|RI 71 - "A Strategy for a Stream-Gaging Network in Maryland"||contact: Publications(email@example.com)|
A STRATEGY FOR A STREAM-GAGING NETWORK
2000, MARYLAND GEOLOGICAL SURVEY REPORT OF INVESTIGATIONS 71
by Emery T. Cleaves and Edward J. Doheny
Water is a keystone resource. In abundance, it supplies cities, industries, and agriculture. To maintain healthy natural and human ecosystems, water must not only be present in adequate quantity, but it must be of suitable quality for its intended use. Water quality depends on the amount, or load, of contaminants, both natural and anthropogenic, that it contains. Accurate assessment of these contaminants requires that the amount of water flowing in a stream or river be known. To quantify streamflow in a given stream or river and the variation of that flow through time, it must be measured by use of stream gages. Monitoring water flow is fundamental to managing and protecting water resources, and requires a collaborative effort by all interested parties, including Federal, State, and local government agencies.
This report was prepared by the Stream-Gage committee of the Maryland Water Monitoring Council. The committee has been guided by the discussions and recommendations of a stream-gaging workshop (convened by the Council on October 16, 1997) and by responses to a data-users questionnaire sent by the Committee to 500 users of stream-gage data.
The Maryland Water Monitoring Council Stream-Gage committee recommends that Maryland's stream-gaging network be increased from 97 gages (in existence as of November 15, 1999) to 157 gages. The additional gages should be activated in stages according to six priority management goals: Coastal Plain Harmful Algal Blooms, small watersheds, core network, Clean Water Action Plan, flood hazard, and other unmet coverage (core/trend network, unmet 6- or 8-digit Hydrologic Unit Codes, unmet spatial coverage, and unmet physical-matrix categories; table 1). Drought assessment is also a major concern, and requires the continued operation of stream gages with long-term records.
Stream gages are operated throughout Maryland to meet numerous water-resources management goals of Federal, State, and local government agencies. Streamflow data are crucial to water-resources management goals in three fundamental ways -- evaluation of current conditions, watershed management and planning, and decision-support systems. Evaluation of current conditions includes issues related to (1) accounting for and tracking the distribution of streamflow, (2) regional and area assessments, (3) water quality, (4) ecosystems and aquatic living resources, (5) recreation, and (6) flood-hazard warning. In the area of watershed management and planning, streamflow data is basic to issues such as stream protection and restoration, water quality forecasting floods and droughts, and living resources (ecosystems). The stream-gaging network is also a vital decision-support system in which streamflow data are collected at the gages and then transmitted to a data-collected center. The data are then placed in a data base that is managed by the US geological Survey. Data from the data base are made publicly available in near real-time on the Internet, or in paper copy. This system supports many information and assessment needs for environmental management purposes, including emergencies such as flooding, contaminant spills, fish kills, or sediment violations, as well as modeling and model calibration, and research.
In recent years, the stream-gaging network in Maryland has varied from 95 active stations in 1985 to 76 active stations by the end of 1995. Ninety-seven stations were being operated as of November 15, 1999. Gaged watersheds range in drainage area from 0.03 square miles to 27,100 square miles. Approximately one-third of the stations have 50 or more years of continuous record. The oldest station in operation in Maryland is on the Potomac River at Point of Rocks (station number 01638500) with continuous record from February 1895 to the present.
|Table 1. Summary of Additional gages recommended for the stream-gaging network in Maryland|
[Note: Because of the multiple uses of stream gages, a gage used for the Coastal Plain Harmful Algal Bloom priority may also provide data for small watershed, flood hazard, core network, and so on. This has been taken into account in tabulating the total additions recommended for each subnetwork]
|Subnetwork priority||Reactivated stations||New stations||Total additions|
|Coastal Plain Harmful Algal Blooms||7||1||8|
|Clean Water Action Plan||0||2||2|
|Other unmet coverage||0||2||2|
To effectively address water-resource management goals, an adequate stream-gaging network for Maryland should include (1) gages that represent most of the region's principal watersheds, (2) various combinations of watershed size, land-use types, and physiography and geology of the State, and (3) gages that are continuously operated for extended periods of time. Because of the great natural range and variation in Maryland's physiography, geology, and watersheds, statewide stream-gage coverage is necessary.
Analysis of the physical matrix clearly indicates that Maryland's best current stream-gage coverage is in the Piedmont East Province. Most watershed-size and development categories in the Piedmont East are represented by at lease one stream gage. The Piedmont West, Blue Ridge, and Valley and Ridge Provinces has very little coverage except for large of regional watersheds with significant flow regulation or diversions. The entire Coastal Plain East in Maryland is represented by only six long-term stream gages. In addition, 13 of 18 of Maryland's large (6-digit Hydrologic Unit Code) watersheds have no active stream gages on their mainstem or tributaries. The Committee recommends activation of 2 new gages to meet this priority. Because of the multiple-use aspect of stream-gages data, only 2 additional gages would be necessary if the other priority subnetwork needs are met.
The stream-gaging network in Maryland also was analyzed in terms of its adequacy for meeting the information needs of a series of subnetworks: Coastal Plain Harmful algal Blooms, small watersheds, core network, Clean Water Action Plan, flood warning, droughts, and nontidal core/trends. Harmful algal blooms, such as Pfiesteria, are a continuing concern in the Chesapeake Bay and the Potomac River, especially in the sub-estuaries. These blooms are thought to be fueled in part by nutrients in streams that discharge into the sub-estuaries. To determine nutrient loadings of streams, streamflow information is combined with water-quality data. In Maryland, 27 stream gages in the Coastal Plain are currently active, down from 51 in operation in previous years. As a result, there are significant gaps in stream-gage coverage, especially on the Eastern Shore. Reactivation of seven gages is recommended (five on the Eastern Shore and two on the Western Shore). The Committee also suggests activation of one new gage in the Oceans/Coastal area of the Eastern Shore, on Trappe Creek.
Analysis of the watersheds across Maryland indicates that more than 50 percent of Maryland's river miles can be categorized as first- or second- order streams. The matrix shows a lack of long-term data in small watersheds of less than 5 square miles. On a statewide basis, only seven stream gages in small watersheds have 10 or more years of systematic record. At present, most stream gages are located on higher-order streams and are too few in number to assess the headwater area of the watersheds. The most significant problem raised at the Maryland water Monitoring Council Stream-gaging workshop in October 1997 was a lack of stations and long-term data in first- and second-order watersheds. Such gages are the key to understanding quantity and patterns in streamflow, groundwater contributions to the streamflow during periods of no runoff, and determination of contaminant loads that may be contributing to diminished water quality in the rest of the watershed. The active stream-gaging network includes 11 stations on first- and second-order watersheds. The Coastal Plain East, Piedmont West, Blue Ridge, and Valley and Ridge Provinces are completely unrepresented in this category. To address this data and information gap, the Committee recommends adding 10 new stream gages on small watersheds and reactivating 11 discontinued gages.
Core network stream gages represent natural hydrologic conditions and trends that reflect the effects of land use, physiography, and geology. They provide a data record needed to assess the effects of natural and manmade changes in Maryland's watersheds over time. In water year 1999, 57 core network stream gages were in operation in Maryland. Although the total number of core network gages in Maryland increased from 51 in 1994 to 57 in 1999, the core network stations continue to change. Most physiographic regions, including the Coastal Plain East, Coastal Plain West, Piedmont West, Blue Ridge, and Valley and Ridge Provinces, are poorly represented. On a statewide basis, Maryland does not have an adequate core network of stream gages at the present time. The Committee recommends that 20 gages be reactivated and 2 new ones be added to address this priority issue.
The Clean Water Action Plan is an initiative designed to fulfill the original goals of the Clean Water Act - fishable, swimmable, and safe water for all Americans (Clean Water Action Plan Technical Workgroup, 1998). As part of the Clean Water Action Plan, the State of Maryland has identified twelve Category 1 priority watersheds where restoration is required, and five Category 3 priority watersheds where protection is required. Of the twelve Category 1 watersheds, five are currently ungaged: (1) Deep Creek Lake, (2) Mattawoman Creek, (3) Upper Elk River, (4) Wye River, and (5) Lower Pocomoke River. Another of the priority watersheds, Upper Monocacy River, has partial coverage, but additional coverage is needed to understand the aquatic systems on a watershed level. The five Category 3 watersheds are related to surface-water reservoirs and are considered high priority for protection. These include (1) Prettyboy Reservoir, (2) Liberty Reservoir, (3) Loch Raven Reservoir, (4) Brighton Dam at the Tridelphia Reservoir and (5) Rocky Gorge Dam at the T. Howard Duckett Reservoir. Prettyboy Reservoir, Liberty Reservoir, and Loch Raven Reservoir do not have stream gages at their outlets. The Committee recommends that two new stream gages be added, in addition to those recommended for subnetwork priorities 1, 2, and 3.
Flood-hazard warning, flood predictions, and identification and assessment of droughts require long-term stream-gage data. Ten years of peak-flow values is generally accepted as a minimum requirement for development of a flood probability estimate. As of water year 1998, Maryland had 43 stream gages that (1) had 10 or more years of continuous data with no breaks in the record, (2) were representative of Maryland's individual physiographic provinces rather than larger, multiple-physiographic regions, and (3) were not affected by extensive or complete regulation that would prevent development of a flood-frequency distribution. The Committee recommends that 2 stream gages be reactivated and 3 new stream gages be established so that flow data needed for flood- and drought-related analyses can be collected in locations where none is presently available.
Below-normal rainfall during 1998 and 1999 resulted in Maryland's most severe drought since those of 1930-31 and 1965-66. Record-low streamflow conditions and reservoir levels led to statewide restrictions on water. Fish kills occurred due to low levels of dissolved oxygen in streams and rivers. In addition, the drought also had severe economic impact due to lost crops and inadequate grazing conditions for livestock. Fifty stream gages in the active network have continuous records dating back through the 1965-1966 drought. These records allow hydrologist to compare and contrast these two major events. Of these 50 gages, 12 have continuous records dating back to the 1930-1931 drought. These data and their comparative value emphasize the need to operate stream gages for long periods of time.
The present core/trends water-quality network focuses on the Piedmont East, Piedmont West, Blue Ridge, and Valley and Ridge Provinces. Reactivation of the 6 discontinued stream gages associated with the network sites in theses areas would strengthen nutrient-loading analyses of the State's watersheds and enhance estimates of Total Maximum Daily Loads that currently are being made by the Maryland Department of the Environment. This can be achieved by Reactivation of stream gages in Subnetwork Priorities 1-6. As the core/trends water-quality network expands into the Coastal Plain East and Coastal Plain West, it could be paired with the existing stream-gage network (currently 27 stream gages) and proposed Reactivation of 7 stream gages to help provide data for nutrient loadings related to Harmful Algal Blooms. Establishment of new stream gages throughout Maryland should take into account the needs of the core/trends network.
The uses and users of stream-gage data were identified through a users survey in the spring of 1998. Five hundred questionnaires were distributed, and 102 responses were received. Twenty specific uses were identified, of which 18 were common to all gages. For each stream gage there were a minimum of 7 and a maximum of 15 users.
The Committee recommends that future stream-gage costs be shared on the basis of data needs and Federal, State or county/municipal interest. Federal interest focuses on basin-scale (6-digit Hydrologic Unit Code watersheds) and regional trends and conditions related to water-quality assessment. Such stream gages should be funded 100 percent by the Federal Government. Shared Federal, State and county/municipal interests include representative 8-digit Hydrologic Unit Code watersheds, Clean Water Action Plan watersheds, water-supply reservoirs, flood-drought hazards, and small watersheds. The costs of these gages can be shared by Federal (50 percent), State (25 percent), and county/municipal agencies (25 percent) through the U.S. Geological Survey Federal-State Cooperative Program, pending availability of such funds. In locations where gaps remain in the spatial coverage and physical matrix categories, the Committee recommends that cost sharing be split between State or county/municipal sources and the U.S. Geological Survey Federal-State Cooperative Program, pending availability of such funds.