Wisconsin Administrative Code › Department of Agriculture, Trade and Consumer Protection › ATCP 20-54 - Agricultural Resource Management › Chapter ATCP 48 - Drainage districts › Subchapter IX - Grants to County Drainage Boards › Appendix A - ESTIMATING WATER SURFACE ELEVATIONS

Current through June 24, 2024
Water Surface Elevations; Base Flow
One may use any of the following methods to estimate the
					 water surface elevation, at base flow, at any point along a district
					 drain:
Base Flow Method 11. Identify the stream to which the
					 district drain discharges. Select the data set from the corresponding drainage
					 basin on pp. 25-401 of Water Resources Data-Wisconsin Water Year 1997.1
2. Calculate the base flow rate by dividing the "90 percent
					 exceeds" value for the period of record by the drainage area of the relevant
					 drainage basin. The resulting value will be expressed in cubic feet per second
					 per square mile (cfsm).
3. Multiply the cfsm value by the area of land (expressed
					 in square miles) which is drained by the district drain to the relevant point
					 along the drain. The resulting value is the base flow rate for the district
					 drain at that point.
4. Calculate base flow depth (at the relevant point along
					 the drain) using the base flow rate, the drain cross-sectional dimensions (at
					 the relevant point along the drain), and Manning's equation for open channel
					 flow.
5. Add the base flow depth to the bottom elevation of the
					 district drain at the relevant point. The resulting value is the base flow
					 elevation at that point.
Base Flow Method 2
Conduct a field survey to measure the dominant discharge
					 elevation in the district drain. The dominant discharge elevation is the lowest
					 elevation at which vegetation is present. If vegetation has been disturbed, the
					 dominant discharge elevation is the interface between unsaturated and saturated
					 soils, as indicated by soil mottling.
Peak Water Surface Elevations; 10-Year 24-Hour Storm Event
One may use the following method to estimate the peak
					 water surface elevation, at any point along a district drain, in the event of a
					 10-year 24-hour storm event:
1. Determine, from Flood Frequency Characteristics of
					 Wisconsin Streams, 2 page 7, the flood-frequency area in which the district
					 drain is located.
2. Calculate the peak flow rate from a 10-year 24-hour
					 storm event using, from Flood Frequency Characteristics of Wisconsin Streams,
					 page 9, the Q10 equation for the relevant flood-frequency area.
3. Calculate the peak flow depth (at the relevant point
					 along the drain) using this peak flow rate, the drain cross-sectional
					 dimensions (at the relevant point along the drain), and Manning's equation for
					 open channel flow.
4. Add this peak flow depth to the bottom elevation of the
					 district drain at the relevant point. The resulting value is the peak water
					 surface elevation, at that point, in the event of a 10-year 24-hour storm
					 event.
Peak Water Surface Elevations; 25-Year 24-Hour Storm
					 Event
One may use the following method to estimate the peak
					 water surface elevation, at any point along a district drain, in the event of a
					 25-year 24-hour storm event:
1. Determine, from Flood Frequency Characteristics of
					 Wisconsin Streams, 3 page 7, the flood-frequency area in which the district
					 drain is located.
2. Calculate the peak flow rate from a 25-year 24-hour
					 storm event using, from Flood Frequency Characteristics of Wisconsin Streams,
					 page 9, the Q25 equation for the relevant flood-frequency area.
3. Calculate the peak flow depth (at the relevant point
					 along the drain) using this peak flow rate, the drain cross-sectional
					 dimensions (at the relevant point along the drain), and Manning's equation for
					 open channel flow.
4. Add this peak flow depth to the bottom elevation of the
					 district drain at the relevant point. The resulting value is the peak water
					 surface elevation, at that point, in the event of a 25-year 24-hour storm
					 event.
1 Water Resources Data-Wisconsin Water Year 1997, by B.K.
					 Holmstrum, D.L. Olson, and B.R. Ellefson; U.S. Geological Survey; Water-Data
					 Report WI-97-1; 1998.
2 Flood Frequency Characteristics of Wisconsin Streams, by
					 William R. Krug, Duane H. Conger and Warren A Gebert; U.S. Geological Survey;
					 Water Resources Investigations Report 91-4128; Madison, Wisconsin, 1992.
3 Flood Frequency Characteristics of Wisconsin Streams, by
					 William R. Krug, Duane H. Conger and Warren A Gebert; U.S. Geological Survey;
					 Water Resources Investigations Report 91-4128; Madison, Wisconsin, 1992.