3.1 Influence of Streambed Depth on the Empirical RTD
The hyporheic zone RTDs generated by the particle tracking algorithm (empirical RTDs, see Methods) become progressively heavy tailed as the dimensionless depth is increased systematically from \(d_{b}^{*}\) =\(0.5\) to \(8\) (Figure \(1A\)). For dimensionless depths greater than,\(d_{b}^{*}>\ 6.2\ \), the shape of the empirical RTD converges to that for an infinitely deep bed (see variations in RTD quantiles in Figure \(1B\)), consistent with the depth threshold reported by Wörman et al. (2002) of \(\ \frac{d_{b}}{\lambda}=1\) (equivalent to\(d_{b}^{*}=\ 2\pi\)).