Subsurface Drainage Discharge Research Articles

Predicted Contribution of Snowmelt to Subsurface Drainage Discharge in Two Subsurface-Drained Fields in Southern Quebec and Ontario

Highlights RZ-SHAW model delivered a satisfactory simulation for winter subsurface drainage discharge. Snowmelt dominated the drainage discharge during the winter and spring snowmelt seasons in southern Quebec. Snowmelt contributed to 29% and 18% of winter and annual drainage discharge, respectively, in southern Ontario. Abstract. Late winter/early spring has been recognized as a critical period for subsurface drainage discharge and associated nutrient losses due to snowmelt and rainfall in croplands under cold, humid climates in North America and Europe. Although the detachment and transport processes of soil particles under snowmelt and rainfall are known to be different, studies quantifying the contribution of snowmelt to winter drainage discharge are limited. This study aims to investigate the contribution of snowmelt to subsurface drainage discharge at two winterized experimental sites in southern Quebec and Ontario, Canada, using observed data and the Root Zone Water Quality Model-Simultaneous Heat and Water model (RZ-SHAW model). The RZ-SHAW model was calibrated and validated against the measured snow depth and year-round subsurface drainage discharge data from 2021 to 2023 at St. Emmanuel, Quebec, and from 2000 to 2003 at Harrow, Ontario. RZ-SHAW demonstrated satisfactory Nash-Sutcliffe model efficiency values (NSE = 0.50) for simulating snow depth, soil temperature, and winter subsurface drainage discharge. The calibrated RZ-SHAW model was used to simulate the contribution of snowmelt to subsurface drainage for the two sites from 1990 to 2022. The snowmelt was predicted to contribute 55% and 44% of the winter and annual subsurface drainage discharge for the cropland in Southern Quebec. In contrast, for the southern Ontario site, the contribution of snowmelt to winter and annual subsurface drainage discharge was 29% and 18%, respectively. Considering that snowmelt in Southern Quebec contributed a significant fraction of winter and annual subsurface drainage discharge, more attention should be devoted to adapting and developing new winter management for nutrient loss in future research in the region. Keywords: Cold region, Cropland drainage, Drainage partition, RZ-SHAW, RZWQM2, Snowmelt, Soil freeze and thaw, Winter subsurface drainage.

Reduction of Nitrate Leaching and Threats to Surface Water Under Conservation Tillage

Highlights Conservation agriculture practice (NT) improved soil organic matter, a principal indicator of soil health, soil health score (SHS) and CO2 respiration, and other soil physical and chemical properties vs. conventional till (CT) practice. Conservation agriculture practice (NT) promoted soil health functions under sufficient precipitation distribution and ample temperature conditions and aided the soil's retention ability to resist nitrate leaching and loads in subsurface drainage discharge systems. Uneven weather conditions, drought, and other variable agronomic practices rendered soil conditions unfavorable to retain nitrate and induced adverse effects by increasing the nitrate leaching and loads in NT vs. CT. The limited experiment period presented significant challenges for the evaluation and synthesizing of soil health motivations and barriers in the NT vs. CT. Abstract. An edge-of-field subsurface drainage discharge system removes excess subsurface water from agricultural fields to improve the conditions of the soil system making them favorable for plant growth. Conversely, edge-of-fields can increase the nitrate (NO3 -) offsite movement to surface water bodies, which ultimately impacts water quality. In St. Johns, MI. Two on-farm large areas were initiated in 2013 for conservation (NT) and conventional till (CT) practices, of which two microscale fields, an area of 4 acres for each, were delineated in 2019 for NT and CT practices under a corn/soybean crop rotation. NT and CT fields were monitored and evaluated through full water years (WYs) 2019-2022. The objective was to use an innovative approach in coupling edge-of-field with soil health assessments to learn how improved soil health functions are influencing nitrate leaching and loads. NT practice enhanced SOM, other physical properties, and soil health parameters, promoting soil health functions compared to CT practice under conditions of adequate precipitation and favorable temperatures. Additionally, it improved the soil's ability to retain and resist nitrate loads in the 2020 water year, with reductions of 9.6 and 18.3 kg/ha, respectively. In 2021, WY nitrate loads reported nearly an equal value in NT vs. CT (4.8 and 4.4 kg/ha, respectively). Factors of uneven weather conditions and drought, variable agronomic practices, and residual nitrogen after corn, rendered soil conditions unfavorable to retain nitrate and induced adverse effects by increasing the nitrate leaching and loads in NT vs CT in 2022 WY (8.1 and 5.8 kg/h, respectively). Therefore, the limited evaluation period (2019-2022 WYs) presented significant challenges and revealed no affirmative evidence that the improved soil health functions under NT reduced the nitrate leaching loads in all WYs of this research. Further research is needed to prove the impact of NT on improving soil health functions to sustainably reduce nitrate leaching and loads in edge-of-fields. Keywords: Conservation no-till (NT), Conventional till (CT), Nitrate load, Soil health functions, Subsurface drainage discharge, Water quality.

Feasibility of Predicting Subsurface Drainage Discharge With DRAINMOD Parameterized by Uncalibrated SURRGO Soil Properties and ROSETTA3

Feasibility of Predicting Subsurface Drainage Discharge With DRAINMOD Parameterized by Uncalibrated SURRGO Soil Properties and ROSETTA3

Comparison of Newly Proposed and Existing Design Approach for Saturated Buffers

Highlights More diverted flow to the buffer does not necessarily mean more nitrate load removal. A design approach should incorporate a nitrate removal component to maximize nitrate load removal. The newly proposed design follows a process-based approach to estimate the annual site-specific nitrate removal. The newly proposed design provided more consistent nitrate load removal regardless of the site conditions. Neglecting exit head loss in the design process leads to an overestimation of diverted flow and nitrate load removal. Abstract. A saturated buffer (SB) is a conservation drainage practice that removes nitrate from subsurface drainage discharge. The reported wide range of nitrate load removal necessitates improvements in design approaches for more consistent performance. There are two SB design approaches: Illinois Natural Resources Conservation Service (Design 1) and McEachran et al. (2020) (Design 2). We proposed a new Design 3 that builds on the previous two designs. In Design 3, the nitrate load removal was simulated for buffer widths ranging from 3 to 30 m with a 0.3-m interval, and the buffer width that maximized the annual nitrate load reduction over the long term was chosen as the SB design. The objective of this study was to identify the best design approaches for maximizing nitrate load removal based on field data. Daily drainage discharge data from two field sites in Michigan were used to design a hypothetical SB length and width for each approach. The designs were compared by applying an identical method to estimate the nitrate load removal for each hypothetical SB system. The method extends Designs 1 and 2 by incorporating a hydrological and nitrate removal component. The results showed that using the minimum recommended buffer width of 9.1 m and the minimum 5% SB design capacity of Design 1 resulted in 25% to 35% of diverted flow to the buffer and 14% to 16% nitrate load removal at the two field sites. However, Design 1 resulted in the lowest nitrate removal compared to Designs 2 and 3 (i.e., 0.3% to 3.4% lower). Designs 2 and 3 consistently provided maximum nitrate load removal regardless of the site conditions, whereas the performance of Design 1 was inconsistent. In conclusion, Designs 2 and 3 were equally good and resulted in higher nitrate load removal compared to Design 1. Keywords: Conservation practice, Exit head loss, Nitrate, Subsurface drainage, Tile drainage, Water quality.

Calibration and Validation of RZWQM2-P Model to Simulate Phosphorus Loss in a Clay Loam Soil in Michigan

Highlights RZWQM2-P was tested and validated for clay loam soil using daily discharge and load data. The model performed satisfactorily in predicting hydrology and TP load, but DRP prediction was unsatisfactory. Inability of the model to simulate P loss in subsurface drainage discharge after fertilization event was one of the reasons for the unsatisfactory model performance. Abstract. Phosphorus (P) loss and transport through subsurface drainage systems is a primary focus for addressing harmful algal blooms in freshwater systems. The recent development of the phosphorus (P) routine of the Root Zone Water Quality Model (RZWQM2-P) has the potential to enhance our understanding of the fate and transport of P from subsurface-drained fields to surface water. However, there is a need to test the model under different fertilization, soil, climate, and cropping conditions. The objective of this study was to test the model's performance with daily drainage discharge, dissolved reactive phosphorus (DRP), and total phosphorus (TP) load collected from a subsurface-drained field with clay loam soil. We calibrated RZWQM2-P using two years of measured data. Subsequently, we validated RZWQM2-P using a year and nine months of measured data. We used the Nash-Sutcliffe model efficiency (NSE) and percentage bias (PBIAS) statistics for the RZWQM2-P model evaluation. The results showed that the model performance was “good” (daily NSE = 0.66 and PBIAS = -7.16) in predicting hydrology for the calibration period. For the validation period, the hydrology prediction of the model was “very good” (daily NSE = 0.76), but it had a “satisfactory” underestimation bias (PBIAS = 23.57). The model’s performance was “unsatisfactory” in simulating DRP for both calibration (daily NSE = 0.31 and PBIAS = -61.50) and validation (daily NSE = 0.32 and PBIAS = 43.68) periods. The P model showed “satisfactory” performance in predicting TP load for both calibration (daily NSE = 0.46 and PBIAS = -32.41) and validation (daily NSE = 0.39 and PBIAS = 42.90) periods, although both periods showed “unsatisfactory” percent bias. The underperformance may have been due to the model’s inability to partition fertilizer P into different P pools under high water tables or ponding conditions when using daily data. In conclusion, the RZWQM2-P model performed well for drainage discharge with daily data, but further investigation is needed to improve the P component of the model. Keywords: Field-scale modeling, Nutrient load, Phosphorus modeling, Subsurface drainage, Tile drainage, Water Quality.

Impact of nitrogen fertilizer timing on nitrate loss and crop production in northwest Iowa.

In the U.S. Midwest, nitrate in subsurface tile drainage from corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] systems is detrimental to water quality at local and national scales. The objective of this replicated plot study in northwest Iowa, performed in 2015-2020, was to investigate the influence of nitrogen (N) fertilizer timing on crop production and NO3 load in subsurface (tile) drainage discharge. Four treatments applied to corn included fall anhydrous ammonia with a nitrification inhibitor (F), spring anhydrous ammonia (S), split-banded urea at planting and mid-vegetative growth (SS), and no N fertilizer (0N). Across crops and years, NO3 -N concentration in subsurface drainage discharge was the same at 11.7mg L-1 for F and S applied anhydrous ammonia (AA). The NO3 -N concentration was statistically lower with SS urea (10mg L-1 ) than F and S, and 0N was lower than SS at 8.3mg L-1 . Average annual NO3 -N loads were not different between any treatments due to plot variability in drainage discharge. Corn responded to N application, with overall mean yield the same for F, S, and SS. There were no agronomic or water quality benefits for applying AA in spring compared with fall, where the F included a nitrification inhibitor and was applied to cold soils. Split-applied urea had a small positive water quality impact but no crop yield enhancement. This study shows that there were improvements to NO3 -N concentration in subsurface drainage discharge, but more nutrient reduction practices are needed than fertilizer N management alone to reduce nitrate load to surface water systems.

Effect of water sampling strategies on the uncertainty of phosphorus load estimation in subsurface drainage discharge.

Accurate phosphorus (P) load estimation in subsurface drainage water is critical to assess the field-scale efficacy of conservation practices. The HydroCycle-PO4 instrument measures real-time total reactive P (TRP) concentration without the need for sample filtration, thereby enabling comparative evaluation of different sampling strategies. The main objective of this study was to evaluate the effects of water sampling strategies on the uncertainty of P load estimation. Hourly TRP concentration and hourly drainage discharge measurements formed the reference P load dataset. Four hypothetical water sampling strategies were evaluated: (a) time-proportional discrete sampling, (b) time-proportional composite sampling, (c) flow-proportional discrete sampling, and (d) flow-proportional composite sampling. All sampling strategies underestimated TRP load compared with the reference dataset. Total reactive P load underestimation changed from 0.2 to 51% as time-proportional discrete sampling intervals increased from 3 h to 14 d. Total reactive P load underestimation changed from 12 to 43% as the time-proportional compositing scenario increased from 1 to 7 d, each with one aliquot per day. In the case of flow-proportional discrete sampling scenario, the lowest (0.6%) and the highest (-5.1%) uncertainties were observed when 1- and 5-mm flow intervals were used. The relative error based on the results provided by the flow-proportional composite sampling ranged from 0.2% when using 1-mm flow interval to -6.7% when using 5-mm flow interval. In conclusion, the flow-proportional sampling strategies provided a more accurate estimate of cumulative P load with fewer number of samples because a greater portion of samples were taken at higher flow rates compared with time-proportional sampling strategies.

Coupling of a subsurface drainage model with a soil reservoir model to simulate drainage discharge and drain flow start

The environmental impact of subsurface drainage and agricultural activities has been widely studied in the literature. Agricultural subsurface drainage modifies the hydrological behavior and accelerates the transfer of pollutants of agricultural origin into surface water during the drain flow period, which is often limited to winter. The main objective of this study is to present a modeling approach allowing an accurate modeling of subsurface drainage discharge and prediction of drain flow start times, by integrating a new conceptual soil reservoir, managing the water flow in the unsaturated zone, to the SIDRA model. A comparison of the model results with field measurements of drainage discharge at the “La Jaillière” site (France) shows that such a model can efficiently simulate drainage discharge (KGE values >0.75) and predict, with good accuracy, the drain flow start time (with a median value of 5 days and a standard deviation of 10 days). The split simple test conducted for the model calibration and validation shows that the model is temporally robust. A sensitivity analysis conducted using the Sobol method on the five model parameters reveals that the drainage discharge simulation is mainly sensitive to the hydraulic conductivity and drainable porosity parameters. On the other hand, the date delimiting drain flow start is sensitive to the soil reservoir parameters. The model's ability to accurately predict the start of drain flow serves to avoid the application of farm inputs (pesticides or fertilizers) during this critical period in order to limit their transfer to surface waters.

Effectiveness of Conservation Crop Rotation for Water Pollutant Reduction from Agricultural Areas.

Legumes included in corn-based crop rotation systems provide a variety of benefits to the subsequent crops and potentially to the environment. This review aims to synthesize available data from the literature on legume N credits and the effects of crop rotations on water quality, as well as to analyze the cost benefits associated with different legume-corn rotation systems. We found that there was much variation in reported values for legume N credits to subsequent corn crops, from both empirical results and recommendations made by U.S. land grant universities. But despite inherent complexity, accounting for this contribution is critical when estimating optimal N fertilizer application rates as part of nutrient management. Results from research on the influence of crop rotations on water quality show that including legumes in corn-based rotation systems generally decreases nitrate-N concentrations in subsurface drainage discharge. Our cost analysis showed that incorporating legumes in cropping systems reduced N fertilizer and pesticide costs compared to conventional cropping systems, i.e., continuous corn and corn-soybean rotations, but extended rotations, such as corn-soybean-alfalfa-alfalfa-alfalfa, are not as profitable as conventional systems in the U.S. Midwest. In comparing continuous corn and corn-soybean rotations, although their impacts on water quality are not significantly different when using overall means from the literature data, corn-soybean rotations are more profitable than continuous corn. When using data from papers that directly compared the two, we found that switching from continuous corn to corn-soybean can provide a benefit of $5 per kg N loss reduction. The cost analysis methods used could be tailored to any location or management scenario with appropriate inputs and serve as a useful tool for assessing cost benefits for other agricultural conservation practices. Legume-corn crop rotations have the potential to be an effective conservation practice with the ultimate goal of improving water quality, and, with further research, these rotations could be made even more effective by integrating them into a multi-practice system.

DRAINMOD-P: A Model for Simulating Phosphorus Dynamics and Transport in Drained Agricultural Lands: II. Model Testing

HighlightsDRAINMOD-P was tested using a dataset from a drained field with desiccation cracks.Surface and subsurface phosphorus losses were mainly in the particulate form.Surface runoff was a major pathway for phosphorus loss in this field.The model performance in predicting edge-of-field phosphorus loss is promising.Abstract. The recently developed phosphorus (P) model DRAINMOD-P was tested using a four-year dataset from a subsurface-drained field in northwest Ohio with significant potential for desiccation cracking or preferential flow. The model satisfactorily predicted subsurface drainage discharge, with a monthly Nash-Sutcliffe efficiency (NSE) of 0.59 and index of agreement (IOA) of 0.89. Lack of annual water budget closure was reported and was likely caused by uncertainty in measured surface runoff and/or modeling approaches representing macropore flow. More than 80% of predicted surface and subsurface P losses were in the particulate form. Surface runoff was the major pathway for P loss, contributing 78% of predicted total P (TP) load. On average, predicted macropore flow represented about 15% of drainage discharge and contributed 21% of DRP loss via subsurface drains. The performance of DRAINMOD-P in predicting monthly dissolved reactive P and TP losses through subsurface drains can be rated as poor (NSE = 0.33 and IOA = 0.60) and very good (NSE = 0.81 and IOA = 0.95), respectively. DRAINMOD-P demonstrated potential for simulating P fate and transport in drained cropland. More testing is needed to further examine newly incorporated hydrological and biogeochemical components of the model. Keywords: Agricultural drainage, Edge-of-field phosphorus load, Macropore flow, Phosphorus model, Sediment yield, Water quality modeling.

Improvement of the Water Erosion Prediction Project (WEPP) model for quantifying field scale subsurface drainage discharge

In the poorly drained regions of the world, subsurface drainage systems are required to remove excess water for crop growth. Plastic drains alter a field’s hydrology by lowering the water table, reducing surface ponding, and reducing surface runoff. One significant concern with the use of subsurface drainage systems is adverse environmental effects because of the modification of the soil water dynamics. Some effects include the reduction of ecological services since wetlands change to croplands, water quality concerns, particularly sediment, nitrogen, and phosphorus losses in agricultural subsurface discharge water, as well as changes in the volume and timing of off-site discharges. Hydrological simulation models predict surface and artificial subsurface flow at different scales. Often in these models, Hooghoudt-based expressions are adapted in their internal algorithms. In this study, the Water Erosion Prediction Project (WEPP) model, developed by the United States Department of Agriculture - Agricultural Research Service (USDA-ARS) for soil and water conservation planning activities, was tested and improved to simulate surface and subsurface discharges. The modified WEPP model was tested and validated on an extensive dataset collected at four experimental sites managed by USDA-ARS within the Lake Erie Watershed. Predicted drainage discharges show Nash-Sutcliffe Efficiency (NSE) values ranging from 0.50 to 0.70, and Percent Bias ranging from −30% to +15% at daily and monthly resolutions. Evidence suggests that the WEPP model can be used to produce reliable estimates of subsurface flow with minimum calibration. Future work includes the extension of the model for quantifying subsurface drainage under controlled water table and watershed-scale simulations.

Adsorption Media for the Removal of Soluble Phosphorus from Subsurface Drainage Water.

Phosphorus (P) is a valuable, nonrenewable resource in agriculture promoting crop growth. P losses through surface runoff and subsurface drainage discharge beneath the root zone is a loss of investment. P entering surface water contributes to eutrophication of freshwater environments, impacting tourism, human health, environmental safety, and property values. Soluble P (SP) from subsurface drainage is nearly all bioavailable and is a significant contributor to freshwater eutrophication. The research objective was to select phosphorus sorbing media (PSM) best suited for removing SP from subsurface drainage discharge. From the preliminary research and literature, PSM with this potential were steel furnace slag (SFS) and a nano-engineered media (NEM). The PSM were evaluated using typical subsurface drainage P concentrations in column experiments, then with an economic analysis for a study site in Michigan. Both the SFS and generalized NEM (GNEM) removed soluble reactive phosphorus from 0.50 to below 0.05 mg/L in laboratory column experiments. The most cost-effective option from the study site was the use of the SFS, then disposing it each year, costing $906/hectare/year for the case study. GNEM that was regenerated onsite had a very similar cost. The most expensive option was the use of GNEM to remove P, including regeneration at the manufacturer, costing $1641/hectare/year. This study suggests that both SFS and NEM are both suited for treating drainage discharge. The use of SFS was more economical for the study site, but each site needs to be individually considered.

Performance of a Ditch-Style Phosphorus Removal Structure for Treating Agricultural Drainage Water with Aluminum-Treated Steel Slag

Several structural, treatment, and management approaches exist to minimize phosphorus (P) transport from agricultural landscapes (e.g., cover cropping and conservation tillage). However, many of these practices are designed to minimize particulate P transport and are not as effective in controlling dissolved P (DP) losses. Phosphorus removal structures employ a P sorption material (PSM) to trap DP from flowing water. These structures have been successful in treating surface runoff by utilizing aluminum (Al)-treated steel slag, but subsurface tile drainage has never been tested with this material. The goal of this study was to evaluate the performance and economics of a ditch-style P removal structure using Al-treated steel slag for treating agricultural subsurface drainage discharge. The structure treated subsurface drainage water from a 4.5 ha agricultural field with elevated soil test P levels. Overall, the structure removed approximately 27% and 50% of all DP and total P (TP) entering the structure, respectively (i.e., 2.4 and 9.4 kg DP and TP removal). After an initial period of strong DP removal, the discrete DP removal became highly variable. Flow-through analysis of slag samples showed that the slag used to construct the structure was coarser and less sorptive compared to the slag samples collected prior to construction that were used to design and size the structure. Results of this study highlight the importance of correctly designing the P removal structures using representative PSMs.

Theoretical analysis and experimental verification of the improved subsurface drainage discharge with ponded water

The improved subsurface drainage is a new drainage technique which has large discharge verified by experiments. It can be used to solve the problems of frequent floods and cultivated land shortage in South China. Considering large-scale applications, a general drainage formula of the improved subsurface drainage with ponded water in a homogeneous and isotropic soil was proposed based on Kirkham equation. Firstly, the drainage formulas based on different assumptions were deduced and verified by laboratory experiment and field test. Additionally, further validation and simplification were studied by numerical simulation in which the critical conditions to distinguish whether the filter was saturated or not were given. Results showed that the proposed formulas passed the validation by laboratory experiment and field test based on Method 1 and Method 2 in which the bottom of the simplified boundary overlapped with the bottom of the drain pipe and the center of simplified boundary located at the center of filter were assumed respectively. The numerical simulation results showed the formula based on Method 1 was more applicable than that based on Method 2. Moreover, for Method 1, that (b0+h0)/d equaled 0.6 could be regarded as the critical boundary between filter saturated and unsaturated working condition. Considering the ratio of drain distance and impermeable layer depth, a more simplified formula was given. In this simplified formula, that drain spacing was three times of impermeable layer depth was a critical condition. The research results could provide scientific basis for improved subsurface drainage design and lay a good foundation for its application. Meanwhile, it would be beneficial to enrich agricultural drainage technologies and promote development of agricultural drainage in China.

Field and numerical experiment of an improved subsurface drainage system in Huaibei plain

New requirements are put forward for agricultural drainage system due to frequent floods and cultivated land shortage in Huaibei plain, China. The improved subsurface drainage is a more efficient drainage system by laying high permeability materials as filter above the drains based on conventional subsurface drainage whose function is limited by soil hydraulic conductivity. Field experiments was used to evaluate the performance of the improved subsurface drainage preliminarily and numerical experiments was used to explore the capacity of the improved subsurface drainage deeply. Based on calibration and validation by field experiment data, HYDRUS model was used to evaluate the impacts of design parameters of filter hydraulic conductivity, filter width and height, drain spacing and depth on improved subsurface drainage discharge with constant ponding depth. Then, water table depths at different distances from the pipe drain for improved and conventional subsurface drainage were simulated under initial conditions of saturated soil and no surface ponding. Besides, the daily water balance under improved subsurface drainage had been also studied. The result of field experiment showed that the discharge of improved subsurface drainage was about 1.9 times of the conventional subsurface drainage discharge under conditions of same surface ponding depths. The results of numerical experiments indicated that the improved subsurface drainage had a real-time drainage function for the reason that cumulative outflow increased by about 87% than conventional subsurface drainage within 12h after beginning draining. The improved subsurface drainage lowered water table to an appropriate depth faster than conventional ones, which could provide a more favourable soil moisture condition for crop growth. Furthermore, through daily water balance analysis of improved and conventional subsurface drainage with different rainfalls and initial water table depths, the results showed that subsurface drainage could reduce surface runoff effectively, especially for improved subsurface drainage. Good drainability of the improved subsurface drainage was beneficial to decrease the amount of soil water storage after rainfall and helpful to shorten subsequent draining time of water table drawdown. The research results could provide scientific basis for improved subsurface drainage design and lay a good foundation for its application. Meanwhile, it would be beneficial to enrich agricultural drainage technologies and promote development of agricultural drainage in China.

Projected climate change effects on subsurface drainage and the performance of controlled drainage in the Western Lake Erie Basin

The US Midwest is expected to experience higher intensity rainfall events along with an increased chance of drought during the mid- and late 21st century under projected future climate scenarios. Development of strategies to mitigate the impact of these projected changes on agricultural production and environmental quality is important for ensuring agricultural resiliency to future climate. This study used the DRAINMOD hydrologic model to simulate subsurface drainage discharge at a field site in the headwaters of the Western Lake Erie Basin using future climate patterns projected by 20 general circulation models. Despite projected increases in rainfall, by the late twenty-first century, subsurface discharge was projected to decrease 7% and 11% under representative concentration pathway (RCP) 4.5 and RCP 8.5, respectively. Reductions in subsurface discharge were attributed to increased temperature and evapotranspiration. The performance of controlled drainage was not projected to change on an annual basis throughout the next century. The benefits of controlled drainage systems as an agricultural best management practice were still evident under the projected climate change of the next century. The role of controlled drainage as a means to potentially retain more crop available water in the soil profile could become critically important under future climate conditions.

Shallow Subsurface Drainage for Managing Seasonal Flooding in Ganges Floodplain, Bangladesh

The impact of shallow subsurface drainage was investigated as a pilot study on a 0.13 ha plot of a farmer's field located in Batiaghata, Khulna District, Bangladesh, in the floodplain of the Bay of Bengal. The drainage design differed from traditional subsurface tile drains in two respects: (i) the depth of drains was shallow (30 cm); and (ii) the design did not include a sump and accessories such as pumps (drainage outlets were tidal). A monsoonal paddy rice crop followed by a winter sunflower crop was evaluated. The experimental treatment was a shallow subsurface drainage system with a drain depth of 0.3 m and drain spacing of 8 m. Measurements of surface flooding depth and groundwater table depth were made weekly and subsurface drainage discharge during managed drainage of the field was measured to determine system responsiveness. The managed subsurface drainage enabled the establishment of the winter sunflower crop 1.5 months earlier than the usual local practice, increased the yield and facilitated safe harvest, avoiding pre-monsoonal rainfall damage. Farmers expressed increased interest in managed subsurface drainage for its potential for early establishment of rabi crops and increased yields in the study area. This study outlines the potential benefits resulting from subsurface drainage in Khulna District. © 2016 The Authors. Irrigation and Drainage published by John Wiley & Sons Ltd.

Computation method of the drainage retention capacity of soil layers with a subsurface pipe drainage system

Methodological procedure for determining the drainage retention capacity (DRC) of surface layers under conditions of unsteady-state groundwater flow was demonstrated. DRC of the drainage system can be defined as a groundwater reservoir situated between the soil surface and the intermediate position of a parabola shaped water table above the drain level. Computation of DRC is based on analytical approximation of the subsurface total drainage discharge in unsteady-state groundwater conditions. DRC formula can serve as a simple tool for immediate estimation that requires only minimum amount of basic information (drainage design parameters, soil hydrology data). DRC is an important phenomenon of drainage policy, an inseparable part of drainage processes, which can mitigate negative impact of climate dynamics. A properly applied drainage policy, with the possibility of manipulating the retention capacities in the soil layers, can significantly improve soil and environmental protection. In agriculture, DRC extended by a drainage system can mitigate the negative effects of hydrological extremes such as floods and droughts.

Climate change and subsurface drainage design: results from a small field-scale catchment in south-western Norway

Measurements on groundwater level and subsurface drain discharge have been carried in a small field-scale catchment from November 2012 to February 2013 in south-western Norway. The main objective of the measurements has been to study the interaction between the subsurface drainage discharge and groundwater level. Different methods were used to analyse the measurements. One method was to study the variation in groundwater level and drain discharge. The measurements showed there were large day to day variations. However, in addition, there were large diurnal variations in both the groundwater level and drain discharge. Also the recession of groundwater level was studied using a two-exponential decay function. During several months the precipitation largely exceeded the long-term precipitation. The measurements showed that drainage system had the capacity to react fast to precipitation-induced rise in groundwater level, resulting in a fast drawdown. The measurements at the small scale field catchment showed that the drainage system is designed and capable to react to high precipitation amounts like those predicted by climate change scenario studies.

Effect of subsurface drainage on water balance and water table in poorly drained paddy fields

The hydrological effects of different drainage systems were investigated as a pilot study in 4.5ha of paddy fields of Sari Agricultural Sciences and Natural Resources University, located at Mazandaran province, Northern Iran (36.3°N, 53.04°E), during two successive growing seasons of rice and canola from July 2011 to May 2012. Experimental treatments were: three conventional subsurface drainage systems including drainage system with drain depth of 0.9m and drain spacing of 30m (D0.9L30), drain depth of 0.65m and drain spacing of 30m (D0.65L30), and drain depth of 0.65m and drain spacing of 15m (D0.65L15); a bi-level subsurface drainage system with drain spacing of 15m and drain depths of 0.65 and 0.9m as alternate depths (Bilevel), and surface drainage system (Control). Water balance components were determined in both rice and canola crop seasons. Measurements of water table depth and subsurface drainage discharge were made daily during drainage periods. In the rice season, the total water supply was 754.6mm, of which 61.7% was lost by evapotranspiration and 16.2–19.1% was lost by deep percolation (DP). In the canola season, the treatments of D0.9L30, Bilevel, D0.65L30 and D0.65L15 were discharged, respectively, 44%, 51.5%, 43% and 60.5% of the total rainfall from the soil profile. Shallow drains were more effective in controlling water table compared with deep drains so that, average of measured water table depths in the representative observation wells of D0.9L30, Bilevel, D0.65L30, and D0.65L15 were 2.1, 15, 24.1, and 32.4cm, respectively. Also, values of SEW30 (sum of excess water) were 3461, 1498, 1038 and 450cm for D0.9L30, Bilevel, D0.65L30 and D0.65L15, respectively. Based on the results, water management through a subsurface drainage system could provide winter cropping condition in the study area.