The historical development of the Darcy-Weisbach equation for pipe flow resistance is examined. A concise examination of the evolution of the equation itself and the Darcy friction factor is presented from their inception to the present day. The contributions of Chézy, Weisbach, Darcy, Poiseuille, Hagen, Prandtl, Blasius, von Kármán, Nikuradse, Colebrook, White, Rouse and Moody are described.

For phosphorus (P) transport from upland areas to surface water systems, the primary transport mechanism is typically considered to be surface runoff with subsurface transport assumed negligible. However, certain local conditions can lead to an environment where subsurface transport may be significant. The objective of this research was to determine the potential of subsurface transport of P along streams characterized by cherty or gravel subsoils, especially the impact of preferential flow paths on P transport. At a field site along the Barren Fork Creek in northeastern Oklahoma, a trench was installed with the bottom at the topsoil/alluvial gravel interface. Fifteen piezometers were installed surrounding the trench to monitor flow and transport. In three experiments, water was pumped into the trench from the Barren Fork Creek to maintain a constant head. At the same time, a conservative tracer (Rhodamine WT) and/or potassium phosphate solution were injected into the trench at concentrations at 3 and 100 mg/L for Rhodamine WT and at 100 mg/L for P. Laboratory flow-cell experiments were also conducted on soil material <2 mm in size to determine the effect that flow velocity had on P sorption. Rhodamine WT and P were detected in some piezometers at equivalent concentrations as measured in the trench, suggesting the presence of preferential flow pathways and heterogeneous interaction between streams and subsurface transport pathways, even in nonstructured, coarse gravel soils. Phosphorus transport was retarded in nonpreferential flow paths. Breakthrough times were approximately equivalent for Rhodamine WT and P suggesting no colloidal-facilitated P transport. Results from laboratory flow-cell experiments suggested that higher velocity resulted in less P sorption for the alluvial subsoil. Therefore, differences in flow rates between preferential and nonpreferential flow pathways in the field led to variable sorption. The potential for nutrient subsurface transport shown by this alluvial system has implications regarding management of similar riparian floodplain systems.

Phosphate treatments can reduce metal dissolution and transport from contaminated soils. However, diammonium phosphate (DAP) has not been extensively tested as a chemical immobilization treatment. This study was conducted to evaluate DAP as a chemical immobilization treatment and to investigate potential solids controlling metal solubility in DAP-amended soils. Soil contaminated with Cd, Pb, Zn, and As was collected from a former smelter site. The DAP treatments of 460, 920, and 2300 mg P kg-1 and an untreated check were evaluated using solute transport experiments. Increasing DAP decreased total metal transported. Application of 2300 mg P kg-1 was the most effective for immobilizing Cd, Pb, and Zn eluted from the contaminated soil. Metal elution curves fitted with a transport model showed that DAP treatment increased retardation (R) 2-fold for Cd, 6-fold for Zn, and 3.5-fold for Pb. Distribution coefficients (Kd) increased with P application from 4.0 to 9.0 L kg-1 for Cd, from 2.9 to 10.8 L kg-1 for Pb, and from 2.5 to 17.1 L kg-1 for Zn. Increased Kd values with additional DAP treatment indicated reduced partitioning of sorbed and/or precipitated metal released to mobile metal phases and a concomitant decrease in the concentration of mobile heavy metal species. Activity-ratio diagrams indicated that DAP decreased solution Cd, Pb, and Zn by forming metal-phosphate precipitates with low solubility products. These results suggest that DAP may have potential for protecting water resources from heavy metal contamination near smelting and mining sites.

[1] Henry Darcy was a distinguished engineer, scientist, and citizen who is remembered for his many contributions in hydraulics, including Darcy's law for flow in porous media. While he has been given full credit for the finding, little insight has been available on the process of his discovery. It is shown that his discovery was the logical result of a lifetime of education, professional practice, and research. Darcy understood both its significance and its relationship to the broader fields of hydraulics and groundwater hydrology. Besides the discovery of Darcy's law, he was the first to show that significant flow resistance occurs within aquifers, the first to recognize the law's similarity to Poiseuille flow, and the first to combine the law with continuity to obtain a solution for unsteady flow.

Planning and strategic management of water resources are contingent on trends in water availability. In this study, the impact of decade-scale variations in annual and seasonal precipitation on streamflow and evapotranspiration ͑ET͒ were identified for 10 watersheds in Nebraska, Kansas, and Oklahoma. In the Great Plains, an upward trend in precipitation over the last two decades of the 20th Century had a strong impact on streamflow and a comparatively weaker impact on ET. Even though precipitation, streamflow, and ET amounts differed between watersheds, the trend due to the precipitation increase was similar for all watersheds. Increased precipitation led to a disproportionately large increase in streamflow and comparatively smaller increase in ET. On average, a 12% increase in annual precipitation led to a 64% increase in streamflow, but only a 5% increase in ET. The seasonal partitioning of the annual precipitation increase was, in most cases, biased toward the fall, winter, and spring, with little or no change during the hot summer months. The strong streamflow response indicated that planning and management of surface-water storage and supply can be critically impacted by decadelong trends in precipitation. The lack of significant increase in precipitation and streamflow during summer suggests that any existing shortages will likely remain despite the observed annual precipitation increase. The ET response suggests that dryland farming and ecosystem vitality could benefit from the increased precipitation in fall, winter, and spring, but the relative impacts are more modest compared to the streamflow response and do not occur during summer when potential ET is greatest. Finally, since the mid-1990s precipitation and streamflow in a number of Oklahoma watersheds have shown a gradual decline from peak values in the late 1980s toward more average conditions. This declining trend in streamflow may be important for planning and management of water resources systems that must meet an increasing demand for water by a growing society while at the same time considering environmental and recreational needs.