DETERMINANTS OF THE OPTIMAL SOIL LOSS TOLERANCE (T-VALUE) FROM A SOCIETAL VIEW POINT---THE STUDY OF MINNESOTA LOWER-UPPER MISSISSIPPI RIVER BASIN

This thesis focused on estimating the downstream damage costs and benefits resulting from cropland erosion of the ten sub-river basins in southeastern Minnesota. Two types of external damage costs, the dredging costs and the recreation related damage costs on the Mississippi River main channel and backwater areas between Pools 4 and 8, were estimated. External benefits of soil erosion also arise from the beneficial uses of dredged materials. A sediment-budget which quantitively described the origins, destinations, and movement of the sediments transported by run-off and by the river was constructed so that external costs and benefits could be attributed to their cropland sources in southeastern Minnesota.; An engineering approach using averting behavior and the round-trip hauling cost ({dollar}3.87/CY) for dredged sand were used to estimate dredging costs and external benefits of dredged materials. A contingent valuation method done by a mail survey was used to gather information concerning the recreation related damage costs due to loss of surface water area.; The estimated results from an analysis of the data indicate that average annual net dredging costs and recreation related damage costs on the Mississippi River respectively range from {dollar}0.07 million (Pool 6) to {dollar}0.88 million (Pool 4) and {dollar}0.08 million (Pool 7) to {dollar}0.67 million (Pool 5A). The annual net external damage costs resulting from man-induced soil erosion on the cropland range from {dollar}0.06 per acre in the Cannon River basin to {dollar}0.86 per acre in the Root River basin.; Two conclusions were reached from this study: (1) On-farm productivity losses are higher than net downstream damages in terms of dredging costs and the recreation related damage costs on the Mississippi River. (2) On-farm high cost soil conservation practices are not economically justified if benefits coming only from preservation of productivity and reduction of net external damage costs on the Mississippi River.; The study results suggest that most off-site damage costs from erosion may occur in the local areas at the second stage of sediment movement. Thus, future research efforts should be focused on estimating the external damage costs caused by the sediment at its second stage movement discussed in the third chapter of this thesis.