The objectives of this Statement of Work are to 1) Continue user interface and capability development on the ATIIM; 2) Develop software documentation and workshop training material; 3) Implement internal and external software beta testing, quality control measures, and PNNL-required software release measures; and 4) Conduct model training workshop and officially roll out the software.

To address the challenge of rapidly characterizing spatiotemporally-complex inundation patterns in a fluvial-tidal system such as the Lower Columbia River and estuary, the Pacific Northwest National Laboratory (PNNL) developed the Area-Time Inundation Index Model (ATIIM). Originally developed as part of the U.S. Army Corps of Engineers-sponsored “Cumulative Effects” project (EST-P-02-04), the ATIIM integrates in-situ, modeled, or scenario-based hourly water-surface elevation (WSE) data and advanced terrain processing of high-resolution terrestrial and bathymetric elevation data (Figure 1). The model establishes and describes patterns in the spatial and temporal relationships of the land and water including non-dimensional area-time and volume-time inundation indices.  The ATIIM uses a spatially-based region-growing wetted-area algorithm that enforces hydrologic connectivity and determines numerous metrics such as site average bankfull elevation, two- and three-dimensional inundation extent/volume, and habitat opportunity. Importantly, it is well suited to represent numerous types of channel network morphologies that represent multiple inlets and outlets, flow-through, and multi-directional flow, while preserving the landscape microtopography, a critical factor in low-lying estuarine environments. Hydrological process metrics such as inundation frequency, duration, maximum area, and maximum frequency area are also calculated and can inform evaluation of proposed restoration sites; e.g., determine relationships between WSE and habitat opportunity, contrast alternative restoration designs, predict impacts of altered flow regimes, and estimate nutrient and biomass fluxes. In an adaptive management framework, this model can be used to provide standardized site comparisons and effectiveness monitoring indicators of changes in the developmental trajectories of restoration sites. The ATIIM is a cost-effective, rapid assessment tool suitable for the desktop planning environment, and represents an advance over methods that estimate inundation but do not enforce hydrological connectivity.

There are three classes of data output produced by ATIIM: 1) spatial data including raster and vector representations of the site under different flow states and restoration designs (Figure 2); 2) data tabular data providing site characteristics and metrics; and 3) graph data derived from the analysis and post-processing of the spatial data (Figure 3).