FORTRAN programming - A self-taught course

Comprehensive programming course begins with numerical systems and basic concepts, proceeds systematically through FORTRAN language elements, and concludes with discussion of programming techniques. Course is suitable either for individual study or for group study on informal basis

Hydraulic properties of soil cores from untrafficked and trafficked areas

The hydraulic conductivity is an important soil parameter that is both difficult and time consuming to measure directly. Several methods have been proposed to estimate soil hydraulic conductivity indirectly. This paper focuses on one method of predi.:ting hydraulic conductivity from knowledge of the soil water retention curve. Water retention curves were measured for 15 undisturbed soil cores. Unsaturated hydraulic conductivity of the same 15 soil cores also was determined directly by using unit gradient measurements. An equation was fitted to each of the retention curves, and a procedure using the fitting parameters was implemented to predict hydraulic conductivity of each core. Predicted and observed hydraulic conductivities are compared. The procedure describes hydraulic conductivity relationships better when observed values of unsaturated hydraulic conductivity are included in the curve fitting process, than when the saturated hydraulic conductivity alone is used as a matching point. Analysis of a data set taken from the literature indicates that observed air permeabilities may also be useful for estimating the unsaturated hydraulic conductivity

An in situ probe‐spacing‐correcting thermo‐TDR sensor to measure soil water content accurately

To reduce the possibility of probe deflections, conventional thermo-time domain reflectometry (T-TDR) sensors have relatively short probe lengths (≤4 cm). However, short probes lead to large errors in TDR-estimated soil water content (θv). In this study, two new 6-cm-long probe-spacing-correcting T-TDR (CT-TDR) sensors were investigated. Compared to conventional 4-cm-long T-TDR sensors, the 6-cm-long CT-TDR sensors reduced errors in TDR-estimated θv. Errors in heat pulse (HP) estimated θv because of probe deflections were reduced when linear or nonlinear probe spacing correcting algorithms were implemented. The 6-cm-long CT-TDR sensors provided more accurate θv estimations than do the conventional 4-cm-long TTDR sensors

Subsurface Flow Barriers to Reduce Nitrate Leaching

Groundwater is a very important natural resource which directly affects many human lives. In the United States, groundwater is the source of about 22 percent of the freshwater used. About 53 percent of the total population and 97 percent of the rural population use groundwater supplies for their drinking water (Moody, 1990). Although contamination of groundwater can occur naturally, agriculture is considered to be one of the most widespread nonprofit sources of groundwater contamination. Among agricultural chemicals, nitrogen-fertilizer has been used most extensively, especially by com producers. About one million tons of nitrogen-fertilizer are used annually in Iowa. In some studies, more than 50 percent of the applied fertilizer nitrogen is not removed by the crop or stored in the soil, and leaching as a form of nitrate is thought to be a major reason for the losses (Blackmer, 1987). Leached nitrate may enter groundwater supplies. Nitrate-nitrogen concentrations found in unsaturated soil below the rootzone of agricultural fields are in the range of 5 to 100 mg!L (Bouwer, 1990). Nitrate-nitrogen concentrations in tile drainage below row crops often exceed 10 mg/L, the U.S.A. drinking water standard (Gast et al., 1978; Baker and Johnson, 1981; Timmons and Dylla, 1981; Baker et al., 1985)

Statistical Outlier Detection (SOD): A computer program for detecting outliers in data

There are no author-identified significant results in this report

Extended methodology for determining wetting properties of porous media

[1] Because most methods for assessing the wettability of porous materials are restricted in their applicability, we developed two new methods for measuring contact angles and particle surface energy. The proposed methods (the Wilhelmy plate method (WPM) and the modified capillary rise method (MCRM)) were tested on 24 soils. For comparison, the water drop penetration time test (WDPTT) and the sessile drop method (SDM) were also applied. It was found that advancing contact angles, measured either with WPM or MCRM, agreed well in the range of 0° to 142°. Sessile drop contact angles were within the domain enclosed by the range of advancing and receding contact angles as determined with WPM. WDPTT, however, was only sensitive in the narrow range of 85° to 115°. We conclude that both WPM and MCRM are reliable methods for determining contact angles and particle surface energy over a wide range of porous material wettabilities

Sensible Heat Observations Reveal Soil-Water Evaporation Dynamics

Soil-water evaporation is important at scales ranging from microbial ecology to large-scale climate. Yet routine measurements are unable to capture rapidly shifting near-surface soil heat and water processes involved in soil-water evaporation. The objective of this study was to determine the depth and location of the evaporation zone within soil. Three-needle heat-pulse sensors were used to monitor soil heat capacity, thermal conductivity, and temperature below a bare soil surface in central Iowa during natural wetting/drying cycles. Soil heat flux and changes in heat storage were calculated from these data to obtain a balance of sensible heat components. The residual from this balance, attributed to latent heat from water vaporization, provides an estimate of in situ soil-water evaporation. As the soil dried following rainfall, results show divergence in the soil sensible heat flux with depth. Divergence in the heat flux indicates the location of a heat sink associated with soil-water evaporation. Evaporation estimates from the sensible heat balance provide depth and time patterns consistent with observed soil-water depletion patterns. Immediately after rainfall, evaporation occurred near the soil surface. Within 6 days after rainfall, the evaporation zone proceeded \u3e 13 mm into the soil profile. Evaporation rates at the 3-mm depth reached peak values \u3e 0.25 mm h−1. Evaporation occurred simultaneously at multiple measured depth increments, but with time lag between peak evaporation rates for depths deeper below the soil surface. Implementation of finescale measurement techniques for the soil sensible heat balance provides a new opportunity to improve understanding of soil-water evaporation