From: Maintenance of Stormwater BMPs

Predicting Sediment Buildup Rate in Wet Ponds

If the sediment buildup rate (depth of sediment accumulated/time) can be accurately estimated, it will be easier to develop optimum long-term plans for sediment excavation. This estimate can be made by using the following procedure:

1. Estimate the average total suspended solids (TSS) input per year to the pond (TSS_in):

where TSS_in = average TSS load entering to the pond per year (kg/year), P = average rainfall depth per year (cm/year), A = watershed area (m²), C = runoff coefficient for the watershed (dimensionless), and EMC_TSS = flow-weighted mean concentration of TSS (mg/L) for one year.

2. Estimate sediment accumulated per year in the pond (Sed_acc):
Figure 1 shows the relationship between input and output TSS loads in wet ponds and was created using data from the International Stormwater BMP Database (www.bmpdatabase.org). This figure can be used to estimate the solids captured in the pond as follows.

where Sed_acc = sediment mass accumulated per year (kg/year), TSS_in = average TSS mass entering the pond (kg/year), and TSS_out = average TSS mass discharging from the pond (kg/year). TSS_out can be read from Figure 1 when TSS_in is known.

3. Estimate the annual sediment buildup rate (R_sed):
In their field study on wet ponds, Polta et al. (2006) reported the water content (WC) and specific gravity (SG_p) of sediment in wet ponds ranging from 0.48 to 0.87 and from 2.04 to 2.72, respectively. This information can be used as input to the following equation to estimate sediment buildup rates.

where R_sed = sediment buildup rate (m/year), p_w = water density (= 1,000 kg/m³), SG_p = specific gravity of sediment (dimensionless), WC = water content (dimensionless), and A_pond = pond surface area (m²).