Evaluation of the Stream-Gaging Network in Delaware
By Edward J. Doheny
Abstract
The stream-gaging network in Delaware is a major component of many types of hydrologic investigations. To ensure that the network is adequate for meeting multiple data needs by a variety of users, it must represent the range of hydrologic conditions and land-use types found in Delaware, and include enough stations to account for hydrologic variability. This report describes the current stream-gaging network in Delaware and provides an evaluation of its representativeness for the State.
Temporal trends in numbers of stations operated during water years 1975-97 are presented for continuous-record stream-gaging stations in Delaware. The results of this analysis indicate (1) significant variability in the number of stations operated over time, especially during water years 1980-84, and 1989-97, (2) most continuous-record stream-gaging stations activated during 1975-97 are not being maintained for sufficient periods of time to account for local temporal hydrologic variations, and (3) stations on streams and rivers in small drainage basins (10 square miles or less), are not being maintained, especially during 1981-97.
Temporal trends were also investigated for low-flow partial-record stations, nontidal crest-stage partial-record stations, tidal crest-stage partial-record stations, and surface-water-quality stations operated in Delaware during water years 1975-97. The results indicate variable and non-systematic activity over time for these types of stations, except for the tidal crest-stage partial- record stations.
An analysis of the representativeness of the active continuous-record stream-gaging network in Delaware reveals that several principal drainage basins in the Coastal Plain Physiographic Province are currently ungaged, and there is significantly less spatial coverage by gaging stations in the Coastal Plain than in the Piedmont Physiographic Province. Analysis of land-use types in drainage basins with active continuous-record stream-gaging stations shows a lack of stations in small, in pre-dominantly forested drainage basins in the Coastal Plain, predominantly urban areas in the Coastal Plain, and in locations in the Piedmont where farmland is predominant. Analysis of 1990 Census population data in drainage basins with active continuous- record stream-gaging stations indicates that approximately 23 percent of Delaware’s inhabitants are residing in drainage basins that are gaged.
A general strategy is presented for improving the current network coverage on the basis of analyses of trends and representativeness. Recommendations from the strategy include (1) maintaining operation of all active continuous-record stream-gaging stations; (2) stronger efforts to maintain operation of new stations for a minimum of 5 years, and preferably for 10 years or more; (3) assigning priority to the Coastal Plain for the activation of new stations to improve coverage; and (4) consideration of ungaged principal drainage basins, land-use characteristics of drainage basins, and locations of projected population growth in future decisions regarding activation of stream-gaging stations. Southern New Castle County and the Leipsic River Basin are presented as examples of locations where gaps in network coverage exist.
An inventory of active and inactive stream-gaging stations in Delaware is presented in Appendix 3. This inventory includes listings of continuous-record stream-gaging stations, low- flow partial-record stations, tidal crest-stage partial-record stations, nontidal crest-stage partial-record stations, and surface-water-quality stations. Maps are included in Appendix 4 to illustrate the spatial distribution of active and discontinued stream-gaging stations in Delaware.
