By Gayle F. Mitchell, Ting Guo, and Nida Igiz
Manmade accelerated soil erosion and the resulting suspension of soil particles in water or air can have detrimental environmental and societal results. Sediment has been identified as the single most common water pollutant, and increased dust is a major contributor to air pollution. Consequently, processes, procedures, practices, and products have been developed, promulgated, studied, and implemented to minimize erosion and resulting sedimentation and dust.
Figure 1. Survey FormTo begin articulating the financial costs and benefits associated with reducing accelerated soil erosion, the International Erosion Control Association (IECA) held an economic summit in 2000. One of the objectives that resulted from that summit was to obtain data on the costs of minimizing erosion and sedimentation for one market segment. Once cost data were obtained, the plan was to address the economic benefits of erosion and sediment control (ESC) for that sector. Based on availability of their data and similarity of agencies, United States departments of transportation (DOTs) were selected as the first sector to study regarding the costs of ESC for highway projects. The main objective was to ascertain annual highway project ESC expenditures.The survey form, shown in Figure 1, and a cover letter were sent to personnel in the 50 state DOTs and in three federal land divisions. Follow-up via telephone and mailing (electronic and postal) was done to increase response. After data were received, respondents were called upon to clarify data and information. Data were standardized into comparable units and entered into spreadsheets. From the data provided by the DOTs, annual total costs for ESC were determined for each responding state, and statistical data were obtained to compare the responses. The majority of states provided data for 2000; some also reported on 1998-2001, which allowed comparisons over time. In addition, ESC total costs were evaluated by categories, including riprap, seeding and mulching, erosion control mats, silt fence, sodding, and hard armor. The total costs for ESC for each state were compared to land area, total lane-miles, and population.Thirty-eight states (or 76%) and two federal land highway divisions responded to the survey. Table 1 provides a summary of the response.Table 1 . Summary of Data Submission for 1998-2001Number of States Providing DataYear62001(6-9 months)302000181999171998Annual Erosion and Sediment CostsFigure 2 presents the annual costs for ESCs applied to highway projects for 30 DOTs and the eastern federal land division. States with the highest reported total erosion and sediment costs in 2000 were Georgia, Texas, and Florida. Rhode Island reported the smallest expenditure. Statistical data on the total annual costs for ESC are given in Table 2.Table 2 . Statistical Annual Erosion and Sediment Costs for DOT Projects in 2000Average$9.01 millionMedian$5.13 millionHighest$38.75 millionLowest$49,136A comparison of erosion and sediment costs as a function of state land area is shown in Table 3.Table 3. DOT Expenditures for ESC per State Land Area in 2000Average$252.6/mi.2Median$118.71/mi.2High$1,492.78/mi.2Low$3.52/mi.2The states with the three highest expenditures per state land area were New Mexico ($1,493/mi.2), Connecticut ($1,139/mi.2), and Georgia ($652/mi.2). Data for per-capita ESC for 2000 are given in Table 4. The average was $2.20/person. Wyoming reported the highest expenditure per capita ($10.1), and Rhode Island the lowest ($0.05).Table 4. DOT Expenditures for ESC Based on PopulationAverage$2.20/personMedian$1.76/personHigh$10.10/personLow$0.05/personOther states with expenditures per capita in the upper range were New Mexico ($7.16), Georgia ($4.73), and Arkansas ($4.66). Figure 3 depicts the total ESC costs per state lane-miles. Three states that spent the most on total erosion and sediment costs (Texas, Georgia, and Florida in 2000) also had the most lane-miles among the reporting states and the highest costs per lane-mile. Table 5 provides statistics as a function of state total lane-miles. Rhode Island, which has the second shortest lane-mile, had both the lowest total annual erosion and sediment expenditures and cost per lane-mile.Table 5. Comparison of DOT Expenditures for ESC Based on Total Lane-MilesAverage$60.12/lane-mileMedian$38.04/lane-mileHigh$310.89/lane-mileLow$3.84 /lane-mileComparison of Annual Expenditures for 1998, 1999, and 2000Of the 19 states and one region reporting total cost data for more than one year, 12 (63.15%) reported increases in ESC annual costs. A representative example is presented for Arkansas in Figure 4. The increase in expenditures from 1998 to 2000 ranged from 2% to 187%, with an average of 67%.Figure 4. Total Annual ESC Costs for Arkansas DOT, 1998-2000
Comparison of Total Expenditures for Different ESCs for 2000 Comparisons were made for seven categories of ESC measures in terms of expenditures per measure. Data were from 30 state DOTs.Riprap. Of the 30 states reporting data for 2000 all except Texas reported costs for riprap. The states spending the greatest percentage of the ESC budgets on riprap were Pennsylvania (72.3%), Louisiana (71.7%), and Kansas (56.4%). The average spent on riprap was $1,964,060, and Illinois spent the most: $7,000,806.Seeding and Mulching. All states reporting data for 2000 indicated expenditures for seeding and mulching. The four that reported spending the highest percentages on seeding were Arkansas (38.3%), Colorado (43.9%), Kentucky (44.9%), and Delaware (35.2%). The average expenditure was $1,601,757, with Texas reporting the highest: about $9.06 million.Erosion Control Mats. Every state reported data on erosion control mats except New Jersey. The average expense was $1,123,176, with Georgia spending the most: $19,936,900.Silt Fence. Every state reported data on silt fences except Montana. The states reporting the highest percentage of total expenditures for silt fences were New Jersey (33.2%), Rhode Island (22.8%), and Maryland (24.4%). The average was $1,004,379, with Texas spending the most: $6,878,261.Sod. Six states did not report data on sodding (Maryland, Nevada, Rhode Island, New Jersey, New Mexico, and West Virginia). Of the states reporting data on sodding for 2000, Florida (37.4%) and Delaware (35.2%) reported the highest percent expenditures. The average amount spent was $878,585. Florida reportedly spent the most at about $14.15 million.Hard Armor. Thirteen states provided no data on hard armor. The four states reporting the highest percent expenditures included Mississippi (27%), North Dakota (24%), West Virginia (21%), and Kansas (17%). The average was $280,605, with Mississippi spending the most: $1,723,184.The aforementioned categories constitute 76% of the total average erosion and sediment costs. The remaining 24% included a variety of items: pipes, straw bales, sediment basins, berms, sandbags, excavation, and others not specifically listed on the survey form. The data in Table 6 provide comparisons for each of the categories.Table 6. Average Costs Spent on Different ESC CategoriesESC CategoryAverage Expenditure% of Total ExpenditureRiprap$1,964,06022.13Seeding and Mulching$1,601,75717.78Erosion Control Mats$1,123,17612.47Silt Fence$1,004,37911.15Sodding$878,5859.75Hard Armor$280,6053.11Others$2,127,00023.61Erosion and Sediment Costs as Percentage of Total Project CostsAmong the states and highway divisions that submitted the survey, 27 states (71%) and two federal land highway divisions provided data for ESC cost as percent of a highway construction projects. Table 7 summarizes some of the statistics. The average percentage of erosion and sediment costs as a function of total highway construction projects costs was about 3% for 2000. Michigan reported the highest percentage, and Kentucky reported the lowest.Table 7. ESC Costs as Percentage of Highway Construction CostsItemStatesStates Plus FLHDTotal Number2729Average Value2.88%2.99%Medium Value2.50%2.56%Highest Value8.00%8.00%Lowest Value0.50%0.50%Engineering Cost as Percent of Highway Construction Project CostsAmong the 40 agencies responding to the survey, 28 provided data for engineering costs as a percent of highway construction projects. Table 8 summarizes the statistics. Engineering costs averaged about 12% of the highway construction costs. Illinois noted the largest percentage, and Wisconsin reported the lowest.Table 8. Engineering Costs as a Percentage of Highway Construction CostsItemStatesStates Plus FLHDTotal Number2628Average Value12.08%12%Medium Value10%10%Highest Value27.5%27.5%Lowest Value5%5%SummaryThe average of total reported annual ESC expenditures in 2000 on state highway projects for 30 state DOTs was $9,010,000. The year’s total ESC expenditures for the 30 states were approximately $270 million. Erosion and sediment costs as a function of total highway construction project costs averaged 3%. The majority of states reporting three years of erosion and sediment costs indicate that they are increasing.
Future plans are to update the data and encourage all states to participate. Data for the benefit side need to be developed and cost/benefit ratios estimated. In addition, plans are to extend the study to other sectors.
Gayle F. Mitchell, Ph.D., P.E., is a professor in the Civil Engineering Department at Ohio University in Athens, OH.
Ting Guo and Nida Igiz are graduate students at Ohio University.
