W. T. Dickinson

Comparison of saturated hydraulic conductivity measured by various field methods.

Field experiments were conducted to compare the saturated hydraulic conductivity (Ks ) measured by four different techniques: Double Ring Infiltrometer (RI), Rainfall Simulator (RS), Guelph Permeameter (GP), and Guelph Infiltrometer (GI). Ks values obtained with the RI and GP were statistically the same, but were significantly lower than those determined by the RS and GI methods. The Ks values obtained with the GP and the GI have greater variability than those obtained with the RI and RS methods. The GP and GI methods require a larger number of measurements (as compared to the RI and the RS methods) to achieve a mean Ks value exhibiting a comparable standard error of estimate.

Sediment-Removal Efficiency of Vegetative Filter Strips

Field experiments on vegetative filter strips (VFS) showed average sediment-removal efficiency varied from 50 to 98% as flowpath length increased from 2.44 to 19.52 m. Almost all of the easily removable aggregates (i.e. aggregates larger that 40 mm in diameter) can be captured within the first five meters of the filter strip. However, the remaining small-size aggregates are very difficult to remove by filtering flow through grass media, as even relatively low levels of turbulent energy in the water is sufficient to keep the finer sediments in suspension. The only effective mechanism for removal of small-size sediments is infiltration. Experiments with appreciable infiltration (low to moderate flow rates on the longer plot lengths), showed removal efficiencies of 90% or higher. The sediment-removal efficiency of the filter strip does not increase much by increasing the width of the filter strip beyond ten meters. Improved efficiency of VFS can be achieved through the installation of a drainage system to increase infiltration.

Application of the CREAMS model in southern Ontario conditions

ABSTRACT Amodified version of the CREAMS model has been calibrated with research plot data on loam soil in Southern Ontario. The modifications include the introduction of seasonal variations in soil erodibility and in soil hydraulic conductivity. The calibration has involved the determination of a set of model parameters to achieve an optimal fit of runoff, soil loss, and phosphorus yield estimates for up to a five year period of record. The hydrology submodel and the soluble phosphorus component of the nutrient submodel fared reasonably well. The performance of the erosion submodel was erratic but within acceptable limits. The particulate phosphorus component of the nutrient submodel did not fare so well.

Seasonal Variability of Hydraulic Conductivity

Seasonal variations in hydraulic conductivity and related properties in Conestogo silt loam are needed for modeling hydrologic responses. Saturated hydraulic conductivity and matric flux potential in the surface layer were field determined during fall (October/November) and spring (March/April) seasons. Laboratory investigations were also conducted to explore the effects of bulk density and temperature on the hydraulic conductivity of frozen soil.

Development of a Management Tool for Vegetative Filter Strips

Vegetative filter strips (VFS) are widely advocated as a BMP to safeguard and /or remediate water quality in streams. This study provides management tools for …

The impact of seepage on soil erosion.

ABSTRACT A laboratory study of the impact of return flow on erosion from a loam and a sand showed that flow rates through the loam were too low to have any effect on the erosion rates. For the sand, on the other hand, return flows caused very dramatic increases in erosion, particularly at a moderate rainfall rate. At a relatively high rainfall rate, however, extensive sheet erosion far outweighed any increased erosion that might have been caused by return flow.

Within-Storm Rainfall Distribution Effect on Soil Erosion Rate

This study investigates the effect of rainfall temporal distribution pattern within a storm event on soil erosion rate and the possibility of using rain power type model for rainfall erosivity. Various rainfall distribution patterns, simulated by rainfall simulator, were used on 1.0 m2 plot of silica sand and loam soil with a minimum of three replications. The results show that the soil erosion rates spiked following every sharp increase in rainfall intensity followed by a gradual decline to a steady erosion rate. Transient effects resulted in the soil erosion rates for an oscillatory rainfall distribution to be more than two fold higher than those obtained for a steady-state rainfall intensity event with same duration and same average rainfall intensity. The 3-parameter and 4-parameter rain power models were developed for a process-based measure of rainfall erosivity. The 4 parameter model yielded better match with the observed data and predicted soil erosion rates more accurately for silica sand under all rainfall distributions, and good results for loam soil under low intensity rainfall. More research is necessary to improve the accuracy of soil erosion prediction models for a wider range of rainfall distributions.

Modeling Pesticide Transport in Subsurface Drained Soils

Transport of chemicals through the soil profile and crop root zone, and the discharge from subsurface drainage lines into surface water can be a significant source of water pollution. This study measured and simulated subsurface drain outflows and atrazine loads in the subsurface drains from a field site in Ottawa, eastern Ontario, Canada, during 1988 and 1989. Corn was grown for silage at the site, and an H-flume with an automated water sampler was used to monitor temporal changes in quantity and quality of subsurface drain outflows from a 14-ha field site. A drainage simulation model, DRAINMOD, was combined with a chemical transport model, GLEAMS, to simulate the chemical transport of atrazine through the soil into the subsurface drain outflow. The model was calibrated with 1989 field data and compared to measured 1988 data. The calibrated DRAINMOD model predicted subsurface drain outflows for 1988 with a coefficient of determination of 0.40 and a standard error of the estimate, Sy/x, of 0.09 mm. Measured Atrazine concentrations exceeded 6 mg/kg on one occasion, but simulated Atrazine concentrations did not exceed 2.5 mg/kg. The model underpredicted atrazine mass in the subsurface drain outflows. Spring underpredictions of atrazine mass discharge was due to underprediction of subsurface drain flows while fall underpredictions were due to under-predictions of atrazine concentrations. Effects of temperature on atrazine half life and adsorption constant may be partially responsible for these results. This integrated model of chemical transport with the drainage simulation model provides a useful tool for studying chemical transport through the soil and crop root zone into surface waters.

PERFORMANCE ANALYSIS OF REINFORCED VEGETATIVE CHANNEL LINING SYSTEMS

Abstract Rolled Erosion Control Products (RECPs) have proven to be successful in reinforcing vegetative channel lining systems and improving their performance in Erosion and Sediment Transport Control (ESTC). Laboratory experiments and numerical simulation performed in the present study have provided a significant step towards: (1) identification of critical processes and effective mechanisms through which RECPs control and reduce erosion and sediment transport; (2) identification of influential index physical, mechanical and hydraulic properties of RECPs with respect to their ESTC performance; (3) investigation of the applicability of existing hydraulic models of turbulent shear flows over wavy, permeable and moveable boundaries to predict the kinematics and dynamics of flow in open-channels lined with RECPs; and (4) modification of the design approach for RECPs, in light of the new findings in this study.

STOCHASTIC ANALYSIS OF GROUNDWATER LEVELS IN A TEMPERATE CLIMATE

Time-based characteristics of groundwater table data have been described by a model with periodic and stochastic components. The periodic component has been analyzed by Fourier Series, and the stochastic component by an Auto-regressive model. The developed model has been used to predict monthly groundwater table values for an area within a temperate climate. On the basis of reasonable agreement between predicted and observed data, the developed model is satisfactory to describe the time-based structure of the groundwater table, and provides a valuable tool for data generation for the longer durations required for the design and operation of many water management projects.