Assessing the performance of the trench infiltration rates has been one of the major areas of research focus at Villanova University. Since the conception of the Villanova University Infiltration Trench, the performance of the trench has seen a significant reduction in infiltration rates. The investigation into this reduction in infiltration rates is a very complex issue. Causes may include seasonal effects, clogging due to sediment, or the system moving toward an equilibrium state. An important aspect of the site to consider when investigating the reduction in infiltration rates is the designed “under sizing” of the trench. The ratio of the drainage surface area to the trench surface area is nearly 160:1, which is a considerably large ratio which potentially made the infiltration trench an "accelerated" research test site.
A simple look at the monthly plots of the depth of water within the trench since 2004 shows the decline in the infiltration rates. In the below plots, the red line represents the depth of water within the trench and the blue lines represent the rainfall. (Click on the links to see an enlarged plot of the monthly data.) Note that the trench is 6 feet deep and there is an overflow pipe at 5.2 feet above the bottom of the trench.
As depicted in the above plots, the infiltration rates (especially at lower levels within the trench) have decreased since the trench was put into operation in July 2004. The time it takes for water to drop from the 3-0 foot range has increased. The decrease in infiltration rates for the bottom 3-0 foot range and the relatively constant infiltration rates in the upper 6-3 foot range suggests that the bottom of the trench has become impaired due to pollutant loading. However, the water is still successfully seeping out the side walls without the detriment of "clogging" pollutants. This may be a normal process in infiltration trench life spans and needs to be investigated further. Pollutant loading (especially regarding total suspended and dissolved solids) has become a major area of research focus at Villanova University for investigating the performance of SCMs.
Another interesting phenomenon observed since the conception of the Villanova Infiltration Trench is the varying rates of infiltration with respect to temperature/season. The plot below shows the average infiltration rates from 1.5 to 0.3 feet of depth within the trench from May 2005 to April 2006. From the plot it can be seen that the infiltration rates are typically the highest in the late summer/early fall seasons, and the lowest infiltration rates are typically observed in the spring.