Site assessment methods for erosion control structures on inland lakes and flowages

Site assessment methods for erosion control structures on inland lakes and flowages. Site assessment methods for erosion control structures on inland lakes and flowages. Applicants and department staff shall use any of the following data requirements and site assessment methods for potentially exempt riprap under s. NR 320.04 (12) and shoreline erosion control structures individual permit applications under s. NR 320.06 for inland lakes and flowages: (1) Calculation of storm-wave height. The department shall provide applicants with worksheets and a web page calculator for the purpose of estimating storm-wave height. The storm-wave height calculator shall be mathematically designed based on Young and Verhagen (1996) and Young (1997) by applying a storm wind speed of 35 miles per hour (51.45 ft/sec), fetch at the applicant’s shore protection site, and the average depth along that fetch. To record fetch, applicants shall measure the longest unobstructed straight-line distance originating from the shore protection site across the water surface to the opposite intersect with the shore. To estimate average depth applicants shall examine a lake map, sum the reported depths along the fetch, and divide by the number of recorded values. At least 5 equally placed intervals along the fetch shall be used. (2) Calculation of erosion intensity. When an applicant or the department believes that, as a result of site conditions, storm-wave height as calculated under sub. (1) may inaccurately predict the degree of erosion, the erosion intensity score may be calculated to determine erosion. The department shall provide applicants with worksheets and a web page calculator for the purpose of calculating erosion intensity. When the department or applicants assess erosion at the shore protection site, they shall apply methods outlined in Table 1 to calculate an erosion intensity score. Wherever erosion intensity and storm-wave height result in different energy categories, the site shall be placed in the category as determined by the erosion intensity score. (3) Bank edge recession measurements. (a) Except as provided in pars. (b) and (c) , the method of measuring bank edge recession shall include all of the following: 1. Establishment of a physical measurement reference line between at least 2 headstakes. 2. Date-imbedded photographs showing the initial installation of the reference line and headstakes. 3. Reference distance measures to the bank lip. 4. Time between separate measurements shall be of 3 months or more during the open-water season. (b) As an alternate to the bank edge recession measurements method identified in par. (a) , if 2 or more years of LiDAR elevation data are available for a site, the LiDAR elevation data may be used to determine the average annual rate of bank edge recession by comparing the horizontal distance the bank lip has moved using a GPS point and dividing this measurement by the difference in the number of years between datasets. (c) As an alternate to the recession measurement methods identified in par. (a) or (b) , the severity of shoreline erosion may be identified using average annual rate, in feet per year, of shoreline recession with measurements from historic aerial imagery over a period of 20 years. This method may be excluded, or the evaluation period abbreviated, if imagery is unavailable or obscured by canopy.