3: Evaluating Projects
In Depth Look: Environmental Scenarios
Sea Level Rise When estimating sea level rise for the project level analysis, we based our two scenarios on the scientific literature. The first, moderate scenario assumes an increase in sea level of 0.27 meters (.81 feet) by in the next 50 years. The second, less optimistic scenario assumes a 0.45 meter (1.4 feet) increase in the next 50 years. The Coastal Protection and Restoration Authority’s Louisiana Applied Coastal Engineering and Science (LACES) Division recently reviewed the latest science on sea level rise. The LACES analysis shows that the range of sea level rise rates we used in our analysis is within the bounds of current scientific projections of the effects of climate change, including recent estimates from the National Research Council (NRC) and the U.S. Army Corps. However, the latest science released afterofwe began our analysis theYears potential for sea level rise Estimates Sea Level Rise Overshows Next 50 to exceed even our less optimistic scenario. As a result, new rates of sea level rise will be incorporated into future project planning and design.
XX Figure 3.4 Scenarios of future eustatic sea level rise based on National Research Council (NRC) and Corps guidance (2011) were used to inform the moderate and less optimistic sea level rise rates over the next 50 years.
.7 Sea Level Rise (meters)
Estimates of Sea Level Rise over Next 50 Years
NRC III (High)
.6 .5
Less Optimistic Scenario NRC II
.4
Moderate Scenario
.3
NRC I (Intermediate)
.2
Current Levels (Low)
.1 0 2010
2020
2030 2040 Year
2050
2060
Marsh Collapse
Fig 3.5
In order to predict future land loss or gain in coastal Louisiana, it is necessary to estimate the ability of a given marsh type to persist in response to salinities and inundation. We convened an expert panel to help us determine the best way to address this uncertainty. Based on their recommendation, marsh collapse thresholds were established for fresh, intermediate, brackish, salt and swamp wetlands. Marsh collapse means that the wetland vegetation can no longer persist and the area will rapidly lose elevation (land loss) and convert from wetland to open water.
84
Louisiana’s Comprehensive Master Plan for a Sustainable Coast