Known Shortcomings and Opportunities for Improvement
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RAS2FIM currently assumed that all HEC-RAS model are composed of a single reach and a single river. It multiple reaches and rivers are in the HEC-RAS geometry file, only the first reach and the first river is evaluated.
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Only steady-state one-dimensional models can be evaluated. Unsteady and 2-dimensional models are not allowed to be used as input to the RAS2FIM workflow.
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Bridges, culverts and in-line structures are allowed in the provided HEC-RAS models. Storage areas, lateral structures, SA/2D Connections and 2D flow areas are not allowed.
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All models provided in RAS2FIM must be created in the same projection (CRS)
- Terrain data provided in by the USGS 3DEP web coverage service is a composite of multiple sources in a variety of horizontal resolutions and accuracy. The RAS2FIM routine that grabs terrain from this service does not know the underlying source. In some portions of the the U.S., the terrain returned my be an up-sampling of a lower resolution source. (Example 3m returned from a 10m USGS source)
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Conflation may return the wrong HEC-RAS model especially for matches with low counts of snapped points. Confluences are the most likely area for a false snap.
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Two HEC-RAS models may 'split' a feature-id. The most popular wins, however a portion of each HEC-RAS model maybe more correct. RAS2FIM simply picks the most popular and ignores the other.
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Scripts may stall when a 'bad' HEC-RAS input is processed. This maybe points in the cross section that do not have increasing station. There are likely several other input file issues that can stall the HEC-RAS process.
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In HEC-RAS, cross sections that do not contain the flows may will assume a glass wall along the edge. While the RAS2FIM routing will run, the glass walling will incorrectly compute a reach averaged depth for the given discharge and introduce error into the Synthetic Rating Curve (SRC).
- While rare, it is possible to compute a non-monotonic synthetic rating curve. This may cause the calculations of interpolation to stall.
- For upstream reaches (strahler stream order 1, the assumption of a constant flow based on the entire contributing drainage area of the reach could lead to an over estimation of flood limits and depth on the upstream end.