November - December 2003: Volume 58, Number 6
Table of Contents
Features
- Insuring best management practices
By Susan Campbell
- Wetland mitigation banking
By Pat Hemminger
Research Editorial
Research
- Simulation of the impacts of flood retarding structures on streamflow for a watershed in southwestern Oklahoma under dry, average, and wet climatic conditions
M.W. Van Liew, J.D. Garbrecht, and J.G. Arnold
- Forage species and canopy cover effects on runoff from small plots
M.L. Self-Davis, P.A. Moore, Jr. T.C. Daniel, D.J. Nichols, T.J. Sauer, C.P. West, G.E. Aiken, and D.R. Edwards
- Vegetative filter strips for reducing atrazine and sediment runoff transport
S.K. Mickelson, J.L. Baker, and S.I. Ahmed
- The economic benefits of soil erosion control: An application of the contingent valuation method in the Alto Genil basin of southern Spain
S. Colombo, J. Caltrava-Requena, and N. Hanley
Departments
- Home Front
- Viewpoint--Ian Hannam
- Raise Your Voice
- Notebook
- Conservogram
Precision conservation for environmental sustainability
(Full text appears in the Journal of Soil and Water Conservation, Vol.58, No. 6) (Click here for PDF)
J.K. Berry, J.A. Delgado, R. Khosla, and F. Pierce
ABSTRACT: With continued population growth and increasing demands on water resources, precision conservation will have an increasing role during this new millennium. It has been reported that world population is expected to be about 9.4 billion by 2050, and that increases in crop yields will have to be achieved primarily from land that is currently under production since most of the world’s arable land is already being cultivated. These increases in population growth and food and water demands will put increasing pressure for development of new more efficient technology and production practices that contribute to higher yields. Since intensive farming can potentially impact soil and water quality, parallel increases in new practices and technology contributing to improved soil and water conservation practices will be needed to help sustain and maintain the needed yield increases from agricultural systems.
Keywords:
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Simulation of the impacts of flood retarding structures on streamflow for a watershed in southwestern Oklahoma under dry, average, and wet climatic conditions
(Full text appears in the Journal of Soil and Water Conservation, Vol.58, No. 6)
M.W. Van Liew, J.D. Garbrecht, and J.G. Arnold
ABSTRACT: Following the devastating floods of the 1940s, thousands of flood retarding structures were constructed in the Great Plains. The impacts of these structures on streamflow characteristics and their effectiveness in reducing floods under dry, average, and wet climatic conditions were investigated in this study. The setting for the study was a 160 km2 (61.9 mi2) experimental watershed in southwestern Oklahoma that contained 13 flood retarding structures, which controlled 65% of the drainage area. Thirty-three years of precipitation and eight years of streamflow data, in conjunction with computer simulations, were used to evaluate changes due to the flood retarding structures in annual, monthly, and daily streamflow characteristics at the outlet of the watershed. Simulation results indicate that installation of the flood retarding structures leads to a decrease in average annual streamflow of about 3%, which was attributed to an increase in average annual evaporation of this same amount due to the free water surface of the reservoirs created by the flood retarding structures. On a monthly time scale, the simulation results showed that under dry climatic conditions, the flood retarding structures caused a reduction in mean streamflow for all months of the year. On the other hand, during average and wet climatic conditions, changes in mean streamflow varied by month with May and October showing the greatest decreases, respectively. As expected, the greatest impact of the flood retarding structures was on daily flow characteristics and maximum daily flows. Noticeable differences include the reduction of maximum daily discharges on the day of a storm event and the increase in streamflow from principal spillway releases in the days immediately following storm events. Annual maximum daily discharges were reduced by about 33%, with the reduction of the 5 and 10-year maximum daily flows being 23.8 to 14.6 cms (840 to 515 cfs) (39%) and from 36.0 to 20.6 cms (1,270 to 727 cfs) (43%), respectively. This study demonstrates the effectiveness of the flood retarding structures in reducing annual peak runoff events, thereby reducing flooding and related property damage. However, the flood retarding structures also reduce low streamflow values by trapping baseflow runoff from drainage areas above the impoundment structures. From a water quality and stream habitat preservation point of view, maintenance of a minimum baseflow can be critical.
Keywords: Flood retarding structures, streamflow, SWAT, watershed simulation
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Forage species and canopy cover effects on runoff from small plots
(Full text appears in the Journal of Soil and Water Conservation, Vol.58, No. 6)
M.L. Self-Davis, P.A. Moore, Jr., T.C. Daniel, D.J. Nichols, T.J. Sauer, C.P. West, G.E. Aiken, and D.R. Edwards
ABSTRACT: Studies have shown that the surface hydrology of a pasture system is influenced by its vegetative characteristics. As research continues on ways to prevent erosion and excessive nutrient loss from agricultural land, the effect that different forage species have on surface runoff requires further investigation. This study sought to evaluate the effect of five forage species at varying canopy heights (one day vs. six weeks growth post-harvest) on surface runoff and infiltration on 6.1 m x 6.1 m (20 x 20 ft) plots fertilized with poultry litter. The five forage species were: Alamo switchgrass (Panicum virgatum Carl Linnaeus), Caucasian bluestem (Bothriochloa caucasia (Trin.) C.E. Hubbard), Greenfield bermudagrass (Cynodon dactylon (L.) Christian Hendrik Persoon), Pete eastern gamagrass (Tripsacum dactyloides (L.) Carl Linnaeus), and Kentucky-31 tall fescue (Festuca arundinacea John H. Schreber). Poultry litter was surface-applied annually at 8.97 Mg ha-1 (4.0 ton/acre). Rainfall simulations (5.0 cm hr-1) (2.0 in hr-1) were used to produce runoff events during spring, summer, and fall to examine seasonal variations. Although there were no statistical differences in runoff volumes between cut canopy and full canopy covers within a single species, runoff volumes were reduced by full canopies, for all seasons, by an average of 18% for all species except bermudagrass. Comparisons of runoff volumes between the different species showed that tall fescue had significantly lesser (30 mm) runoff for three of the four runoff events. There were no differences in runoff between the other four species, for any runoff event. Infiltration was on average 19% greater in tall fescue plots for all runoff events, compared to the other four species. Neutron probe data supported these results, with tall fescue plots consistently having average profile volumetric water content from 3 to 5 m3 m-3 (9.8 to 16.4 ft3 ft-3) lower at the 20 and 35 cm (7.9 and 13.8 in) depths. Results of this study show that tall fescue, when directly compared to the other forages in this study, is more effective at reducing runoff volumes and increasing infiltration, thereby reducing edge of field loss in forage systems.
Keywords: Gamagrass, ground cover, infiltration, runoff, simulated rainfall, switchgrass
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Vegetative filter strips for reducing atrazine and sediment runoff transport1
(Full text appears in the Journal of Soil and Water Conservation, Vol.58, No. 6)
S.K. Mickelson, J.L. Baker, and S.I. Ahmed
ABSTRACT: A rainfall simulation study was performed on twelve vegetative filter strips (VFS), six 1.5 ¥ 4.6 m (5 ¥ 15 ft) long, and six 1.5 ¥ 9.1 m (5 ¥ 30 ft) long, to determine: (1) the effects of vegetative filter strips on atrazine and sediment transport in runoff inflow with an average of 7,650 mg L-1 (0.0638 lb gal-1) sediment (WS) and no-sediment (NS), and (2) the effects of vegetative filter strips length (4.6 and 9.1 m) (15 and 30 ft), and thus area ratio (with constant width), on atrazine and sediment transport. Herbicide runoff losses were simulated by adding a dilute atrazine solution as inflow (with sediment and without sediment) to the upper end of the vegetative filter strips. The with-sediment (WS) treatment was used to represent conventional tillage, while the without-sediment (NS) treatment represented no-tillage. Atrazine, and bromide (Br-) as a hydrologic tracer, were dissolved in the inflow to the vegetative filter strips at a concentration of approximately 1 and 23 mg L-1 (8.345 and 192 lb (mil gal)-1), respectively. The results showed that for the with-sediment inflow treatment, the 87% reduction in sediment transport for the 9.1 m (30 ft) vegetative filter strips was significantly (P = 0.05) greater than the 71% reduction for the 4.6 m (15 ft) vegetative filter strips. There was no significant difference in atrazine transport between the with-sediment and without-sediment treatments, but the 80% reduction in atrazine tra`port for the 9.1m (30 ft) vegetative filter strips was significantly greater than the 31% reduction for the 4.6 m (15 ft) vegetative filter strips. Infiltration of inflow was a dominant factor in reducing atrazine transport with vegetative filter strips, and the Br- data showed that a higher proportion of inflow infiltrated than did rainfall.
Keywords: BMP, bromide, herbicide, nonpoint pollution
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The economic benefits of soil erosion control: An application of the contingent valuation method in the Alto Genil basin of southern Spain
(Full text appears in the Journal of Soil and Water Conservation, Vol.58, No. 6)
S. Colombo, J. Calatrava-Requena, and N. Hanley
ABSTRACT: Soil erosion results in many off-site negative effects such as eutrophication of waterways and impacts on landscape quality. Because these off-site effects are rarely “captured” in markets they are often given too little weight in policy decisions. In this paper, we apply the contingent valuation method (CV) to estimate the benefits of a soil erosion control program in the Alto Genil area of southern Spain to the general public. Our survey design attempts to reduce part-whole bias by getting respondents to also value other, substitute environmental programs. Our main finding is that a majority of the catchment’s population is willing to pay to reduce off-site damages, and that current off-site damages impose costs of around 4-7 million euros1/year, or around 42-72 euros/hectare/year (17-29 euros/acre/year). Reminding respondents about substitute environmental projects is found to have a significant impact on the value placed on soil erosion control.
Keywords: Contingent valuation, externalities, off-farm impacts, soil erosion, substitution effects
