The average inflow to the Sound in 7 consecutive days of a dry 

 weather period may be expected to go below 3^000 cfs (0.18 cfs per square 

 mile) once in ten years. Regulation of the three principal streams entering 

 the Sound holds the dry-weather inflow at a higher level than would occur 

 without regulation. The 7-day, 10-year annual minimum runoff from unregulated 

 tributaries in the mainland part of study area ranges from 0.01 to 0.05 cfs 

 per square mi le. 



4.3 Coastal streams 



The 66 mainland coastal streams flowing directly into the Sound, 

 other than the Thames, Connecticut and Housatonic Rivers, have a combined 

 drainage area of 1,467 square miles. The three largest are the Pawcatuck 

 River (304 square miles), the Q.uinnipiac River (166 square miles), and the 

 Saugatuck River (93.2 square miles). Drainage areas of the other coastal 

 streams vary from about 1 to 64 square miles, with most ranging from 3 to 

 30 square mi les. 



The average annual runoff from a sample of mainland coastal streams 

 (mean drainage area less than 10 square miles) is 1.8 cfs per square mile; 

 the average monthly runoff varying from a high of 3.9 cfs per square mile in 

 March to a low of 0.5 cfs per square mile in August. The 7-day, 10-year 

 annual minimum runoff is estimated to be about 0.01 cfs per square mile, 

 which is probably close to the lowest 10-year runoff to be expected from the 

 mainland coastal streams. 



An estimated 77 cfs (50 mgd) is discharged into the Sound from 

 coastal streams on Long Island. The four continuously gaged streams that 

 flow into the Sound (Glen Cove Creek, Mill Neck Creek, Cold Spring Brook and 

 the Nissequogue River) have surface drainage areas of 7 to 27 square miles 

 and average annual runoff of 4.6 to 42.1 cfs. In comparison with mainland 

 streams, the variation in annual and average monthly runoff is small. For 

 example, the average monthly flow of the Nissequogue River during the highest 

 average month (March) is 45.6 cfs, only 1.2 times greater than the lowest 

 average month (October) . 



Under natural conditions 90 to 95 percent of Long Island stream- 

 flow consists of ground-water discharge and as a result the correlation be- 

 tween surface drainage areas and average flows is poor. In areas of urban 

 development, however, direct runoff constitutes a much higher percentage of 

 total discharge. 



4.4 Annual maximum streamflows 



The mean of the annual maximum discharges (the "mean annual flood") 

 for the continuous-record stations in and near the mainland part of study area 

 ranges from 10 cfs per square mile for a drainage area of 10,000 square miles 

 to about 50 cfs per square mile for a drainage area of 10 square miles. The 

 maximum discharge of the Connecticut River near Middletown (10,900 square mile 

 basin) was 267,000 cfs on March 12, 1936, while combined maximum discharge for 

 the seven largest rivers flowing to the Sound (gaged drainage area of 13,900 

 square miles) was more than 400,000 cfs in March 1936 and in August 1955. 



22 



