Despite the popularity of the permeable pavements in urban areas in recent years, a few empirical equations have been developed to estimate the time of concentration (Tc) on pervious surfaces, and almost none of them is evaluated over the permeable pavements. In this paper, we aim to investigate the effect of low impact development (LID) on Tc and develop a new equation for estimating overland flow Tc compatible with both permeable and impermeable pavements in small urban watersheds with a semi-arid climate. An experimental model was devised to determine the new equation. Synthetic rainfall (22–40 mm.h⁻¹) was applied to a rectangular shaped (6 m × 1 m) test watershed with an adjustable longitudinal slope (0.5–8%) and zero lateral slope. Porous asphalt and permeable interlocking concrete paver (PICP) were employed as the permeable pavements. Then, to validate the obtained equation from experimental data, a field study was conducted over a 1-ha watershed during a Low intensity (<4 mm.h⁻¹) rain event. The comparison between 13 empirical and semi-empirical equations (including the one developed in this study) for estimating Tc in the test condition indicates that Chen and Wong’s equation with −0.03 bias and the Nash-Sutcliffe efficiency (NSE) equal to 0.9 and 0.7 for impervious and pervious surfaces respectively is the most precise equation. On the other hand, for the field study, the newly developed formula outperformed other equations and estimated the Tc with a 3.7% error. Moreover, the results of experiments on the PICP surface showed that replacing 10 to 15% of an urban watershed surface by PICP in a region with the rainfall intensity less than 40 mm.h⁻¹ and storm duration less than 1 h causes a considerable reduction (almost 100%) in the surface runoff.

Graphical abstract

尽管近年来渗透性路面在城市地区普及，但是已经开发了一些经验方程式来估计透水表面上的浓缩时间（Tc），并且几乎没有一个在渗透性路面上进行评估。在本文中，我们旨在研究低影响发展（LID）对Tc的影响，并开发一种新的方程式，以估算半干旱气候小城市集水区中与可渗透和不可渗透路面均兼容的陆上流量Tc。设计了一个实验模型来确定新方程。合成降雨（22–40 mm.h ^-1）应用于矩形（6  m  ×1  m））测试分水岭，其纵向坡度可调节（0.5–8％），横向坡度为零。多孔沥青和透水互锁混凝土摊铺机（PICP）被用作透水路面。然后，为了验证从实验数据中获得的方程式，在低强度（<4 mm.h ^-1）期间对1公顷流域进行了实地研究）下雨事件。在测试条件下估算Tc的13个经验和半经验方程（包括本研究中开发的方程）之间的比较表明，Chen和Wong方程的偏差为-0.03，纳什-舒特克里夫效率（NSE）分别为0.9和0.7对于不透水和透水的表面分别是最精确的方程。另一方面，在现场研究中，新开发的公式优于其他公式，并以3.7％的误差估算了Tc。此外，在PICP表面上进行的实验结果表明，在降雨强度小于40 mm.h ^-1和风暴持续时间小于1 h的区域中，用PICP代替了10％至15％的城市集水区表面（几乎100％）在地表径流中。

图形概要