R. S. Broughton

Errors in the Thiessen technique for estimating areal rain amounts using weather radar data

Abstract High-resolution radar data were used to estimate rainfall accumulation patterns for thirteen summer storms. The Thiessen polygon method is used to estimate average rainfall over the Yamaska Basin. Thiessen estimates were compared to estimated radar rainfall averages over the basin. Errors for the thirteen storms analysed gave values between 3% and 69% for the whole basin.

Flood hydrograph simulation model

Abstract A model with a minimum number of parameters has been conceived and developed to simulate direct runoff hydrographs when given3the required input data. Rainfall and runoff data from 39 storms over four watersheds were used for this purpose. The model takes into account both the basin and rainstorm characteristics. A computer model was developed for the computations. The physical aspects of the model are expressed by division of the drainage area into isochronal sub-areas. Formulae were developed which permit computations of water loss parameters as variables dependent on antecedent precipitation. These formulae, together with a watershed lag, obtained by optimization or by the measurement of basin parameters, were used to simulate the runoff hydrograph for a watershed. The model was applied to Runnets watershed which has not been used for the development of the model. Good agreement was found between the simulated and observed hydrographs.

spacing Drains to Maximize Revenue Increases

ABSTRACTPROCEDURES were developed to compute corn crop loss for different depths and durations of high water table conditions, based on available data, and to calculate the revenue increases from a subsurface drainage system designed with different spacings in soils with various hydraulic conductivities. Seventy-six years of weather data were used for the analysis. At a condition approximating no subsurface drainage, the crop loss was found to be approximately 50 percent of the normal production. The spacing required to ob-tain maximum revenue increases was found to be sensitive to soil hydraulic conductivity, but insensitive to interest rate, amortization period and installation cost.

Monitoring and decision-making processes for operating agricultural production systems

Abstract Agricultural systems contain many inter-relationship factors which are uncertain or even unknown. Forecasting future situations is a difficult task under these uncertain conditions. Agricultural systems, however, are relatively flexible and can be adapted to new and unforeseen situations. Therefore, it is of importance to operate agricultural systems in such a way as to use their flexibility as a means of compensating for possible losses, and to take advantage of unforeseen events. One of the models which might be suitable for operating real agricultural systems under uncertainties is the Sequential Ad-hoc Linear Model. Detailed descriptions of two of the basic processes of this model, namely those of monitoring and decision making, are given in this paper. Examples taken from a real agricultural system are presented to demonstrate the application of the methodology.

Fertilizers and Subirrigation with Saline Water Affects Yield of Green Peppers in Lysimeters

ABSTRACT An experiment was undertaken at the McGill University experiment station at Ste-Anne de Bellevue, Canada, to study the effect of different fertilizers on green pepper yield as it is influenced by saline water supplied through a subirrigation system, which was used to supplement water stored in the soil. Green peppers (Capsicum annuum L.), cv. Bellboy, were grown in field lysimeters filled with a sandy loam soil. The lysimeters were covered with plastic sheets to prevent rainfall/surface water entry. Water having salinities of 1, 3, 5, and 7.5 dS·m−1, was applied through the bottoms of the lysimeters, and steady-state water tables were maintained at 0.45 or 0.9 m from the surface. The soil solution salinity in the soil profile remained less than 3.5 dS·m−1 during the growing season, and there was no appreciable increase in soil solution salinity in the root zone. Five rates of fertilizers were applied on the soil surface. The highest yield was obtained when all three nutrients, N, P, and K were applied at the recommended rates. The highest rate of N decreased pepper yield due to vigorous vegetative growth. Although the rate of P did not significantly increase yield when applied with K only, the yield significantly increased (P ≤ 0.05) when P was applied with K and N. Average yield ranged from 706 to 1,229 g/plant. There was no interaction of fertilizer with water table depth or irrigation water salinity. It appears that water with salinities up to 7.5 dS·m−1 could be used to supplement the stored fresh water in the soil profile using a subirrigation system for growing moderately salt-sensitive crops such as green peppers.

Development and testing of an agricultural land drainage simulation model

Abstract A deterministic computer model was developed to simulate runoff, on an hourly basis, from agricultural lands with surface and subsurface drainage. The model simulates the major hydrologic and hydraulic processes occurring both above and below the soil surface. The theoretical concepts of the algorithms are described. The model was tested on two fields, one with subsurface drainage and the other with surface drainage only. Simulated hydrographs were compared with measured hydrographs during the 1985 growing season. The results showed that the model performed reasonably well. There was no difference between the measured and simulated parameters of peak discharge, runoff depth and time of peak discharge at the 0.05 level of significance.

Measurements of Head Losses in a Subirrigation System

ABSTRACT THE head losses were measured in a subirrigation system on a sandy loam soil in southern Quebec during the Summer of 1985. The measurements included entrance head loss from a control chamber, friction head loss in drain pipes, exit head loss from perforations in the pipe and divergence head loss in the soil around drain pipes. The head losses were found to be a function of the flowrate in the subirrigation system. For the experimental setup, total head losses were found to be about 55 cm for an average water inflow of 30 L/min in the control chamber. It was found that the exit head loss from perforations in pipes is the most significant head loss in the subirrigation system. It was 75% of the total head loss in the subirrigation system.

A regret function for agricultural production systems

Abstract Decision-making under uncertainty is a difficult task, involving risks. Since losses are to be expected although not necessarily through the decision-makers fault, a regret concept is adopted. A regret concept and a regret function, based on a linear programming model, are suggested, using analysis of the sensitivity of the optimal plan to changes in random prices and in the amounts of available resources and estimates of the probabilities that each of the random variables will drop below a critical value. The use of this regret function, as an aid in decision-making, to evaluate the plan at the planning stage is explained and clarified by examples and a case study.