9 



£. USGS quadrangle maps. Is there a significant, well-defined 

 drainage through the area? Is the area within a maior flood- 

 plain or tidal area? What range of elevations occur in the 

 area, especially in relation to the elevation of the nearest 

 perennial watercourse? 



b. NWI overlays or maps. Is the area shown as a wetland or 

 deepwater aquatic habitat? l\Tiat is the water regime modifier? 



c. EIAs, EISs, or GDMs that describe the project area. Extract 

 any pertinent hydrologic data. 



d. Floodplain management maps. These maps may be used to extrap- 

 olate elevations that can be expected to be inundated on a 1-, 

 2-, 3-year, etc., basis. Compare the elevations of these fea- 

 tures with the elevation range of the project area to determine 

 the frequency of inundation. 



e. Federal, State, and local government documents (e.g. CE 

 floodplain management maps and profiles) that contain 

 hydrologic data. Summarize these data. 



f. Recent (within past 5 years) aerial photography that shows the 

 area to be inundated. Record the date of the photographic 

 mission. 



£. Newspaper accounts of flooding events that indicate periodic 

 inundation of the area. 



h. SCS County Soil Surveys that indicate the frequency and 



duration of inundation and soil saturation for area soils. 



CAUTION: Data provided only represent average conditions for a 

 particular soil series in its natural undrained state, and can- 

 not be used as a positive hydrologic indicator in areas that 

 have significantly altered hydrology. 



i. Tidal or stream gage data for a nearby water body that 



apparently influences the area. Obtain the gage data and 

 complete (1) below if the routine approach is used, or 

 (2) below if the comprehensive approach is used (OMIT IF GAGING 

 STATION DATA ARE UNAVAILABLE) : 



(1) Routine approach. Determine the highest water level 



elevation reached during the growing season for each of 

 the most recent 10 years of gage data. Rank these eleva- 

 tions in descending order and select the fifth highest 

 elevation. Combine this elevation with the mean sea level 

 elevation of the gaging station to produce a mean sea 

 level elevation for the highest water level reached every 

 other year. NOTE: Stream gage data are often presented 

 as flow rates in cubic feet per second. In these cases, 

 ask the CE District's Hydrology Branch to convert flow 

 rates to corresponding mean sea level elevations and 

 adjust gage data to the site. Compare the resulting ele- 

 vations reached biennially with the project area eleva- 

 tions. If the water level elevation exceeds the area 



A9 



