MONITORING AND DATA ON MINNESOTAS RIVERS
Monitoring is essential to policy, planning, and management of Minnesotas streams and rivers. Monitoring efforts focus on both the quantity of water flowing in Minnesotas streams and rivers and its quality. Numerous federal, state and local agencies, as well as some non-governmental organizations, engage in monitoring activities. This chapter provides an overview of monitoring activities affecting Minnesotas rivers and streams and the agencies responsible for collecting, analyzing, reporting and storing the information. The discussion focuses first on flow-related monitoring activities and then examines water quality-related endeavors.
RIVER AND STREAM FLOW MONITORING
Flow-related monitoring activities permit tracking of stream flow conditions and forecasting extreme events such as floods and droughts. Monitoring data accumulated over many years enable managers to describe flow characteristics, assess in-stream flow needs, define available supplies, and ensure adequate water availability to meet long-term needs. These data also contribute to understanding how stream flow conditions in the state affect water quality and ecosystems.
Formal water quantity-related monitoring began in Minnesota with rainfall record-keeping in the early 1800s. The collection of stream-flow data began in 1909 when the U.S. Geological Survey (USGS) and Minnesota state agencies entered into cooperative agreements for the systematic collection of stream-flow records. State agencies that assist in collecting data through cooperative agreements with the USGS include the DNR, PCA, and Department of Transportation (MDOT); watershed management organizations, native American tribal government organizations, and watershed and conservation districts also have such agreements.
In the late 1930s, the USGS began a national stream gaging program with the establishment of a network of state-USGS gaging stations. Gaging stations measure the streams stage (water level) and discharge rate (rate of flow). This national network is the principal tool used to measure surface-water supplies in each state. Stream gages with continuous stage-recording devices provide an ongoing record of stage and individual measurements of discharge. Agencies also obtain high-flow data by discrete measurements at partial-record stations.
The size of the stream-gage network in Minnesota reached its peak in 1975 with 150 continuous-recording gage sites. In 1989, technological advances allowing real-time electronic data collection and transmission at stations enhanced network capabilities. However, because of federal and state budgetary cuts, only 104 continuous-recording gaging stations have been in operation since 1993. Only 43 of the 81 major watersheds in Minnesota contain continuous recording gages. The locations of gaging stations operated by the USGS and DNR are shown in Figure 5.1.
The National Weather Service River Forecast Center uses stream gage data in order to model flows and forecast river flooding. About 95% of the gaging sites used by the NWS are shared with state agencies and the USGS. Where continuous data are not available, the NWS collects data manually. Data at these sites are collected on a daily basis during critical periods of high flow. The NWS uses its data to issue daily flow reports and to forecast future flows. It stores the data for only 30 days; however, the information is available to other agencies. The U.S. Army Corps of Engineers (Corps) also relies on stream flow monitoring data in the operation of its reservoirs, locks, and dams. It partially funds sites it shares with the USGS in the Upper Mississippi River Basin.
Flow Data Analysis, Reporting and Storage
Stream-flow data for Minnesota consists of information on stages (water levels) and discharge rates (flow in cubic feet per second). These data, in conjunction with other factors that may affect the relationships between stage and discharge rates, such as weather records, are used to construct stage-discharge relation curves or tables. Stage-discharge curves and tables are used to provide estimates of daily mean discharge rates from daily mean stage data.
The Water Resources Division of the USGS stores the data from Minnesotas gaging stations in the national USGS Streamflow database called WATSTORE. The USGS publishes an annual report for the state entitled Water Resources Data - Minnesota, for each water year. The USGS water year, beginning October 1 and ending September 30, is identified by the calendar year in which it ends. Annual flow data also are available on-line from the USGS at http://h2o.er.usgs.gov/.
The Stream Flow Unit of the Minnesota DNR gathers and analyzes data on rivers and streams throughout Minnesota. The unit produces a weekly report on stream flow conditions during the open water season for water managers and other concerned interests. Data from these reports come from a variety of federal, state, and regional agencies and volunteer gage readers. The DNR also prepares special reports when conditions within certain rivers and streams approach significantly low- or high-flow levels. The DNR identifies several threshold levels for each gaging station and time of year: Q90 - stream flow is at least this high 90 percent of the time; Q75 - stream flow is at least this high 75 percent of the time; Q25 - stream flow is as high as this only 25 percent of the time, and; Q10 - stream flow is as high as this only 10 percent of the time (Table 5.1).
When flows fall below the Q90 level, the river is considered to be in a critically low flow condition, and it is closely monitored as long as flows remain below the threshold. The DNR Division of Waters may restrict appropriation of water from the river to maintain adequate flow for in-stream needs such as fish and wildlife and ensure adequate supplies for higher priority users such as municipal supplies and for power generation. At the other end of the spectrum, critically high levels, those exceeding the Q10 level, indicate potential flood conditions that threaten damage to property. Flood flows are generally defined using the flood stages identified by the NWS or other agencies. In watersheds where a flood stage has not been identified, the highest monthly Q10 is used as an interim estimate of flood flow.
5.1 Definition of DNR Threshold Stream Flow Values
Based on historical monitoring data.
Using the Stream and Watershed Information System under development at the Minnesota Land Management Information Center (LMIC), interested people can compare and analyze different kinds of water and land related data. The Legislative Commission on Minnesota Resources funded its development in 1991. Presently, Geographic Information System (GIS) data have been created, and some data from monitoring agencies have been integrated to the map layers. Data can be obtained online at the LMIC website (www.lmic.state.mn.us).