D B 20 feet above the gage datum, or an elevation of 275.83 feet. A flood in July 1994 established a record gage height of 34.11 feet, or 289.94 feet above sea level. This corresponds to the 290-foot contour line on the map. Trace the 290-foot contour line on both sides of the Flint River and label the area within these contours where the land is lower than 290 feet 1994 Flood Hazard Zone. Name two essential public utilities or facilities that were submerged by the flood, and infer the possible impact that flooding those facilities might have had on the environment and on quality of life in Montezuma, Oglethorpe, or downstream communi- ties after the flood. C Notice line X-Y near the top center part of Fig. A12.7.1. 1. The map shows the Flint River at its normal stage. What is the width of the Flint River at its normal stage along line X-Y? ft 2. Approximately how wide was the river along this line when it was at maximum flood stage (290 feet) during the July 1994 flood? ft marshy land between the river and the steep escarpments that develop by erosion during floods. Notice the floodplain of the Flint River along line X-Y on the map in Fig. A12.7.1. The floodplain is the relatively flat, 1. What is the elevation of the floodplain at point Z near line X-Y, expressed in feet above sea level? ft ft 2. How deep was the water that covered that floodplain at point Z during the 1994 flood? 3. How did you derive your answer? or abnormal magnitude for this river? Explain your reasoning. 4. Did the 1994 flood stay within the floodplain and its bounding valley slopes? Does this suggest that the 1994 flood was of normal E The USGS has compiled a list of the highest water levels in the Flint River at the Montezuma gaging station for 114 years (1897 and 1905-2017). Parts of the data have been summarized in the Flood Data Table in Fig. A12.7.2. Flood Data Table Recurrence Intervals for Selected, Ranked, Annual Highest Stages of the Flint River over 114 Years of Observation (1897 and 1905-2017) at Montezuma, Georgia (USGS Station 02349605, data from USGS) River elevation Percent chance Number of years of data (n) Rank of annual highest river stage (S) Year River elevation above gage (gage height), in feet (GH) From Result of sorting Gage elevation (datum) above sea level, in feet (GD) above sea level, in feet (RE) Recurrence interval (RI), in years Probability of occurring in any given year of occurring in any given year USGS by maximum From From gage height USGS From USGS USGS RE = GH + GD 114 RI = (n+1)/S "1 in RI" S/(n+1) or 1/ 114 114 114 114 12345 1994 34.11 255.83 289.94 1929 1 in 27.40 255.83 283.23 1 in 1990 26.05 255.83 281.88 1 in 1897 26.00 255.83 281.83 1 in 1949 25.20 255.83 281.03 1 in 114 10 9% 1961 24.00 255.83 279.83 11.5 1 in 11.5 13% 114 15 1944 22.40 255,83 278,23 7.7 1 in 7.7 17% 114 20 1966 21.65 255.83 277.48 5.8 1 in 5.8 20% 114 30 1979 20.72 255.83 276.55 3.8 1 in 3.8 358 1 in 2.9 114 40 1980 19.38 255.83 275.21 2.9 1 in 2.3 114 50 1957 18.70 255.83 274.53 2.3 1 in 1.9 1.9 114 60 1921 18.00 255.83 273.33 1 in 1.6 1.6 114 70 1953 17.40 255.83 273.23 1.4 114 80 1956 16.10 255.83 271.93 1.3 114 90 1955 14.40 255.83 270.23 1.2 114 100 1918 13.30 255.83 269.13 1.0 1941 9.30 255.83 265.13 1 in 1.4 1 in 1.3 1 in 1.2 1 in 1.0 1 in 1.0 43% 52% 61% 10% 184 574 1.0 7.39 255.83 263.22 Name: apping, Assessment, and Risk Course/Section: Activity 12.7 Date: a river. You will use your analysis to identify flood hazard zones. Learning GOAL You will use maps and data to analyze the area, frequency, and magnitude of flooding in the floodplain of A On the portion of the 7.5-minute topographic map of Montezuma, Georgia (Fig. A12.7.1), locate the gaging station on Flint River in the middle of the map. The center of the map is near latitude 32.30°N, longitude 84.05°W. The elevation from which the gage measures changes in river level—the gage datum-is at an elevation of 255.83 feet above sea level, and the height of the river relative to this datum is called the gage height or stage. The river is considered to be at flood stage when the gage height is CAMP RD 49 90 28 BUCK CREEK BYP Mobile home park Post Office 128 214 300 Buck Creek Oglethorpe Mill Creek Chase Lake Chase Lake Dam 0 Figure A12.7.1 300 Sewage treatment pond 008- SAGEO 300- Z Gaging station 49 95 90 26 North Contour interval 10 Feet Flir 1 km 5000 ft Flint-River Bethel Church 300 Cole Dam School Montezuma 49 Felton Cemetery 90 45 Drinking water filtration plant Creek Sp pring. 90 300 E.RAILRO Beaver Creek Montezuma Post Office e Georgia Power Co -Hospital- 90 Spring Creek PondSpring Creek Pond Dam Travelers Rest Travelers Rest Cemetery 337