## 4 Discussion
Moreover, multiple designs exist within each inlet type: whether a curb opening inlet is depressed or recessed or undepressed when compared to the roadway line and curb line, which alters the capture capacity immensely. Considering different type of inlets also results in different clogging patterns--from tree leaves to plastic bags to wheels of parked vehicles--beyond any sediment. Additionally, recent studies aim for larger structures [40], as placing fewer inlets may be more cost-effective, and thus, for some geometries, inlet capacity may not be a limiting factor. The purpose here was to comprehend the impact of slope orientation on the spacing, and the link between these results and inlet capacity is lacking, but this could easily be determined with the known inlet capacities for each region. In addition, untested is how increasing the cross slope gradually from the crown line could impact the results, which is not favorable for highways but could be applied to local roads, which might help optimize designing wider roads without considering hydroplaning, to an extent. [PERSON] and [PERSON] [17] focus only on water-film thicknesses over the lanes; in contrast, here the focus is on inlet spacing under constrained gutter flow depths. Based on [PERSON] et al. [13], limiting water-film thickness to 4 mm is reasonable to prevent hydroplaning risks. HEC-22, however, states that at 89 km h\({}^{-1}\), hydroplaning occurs at 2 mm thickness. The drastic change between the 2 and 4 mm is obvious when looking at Figures 6 and 8, for a highway setting, which creates less tolerance to hydroplaning due to high speeds. If it is desired to keep the cross slope at or below 4% (as advised by HEC-22, pp. 4-4 and 4-5), designing for multilane highways appears unpromising at environments with above 100 mm h\({}^{-1}\) rainfall. This sets a real challenge at steeper terrains. HEC-22 recommends inlet spacing to be between 90 and 150 m. The results show, in certain cases, that spacings can reach kilometers, especially under low precipitation conditions. However, the interest in this study is on the limited conditions. Looking at Figure 7 (and knowing a cross slope of 1% is in fact unreasonably low and 1.5% is recommended as a practical minimum), apart from a few exceptions with low grades in three- and four-lane roadways, the allowable spacing values do not constitute any major restrictions in a highway setting (3 m shoulder) in terms of recommended spacing. In the local setting, however, with a maximum spread of 1.8 m, maximum allowable inlet spacing becomes a limitation in many orientations (Figure 4) and slope optimization becomes crucial. If the maximum flow depth is limited to 3 cm, then the limitations are inescapable and become a major restriction to spacing consideration (Figure 5), which is consistent with the conclusion of [PERSON] and [PERSON] [19], who found exponential increase in inlet spacing with increasing maximum spacing. (This means decreasing maximum flow depths (as [PERSON] et al. [20] suggest) or the spread results in drastic variations). Our results show that some orientations have no practical inlet spacing limitations when investigated under controlled flow depths. Other orientations, however, limit the maximum allowable spacing and thus increase the possible cost as a result of increased inlet number. This, however, is a statement from a limited traditional perspective of stormwater management unfounded in sustainable stormwater management and green infrastructure practices. Rapid removal of flow is no longer considered a best management practice, and current studies focus on ways to estimate the capture capacity of smaller inlets as a better practice [41; 42]. Thus, from a multidisciplinary approach, the limited spacing may still be cost-effective and justifiable. While we limited the flow depth to 3 cm, [PERSON] et al.