Effect of urban soil compaction on infiltration rate

ABSTRACT:

Inadvertent soil compaction at the urban lot scale is a process that reduces infiltration rates, which can lead to increased stormwater runoff. This is particularly important in low impact development strategies where stormwater is intended to infiltrate rather than flow through a traditional stormwater network to a detention basin. The effect of compaction on infiltration rates on sandy soils in North Central Florida was measured with a double ring infiltrometer on urban construction sites and across various levels of compaction. Average non-compacted infiltration rates ranged from 377 to 634 mm hr⁻¹ (14.8 to 25.0 in hr⁻¹) for natural forest, from 637 to 652 mm hr⁻¹ (25.1 to 25.7 in hr⁻¹) for planted forest, and 225 mm hr⁻¹ (8.9 in hr⁻¹) for pasture sites. Average infiltration rates on compacted soils ranged 8.175 mm hr⁻¹ (0.3-6.9 in hr⁻¹), 160 to 188 mm hr⁻¹ (6.3 to 7.4 in hr⁻¹), and 23 mm hr⁻¹ (0.9 in hr⁻¹) for the same respective sites. Although there was wide variability in infiltration rates across both compacted and non-compacted sites, construction activity or compaction treatments reduced infiltration rates 70 to 99 percent. Maximum compaction as measured with a cone penetrometer occurred in the 20 to 30 cm (7.9 to 11.8 in) depth range. When studying the effect of different levels of compaction due to light and heavy construction equipment, it was not as important how heavy the equipment was but whether compaction occurred at all. Infiltration rates on compacted soils were generally much lower than the design storm infiltration rate of 254 mm hr⁻¹ (10.0 inches hr⁻¹) for the 100-yr, 24-hr storm used in the region. This implies that construction activity in this region increases the potential for runoff and the need for large stormwater conveyance networks not only due to the increase in impervious area associated with development but also because the compacted pervious area effectively approaches the infiltration behavior of an impervious surface.