FAQs: Predictive Models
1. What do the models do?
First, the models assess how the coast will change in 50 years if no further action is taken to restore Louisiana’s coastal ecosystem and reduce flooding risks. Second, the models assess how the coast will change in 50 years if certain protection and restoration projects are constructed. This information will help the state decide which projects represent the best investment for Louisiana.
2. How do the models make these predictions?
Modeling teams working on the Planning team start by describing the existing ecosystem. In order to describe alligator habitat, for example, a modeling team would identify the things that are important to alligators, such as water salinity and the amount of wetlands. The team would then use models to predict how those conditions will change in the future through mathematical formulas and computer processing. In the alligator habitat example, the model would predict possible changes to salinity and wetlands. The model would also predict changes to the alligator habitat if different groups of restoration or protection projects were implemented.
3. What form do these predictions take?
The model outputs show how coastal conditions could change over time. These outputs are produced as series of numbers in large text files or Excel spreadsheets. In order to show what these numbers mean in words or pictures that can be more readily understood, the MPDT will examine each set of model results and find ways to depict the output appropriately, using maps, charts, graphs, or text.
4. What kind of models is the state using?
The models are organized into seven groups. Each group represents a different aspect of how the coastal landscape changes over time. Some of these groups include many individual models. For example, there are 15 separate species habitat models within the Upper Trophic Levels group. The seven model groups are:
a. Storm Surge/Waves
This module predicts the effects of restoration (marsh creation) and structural protection (levee) projects on storm surge depth and wave height from hurricanes with a range of size and intensities. The module uses output from the Morphology and Vegetation modules to determine landscape characteristics, and provides information on flood depths for use by the Risk Assessment module.
b. Risk Assessment
This module predicts economic damage that would be caused by storm surge flooding and waves. The model assumes that this flooding would result from levee overtopping and/or inundation in areas without structural protection. For enclosed levee systems we also factored in the possible failure of flood protection structures. The module receives input from the Storm Surge/Waves modules, and its output is used to estimate the reduction in damages that could occur in given locations if a given structural or nonstructural project is implemented.
This module predicts changes to open waterbodies within estuaries. The component models evaluate water levels, salinity patterns, sediment delivery, and some aspects of water quality. The module uses output from the Morphology modules to determine landscape characteristics. Module output is used by the Morphology, Vegetation, and Upper Trophic Level modules to estimate effects under Future Without Action and Future With Action conditions.
d. Wetland Morphology
This module predicts changes in wetland areas, taking into account the loss of existing wetlands, the creation of wetlands by both natural and mechanical processes, and the fate of those newly created wetlands. This module uses salinity and water level data from the Eco-hydrology module and provides information on land configuration to the Storm Surge and Upper Trophic Level modules.
e. Barrier Shoreline Morphology
This module predicts changes in the shape, location, and elevation of barrier islands over time, including land gains resulting from restoration activities, as well as land loss from wave erosion, sea level rise, and subsidence. It is based on understanding gained during the Barrier Island Comprehensive Monitoring program as well as years of research. It uses inputs from the Morphology module to predict the volume of tidal waters moving into inlets, and its output concerning the change in size of these inlets is used by the Eco-hydrology model.
This module predicts the location and type of vegetation that will be found throughout the coast, including submerged aquatic vegetation. It is based on understanding about the conditions influencing plant growth and newly available data from the Coastwide Reference Monitoring System. The module receives input on landscape and water quality characteristics from the Morphology and Eco-hydrology modules, respectively, and its output is used by the Storm Surge/Waves and Upper Trophic Level modules.
g. Upper Trophic Level
This module predicts how well Louisiana’s future coast will provide habitat for commercially and recreationally important coastal species and other key ecosystem services. The module uses inputs from the Eco-hydrology, Morphology, and Vegetation modules to produce habitat suitability indices for American alligator, muskrat, river otter, spotted sea trout, brown shrimp, white shrimp, largemouth bass, gadwall, green-winged teal, mottled duck, neotropical migrants, roseate spoonbill, wild-caught crawfish, and eastern oyster. These species were selected for one or more of the following reasons: they are thriving in coastal Louisiana, they are of commercial or recreational importance, and/or their habitat would likely be either increased or decreased by restoration and protection projects.
5. Who is doing this work?
Each of the seven model groups was created by a team with expertise in that field. Workgroup members come from a variety of backgrounds; some members hail from federal agencies, some from state universities, and some from the private sector. Many of the workgroup members have been involved in modeling efforts for previous Louisiana coastal plans, but some are new to this type of work. Approximately 60 people are working on the modeling effort, not counting Planning Team members who are assisting them.
6. How did the state decide which models to use?
To reflect restoration outcomes, the models looked at how land changes throughout the coast—where land is building and where it’s disappearing. The models also evaluated ecosystem services, the benefits provided to people by Louisiana’s coast. These range from providing the right conditions for oysters and shrimp, to ecotourism and storm surge attenuation. As a starting point for creating the list of ecosystem services, the Coastal Protection and Restoration Authority and the Planning Team reviewed the Millenium Ecosystem Assessment (http://www.maweb.org/en/Condition.aspx) and identified key ecosystem services that the Louisiana coast provides. This helped spur thinking about which models the state would need for the 2012 Coastal Master Plan.
To reflect protection outcomes, storm surge and damage models were selected based on their availability, previous use in similar studies, and their ability to deliver information required, such as the need to assess the effect of flooding if levees are overtopped. Some of the required models were already available and inputs just needed to be changed to meet the state’s needs. In other cases, especially for estimating economic damages, it was necessary to build new models based on previous studies.
7. What kind of computer runs these models?
Most of the models can be run on a desktop computer. Others, especially the storm surge model, run more efficiently on computer clusters or on super computers.
8. How long does it take to run a model?
Different models have different run times, depending on the spatial scale and the length of the simulation. The storm surge model can take hours, whereas some of the species models only take seconds or a few minutes.
9. At what spatial scale and time step do the models operate?
Different processes are being modeled at different scales. The Vegetation model, for example, does not need much time to complete a 50-year simulation, so it is run at a relatively small scale (500 square meters). This means that the percent of different types of vegetation is given for each 500 square meter area in the region being studied. The Eco-Hydrology model, on the other hand, is much more complex, because it models many variables such as salinity, water level, and sediment, as well as water quality variables like nitrogen and phosphorus. Given this complexity and the need to model hundreds of projects, the Eco-Hydrology model uses a larger spatial scale (tens of square kilometers). If eco-hydrology outputs were predicted at a smaller scale, the model run time would be too lengthy, and the time and cost involved would be prohibitive. Time steps also vary from months to years, depending on the model.
10. Who checks the models to make sure they are performing correctly?
A Technical Advisory Committee meets monthly to provide guidance on model assumptions, inputs, and other technical details. The 2012 Coastal Master Plan Science and Engineering Board provides broad evaluations of the modeling effort’s overall direction. Once the models are complete, they will be evaluated using the U.S. Army Corps of Engineers (USACE) Planning Model Certification procedure. Besides giving the state a useful quality check, using this procedure will ensure that the 2012 Coastal Master Plan models pass muster with the USACE and can be used in tandem with the USACE’s own planning efforts.
11. Who owns the models once they are developed? What is the state going to do with them?
The state of Louisiana, through Coastal Protection and Restoration Authority (CPRA), is funding the development and application of the models. The models will be the state’s property, and CPRA’s Louisiana Applied Coastal Engineering and Science (LACES) Division will be the repository for the models after the 2012 Coastal Master Plan is done. The state hopes to set up a structure that will upgrade the models regularly based on technological advances and new information gained.