Statistical characteristics of stream discharge in tributaries of selected estuaries in southern New Jersey

This report presents the results of a study, done in cooperation with the New Jersey Department of Environmental Protection, to analyze the characteristics of stream discharge for tributaries of the estuaries of the Metedeconk, Toms, Great Egg Harbor, Tuckahoe, and Maurice Rivers.The following statistics were calculated for selected streamflow-gaging stations:(1) mean annual and mean monthly discharge, and (2) lowest annua] 7-day mean discharge for selected recurrence intervals.Values of lowest annual 7-day mean discharge were calculated for the entire year and for the 3-, 4-, 5-, and 6-month periods of greatest tributary discharge.The monthly variation in discharge was examined.Values of discharge at different stations were converted to runoff and compared; runoff is expressed as discharge per unit area of drainage for a given period.Tests for trend were conducted on values of monthly discharge and lowest annual discharges at continuous-record stations.Statistics were determined from discharge records of the U.S. Geological Survey.The monthly variation in discharge is similar for most streams in the study area; discharge is greatest during March and April and least during August, September, and October.The 3-, 4-, 5-, and 6-month periods of greatest discharge are February through April, January through April, January through May, and December through May, respectively.Mean annual runoff is greater in the tributaries of the Metedeconk and Toms River estuaries than in the tributaries of the other estuaries.Runoff in tributaries of these two basins ranges from 24 to 29 inches per year; the corresponding range for tributaries of the other estuaries is 16 to 23 inches per year.Trend analysis showed that values of lowest annual discharges at continuous-record stations on tributaries of all five estuaries decreased during water years 1970-89.For four stations, values of 183-day lowest annual discharge during the complete year decreased; for three stations, values of lowest annual 7-or 30-day mean discharge during the 3-, 4-, 5-, and 6-month periods of greatest discharge decreased.There were no trends in monthly discharge for water years 1970-89.For other periods tested, there were no trends either in lowest annual discharges or monthly discharges.Discharge statistics at the heads of tide were calculated from the period-of-record characteristics at continuous-record stations and characteristics determined for partial-record stations.Results show that discharge at the heads of tide of the estuaries is directly related to the drainage area.Drainage areas and discharge are greatest for the Great Egg Harbor and Maurice Rivers, whose mean annual discharges are 340 and 310 cubic feet per second, respectively.Mean annual discharges of the Toms and Metedeconk Rivers are 220 and 140 cubic feet per second, respectively.Drainage area and discharge of the Tuckahoe River are the smallest of the estuaries studied; mean annual discharge is 43.9 cubic feet per second.