Antecedent Moisture Conditions Research Articles

Seasonal and event‐based drivers of runoff and phosphorus export through agricultural tile drains under sandy loam soil in a cool temperate region

AbstractFrequent algal blooms in surface water bodies caused by nutrient loading from agricultural lands are an ongoing problem in many regions globally. Tile drains beneath poorly and imperfectly drained agricultural soils have been identified as key pathways for phosphorus (P) transport. Two tile drains in an agricultural field with sandy loam soil in southern Ontario, Canada were monitored over a 28‐month period to quantify discharge and the concentrations and loads of dissolved reactive P (DRP) and total P (TP) in their effluent. This paper characterizes seasonal differences in runoff generation and P export in tile drain effluent and relates hydrologic and biogeochemical responses to precipitation inputs and antecedent soil moisture conditions. The generation of runoff in tile drains was only observed above a clear threshold soil moisture content (~0.49 m3·m−3 in the top 10 cm of the soil; above field capacity and close to saturation), indicating that tile discharge responses to precipitation inputs were governed by the available soil‐water storage capacity of the soil. Soil moisture content approached this threshold throughout the non‐growing season (October – April), leading to runoff responses to most events. Concentrations of P in effluent were variable throughout the study but were not correlated with discharge (p > 0.05). However, there were significant relationships between discharge volume (mm) and DRP and TP loads (kg ha−1) for events occurring over the study period (R2 ≥ 0.49, p ≤ 0.001). This research has shown that the hydrologic and biogeochemical responses of tile drains in a sandy loam soil can be predicted to within an order of magnitude from simple hydrometric data such as precipitation and soil moisture once baseline conditions at a site have been determined. Copyright © 2016 John Wiley & Sons, Ltd.

Flash flooding in small urban watersheds: Storm event hydrologic response

AbstractWe analyze flash flooding in small urban watersheds, with special focus on the roles of rainfall variability, antecedent soil moisture, and urban storm water management infrastructure in storm event hydrologic response. Our results are based on empirical analyses of high‐resolution rainfall and discharge observations over Harry's Brook watershed in Princeton, New Jersey, during 2005–2006, as well as numerical experiments with the Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model. We focus on two subwatersheds of Harry's Brook, a 1.1 km2 subwatershed which was developed prior to modern storm water management regulations, and a 0.5 km2 subwatershed with an extensive network of storm water detention ponds. The watershed developed prior to modern storm water regulations is an “end‐member” in urban flood response, exhibiting a frequency of flood peaks (with unit discharge exceeding 1 m3 s−1 km−2) that is comparable to the “flashiest” watersheds in the conterminous U.S. Observational analyses show that variability in storm event water balance is strongly linked to peak rain rates at time intervals of less than 30 min and only weakly linked to antecedent soil moisture conditions. Peak discharge for both the 1.1 and 0.5 km2 subwatersheds are strongly correlated with rainfall rate averaged over 1–30 min. Hydrologic modeling analyses indicate that the sensitivity of storm event hydrologic response to spatial rainfall variability decreases with storm intensity. Temporal rainfall variability is relatively more important than spatial rainfall variability in representing urban flood response, especially for extreme storm events.

Hydrological response of an afforested catchment in a Mediterranean humid mountain area: a comparative study with a natural forest

AbstractThe effects of afforestation on water resources are still controversial. The aim of this paper is to (i) analyse the hydrological response of an afforested area in the Central Pyrenees and (ii) compare the hydrological response of an afforested area with the response observed in a natural undisturbed forest. The Araguás catchment was cultivated until the 1950s, and then afforested with pines in an effort to control the active degradation processes. The hydrological response was variable and complex, because the discharge was generated by a combination of distinct runoff processes. The hydrological response showed that (i) afforestation produced moderate peak discharges, stormflows and recession limbs, and long rising limbs; (ii) no one single variable was able to explain the hydrological response: rainfall volume and intensity did not explain the hydrological response and antecedent rainfall and initial discharge (indicating antecedent moisture conditions) did play an important role; (iii) seasonal differences were observed suggesting different runoff generating processes; and (iv) the effect of forest cover on peak discharges became less important as the size of the hydrological event increased. The stormflow coefficient showed a clear seasonal pattern with an alternation between a wet period, when the catchment was hydrologically responsive, and a dry summer period when the catchment rarely responded to any event, and two transitional periods (wetting and drying). Compared with a natural forest, the afforested area recorded greater flows and peak discharges, faster response times and shorter recession limbs. Afforestation reduces the water yield and the number of floods compared with non‐vegetated areas and abandoned lands. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of irrigation intensity on preferential solute transport in a stony soil

ABSTRACTIf irrigation intensity exceeds soil infiltration capacity, water may flow preferentially down cracks and large pores. In this situation, solute transport will involve only a fraction () of the soil’s water and leaching rate may be affected. To assess whether irrigation intensity affects preferential solute flow, an experiment was performed at Lincoln using 12 steel-encased lysimeters with a Lismore Stony Silt Loam soil under two irrigation intensities, 5 and 20 mm h–1. Burns’ equation was used to describe the measurements of non-reactive tracer concentration as a function of drainage. Under dry antecedent moisture conditions, bromide transport was not significantly different under the different irrigation rates, even though strong preferential leaching occurred, with of 0.23. For chloride, was 0.85 and 0.58, for 5 and 20 mm h–1 respectively, sufficient evidence to confirm the effect of irrigation intensity (P < 0.05). By assuming to be 1.00 for the median rainfall at Lincoln, an exponential function was fitted to the data, suggesting a lower limit of 0.35 for under moist conditions. Implications for nutrient leaching are discussed.

Flash floods in Mediterranean ephemeral streams in Valencia Region (Spain)

Summary Ephemeral streams are typical Mediterranean fluvial systems with high risk of flash flooding, and few data are available about these systems in most locales. However, the SAIH network (Automatic Hydrological Information Systems) of the Jucar River Water Authority has been providing detailed information about ephemeral streams in Spain every 5 min since 1988. Using these data, we evaluated the processes of rainfall–runoff conversion and flood generation in five Mediterranean ephemeral streams ranging in size from 25 to 450 km 2 . To provide a general framework for hydrological analysis, the study included 142 flash flood events registered between 1989 and 2007. A more detailed analysis was conducted for the Carraixet Basin under the dry antecedent moisture condition (AMC I) to evaluate the influence of rainfall on the basin’s response. A simple index called Momentum of Maximum Intensity (MMI) was developed to describe the influence of rainfall intensity on hydrograph. Correlations between the main indicators of precipitation and flow also were assessed. Results showed that flash floods were generally generated by average accumulated rainfall of around 100 mm at high intensities that could exceed 300 mm/h. Initial abstractions and average water losses during the rainfall–runoff conversion processes were very important (runoff coefficients of 6% and runoff thresholds of 62 mm). No correlation was found between initial abstractions ( I a ) calculated from the basin characteristics and runoff thresholds ( P 0 ) empirically obtained, which create some doubts about the validity of I a method for predicting floods in ephemeral streams. Accumulated rainfall was very important for flood volume, peak flow and water balance indicators, whereas intensity indicators were more related to the response times of the basins. Rainfall intensity variables influenced lag time. Accumulated rainfall, in combination with high reduced mean intensity and low persistence, were a good predictor for high peak flow. Finally, the analysis revealed two types of events. The first type, typical of summer and early autumn, consists of fast events characterized by intense rainfall concentrated at the beginning of the storm and high values of persistence and irregularity. The basin responds quickly and generates hydrographs that resemble the pattern of rain. The second type, representative of winter and spring, corresponds to less intense events. Although they accumulate more rain, maximum intensities are lower and occur at the end of the episode. The response of the basin is late, and hydrographs are quite different from hyetographs and very influenced by the basin.

Hillslope-storage and rainfall-amount thresholds as controls of preferential stormflow

Summary Shallow saturated subsurface flow is a dominant runoff mechanism on hillslopes of headwater catchments under humid temperate climate. Its timing and magnitude is significantly affected by the presence of preferential pathways. Reliable prediction of runoff from hillslope soils under such conditions remains a challenge. In this study, a quantitative relationship between rainfall, stormflow, and leakage to bedrock for hillslopes, where lateral preferential runoff represents a dominant part of the overall response, was sought. Combined effects of temporal rainfall distribution and initial hillslope saturation (antecedent moisture conditions) on stormflow, leakage to bedrock, and overall water balance were evaluated by conducting simulations with synthetic rainfall episodes. A two-dimensional dual-continuum model was used to analyze hydrological processes at an experimental hillslope site located in a small forested headwater catchment. Long-term seasonal simulations with natural rainfall indicated that leakage to bedrock occurred mostly as saturated flow during major runoff events. The amount of rainfall needed to initiate stormflow appeared as a dynamic hillslope property, depending on temporal rainfall distribution, initial hillslope storage, and the spatial distribution of soil water within the hillslope. No single valued rainfall threshold responsible for triggering stormflow was found. Rainfall–stormflow as well as rainfall–leakage relationships were found highly nonlinear for low initial hillslope saturations. Temporal rainfall distribution affected the amount of rainfall necessary to initiate stormflow more than it did the amounts of stormflow or leakage to bedrock. In spite of a simple hillslope geometry with constant slope and parallel soil–atmosphere and soil–bedrock interfaces considered in the analysis, the applied model predicted a hysteretic behavior of storage–discharge relationship. The results showed a mutual interplay of components of hillslope water balance exposing a nonlinear character of the hillslope response. The study provided a quantitatively coherent insight in the hydraulic functioning of hillslopes where preferential flow constitutes a dominant part of stormflow.

Variabilité spatiotemporelle sur le long terme des précipitations en zone aride en Australie et conséquences sur la recharge

Quantifying dryland groundwater recharge as a function of climate variability is becoming increasingly important in the face of a globally depleted resource, yet this remains a major challenge due to lack of adequate monitoring and the complexity of processes involved. A previously unpublished and unique dataset of high density and frequency rainfall measurements is presented, from the Fowlers Gap Arid Zone Research Station in western New South Wales (Australia). The dataset confirms extreme spatial and temporal variability in rainfall distribution which has been observed in other dryland areas and is generally explained by the dominance of individual storm cells. Contrary to previous observations, however, this dataset contains only a few localised storm cells despite the variability. The implications of spatiotemporal rainfall variability on the estimation of groundwater recharge is assessed and show that the most likely recharge mechanism is through indirect and localised, rather than direct, recharge. Examples of rainfall and stream gauge height illustrate runoff generation when a spatially averaged threshold of 15–25 mm (depending on the antecedent moisture conditions) is exceeded. Preliminary assessment of groundwater levels illustrates that the regional water table is much deeper than anticipated, especially considering the expected magnitude of indirect and localised recharge. A possible explanation is that pathways for indirect and localised recharge are inhibited by the large quantities of Aeolian dust observed at the site. Runoff readily occurs with water collecting in surface lakes which slowly dry and disappear. Assuming direct groundwater recharge under these conditions will significantly overestimate actual recharge.

Spatial and temporal occurrence of preferential flow in a forested headwater catchment

Summary The highly dynamic nature of preferential flow in time and space makes it challenging to identify and analyze its occurrence at the catchment scale. Novel analysis methods using soil moisture sensor response times offer an opportunity to investigate catchment-wide controls on preferential flow. The aim of this study was to identify factors that control preferential flow occurrence based on 3-year soil moisture monitoring using a wireless sensor network in the Wustebach catchment, Germany. At 101 locations, the sensor response times at three depths (5, 20, and 50 cm) were classified into one of four classes: (1) non-sequential preferential flow, (2) velocity-based preferential flow, (3) sequential flow, and (4) no response. A conceptual model, postulating that preferential flow in the Wustebach catchment is dominated by differences in soil type, landscape position, and rainfall input, was proposed for hypothesis testing. To test the conceptual model, the classification results were combined with spatial and event-based data to understand and identify controlling factors. Spatial parameters consisted of hydrological, topographical, and soil physical and chemical parameters. Temporal factors included precipitation characteristics and antecedent soil moisture conditions. The conceptual model as proposed could only be partly confirmed. Event-based occurrence of preferential flow was highly affected by precipitation amount, with a nearly catchment-wide preferential response during large storm events. During intermediate events, preferential flow was controlled by small-scale heterogeneity, instead of showing catchment-wide patterns. The effect of antecedent catchment wetness on the occurrence of preferential flow was generally less profound, although a clear negative relationship was found for precipitation events with more than 25 mm. It was found that spatial occurrence of preferential flow was however governed by small-scale soil and biological features and local processes, and showed no obvious relationship with any of the selected spatial parameters. Overall, the results demonstrate that sensor response time analysis can offer innovative insights into the spatial–temporal interrelationship of preferential flow occurrence.

Antecedent conditions, hydrological connectivity and anthropogenic inputs: Factors affecting nitrate and phosphorus transfers to agricultural headwater streams

This paper examines relationships between rainfall–runoff, catchment connectivity, antecedent moisture conditions and fertiliser application with nitrate-N and total phosphorus (TP) fluxes in an arable headwater catchment over three hydrological years (2012–2014). Annual precipitation totals did not vary substantially between years, yet the timing of rainfall strongly influenced runoff generation and subsequent nitrate-N and TP fluxes. The greatest nitrate-N (>250kgNday−1) and TP (>10kgTPday−1) fluxes only occurred when shallow groundwater was within 0.6m of the ground surface and runoff coefficients were greater than 0.1. These thresholds were reached less frequently in 2012 due to drought recovery resulting in lower annual nitrate-N (7.4kgNha−1) and TP (0.12kgPha−1) fluxes in comparison with 2013 (15.1kgNha−1; 0.21kgPha−1). The wet winter of 2013 with elevated shallow groundwater levels led to more frequent activation of sub-surface pathways and tile drain flow. Throughout the period, dry antecedent conditions had a temporary effect in elevating TP loads. Evidence of TP source exhaustion after consecutive storm events can be attributed to the repeated depletion of temporarily connected critical source areas to the river network via impermeable road surfaces. Fertiliser application varied considerably across three years due to differences in crop rotation between farms, with annual N and P fertiliser inputs varying by up to 21% and 41%, respectively. Proportional reductions in annual riverine nitrate-N and TP loadings were not observed at the sub-catchment outlet as loadings were largely influenced by annual runoff. Nitrate loadings were slightly higher during fertiliser application, but there was little relationship between P fertiliser application and riverine TP load. These data indicate that this intensive arable catchment may be in a state of biogeochemical stationarity, whereby legacy stores of nutrients buffer against changes in contemporary nutrient inputs.

Hydrologic impacts of subsurface drainage at the field scale: Climate, landscape and anthropogenic controls

Installation of subsurface drainage systems is one of the most common modifications of the agricultural landscape, and while it is well accepted that these systems alter the hydrologic regime, the nature and magnitude of such alterations remains poorly understood. We explore the impact of drainage systems using the field-scale model DRAINMOD and rainfall and soils data for Iowa. Our objective is to understand how climate, landscape and anthropogenic controls modify the hydrological response at the field scale. We show that drainage systems do not significantly alter the annual peak flows (QP). This is because QP is typically generated by the largest storms of the year for which the additional soil storage created by the drains does not significantly alter the total quick-flow volume of water entering the streams, and thus the hydrograph peaks. We identify a threshold storm size (∼6cm/day for Iowa) beyond which tiles have minimal impact on the peak flow. Effects are apparent, however, for peak flows generated by other storms in which the percent of peak flow reduction is a function of the storm size and the antecedent moisture conditions. The effect of the drains on runoff production is further investigated using the daily Flashiness Index (FI). For soils with high hydraulic conductivity (K), tile drains increase the FI due to faster flow routing through subsurface drains, while for soils with low K, drainage decreases flashiness due to availability of increased soil storage that reduces surface runoff. We conclude that tile drains homogenize spatial patterns in hydrologic response by minimizing response differences between soil types. Furthermore, we investigate the effects of tile spacing and show that the FI decreases with an increase in drain spacing up to an optimal spacing (SM), beyond which FI increases with greater spacing. The FI-SM relationship was found to be a function of soil type and rainfall intensity, with the U-shaped behavior more apparent for low K soils and high rainfall intensity.

A versatile index to characterize hysteresis between hydrological variables at the runoff event timescale

AbstractThis study presents a versatile index for the quantification of hysteretic loops between hydrological variables at the runoff event timescale. The conceptual development of the index is based on a normalization of the input data and the computation of definite integrals at fixed intervals of the independent variable. The sum, the minimum and the maximum of the differences between integrals computed for the rising and the falling curves provide information on the direction, the shape and the extent of the loop. The index was tested with synthetic data and field data from experimental catchments in Northern Italy. Hysteretic relations between streamflow (the independent variable) and soil moisture, depth to water table, isotopic composition and electrical conductivity of stream water (dependent variables) were correctly identified and quantified by the index. The objective quantification of hysteresis by the index allows for the automatic classification of hysteretic loops and thus the determination of differences in hydrological responses during different events. The index was also used to examine the seasonal dynamics in the relation between streamflow and soil moisture and captured the switch in the direction of the loop with changes in event size and antecedent wetness conditions. The sensitivity of the index to the temporal resolution of the measurements and measurement errors was also tested. The index can successfully quantify hysteresis, except for very noisy data or when the temporal resolution of the measurements is not well suited to study hysteresis between the variables. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Changes in seasonality and timing of peak streamflow in snow and semi‐arid climates of the north‐central United States, 1910–2012

AbstractChanges in the seasonality and timing of annual peak streamflow in the north‐central USA are likely because of changes in precipitation and temperature regimes. A source of long‐term information about flood events across the study area is the U.S. Geological Survey peak streamflow database. However, one challenge of answering climate‐related questions with this dataset is that even in snowmelt‐dominated areas, it is a mixed population of snowmelt/spring rain generated peaks and summer/fall rain generated peaks. Therefore, a process was developed to divide the annual peaks into two populations, or seasons, snowmelt/spring, and summer/fall. The two series were then tested for the hypotheses that because of changes in precipitation regimes, the odds of summer/fall peaks have increased and, because of temperature changes, snowmelt/spring peaks happen earlier. Over climatologically and geographically similar regions in the north‐central USA, logistic regression was used to model the odds of getting a summer/fall peak. When controlling for antecedent wet and dry conditions and geographical differences, the odds of summer/fall peaks occurring have increased across the study area. With respect to timing within the seasons, trend analysis showed that in northern portions of the study region, snowmelt/spring peaks are occurring earlier. The timing of snowmelt/spring peaks in three regions in the northern part of the study area is earlier by 8.7– 14.3 days. These changes have implications for water interests, such as potential changes in lead‐time for flood forecasting or changes in the operation of flood‐control dams. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Classifying hydrological events to quantify their impact on nitrate leaching across three spatial scales

Summary Nitrate is one of the most important sources of pollution for surface waters in tile-drained agricultural areas. In order to develop appropriate management strategies to reduce nitrate losses, it is crucial to first understand the underlying hydrological processes. In this study, we used Principle Component Analysis (PCA) and Linear Discriminant Analysis (LDA) to analyze 212 discharge events between 2004 and 2011 across three spatial scales (68 events at the collector drain, 72 at the ditch, and 72 at the brook) to identify the controlling factors for hydrograph response characteristics and their influence on nitrate concentration patterns. Our results showed that the 212 hydrological events can be classified into six different types: summer events (28%), snow-dominated events (10%), events controlled by rainfall duration (16%), rainfall totals (8%), dry antecedent conditions (10%), and events controlled by wet antecedent conditions (14%). The relatively large number of unclassified events (15%) demonstrated the difficulty in separating event types due to mutually influencing variables. NO 3 -N concentrations showed a remarkably consistent pattern during the discharge events regardless of event type, with minima at the beginning, increasing concentrations at the rising limb, and maxima around peak discharge. However, the level of NO 3 -N concentrations varied notably among the event types. The highest average NO 3 -N concentrations were found for events controlled by rainfall totals (NO 3 -N = 17.1 mg/l), events controlled by wet antecedent conditions (NO 3 -N = 17.1 mg/l), and snowmelt (NO 3 -N = 15.2 mg/l). Average maximum NO 3 -N concentrations were significantly lower during summer events (NO 3 -N = 10.2 mg/l) and events controlled by dry antecedent conditions (NO 3 -N = 11.7 mg/l). The results have furthermore shown that similar hydrological and biogeochemical processes determine the hydrograph and NO 3 -N response on storm events at various spatial scales. The management of tile-drained agricultural land to reduce NO 3 -N losses should focus explicitly on flow events and, more specifically, active management should preferably be conducted in the winter season for discharge events after snowmelt, after heavy rain storms and when the soil moisture conditions are wet.

The Impact of Assumed Error Variances on Surface Soil Moisture and Snow Depth Hydrologic Data Assimilation

Accurate knowledge of antecedent soil moisture (SM) and snow depth (SD) conditions is often important for obtaining reliable hydrological simulations of stream flow. Data assimilation (DA) methods can be used to integrate remotely sensed (RS) SM and SD retrievals into a hydrology model and improve such simulations. In this paper, we examine the impact of assumed model and observation error variance on stream flow estimates obtained by assimilating RS SM and SD data into a lumped hydrological model. The analysis is based on both synthetic and real DA experiments conducted within the Tuotuo River watershed at the headwaters of the Yangtze River. Synthetic experiments demonstrate that, when the true model error variance is small, DA is more sensitive to the overestimation of the error variance than to its underestimation. Conversely, if the true variance is large, DA is sensitive to the assumed model error variance but not the underestimation of the observation error variance. Given this sensitivity, the maximum a posteriori (MAP) estimation method is applied to accurately estimate model and observation error variances. In general, MAP is able to identify model and observation error parameters associated with an accurate stream flow analysis. However, its utility is somewhat limited by equifinality with regard to observation error statistics.

Soil moisture dynamics at high temporal resolution in a semiarid Mediterranean watershed with scattered tree cover

AbstractSubsurface water flows play a key role in the distribution of water and solutes and thereby in the water availability for plants. However, the characterization of different flow processes (i.e. matrix and preferential flow), the frequency and factors that cause them, is relatively rare. This characterization enables a better understanding of spatio‐temporal variability of water resources and allows for the design of models to be improved. Using a method based on the time derivative of soil moisture variation known as maximum wetting slope, types of soil wetting processes were classified and quantified. For this, capacitance sensors, which registered the volumetric water content at high temporal resolution (30 min) for more than two hydrological years, were installed at different depths and placed in soil moisture stations with different vegetation covers, lithology and topographic position. Results indicated that there is a general behaviour or pattern of soil moisture dynamics in the catchment with a dominant occurrence of slower soil wetting processes (&gt;50%), caused by matrix flows, and a low occurrence of those faster processes (&lt;30%), originated by preferential flows. Nevertheless, when the total volume of water is considered, preferential flow becomes the dominant process, so that the ecological role of both flow types becomes prominent in water‐limited environments. Statistical multivariate analyses based on data‐mining techniques proved that although both flow types depend on variables associated with precipitation and antecedent soil moisture conditions, faster soil wetting processes are mainly related to variables such as rainfall intensity and topography, while slower soil wetting processes are related to flow velocity, soils or vegetation. Copyright © 2015 John Wiley &amp; Sons, Ltd.

SENSITIVITY ANALYSIS OF RAINFALL RECHARGE MODEL FOR A NOISY DATA

Groundwater resource estimation with particular focus on the estimation of annual replenishable recharge is an important task. For the accurate assessment of groundwater resource, the recharge from rainfall is to be estimated correctly. In the present study, a rainfall recharge model is presented considering both instantaneous recharge and delayed recharge contribution to the groundwater. The model estimates these parameters at zonal level on a regional scale considering three different antecedent moisture conditions. The parameter estimation model is developed using output error criterion. The model uses Gauss-Newton algorithm for minimization; where the objective is to minimize the least square error between observed and computed recharge or water level change. The model is applied on one hypothetical system and on one real field problem. Sensitivity analysis of the parameters are also studied using parameter perturbation method. The results indicate that the proposed rainfall recharge model can be conveniently used for estimation of rainfall recharge. This is highly useful in hard rock areas where the major contribution to groundwater is from rainfall during only in monsoon season.

Event-based prediction of stream turbidity using a combined cluster analysis and classification tree approach

Summary Stream turbidity typically increases during streamflow events; however, similar event hydrographs can produce markedly different event turbidity behaviors because many factors influence turbidity in addition to streamflow, including antecedent moisture conditions, season, and supply of turbidity-causing materials. Modeling of sub-hourly turbidity as a function of streamflow shows that event model parameters vary on an event-by-event basis. Here we examine the extent to which stream turbidity can be predicted through the prediction of event model parameters. Using three mid-sized streams from the Mid-Atlantic region of the U.S., we show the model parameter set for each event can be predicted based on the event characteristics (e.g., hydrologic, meteorologic and antecedent moisture conditions) using a combined cluster analysis and classification tree approach. The results suggest that the ratio of beginning event discharge to peak event discharge (an estimate of the event baseflow index), as well as catchment antecedent moisture, are important factors in the prediction of event turbidity. Indicators of antecedent moisture, particularly those derived from antecedent discharge, account for the majority of the splitting nodes in the classification trees for all three streams. For this study, prediction of turbidity during streamflow events is based upon observed data (e.g., measured streamflow, precipitation and air temperature). However, the results also suggest that the methods presented here can, in future work, be used in conjunction with forecasts of streamflow, precipitation and air temperature to forecast stream turbidity.

Application of remote sensing and geographical information system for generation of runoff curve number

Watershed is an ideal unit for planning and management of land and water resources (Gajbhiye et al., IEEE international conference on advances in technology and engineering (ICATE), Bombay, vol 1, issue 9, pp 23–25, 2013a; Gajbhiye et al., Appl Water Sci 4(1):51–61, 2014a; Gajbhiye et al., J Geol Soc India (SCI-IF 0.596) 84(2):192–196, 2014b). This study aims to generate the curve number, using remote sensing and geographical information system (GIS) and the effect of slope on curve number values. The study was carried out in Kanhaiya Nala watershed located in Satna district of Madhya Pradesh. Soil map, Land Use/Land cover and slope map were generated in GIS Environment. The CN parameter values corresponding to various soil, land cover, and land management conditions were selected from Natural Resource Conservation Service (NRCS) standard table. Curve number (CN) is an index developed by the NRCS, to represent the potential for storm water runoff within a drainage area. The CN for a drainage basin is estimated using a combination of land use, soil, and antecedent soil moisture condition (AMC). In present study effect of slope on CN values were determined. The result showed that the CN unadjusted value are higher in comparison to CN adjusted with slope. Remote sensing and GIS is very reliable technique for the preparation of most of the input data required by the SCS curve number model.

Understanding Groundwater Storage Changes and Recharge in Rajasthan, India through Remote Sensing

Groundwater management practices need to take hydrogeology, the agro-climate and demand for groundwater into account. Since agroclimatic zones have already been demarcated by the Government of India, it would aid policy makers to understand the status of groundwater recharge and discharge in each agroclimatic zone. However, developing effective policies to manage groundwater at agroclimatic zone and state levels is constrained due to a paucity of temporal data and information. With the launch of the Gravity Recovery and Climate Experiment (GRACE) mission in 2002, it is now possible to obtain frequent data at broad spatial scales and use it to examine past trends in rain induced recharge and groundwater use. In this study, the GRACE data were used to estimate changes to monthly total water storage (TWS) and groundwater storage in different agroclimatic zones of Rajasthan, India. Furthermore, the long-term annual and seasonal groundwater storage trends in the state were estimated using the GRACE data and the trends were compared with those in rainfall data. The methodology based on GRACE data was found to be useful in detecting large scale trends in groundwater storage changes covering different agroclimatic zones. The analysis of data shows that groundwater storage trends depend on rainfall in previous years and, therefore, on the antecedent moisture conditions. Overall, the study indicates that if suitable groundwater recharge methods and sites are identified for the state, there is potential to achieve more groundwater recharge than what is currently occurring and, thus, enhancing the availability of water for irrigated agriculture.

Woodchip Heavy-Use Area Effluent Quality, Quantity, and Hydrologic Design Considerations

<abstract> <b><sc>Abstract. </sc></b>Woodchip heavy-use areas (aka ‘out-wintering pads,‘ ‘woodchip pads‘) are attractive options for livestock producers wanting to protect pastures during sensitive times due to their reduced cost and increased animal comfort compared to concrete. The effluent production, and potential environmental impact, of these systems is uncertain and engineers need reliable guidance for design of corresponding wastewater handling systems. The objectives of this project were to 1) evaluate the hydrologic performance of a woodchip heavy-use area installed in the Northeastern United States over two years of operation, and 2) improve estimation of effluent production methods and design guidance using measured data. Precipitation and effluent volumes were measured over 23 months and nutrient concentration of effluent from multiple storms was analyzed. A water balance was determined. Measured data indicated that 24% of the incoming precipitation became effluent over the study period, but effluent production was much greater during the winter months (37%) than during the non-winter months (17%). Evaporation dominated water outflows from the system (67%-84%). Absorption and evaporation of moisture by the woodchip media, and resulting antecedent moisture condition, greatly influence effluent production. Regionally-specific runoff coefficients are compared to other design approaches and presented as appropriate for effluent volume estimation. Nutrient concentration of effluent was generally lower than reported values from other woodchip, earthen, and concrete open lot studies. Additional research is needed.