Riparian zones are transitional areas between aquatic and terrestrial ecosystems. They play a very important ecological role in both ecosystems. The accuracy of ecological assessments of riparian zones fundamentally depends on how riparian boundaries are delineated. Current policies rely on strict, fixed buffer zones, which lead to generalization. This study evaluates how boundary sensitivity affects the Riparian Strip Quality Index (RSQI). This study compares three delineation methods (Upland Terrace, Fixed-width buffer, and slope-based) in the downstream Ayung River, Bali. Statistical analysis indicated that the delineation method affected the ecological assessment outcomes (η² = 0.49). The fixed-width buffer delineation method tends to underestimate riparian quality by including non-contributing built-up areas (27.23%). In contrast, the Upland Terrace method shows more ecologically representative results and has no significant score difference with slope-based delineation (Wilcoxon Z = -0.75). RSQI evaluations showed significant spatial variability. It also indicated local degradation in urbanized segments (RSQI dropping to 50.09–59.77 in Segments 1 and5), and pristine environmental quality where segments are dominated by natural vegetation (RSQI = 94.41 in Segment 9). These findings show the disadvantages of current regulations that use a generalized delineation method. To improve urban river management, policymakers need to consider a transition to geomorphology-based boundary delineations and carry out targetedrestoration in degraded areas.
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