Task 3 - Piers and Shading

Shading characterization under existing piers

The research was initially conducted in May-June 2006 using field studies of 30 piers and the amount of shading they produce (Fig 3). A total of 10 piers were located in Harrison county and 20 in Jackson county (Map 1). A variety of heights above the marsh, width of pier decking, and spacing between decking boards was investigated for a total of 66 profiles across the width of the piers (Table 1). Data were converted to percent shading by comparing to incident solar irradiance measured on the decking of the pier concomitant with measurements under the pier. Pier height did not affect shading levels, the range of shading was 80-95% of sunlight under all piers measured. Pier width affected the area impacted, with wider piers affecting a larger area (Fig 1). Similar data were obtained from a re-analysis of 10 piers in Jackson county conducted in Jan- Feb 2008. The data from this part of the study will aid in future management decisions on the implementation of waterfront construction that impacts marine wetland areas, as well as, improving waterfront construction design.

Conclusions of this analysis of shading effects from existing pier structures include:

1. Taller piers do allow more light to pass under the structure, but tended to also be wider as many of these were public access piers. Taller piers may come with additional impacts to the marsh from construction practices that neccesitate large and heavy machinery to install pier pilings.

2. Short and narrow piers were more common along protect marsh edges along bayous and canals. These may have been installed by the homeowner and often also allowed the vegetation to grow densely along the edge, in many cases with the vegetation canopy being taller than the pier height.