------------------------------------------------------------------------------------- discharge in ft3/s .XX X.X XX XXX XXX0 concentration, * X XX XXX XXX0 in mg/L Sediment dis- ** ** XX XXX XXX0 charge, in english short tons per day --------------------------------------------------------------------------------------------------------------------- * <0.5 mg/L, report as <0.5 mg/L; 0.5 mg/L to 1 mg/L, report 1 mg/L ** <0.005 report 0 ton; >0.005 to 0.01 ton report 0.01 ton; >0.01 to 0.09 report to nearest 0.01 ton; 0.10 to 99 report 2 significant figures.
This database represents 1,593 stations that have an average period of record of 5.3 years. The period of record for individual stations range from one day to 44 years, and 13 percent of the stations have 10 years or more of record. The drainage area for these stations ranges from 0.002 to 1,893,800 sq km and the median drainage area for all stations is 767 sq km (Fig. 1).
The database was screened for errors that were easily identified by a computer algorithm. This check on daily entries included: 1) Missing streamflow value, 2) concentration greater than zero when streamflow and sediment discharge are both zero, 3) concentration zero when streamflow and sediment discharge are greater than zero, 4) only sediment discharge reported, 5) streamflow zero when concentration and sediment discharge are greater than zero, and 6) computed daily loads are in excess of \x91\\x91\\x9f\±\x9f\ 30 percent of the reported sediment discharge in the database. Although some of the entries reported under this algorithm may not be in error, this screening provides some indication of problems and provides a flag on sites in the database that may need further review. This screening procedure identified problems with 3.5 percent of all days of record. Missing streamflow represents about one third of the days with errors which suggests that much of this error can be eliminated.
These problems identified by the computer screening will be examined and the database updated as corrections are identified. Those individuals who have identified errors or have corrections available are urged to contact Randy Parker through the e-mail address given on the main page of this database.