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Limitation

  • TIN data

    Since the TIN data is the foundation of creating geometric data during pre-processing and floodplain mapping during post-processing, the inaccuracy of TIN map is considered a significant limitation. There is some noticeable limitation in TIN quality at some location in the floodplain due to the contours resolution.

  • Cross-sections

    Digitizing cross-section layer is considered one of the most important steps during pre-processing, and hydraulic analyses and floodplain mapping are both based on cross-sections. Consequently, any errors of the cross-section will reflect on the final results. Due to lack of field investigation, all cross-sections for this project is drawn manually based on aerial photos and TIN maps, which means there is no validation process of the correctness of cross-sections. In this point, the cross-section is able to be considered a non-negligible limitation.

  • Land use layer

    There is no existing land use layer with appropriate Manning’s n values. For this project, Manning’s n values are manually assigned based on the table mentioned above (Chow, 1959). 

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  • Flood Intensity Estimation

    Flow Data gaps will cause inaccuracy of flood intensity estimation and there is a better log curve called log-Pearson Type 3 to be able to improve the estimation results.

Recommendation

All the limitations identified of the project bring a negative contribution to the quality of final results, and the following section provides a set recommendations aimed to improve the accuracy of future floodplain mapping or analyses.

  1.     New generated cross-sections should be investigated for Chilliwack River and Tributaries in the area. Cross-sections should be surveyed looking at downstream direction, and they are supposed to be wide enough to span the whole floodplain area.

  2.     The accuracy of DEM data (TIN) should be improved, and the new cross-sections should be based on the accurate TIN model.

  3.     The land use shape file with appropriate Manning’s n should be verified based on the field invested data. In this point, Manning’s values could be automatically and accurately assigned to each cross-section during the pre-processing phase.

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