Infiltration capacity of roadside filter strips with non-uniform overland flow

The average percentage infiltration of the medium road runoff rate (1.55 × 10−4 m2/s, without direct rainfall) experiments performed in fall was 85% and in spring 70%. For the high road runoff rate (3.1 × 10−4 m2/s, without direct rainfall) tests the average amount of water infiltrated was 47% and for the low road runoff rate (7.76 × 10−5 m2/s, without direct rainfall) tests it was 69%, both set of tests performed in spring and summer. The saturated hydraulic conductivity of swale soil was high, relative to the values typical of laboratory permeameter measurements for these types of soils. This is believed to be due to the macropores generated by vegetation roots, activity of macrofauna (e.g. earthworms), and construction/maintenance procedures. The trend was to have more infiltration when the saturated hydraulic conductivity was higher and for a greater side slope length, as expected. The vegetation, type of soil and length of the side slope are important to consider for constructing and maintaining roadside swales that will be efficient as stormwater control measures. These measurements indicate that the filter strip portion of a roadside swale typically infiltrates a substantial fraction of road runoff. However, the measurements do not incorporate the influence of direct rainfall upon the infiltration into filter strips.