The results indicated that soil erosion rate is higher in areas where the land use is agricultural compared to the suburban area. Upon examination of our data we also found some other interesting information. The data collected the day after a severe thunderstorm (see Data & Calculations for 7/10/97), estimated the erosion rate approximately two times greater in the crop area (1.08 mm/yr) than the suburban area (0.452 mm/yr). The same test was repeated after a seven day dry period (7/16/97). The erosion rate was still greater in the crop area site, however, the erosion rate decreased from 1.08 mm/yr to 0.842 mm/yr at the crop site area.
Unlike the erosion rate in the crop area site, the erosion rate of the suburban area slightly increased from 0.452 mm/yr (data collected from 7/10/97) to 0.507 mm/yr (data collected 7/16/97). It was our prediction that this increase may have been caused by watering lawns, washing cars, and other water usage in the suburban area during the seven day dry period. The measured dissolved load also increased from 0.137 g/L to 0.172 g/L during that seven day dry period. We thought this was a significant increase, however, no dissolved test were run to determine what substance(s) may have caused the increase.
It was interesting to compare the amount of dissolved load in the two different areas. The dissolved load was greater than an estimated 30% of the suspended sediment load in both areas. Nitrate, phosphate, and chlorine test would be necessary to determine if these areas had high concentrations of dissolved material that would account for the high amount of dissolved load.
In conclusion, there is always a lot of room for error in measuring soil erosion. The water discharge will always be an approximation based on the average depth and velocity. Estimations are also used to measure the bed load and soil density. We must keep in mind that this is only a crude estimation of the soil erosion that may occur in one year. This is a good experiment to illustrate that erosion rates will change over a period of time.