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Solution Center for Nutrient Management
Solution Center for Nutrient Management
University of California
Solution Center for Nutrient Management

Nutrient Management Research Database

General Information

Research Title

Rainfall runoff and erosion in Napa Valley vineyards: effects of slope, cover and surface roughness

Research Specifications

Crop: Wine Grapes
Soil Type: Fagan series
County, State: Napa, California
Year: 2000

Authors

Battany, M.C and Grismer, M.E.

Summary/Abstract from Original Source

The effects of slope, cover and surface roughness on rainfall runoff, infiltration and erosion were determined at two sites on a hillside vineyard in Napa County, California, using a portable rainfall simulator. Rainfall simulation experiments were carried out at two sites, with five replications of three slope treatments (5%,10% and 15%) in a randomized block design at each site (0.64 m2 plots). Prior to initiation of the rainfall simulations, detailed assessments, not considered in previous vineyard studies, of soil slope, cover and surface roughness were conducted. Significant correlations (at the 95% confidence level) between the physical characteristics of slope, cover and surface roughness, with total infiltration, runoff, sediment discharge and average sediment concentration were obtained. The extent of soil cracking, a physical characteristic not directly measured, also affected analysis of the rainfall runoff erosion process. Average cumulative runoff and cumulative sediment discharge from site A was 87% and 242% greater, respectively, than at site B. This difference was linked to the greater cover, extent of soil cracking and bulk density at site B than at site A. The extent of soil cover was the dominant factor limiting soil loss when soil cracking was not present. Field slopes within the range of 4-16%, although a statistically significant factor affecting soil losses, had only a minor impact on the amount of soil loss. The Horton infiltration equation fot field data better than the modified Philip's equation. Owing to the variability in the 'treatment' parameters affecting the rainfall-runoff-erosion process, use of ANOVA methods were found to be inappropriate; multiple!factor regression analysis was more useful for identifying significant parameters. Overall, we obtained similar values for soil erosion parameters as those obtained from vineyard erosion studies in Europe. In addition, it appears that results from the small plot studies may be adequately scaled up one to two orders of magnitude in terms of land areas considered. Copyright 1999 John Wiley &Sons, Ltd.

Research Highlights

Design and Methods

  • The research was conducted at a commercial vineyard in southern Napa County, California, at an average elevation of approximately 55 m above sea level, with maximum slopes of 17% within the study area.
  • Merlot and Chardonnay vines were planted in straight rows, in an east-west orientation, 3m apart, oriented parallel with the slope direction.
  • A strip of soil .5m wide on either side of the vine trunks was kept clean of weed growth with herbicide applications.
  • 2 hillside sites were selected, and regions with slopes of 5, 10 and 15% were selected.
  • Individual plots for both sites were marked in a 2x3 complete randomized block design.
  • There were five replications per 'treatment' at each site for a total of 30 plots.
  • The parameters for each plot were slope (%), cover (%), surface roughness (equivalent cm), cumulative runoff (cm), cumulative sediment discharge (g/m2) and the average sediment concentration (g/L).
  • Rainfall simulations were performed using a drop-former unit, covering an area of 1 meter squared, with a drop fall height of 3.5m. Soil cores were taken for volumetric water content and bulk density measurements both before and after the rainfall simulation.
  • Linear regression techniques were used to analyze the correlation between individual plot physical characteristics and then to evaluate the correlation between each of the runoff/erosion parameters and plot physical characteristics.
  • Horton and Philip's infiltration equations were also compared.

Results

  • Runoff and infiltration rates did not reach steady-state values for nearly half of the rainfall simulations, particularly at site B where soil cracking was encountered.
  • The small plot size was susceptible to variations in surface topography.
  • The Horton's infiltration equation performed better than the Philip's equation in terms of goodness-of-fit as evaluated by the residual sum of squared errors term.
  • Comparison of average runoff/erosion parameter values indicated that soil cover was the primary treatment factor affecting erosion and runoff, rather than slope.
  • However, although cumulative runoff decreased with increasing cover, the correlation for combines sites was poor (r squared =.15).
  • The extent of soil cracking, not measured in this study, may be important in the analysis of the rainfall-funoff-erosion process.

Additional Information

Tags (links to other subject matter in database)

University
of
California
Division of Agriculture
and
Natural Resources
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