Lake Ogallala Bathometric Project

Transcription

1 THE CENTRAL NEBRASKA PUBLIC POWER AND IRRIGATION DISTRICT Lake Ogallala Bathometric Project Mitigation Area Vegetation Monitoring Year 2 Mark Peyton 9/20/2012

2 Lake Ogallala Bathometric Project Mitigation Area Vegetation Monitoring Year 2 September, 2012 INTRODUCTION Over the winter of 2009 and 2010 the Central Nebraska Public Power and Irrigation District excavated 152,000 yard 3 of material in a 6,200 long canal in Lake Ogallala to help change circulation within the lake. In the process of excavating the materials 5.2 acres of wetland were impacted. To mitigate for the wetland impact 10.4 acres of a constructed wetland were required. Central utilized approximately 80,000 yards 3 of the excavated material which was placed on the Lake bottom to form a bench duplicating the elevation of the existing wetland. This material created a Mitigation Spoil of 11 acres. To establish the Mitigation Spoil Wetland, cattails (Typha latifolia) were removed from that portion of the existing wetland that was to be impacted and placed upon the Spoil area. In addition seed harvested in natural wetlands in Nebraska (provided by the U. S. Fish and Wildlife s Rainwater Basin Joint Venture) along with a commercially purchased seed mix was spread in March of To assess the development of the mitigation wetland, Central under its 404 Permit though the Corps of Engineers, agreed to conduct five years of vegetation monitoring. This report provides data from the Second Year of that Monitoring. METHODS Prior to the construction of the Project it was decided to establish six transects running north and south through the proposed mitigation area, 100 meters apart. Following the construction and as the monitoring protocol was put into use it was discovered that two transects lie outside the 1acre mitigation area as constructed, and hence are in water too deep for plant germination. Figure #1 shows the pre-construction transect locations.

3 Figure #1. Wetland Mitigation Transects at Lake Ogallala Sample plots were established along transects #1 - #4. The plots were located every 100 along each transects beginning at the edge of the excavated channel and then running north to the undisturbed vegetation of the existing wetland. Latitude and Longitude of each plot is given in Table #1. Table #1. Lake Ogallala Mitigation Transect and Plot Locations Transect # Plot 1 Plot 2 Plot 3 Plot 4 #1 101* 39' 26.2" 101* 39' 26.2" 101* 39' 26.2" 101* 39' 26.2" 41* 13' 08.5" 41* 13' 09.3" 41* 13' 10.4" 41* 13' 11.4" #2 101* 39' 21.3" 101* 39' 21.3" 101* 39' 21.3" 101* 39' 21.3" 41* 13' 07.5" 41* 13' 08.5" 41* 13' 09.0" 41* 13' 09.7 #3 101* 39' 16.1" 101* 39' 16.1" 101* 39' 16.1" 101* 39' 16.1" 41* 13' 04.1" 41* 13' 05.0" 41* 13' 05.9" 41* 13' 06.7" #4 101* 39' 11.6" 101* 39' 11.6" 101* 39' * 39' * 13' 02.5" 41* 13' 03.4" 41* 12' * 12' 00.4 *Note: Coordinates given in red fall in water too deep for plant growth Plots were located in the field using a Garmin etrex Venture HC handheld GPS unit. A meter 2 area is established at each plot location and plant density and type is recorded. If the plot is under water at the time of monitoring, water depth in inches is recorded.

4 RESULTS In 2012, 12 of 16 plots were monitored. The other four plots were located in water depths of greater than three feet (meter) and had no terrestrial/wetland plants (Table #1). Plots monitored in 2012, along with the locations of what would have been the northern most plots on Transects #5 and #6 are shown on the aerial photo in Figure #2. In addition the location of these Transects are shown on the pre-build schematic of the project (Figure #3). #1 #2 #3 #4 #5 #6 Figure #2: Aerial Photo Showing Monitoring Plot Locations at Lake Ogallala Figure #3: Project Schematic Showing Monitoring Plot Locations at Lake Ogallala

5 During the initial baseline monitoring of 2010 it was noted that the cattails that had been removed from the wetland during excavation of the channel and placed upon the Mitigation Spoil had taken root and had established themselves. We did not note extensive germination of young plants from the seeding, however. In September of 2011, the 1 st full year of Monitoring following completion of the Project, the transplanted cattails were as thick as those that were not impacted by the Project. As to the rest of the area, six of the 13 plots above water contained young cattails or bulrush (Schoenoplectus sp). In 2012 ten (10) of the 12 plots above water contained young cattails, bulrush, cockleburs, and other plants indicating that establishment of wetland plants in the Mitigation Spoil area is continuing. Cattails, the most common plant found in the area of wetland impacted by the Project, generally germinate and grow in water that is less than 2.5 in depth, however, once established they can survive in water up to 10 deep as well as on dry land for extended periods of time (Rook, 2004 and Ditomaso and Healy 2003 ). To promote the development of cattails and other wetland plants the design for the Mitigation Spoil Pile was a bench ranging in elevation from MSL to MSL. These elevations are the typical high and low elevations of the Lake during normal operations thus ensuring a variety of water depths within the range for the establishment of cattails, bulrush and other wetland plants. Following completion of the project the elevation of Lake Ogallala was operated within these elevations during the growing seasons of 2010, 2011 and 2012 (Figure #4)

6 Elevation Above 3100' MSL 26.5 Figure #4: Lake Ogallala, Nebraska Daily Elevation as Record at Midnight 2010, 2011, and Maximum Operation Elevation Minimum Operation Elevation Ma y Ma y Jun Jun Jul Date Jul Aug Aug Sep Sep As can be seen in Figure #4 the day to day elevation variation during the growing season of 2012 as measured at midnight was slightly higher in 2012 than in 2011, but the difference was insignificant, however, in general the lake was kept at higher levels than in 2010 and 2011 (average elevation in 2010 was msl, in 2011 it was msl, and in 2012 it was msl). Once again, the average depth of the water was close to the upper range of depths designed for the Mitigation Area and at those depths the establishment of plants will be slower than in the more shallow regions. This is exactly what we are seeing two years into the five-year evaluation period of the effectiveness of the Mitigation activities. On the day the 2012 Monitoring was conducted the elevation of Lake Ogallala was , or 1.6 lower than in Once again, except for the southernmost plot in Transect #1, the plots in Transects #1 and #2 were above water. Along Transect #3 the average depth of water was 0.23 with one plot above water. All three plots along Transect #4 were above water. Figures #5 9 are photos showing the plots and transects on September 8, 2011.

7 A;lkj Plot #1 Plot #2 Plot #3 Plot #4 Figure #5: Photos of the plots along Transect #1. Plot #2-1 Plot #2-2 Plot #2-3 Figure #6: Photos of the plots along Transect #2 Plot #3-1 Plot #3-2 Plot #3-3 Plot #3-4 Figure #7: Plot #3-1 along Transect #3 Figure #8: A panoramic view of the Mitigation Area from the East edge

8 Figure #9: Looking North along Transect #1 showing the extensive growth of cattails to the east (the transplanted cattails) and the new bulrush and other plants that have established on the sand. SUMMARY Monitoring during Year-2 of the 5-year monitoring time period shows that wetland plants, specifically cattails and bulrush, are continuing to colonize the Mitigation Spoil area as expected. Establishment of these plants is occurring in the more shallow areas of the Spoil area to the west, however, cattails and other wetland plants have an ability to spread through the use of rhizomes into deeper waters and it is expected that as time progresses the deeper areas to the east in the 1acres of the Mitigation Spoil Area will also be colonized. REFERENCES CITED: Ditomaso, Joseph M., and Evelyn A. Healy. Aquatic and riparian weeds of the West ANR Publications. 442pp.

9 Rook, Earl J.S. Flora, Fauna, Earth and Sky, The Natural History Of The Northwoods. Internet source, Typha latifolia, the Common Cattail.