(Area of watershed, 75.2 square miles.) ---------+--------------------+------------------------------- | Per Square Mile. | Rainfall. Month. +--------------------+----------+----------+--------- |Cubic Feet |Million |Collected,|Per Cent | Total, |per Second.|Gallons |Inches. |Collected.| Inches. | |per Day.| | | ---------+-----------+--------+----------+----------+--------- January | 1.937| 1.252| 2.233| 51.6| 4.33 February | 2.904| 1.877| 3.050| 71.7| 4.26 March | 4.489| 2.901| 5.175| 117.4| 4.41 April | 3.124| 2.019| 3.485| 107.5| 3.24 May | 1.680| 1.086| 1.936| 58.1| 3.33 June | .735| .475| .821| 28.0| 2.93 July | .305| .197| .352| 9.3| 3.77 August | .478| .309| .551| 13.3| 4.16 September| .376| .243| .419| 13.0| 3.23 October | .829| .536| .956| 21.9| 4.37 November | 1.474| .953| 1.645| 39.0| 4.22 December | 1.612| 1.042| 1.859| 51.9| 3.58 +-----------+--------+----------+----------+-------- Year | 1.655| 1.070| 22.482| 49.1| 45.83 ---------+-----------+--------+----------+----------+-------- =168. Run-off of Sudbury Watershed.=—Table VIII has been given by Mr. Charles W. Sherman, as representing the average yield of the Sudbury watershed for the period 1875 to 1899, inclusive, expressed in several different ways. The average rainfall was 45.83 inches, and the percentage which represents the run-off is 49.1 per cent of the total. The average monthly run-off varies from .305 cubic foot (for July) to 4.489 cubic feet (for March) per second per square mile. As a general rule it may be stated that the average run-off from the drainage areas of New England streams amounts very closely to 1,000,000 gallons per square mile per day. The area of the Sudbury watershed is 75.2 square miles, with 6.5 per cent of that total area occupied by the surface of lakes or reservoirs. As will presently be seen, the amount of exposed water surface in any watershed has an appreciable influence upon its run-off.