1987 Wetland Delineation Manual - The Wetlands Regulation Center
1987 Wetland Delineation Manual - The Wetlands Regulation Center
1987 Wetland Delineation Manual - The Wetlands Regulation Center
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<strong>Wetland</strong> Delination <strong>Manual</strong>, <strong>1987</strong> 36<br />
(1) Routine approach. Determine the highest water level elevation reached during the growing<br />
season for each of the most recent 10 years of gage data. Rank these elevations in descending<br />
order and select the fifth highest elevation. Combine this elevation with the mean sea level<br />
elevation of the gaging station to produce a mean sea level elevation for the highest water level<br />
reached every other year. Stream gage data are often presented as flow rates in cubic feet per<br />
second. In these cases, ask the CE District's Hydrology Branch to convert flow rates to<br />
corresponding mean sea level elevations and adjust gage data to the site. Compare the<br />
resulting elevations reached biennially with the project area elevations. If the water level<br />
elevation exceeds the area elevation, the area is inundated during the growing season on<br />
average at least biennially.<br />
(2) Comprehensive approach. Complete the following:<br />
(a) Decide whether hydrologic data reflect the apparent hydrology. Data available from the<br />
gaging station may or may not accurately reflect the area hydrology. Answer the following<br />
questions:<br />
• Does the water level of the area appear to fluctuate in a manner that differs from that of the<br />
water body on which the gaging station is located? (In ponded situations, the water level of the<br />
area is usually higher than the water level at the gaging station.)<br />
• Are less than 10 years of daily readings available for the gaging station?<br />
• Do other water sources that would not be reflected by readings at the gaging station appear to<br />
significantly affect the area? For example, do major tributaries enter the stream or tidal area<br />
between the area and gaging station?<br />
If the answer to any of the above questions is YES, the area hydrology cannot be determined<br />
from the gaging station data. If the answer to all of the above questions is NO, PROCEED TO<br />
(b).<br />
(b) Analyze hydrologic data. Subject the hydrologic data to appropriate analytical procedures.<br />
Either use duration curves or a computer program developed by WES (available from the<br />
Environmental Laboratory upon request) for determining the mean sea level elevation<br />
representing the upper limits of wetland hydrology. In the latter case, when the site elevation is<br />
lower than the mean sea level elevation representing a 5-percent duration of inundation and<br />
saturation during the growing season, the area has a hydrologic regime that may occur in<br />
wetlands. NOTE: Duration curves do not reflect the period of soil saturation following<br />
dewatering.<br />
When all of the above have been considered, PROCEED TO STEP 9.<br />
• STEP 9 - Determine Whether Hydrology Is Adequately Characterized. Examine the<br />
summarized data and determine whether the hydrology of the project area is adequately<br />
25 February 1997 Environmental Techncal Services Co. 834 Castle Ridge Rd Austin, Texas 78746