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Streams Affecting Jamestown Jamestown is directly affected by two moun- tain streams that converge at a point located just below the Ward Street Culvert at the westem edge of town (see Appendix B - Map of Streams). James Creek, joined by the Little James Creek at Ward Street, flows through the center of town in west-east direction pass- ing under the Anderson and Main St. bridges before heading eastward down James Can- yon. Further downstream, James Creek even- tually joins Lefthand Creek which itself continues to flow east until it meets St. Vrain Creek near Longmont. James Creek provides the primary source of water for the commu- nity of Jamestown. A new filtration system has recently been completed and the intake pipe is located along the James Creek, up- stream from its confluence with the Little James. James Creek, flowing from the west, has a total drainage area of about 18.7 square miles at its downstream confluence with Lefthand Creek. The Little James Creek, flowing into town from the northwest, drains approxi- mately 3 square miles where it meets James Creek in town. Approximately 1.1 miles out- side ofthe town proper, there is an unnamed tributary to the Little James that has sub- stantial potential to impact Jamestown in the event of a future severe rainfall event. The unnamed tributary to the Little James Creek is classified as intermittent and it runs directly through the old Burlington Mine site just southeast of Balarat road. This heavily mined area is littered with debris and con- tains a filled-to-capacity tailings pond of un- known volume located approximately 100 yards upstream from the confluence with Lit- tle James Creek. Located directly below this Figure - 4 - Road Embank1rU!nt Above Ja1rU!stown confluence, there is a dirt road embankment approximately 40 ft high and 60 ft long that crosses the Little James and forms a potential impoundment for flood waters draining into the Little James and its tributary. A culvert pipe 5 ft in diameter runs undemeath the embankment but the likelihood of its clogging in a storm preceding a flood event is extremely high. Indeed, the Flood Insurance Study con- ducted in 1983 by FEMA shows the 50-yr., the 100-yr., and the 500-yr. flood events topping over this privately owned dirt embankment. What is a 100 yr. Flood Event? The science of predicting the effect of floods on lives and property falls largely to hydrolo- gists. They estimate future floods by studying the past behavior of a stream. Floods are often categorized according to their return interval -10-,50-,100-, and 500-year floods. Each flood interval is related to a percent chance that a flood may actually occur within a given year. This has caused considerable confusion at times: a 100-year flood does not happen with absolute regularity every 100 years. Rather, a 1oo-year flood may occur at 4