The Great Lakes Water Balance
Data Availability and Annotated Bibliography
By Brian P. Neff and Jason R. Killian

Introduction | Hydrological Information | Forecasts and Summary

Runoff

Runoff to the Great Lakes includes all water entering the lakes through rivers, streams, and direct overland flow. River and stream discharges to the Great Lakes are calculated using stage data collected at gaging stations as close to each Great Lake as practical. These stage data are compared to stage-discharge relationships developed for each station and discharges are estimated. In both the US and Canada, these relationships are frequently reviewed and updated as often as necessary. Gaging stations used to calculate runoff to the Great Lakes are usually several miles inland, rather than at the mouth of the river. The reasons for this practice are outlined in Rantz and others (1982, p. 5-8). Correction factors are usually applied to the gaged flows in an attempt to account for probable changes in flow between the gaging station and the lake. Runoff is estimated for other ungaged areas in the same manner (Lee 1992). Stream flow data are reported by the USGS and the Water Resources Branch of Environment Canada (EC), but neither agency reports values for runoff in ungaged areas. Calculated runoff is reported elsewhere (Croley and others 2001). Overland flow is considered to be an insignificant input to the lake and therefore few attempts have been made to estimate the amount. It is believed that direct overland flow is accounted for when estimations are made for ungaged areas. Figure 1 shows the approximate location of all current (2002) gaging stations in the Great Lakes basin.

Canadian Data 

Most Canadian stream flow data are collected, managed, and archived by the Water Survey of Canada (WSC), a department of EC. This includes data from 316 currently operating stream gages, as well as historical data for nearly 600 discontinued stations. Stage heights are measured hourly to a resolution of 1 millimeter and used to calculate discharge. Daily, monthly, and annual discharge rates are calculated based on these measurements. All stream flow data are stored for up to six weeks by on-site data loggers and then retrieved by WSC field technicians for analysis. These data are reviewed prior to publication. Real time stream flow data are available in Canada, but only on a "cost share" basis. Discharge measurements are recorded in cubic meters per second, to three significant digits but not more than three decimal places. Exceptions to this standard are made for weir stations where four decimal places may be used. All published data are reported to a maximum of three decimal places. EC assures the quality of all published data, which is generally available 9 months after the close of the previous water year. More recent data are available, but are considered provisional until publication. All data, including both recent and historical data, are available on the HYDAT CD-ROM, available from Environment Canada and Greenland Engineering at a cost of $750 CAN. A web-based version of the HYDAT CD-ROM is planned, but no release date has been set. Other software, including the streamflow tool kit, is also available for manipulation of the HYDAT CD data sets. 

United States Data 

All United States streamflow data are collected, managed, and archived by the United States Geological Survey (USGS). This includes data for 327 currently operating stream gages in 89 distinct watersheds draining to the Great Lakes, as well as historical data for nearly 900 discontinued stations. Stage heights are measured every 15 minutes to a resolution of 1/10 inch and used to calculate discharge. These discharge values are reported to the nearest hundredth of a cfs for flows less than 1.0 cfs; to the nearest tenth of a cfs for flows ranging from 1.0 and 10 cfs; to the nearest whole number between 10 and 1000 cfs; and to three significant figures for all flows greater than 1000 cfs. Daily, monthly, and annual discharge rates are calculated based on these 15-minute measurements. The data are cataloged and reviewed prior to publication. The USGS assures the quality of all published data, which is generally available 6 months after the close of the previous water year. More recent data are available as well, but are considered provisional until publication. All data are available from the National Water Information System (NWIS) online free of charge, or on a state-by-state basis in annual Water Resources Data reports published in each district.

References

• Bibliographies of selected references

• Full reference list

• Sources of Hydrological data and information

This report is prepared by USGS in cooperation with the Great Lakes Commission.

The Great Lakes Commission is a  multi-agency, multi-disciplinary, multi-faceted team approach to addressing the science and policy of a Great Lakes water management regime will produce such application-oriented products as a water use web site, updated annual water use inventories, ecological evaluations of the system, and an integrated binational role for future Great Lakes-St. Lawrence endeavors.