Project Results - Runoff Quantity

The amount of eroded soil and dissolved pollutants that move from construction sites to nearby lakes or streams is controlled, in part, by the quantity of runoff produced during a storm.

Compost-treated areas produced significantly less runoff during high intensity rainfall (4 inches per hour) than conventionally-treated roadside areas.

Table 1. Mean runoff from un-vegetated test plots during a 30-minute high-intensity (~ 4 inches / hour) rain storm.
Material Biosolids Yard Waste Bio-industrial Compacted Subsoil Topsoil
Geometric mean runoff (mm) during 30-minute rainfall
0.13a
<0.01a
0.08a
26.22b
15.54b
Means within the same row with different letter designations and cell color are significantly different (p<0.05).
Highest
Lowest
  • As shown in table 1, runoff from compost-treated areas during a 30-minute high intensity rain storm was less than 0.8% of the runoff from areas treated with topsoil, and 0.5% or less of that from compacted subsoil.
     
  • Although the amount of runoff from the yard waste compost (shown in table 1) appears to be less than from the other two composts, these differences are not statistically significant.
     
  • Due to the water absorbing capacity of the compost, initiation of runoff from compost-treated areas was significantly delayed.  While compacted subsoil and topsoil typically began producing runoff within 5 to 8 minutes after rainfall began, areas treated with any of the three types of compost took, on average, 30 – 60 minutes to begin producing runoff (shown in table 2) . Since most naturally-occurring high-intensity storm events last less than 30 minutes, compost treatments would be expected to reduce the total number of storms each year that produce runoff.
Table 2. Mean time to initiate runoff from un-vegetated test plots.
Material Biosolids Yard Waste Bio-industrial Compacted Subsoil Topsoil
Mean time (min)
31.08c
56.92d
32.17c,d
4.67a
7.83b
Means within the same row with different letter designations and cell color are significantly different (p<0.05).
Shortest
Longest
  • The reductions in quantity and frequency of runoff provided by compost treatments were similar under both un-vegetated and vegetated conditions.  These results show that compost blankets can provide storm water runoff control (and erosion control) on construction sites before vegetative cover can  be established.
 
  • Compost-treated embankments produced significantly less runoff than conventionally-treated areas.
  • Even at rainfall intensities of nearly 4 inches per hour, the water absorbing capacity of the compost blankets caused runoff to be delayed, on-average, by 1/2 hour or more.