Arroyo Grande Creek Flood Control Channel Vegetation Management: A Photo Series

Transcription

1 Arroyo Grande Creek Flood Control Channel Vegetation Management: A Photo Series The Way It Was For several decades, all vegetation growth was discouraged in the AG Creek flood control channel, as shown in Figures 1 and 2. Figure : AG Creek flood control channel, at Highway 1 Bridge, shortly after levee construction. Figure 2. January 1997: Although intensity of channel maintenance had diminished over the years due to budgetary and environmental constraints, in 1997 there was still little riparian corridor vegetation in the flood control channel, as shown in this photograph looking upstream from 22 nd Street Bridge. This contrasts dramatically with riparian corridor vegetation shown in Figures 3-15, below.

2 22 nd Street Bridge Four seasons of vegetation management in photos This series of twelve photos (Figures 3-15) taken from the same location illustrate the results of vegetation management on the Arroyo Grande Creek flood control channel from 2004 through early 2008, including regrowth of willows by the following year. Location: looking upstream from the 22 nd Street Bridge on Arroyo Grande Creek, a few hundred feet east of the LCP coastal zone. Figure 3. December 2004: Before vegetation work. Figure 4. December 2004: After vegetation work, with willows beginning to drop their leaves for winter.

3 Four seasons of vegetation thinning (continued) Figure 5. August 2005: Regrowth: picture shows growth of vegetation since the previous fall. Figure 6. November 2005: After thinning several weeks earlier.

4 Four seasons of vegetation thinning (continued) Figure 7. April 2006: Increased channel capacity due to vegetation management the previous fall was credited with enabling the channel to handle heavy flows during winter and early spring of (Note: this photo was taken after the peak flow had partially subsided.) Figure 8. June 2006: Regrowth of channel vegetation by beginning of summer.

5 Four seasons of vegetation thinning (continued) Figure 9. October 19, 2006: Right (south) side thinned by CCCs a few days earlier, while the left (north) side and center island remained unthinned due to presence of red-legged frogs. Figure 10. January 28, 2007: Willows have dropped leaves for winter. Note shrubby willow sprouts at base of trees on left bank, which was not thinned in 2006 due to presence of red-legged frogs.

6 Four seasons of vegetation thinning (continued) Figure 11. March Willows leafing out at beginning of spring Figure 12. May 18, 2007: Willows and herbaceous ground foliage show spring regrowth.

7 Four seasons of vegetation thinning (continued) Figure 13. July 3, 2007: Further growth before thinning by CCCs later in summer. Figure 14. January 9, 2008: As willows are dropping leaves for winter, residual effects of thinning and trimming of lower branches during summer 2007 are visible in the openness between lower willow trunks. The creek in this reach had been dry during much of summer 2007, and no red-legged frogs (RLF) were observed during day and evening surveys. Absence of RLF allowed thinning on north (left) side of creek in summer 2007 for first time since annual vegetation maintenance activities resumed in 2004.

8 Four seasons of vegetation thinning (continued) Figure 15. May 13, 2008: Willows have leafed out and sent up root and side sprouts. Pruning of these new shoots is needed to reduce vegetative roughness before the wet season.

9 Before and after photos from mid-channel in coastal zone, Figure 16 contrasts one side of the channel after thinning versus the other side before thinning in September 2005, and Figure 17 shows the same reach the following summer, In 2007, both sides of the channel were thinned, as shown in Figures 18 and 19, and Figures 20 and 21 show conditions in May Note that the thinned and pruned willows continue to provide near closed-canopy shade for creek, while remaining open near base, facilitating water movement during heavy flows. Herbaceous ground vegetation, which is not pruned, provides cover for small wildlife. Figure 16. Sept 2005: vegetation work completed on right (north) side; left (south) side still to be done. Figure 17. June 2006: Regrowth nine months after vegetation work completed on both sides of the creek, before pruning later that summer.

10 Figure 18. May 2007: Looking downstream from location near Figures 13 and 14, willows retain benefits from previous year pruning, and required little work during Figure 19. May 2007: Looking upstream from same stream reach as Figure 15 above.

11 Figure 20. May 2008: Looking downstream in coastal zone above Guiton crossing. Continued benefits of previous years vegetation work are visible, with only minimal pruning necessary this year to maintain openness between willow trunks close to the creek during the coming winter to allow stormflow. Figure 21. May 2008: Looking upstream in coastal zone above Guiton crossing, showing stream canopy cover.