Antecedent Soil Water Conditions Research Articles

Manual packing and soil reuse effects on determination of saturated hydraulic conductivity of a loam soil

Performing laboratory measurement of saturated hydraulic conductivity, Ks, of sieved soil is important for many scientific purposes such as testing theories and methods to determine Ks. A given soil mass can be used only once or it can be reused after a previous use. Little is known on the dependence of the Ks measurements on both the applied packing method and the reuse of the same soil mass. This lack of knowledge makes comparisons among different investigations more or less uncertain. Four packing methods were tested on an initially dry loam soil by measuring Ks with the simplified falling head (SFH) technique. The four methods differed by the used compacting procedure (dropping from a given height, pestle imparting vertical and radial forces on the pressed soil surface) and the number of soil layers disposed at each step of the procedure. Changes in Ks due to the reuse of the same soil mass were also determined. Depending on the packing method and the number of times a given soil mass was used, the means of Ks varied from 51 to 110 mm h−1, with a ratio between these two extremes of 2.2, and the coefficients of variation, CVs, ranged between 10 and 36%, depending on the developed dataset (sample size, N = 15 for each dataset). Therefore, the packing method and the reuse of the same soil had a moderate effect on determination of Ks. For a given pre-treatment of the soil mass, the lowest variability of Ks was detected by using the pestle, probably because this simple device favored homogenization of the soil and enhanced the contact with the walls of the cylinder. With the pestle, reusing the soil once was enough to pass from a medium (CV = 23–27%) to a low (CV = 12%) variation of Ks. Taking into account that the best procedure yields the lowest variability of the individual Ks measurements, the conclusion was that the pestle and a previously wetted soil should be used. In the future, additional experiments should be carried out on other soils, in different antecedent soil water conditions and with other laboratory measurement methods of Ks. This study provided new information on soil sample preparation methods and it showed that simple procedures could be applied for preparing different samples with similar Ks values.

Soil water storage, rainfall and runoff relationships in a tropical dry forest catchment

AbstractIn forested catchments, the exceedance of rainfall and antecedent water storage thresholds is often required for runoff generation, yet to our knowledge these threshold relationships remain undescribed in tropical dry forest catchments. We, therefore, identified the controls of streamflow activation and the timing and magnitude of runoff in a tropical dry forest catchment near the Pacific coast of central Mexico. During a 52 day transition phase from the dry to wet season, soil water movement was dominated by vertical flow which continued until a threshold soil moisture content of 26% was reached at 100 cm below the surface. This satisfied a 162 mm storage deficit and activated streamflow, likely through lateral subsurface flow pathways. High antecedent soil water conditions were maintained during the wet phase but had a weak influence on stormflow. We identified a threshold value of 289 mm of summed rainfall and antecedent soil water needed to generate >4 mm of stormflow per event. Above this threshold, stormflow response and magnitude was almost entirely governed by rainfall event characteristics and not antecedent soil moisture conditions. Our results show that over the course of the wet season in tropical dry forests the dominant controls on runoff generation changed from antecedent soil water and storage to the depth of rainfall.

Revealing the relative influence of soil and topographic properties on soil water content distribution at the watershed scale in two sites

Summary Soil and topographic properties are two important factors controlling soil water content (SWC) distribution in a horizontal dimension. The objective of this study was to use structural equation modeling (SEM) to reveal the relative influence of soil and topographic properties on SWC distribution at the watershed scale. Experiments were conducted in two representative sites: St. Denis National Wildlife Area (SDNWA) in the Canadian prairie landscape with a humid continental climate, and LaoYeManQu (LYMQ) watershed on the Chinese Loess Plateau with a cold semi-arid environment. Soil water contents were measured along a 576 m long transect at the SDNWA and over an area of 20 ha at the LYMQ. The influences of soil and topographic properties on SWC were determined at various soil layers and under various antecedent soil water conditions. Results showed that soil and topographic properties jointly controlled SWC distribution at the SDNWA, but soil properties contributed more to SWC variability than topographic properties. At the LYMQ, only soil properties dominated SWC distribution. The influences of soil and topographic properties at the SDNWA were stronger under wetter conditions, whereas the influence of soil properties at the LYMQ presented slight differences between different antecedent soil water conditions. The influence of soil properties decreased and then increased with depth from 0–20 cm to 120–140 cm at the SDNWA, whereas the influence of topographic properties at the SDNWA and the influence of soil properties at the LYMQ decreased with depth. This study implied that SWC was a local and nonlocal control in the humid continental climate, whereas only a local control operated in the cold semi-arid environment.

Predicting Water Table Response to Rainfall Events, Central Florida

A rise in water table in response to a rainfall event is a complex function of permeability, specific yield, antecedent soil-water conditions, water table level, evapotranspiration, vegetation, lateral groundwater flow, and rainfall volume and intensity. Predictions of water table response, however, commonly assume a linear relationship between response and rainfall based on cumulative analysis of water level and rainfall logs. By identifying individual rainfall events and responses, we examine how the response/rainfall ratio varies as a function of antecedent water table level (stage) and rainfall event size. For wells in wetlands and uplands in central Florida, incorporating stage and event size improves forecasting of water table rise by more than 30%, based on 10 years of data. At the 11 sites studied, the water table is generally least responsive to rainfall at smallest and largest rainfall event sizes and at lower stages. At most sites the minimum amount of rainfall required to induce a rise in water table is fairly uniform when the water table is within 50 to 100 cm of land surface. Below this depth, the minimum typically gradually increases with depth. These observations can be qualitatively explained by unsaturated zone flow processes. Overall, response/rainfall ratios are higher in wetlands and lower in uplands, presumably reflecting lower specific yields and greater lateral influx in wetland sites. Pronounced depth variations in rainfall/response ratios appear to correlate with soil layer boundaries, where corroborating data are available.

Responses of evapotranspiration at different topographic positions and catchment water balance following a pronounced drought in a mixed species eucalypt forest, Australia

Across southern Australia, a large proportion of urban water supply is sourced from mountainous catchments forested with native eucalypts. Mixed species eucalypt forest (MSEF) is the most common forest type in this region and occurs on relatively dry, fire prone sites, yet factors controlling forest water use and stream flow in response to topography, disturbance and drought are poorly understood. This study investigated the patterns and drivers of water balance over a 4 year period in a 1.36 km2, MSEF catchment by: quantifying spatial and temporal variability in evapotranspiration (Et) and its components; evaluating the abiotic, structural and physiological factors controlling water use across the catchment; and testing the effects of antecedent soil water conditions on water fluxes after drought. This was done using a ‘bottom up’ measurement approach that included stream flow and Et (sap flow, interception troughs and evaporation dome) and a simple empirical model of Et to track catchment response to drought. Spatial variability was considerable, with 40% lower rates of Et at an up slope plot compared to mid and bottom slope plots. Tree transpiration was the dominant flux annually and was correlated to reference Et (r2 = 0.35–0.80), implying strong limitation by atmospheric demand across the catchment. Annual Et totals were relatively consistent between years (841 ± 34 mm) despite large variation in rainfall (463–1179 mm y−1). Annual stream flow represented a very small proportion of the water budget (<2% of rainfall) and showed little recovery from the drought period. The modelling showed that the change in soil water storage following drought was large (up to −330 mm) and was responsible for decreased rates of stream flow. These findings show that Et in the MSEF is sensitive to topography and demand limitation and suggests that water yield in this forest type may be particularly sensitive to future climatic change as shown by the sustained effect of drought on catchment water balance.

Rainfall-Runoff Modeling: Comparison of Two Approaches with Different Data Requirements

Among several hydrological models developed over the years, the most widely used technique for estimating direct runoff depth from storm rainfall i.e., the United States Department of Agriculture (USDA) Soil Conservation Service’s (SCS) Curve Number (CN) method was adopted in the present study. In addition, the Muskingum method, which continues to be popular for routing of runoff in river network, was used in the developed model to route surface runoffs from different subbasin outlet points up to the outlet point of the catchment. SCS CN method in combination with Muskingum routing technique, however, required a detailed knowledge of several important properties of the watershed, namely, soil type, land use, antecedent soil water conditions, and channel information, which may not be readily available. Due to this complexity of semi-distributed conceptual approach (SCS CN method) and non-linearity involved in rainfall-runoff modeling, researchers also attempted another less data requiring approach for runoff prediction, i.e., the neural network approach, which is inherently suited to problems that are mathematically difficult to describe. The purpose of this study was to compare the rainfall-runoff modeling performance of semi-distributed conceptual SCS CN method (in combination with Muskingum routing technique) with that of empirical ANN technique. The models were coded in C language and to make them user friendly, a Graphical User Interface (GUI) was also developed in Visual Basic 6.0. The developed models were tested for Kangsabati catchment, situated in the western part of West Bengal, India. Monsoon data of 1996 to 1999 were used for calibration of the models whereas they were validated for another four years (1987, 1989, 1990, and 1993) monsoon data. Modeling efficiency (ME) and coefficient of residual mass (CRM) were used as performance indicators. Results indicated that for Kangsabati catchment, the empirical runoff prediction approach (ANN technique), in spite of requiring much less data, predicted daily runoff values more accurately than semi-distributed conceptual runoff prediction approach (SCS CN method).

Corn stover removal impacts on micro-scale soil physical properties

Crop residues are a potential source for biofuel production. Yet, impacts of removal of corn ( Zea mays L.) stover and other residues as biofuel feedstocks on micro-scale soil properties affecting the behavior of the whole soil are not well understood. Data on both macro- and micro-scale soil properties under different scenarios of stover management are needed to define the threshold levels of stover removal. Previous studies on stover removal impacts on soil properties have primarily focused on macroscale properties and little or not on microscale properties. Thus, this study was designed to assess impacts of annual stover removal for 3 consecutive years at rates of 0, 25, 50, 75, and 100% on soil physical properties at the aggregate level under no-tillage (NT) continuous corn systems in a Rayne silt loam (RSL) (fine-loamy, mixed, active, mesic Typic Hapludult) with 10% slope, Celina silt loam (CSL) (fine, mixed, active, mesic Aquic Hapludalfs) with 2% slope, and Hoytville clay loam (HCL) (fine, illitic, mesic Mollic Epiaqualfs) with < 1% slope in Ohio. Aggregates were sensitive to stover removal particularly in the 0- to 10-cm soil depth. Stover removal reduced aggregate stability, tensile strength (TS), water retention (WR), and subcritical water repellency, while it increased water sorptivity but had no effect on pore-size distribution within an aggregate. The interaction of aggregate stability, strength, and subcritical water repellency with aggregate water potential was highly significantly, indicating that the magnitude of changes in aggregate structural properties due to stover removal depended on the variable antecedent soil water conditions. The aggregate stability and strength decreased while water repellency increased with increasing water potential. Impacts of stover removal on the clayey soils were equal to or higher than those on silt loam soils. Removal at rates ≥ 25% reduced the raindrop kinetic energy (KE) required to break aggregates by 13 times at HCL, while removal at rates ≥ 50% reduced the KE by 2 to 3 times at RSL and CSL for air-dry aggregates. The KE and TS decreased with increasing soil water potentials. The TS was reduced by 10% to 30% at all water potentials at RSL, by 20% to 35% between − 0.1 and − 1.5 MPa, and by 2.2 times at − 166 MPa at CSL, and by 2 to 3 times between − 1.5 and − 166 MPa at HCL under complete stover removal. Removal of stover at rates ≥ 50% reduced subcritical water repellency by 2 to 10 times in all soils. Overall, stover removal altered micro-scale soil properties, and complete stover removal had the most detrimental effects. Based on the data from previous studies on macroscale soil properties and this study, stover removal adversely affects both macro- and micro-scale soil properties.

Factors controlling soil water-recharge in a mixed European beech (Fagus sylvatica L.)?Norway spruce [Picea abies (L.) Karst.] stand

The spatial dynamics of soil water-recharge in a forest stand is the product of a number of interacting processes. This study focuses on the role of tree species and antecedent soil water content upon horizontal and vertical patterns of soil water recharge in heavy clay soils of a mixed European beech–Norway spruce stand and of a pure Norway spruce stand after rewetting periods with different rain quantities and intensities. Volumetric water content (VWC) was measured at 194 locations across 0.5-ha plots in each stand using time-domain reflectometry (TDR) with fixed 30- and 60-cm vertical waveguides. This was repeated 28 times (as close as possible) before and after rewetting periods during the vegetation seasons in 2000 and 2001. In addition, the locations of all trees within the plots were recorded. Geostatistics was used to describe the spatial correlation between VWC measurements and to interpolate soil water recharge in space. Spatial patterns of soil water recharge were then evaluated according to antecedent soil water-content and tree species distribution. Open-field precipitation of 30 mm (maximum intensity 10 mm h−1) on extremely dry initial soil conditions resulted in higher subsoil (30–60 cm soil depth) recharge and erratic recharge patterns. This was presumably due to preferential flow in opening shrinkage cracks of the heavy clay soil. A comparable quantity and intensity of rainfall under moderately dry antecedent soil water conditions resulted in almost exclusively topsoil (0–30 cm soil depth) water recharge and patterns of recharge that were clearly related to tree species distribution. The higher recharge around beech trees can be attributed to the lower interception rates there. Spatial patterns of soil water recharge reflect patterns of antecedent soil water conditions.

Intra-storm study of solute chemical composition of overland flow water in two agricultural fields.

Few studies have assessed the transport of dissolved nutrients at the field scale under natural rainfall conditions. Hysteresis between dissolved nutrients and discharge behavior can complicate such assessments and this effect has only been examined qualitatively. In this study, we investigated factors contributing to short-term variations of dissolved cation (Ca, Mg, Na, and K) and anion (soluble reactive phosphorus [SRP], NO3, and SO4) concentrations in runoff water and developed a quantitative method to study their hysteretic behavior. Within-storm variations of dissolved nutrient concentrations were determined in two agricultural fields during four natural rainfall events along with discharge, sediment, antecedent soil water conditions, and nutrient contents. For each event, nutrient loads were plotted against discharge during the rising and falling limb of the runoff hydrograph. The resulting hysteresis curves were characterized by an index H, which is the ratio between the integrated areas under the rising and falling curves of the hydrograph. Results showed that nutrient concentrations increased with time during each event. Counterclockwise (H < 1) hysteresis, occurring when the falling limb had larger loads, was found when soils were initially dry whereas clockwise hysteresis (H > 1) was associated with prior wet soil conditions. Two hypotheses are suggested to explain these variations. First, suspended sediments could have acted as a sink for dissolved nutrients and the sensitivity of nutrients to hydrological conditions was determined by their preferential sorption on these sediments. Second, movement of nutrients into runoff occurred more readily as soils became wetter during an event.

Hydrological applications of satellite data: 1. Rainfall estimation

In this study we investigate the ability of satellite visible and infrared data to produce reliable rainfall amount estimates that could be used by hydrological models to predict streamflow for large basins. Rainfall estimates are obtained by (1) classification of clouds to raining and nonraining clouds and (2) applying a multivariate statistical model between rainfall and indices derived from the satellite observations. Satellite data corresponding to 180 randomly selected days in the period May‐September 1982–1988 are used in this study that focuses on the estimation of daily rainfall. The Des Moines River basin in the midwestern United States is the application area. The correlation coefficient between model‐predicted and rain gauge‐observed mean areal precipitation over areas of order 10,000 km2 is found to be about 0.85. In an example application the satellite rainfall estimates are used to force the operational National Weather Service hydrologic forecast model for a subbasin of the Des Moines River basin. The model has been calibrated with rain gauge data. The results show that differences between rain gauge and satellite rainfall input generate differences in flow forecasts and upper soil water model estimates, which are a function of the antecedent soil water conditions. A companion paper [Guetter et al., this issue] quantifies the effects that the differences between rain gauge and satellite rainfall estimates have on flow and upper soil water model predictions for various spatial scales and for hydrologic models calibrated with and without satellite data.

Soil water content at R-5. Part 1. Spatial and temporal variability

This paper, the first part in a two-part series, is concerned with the interpretation of spatial and temporal variations in soil water content across a small rangeland catchment; two data sets are examined. The first data set is comprised of 25 728 soil water content measurements made at 34 sites over an 8 year period. The second data set consists of individual soil water content measurements made at 247 sites over a 6 day period. Geostatistical methods are used to describe variations in soil water content; general characterizations are made. In the companion paper the impact of antecedent soil water conditions is investigated for a suite of R-5 event simulations with a quasi-physically based rainfall-runoff model.

Physically based hydrologic modeling: 1. A terrain‐based model for investigative purposes

THALES, a simple distributed parameter hydrologic model is presented and applied to two catchments in Australia and the United States, each with different dominant hydrologic responses. The model simulates Hortonian overland flow and runoff from saturated source areas and is used to identify some of the barriers to modeling the hydrology of small catchments. At Wagga Wagga in New South Wales, Australia, runoff is produced from saturated source areas, whereas on the Lucky Hills catchments at Walnut Gulch in Arizona, Hortonian overland flow processes dominate. Simulations at Wagga Wagga are based on published parameters and field data measured as part of an intensive field program and result in a relatively poor fit of the outflow hydrographs for a series of storms. The simulated position and growth of saturated areas coincides with the limited available information, indicating that at least the gross effects of subsurface water movement are being represented. For the Lucky Hills catchments, the hydrographs at the catchment outlet and points within the catchment are simulated for a storm series. The results are highly dependent on the parameter values, which are poorly defined, highlighting the lack of measured field data and lack of methodology for the collection of data at a scale appropriate for such models. The model structure is also shown to have a major influence on the output. The influence of simulating surface flow as sheet flow or rill flow or through a series of ephemeral gullies, as well as the choice of the surface roughness parameter and antecedent soil water conditions, is shown to have a profound effect on the distributed flow depth and velocity predictions. By fitting model parameters, a simulation assuming Hortonian overland flow produced similar results at the catchment outlet to those based on partial area runoff. These results are of concern since it is common to calibrate and verify hydrologic models based on the accuracy with which the catchment outflow is predicted. The internal estimates of flow characteristics following such a calibration often provide the input to sediment and nutrient transport models. Models such as THALES produce an enormous amount of information and have the theoretical potential to provide a “universal” tool for the representation of hydrologic response. However, problems of verification and validation of such models are acute. These problems relate to the difficulty in measuring/deriving parameters a priori, measurement of the catchment response in sufficient detail for testing, and the validity of the fundamental assumptions and algorithms used in model development.

Hydrology of two forested wetlands that receive pumped agricultural drainage water in Eastern North Carolina

Wetlands have been recommended for buffering the impact of agricultural drainage water on tidal rivers and estuaries. This two-year study documented the hydrology of two wetland buffer areas in eastern North Carolina that received pumped agricultural drainage water. The hydrology of both sites was documented by monitoring rainfall and pumping rates and by monitoring water surface elevations over a network of stations on each wetland. Water velocities and wetland roughness coefficients were determined by dye tracer studies on the wetlands. The pumping rates of drainage water onto the wetlands were highly variable, depending on the amount and intensity of rainfall and on the antecedent soil-water conditions on the agricultural area. The two study sites, Laurel Bay (LB) and Northwest Fork (NF), differed in that the wetland at LB was larger in area and received drainage water from a smaller agricultural area. Water depth on the wetland at LB increased by as much as 210 mm in response to pumping compared to a 380 mm maximum increase in water depth at NF. Measured velocities of the pumped water on the LB wetland ranged from 400 to 900 m/d compared to 1600 to 4600 m/d at NF. Factors causing lower velocities on the LB wetland were lower ground slope from the pumps to the receiving stream, greater resistance to flow, lower pumping rates, and better distribution of the pumped water (facilitated by a canal that distributed pumped water laterally before entering the wetland). Lower velocities will result in greater residence times and greater pollutant removal on the wetland.