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Most widely used nonpoint source models associate pollutant loads almost exclusively with land use via pollutant export coefficients and some kind of runoff coefficient. Not surprisingly, the range of management options suggested by such models' simulations are largely linked to changes in land use. This problem is addressed by developing models of dissolved phosphorus (DP) mobility for specific agricultural sources: manure, fertilizers, soil/plant complexes, and impervious surfaces and those associated with baseflow P loads. These models are coupled with a spatially distributed hydrologic model, the variable source loading function model. The model was applied to a small (164 ha), upstate New York watershed and tested against 1996-2000 stream flow and DP data. The source-specific model required no direct calibration of parameters compared to eight parameters needed in a similar export coefficient type model. Both models predicted stream DP loads well but the source-specific model provided additional insights into, for example, how much DP in the stream was derived from accumulated soil P as opposed to direct leaching from manure. This type of information is necessary to develop and assess a full range of options for best management practices, especially those that involve nonstatic activities such as manure spreading. DOI: 10.1061/(ASCE)0733-9372(2009) 135:1 (25) CE Database subject headings: Phosphorus; Watersheds; Agriculture; Water pollution; Nonpoint pollution.

The most common form of onsite domestic wastewater treatment in the United States is the septic system. Although the design of these systems has been well established, no systematic evaluation of septic system performance exists for sloping hardpan soils. In this paper, we develop a simple hydrologic model for assessing the probability of failure for a set of hydrologic conditions, septic loading rates, and soil and landscape parameters that are readily available for sloping soils. To demonstrate the model capabilities, input data for a septic field of a two-person residence in the New York City drinking water basin in the Catskills was utilized. Our analysis showed that the saturated hydraulic conductivity, depth to the impermeable layer, and slope of the drain field are critical parameters to assess in the design and siting of these systems. We concluded that septic systems perform poorly in undulating landscapes where the hydraulic conductivity is low and the impermeable layer is close to the surface. Under prolonged rainfall conditions on these soils, the septic field and downslope field saturate, causing hydraulic failure of the septic system and saturation in the downslope field; as a result, effluent may be routed directly to streams via overland runoff. DOI: 10.1061/(ASCE)0733-9372(2006) 132:10(1289) CE Database subject headings: Hydrology; Evaluation; Slopes; Wastewater treatment; Waste disposal.

The often rapid arrival of pesticides at the ground water has been explained by the concept of preferential movement of water and solutes through the soil. To facilitate understanding of these transport processes, a drainage study was conducted by applying a nonadsorbed tracer to plots drained by subsurface drains. Three management practices were employed: no-till, conventional-till, and conventional-till with incorporation of the tracer. The plots were irrigated with 71-203 mm of water. Drainage line outflow and tracer concentration in the outflow were monitored for up to 52 hr. The resulting soil profiles were analyzed for tracer concentration. The main effect of plowing and incorporating the tracer was a more uniform concentration in the resulting profile. A simple mixing-layer model was used to predict the rate at which the tracer was transported out of the root zone into the layers below. The model was found to be in reasonable agreement with drainage outflow patterns, especially from the incorporated plots. These results may be helpful for future development of best-management practices for controlling the effects of agriculture on environmental pollution.

Simple methods for predicting runoff from watersheds are important in engineering practice, particularly in flood forecasting and water-balance calculation. In this paper, we illustrate that the often used SCS runoff curve-number approach in its most elementary form can be derived from assuming that only the saturated areas contribute to direct runoff. With this approach the initial abstraction or the amount of water required before runoff starts is equal to air-filled pore space per unit area for the most shallow soil in the watershed. Air-filled pore space throughout the year was calculated with aid of the simple water balance employing the Thornthwaite-Mather procedure for the most shallow soil in the watershed. By plotting the effective precipitation defined as the amount of precipitation minus the initial abstraction against the observed runoff for two watersheds in Australia and three in the northeastern United States we found that the SCS curve-number equation in its elementary form fitted the data well.

The Soil Conservation Service Curve Number (SCS-CN) method is a widely used empirical rainfall-runoff equation. Although the physical basis of the method has been debated, several researchers have suggested that it can be used to predict the watershed fraction that is saturated and generating runoff by saturation excess from variable source areas (VSAs). In this paper, we compare saturated runoff-contributing areas predicted with the VSA interpretation of the SCS-CN method with field-measured VSAs in a 0.5 ha hillslope in central New York State. We installed a trench below a VSA and simultaneously recorded water flux from different soil layers at the trench face and water table dynamics upslope of the trench. This setup allowed us to monitor runoff initiation and saturation-excess overland flow in response to rainfall and different water table depths in the hillslope during 16 storm events. We found that the SCS-CN method accurately predicted the observed VSA and showed best agreement if the VSA was defined as the area where the water table was within 10 cm of the soil surface. These results not only demonstrate that the VSA interpretation of the SCS-CN method accurately predicts VSA extents in small watersheds but also that the transient water table does not necessarily need to intersect the land surface to cause a storm runoff response. [ABSTRACT FROM AUTHOR]

This study was a statistical evaluation of the prevalence of infiltration excess runoff (i.e., Hortonian flow) for undeveloped areas within New York City (NYC) watersheds. Identifying the hydrological processes generating runoff is central to developing watershed management strategies for protecting water quality. Fifteen-minute rainfall data from East Sidney, N.Y. (1971-2002) were used as maximum observed intensities. Maximum exceedance analyses were performed on a monthly basis to investigate seasonal rainfall intensity trends. Hortonian flow was assumed to occur whenever the rainfall intensity exceeded the soil permeability. Soil permeabilities were obtained from the U.S. Natural Resource Conservation Service soil survey. Results show that Hortonian flow is unlikely to occur anywhere for events smaller than the 3-year 15-min event. Only for the summer months, May-August, is Hortonian flow expected for 15-min intensities of <10-year magnitude. However, the summer results are overpredicted by this analysis because these months typically have the driest soil conditions and thus the highest infiltration capacity. This analysis concludes that infiltration excess runoff is not a dominant runoff process in undeveloped portions of NYC watersheds. [ABSTRACT FROM AUTHOR]

Presents a corrected reprint of an article published in the "Journal of Hydrologic Engineering".