Field water table measurements were taken at two sites in Southern Quebec in order to validate DRAINMOD, a field scale water table management model. Two growing seasons of data were collected on a loamy sand soil near Sorel, Quebec and one year of data on a clay soil to the south-west of Montreal. Several water table management schemes were investigated, ranging from conventional subsurface drainage to automated subsurface irrigation. / DRAINMOD was used to simulate the measured water table fluctuations and relative corn crop yields over the growing season. Verification of the model was needed to determine if it could be a useful tool in the design and operation of water table management systems for the Quebec region. / It was found that DRAINMOD output closely simulated the water table fluctuations for conventional drainage and subsurface irrigation plots provided no exceptional circumstances existed. More study is needed in some areas such as bedded fields and in the use of fluctuating water level control structures.

Thesis (M.Sc.)--Victoria University of Wellington, 2008. / Includes bibliographical references.

<p>Hydrological modeling has been a valuable tool to understand the processes governing water distribution, quantity, and quality of the planet Earth. Through models, one has been able to grasp processes such as runoff, soil moisture, soil erosion, subsurface drainage, plant growth, evapotranspiration, and effects of land use changes on hydrology at field and watershed scales. The number and diversity of water-related challenges are vast and expected to increase. As a result, current models need to be under continuous modifications to extend their application to more complex processes. Several models have been extensively developed in recent years. These models include the Soil and Water Assessment Tool (SWAT), Variable Infiltration Capacity (VIC) model, MIKE-SHE, and the Water Erosion Prediction Project (WEPP) model. The latter, although it is a well-validated model at field scales, the WEPP watershed model has been limited to small catchments, and almost no research has been introduced regarding water quality issues (only one study).</p><p>In this research, three objectives were proposed to improve the WEPP model in three areas where either the model has not been applied, or modifications can be performed to improve algorithms of the processes within the model (e.g. erosion, runoff, drainage). The enhancements impact the WEPP model by improving the current stochastic weather generation, extending its applicability to subsurface drainage estimation, and formulating a new routing model that allows future incorporation of transport of reactive solutes.</p><p>The first contribution was development of a stochastic storm generator based on 5-min time resolution and correlated non-normal Monte Carlo-based numerical simulation. The model considered the correlated and non-normal rainstorm characteristics such as time between storms, duration, and amount of precipitation, as well as the storm intensity structure. The model was tested using precipitation data from a randomly selected 5-min weather station in North Carolina. Results showed that the proposed storm generator captured the essential statistical features of rainstorms and their intensity patterns, preserving the first four moments of monthly storm events, good annual extreme event correspondence, and the correlation structure within each storm. Since the proposed model depends on statistical properties at a site, this may allow the use of synthetic storms in ungauged locations provided relevant information from a regional analysis is available.</p><p>A second development included the testing, improvement, and validation of the WEPP model to simulate subsurface flow discharges. The proposed model included the modification of the current subsurface drainage algorithm (Hooghoudt-based expression) and the WEPP model percolation routine. 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 subsurface 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 the WEPP model can be used to produce reliable estimates of subsurface flow with minimum calibration.</p><p>The last objective presented the theoretical framework for a new hillslope and channel-routing model for the Water Erosion Prediction Project (WEPP) model. The routing model (WEPP-CMT) is based on catchment geomorphology and mass transport theory for flow and transport of reactive solutes. The WEPP-CMT uses the unique functionality of WEPP to simulate hillslope responses under diverse land use and management conditions and a Lagrangian description of the carrier hydrologic runoff at hillslope and channel domains. An example of the model functionality was tested in a sub-catchment of the Upper Cedar River Watershed in the U.S. Pacific Northwest. Results showed that the proposed model provides an acceptable representation of flow at the outlet of the study catchment. Model efficiencies and percent bias for the calibration period and the validation period were NSE = 0.55 and 0.65, and PBIAS = -2.8% and 2.1%, respectively. The WEPP-CMT provides a suitable foundation for the transport of reactive solutes (e.g. nitrates) at basin scales.</p><p><br></p>

Subsurface tile drainage is a common management practice implemented by farmers throughout the Midwest in fields that have poorly drained soils. Tile drainage has several benefits including increased productivity, reduced erosion, and increased trafficability. However, relatively little is known about the long-term change of soil properties that may occur as a result of subsurface drainage. Careful monitoring of tile drains at the long-term experimental site at the Southeast Purdue Agricultural Center led to the observation of faster drain flow than in the past, with hydrographs of the flow showing flashier peaks, suggesting that more preferential flow paths have developed over time. The overall goal of this study was to characterize possible evolution of physical and hydraulic properties of this silt loam soil after 35 years of subsurface drainage. Bulk density and water retention were measured in May of 2018 at 0-5 cm, 5-15 cm, and 15-30 cm in all plots and again in July of 2019 in the 5 m and 40 m spacings at four different horizons down to depths of approximately 100 cm, rather than set depth increments. Bulk density results from both sets of sampling show the 5 m spacing to have a significantly lower bulk density than the 40 m spacing in the top 30 cm of soil, although the difference was small. Differences in water retention among treatments were too small to be physically meaningful. Saturated hydraulic conductivity results measured by three different methods were highly variable and no differences were detected. In soils with naturally weak structure, low organic matter, and low clay content, like the soil in this study, the processes responsible for soil aggregation, structure stabilization, and lowering bulk density are inherently slow and may require longer than 35 years of subsurface drainage to produce significant changes in the physical properties measured.

Subsurface drainage (SSD) has been used to remove excess water from fields in the United States upper Midwest for more than a century, but only since the last decade in the Red River Basin of the North in North Dakota (ND). The water leaving from a SSD system can affect both the quality and quantity of water that flows to a surface water system. Therefore, determination of the water balance components is the first step to study the impact of SSD on water quantity, while evapotranspiration (ET), one of the most important components in the water balance, needs to be accurately measured for SSD field. A field experiment was conducted to study the water balance in SSD and undrained (having no artificial drainage system) fields in southeast ND. The field had three different water management systems: 22 ha undrained (UD), 11 ha subsurface drained, and the remaining 11 ha subsurface drained and subsurface irrigated. The ET rates were measured directly using an eddy covariance (EC) system for the SSD and UD fields. The changes in water table were monitored in 8 wells installed in both fields. Rainfall, SSD drainage volume, and soil moisture at six different depths at two locations were measured in both fields. The measurements were conducted in the growing seasons of 2009 and 2010. The ET rates were calculated for two different field crops: Com (Zea Mays) in 2009 and soybean (Glycine Max) in 2010. Crop coefficient (Kc) value was also developed using the ET measured by the EC system and the reference ET (ETref) estimated using the American Society of Civil Engineers Environmental and Water Resources Institute (ASCE-EWRI, alfalfa) method. The ETref was also estimated using the ASCE-EWRI grass and the Jensen Haise (JH) methods. The results indicated that the water table in the SSD field was lower during spring and fall than that in the UD field. The shallow water table and high soil moisture content in the spring and fall have resulted in higher ET rates in the UD field. In the summer, SSD field has favorable soil moisture at the root zone depth; the ET in the SSD field was 30% and 13% higher than that in UD field in summer 2009 and 2010, respectively. For the entire growing season, the ET in the SSD field was 15% higher compared to UD field and the difference was minimal in 2010. Though there were differences in the ET values, they were not statistically different. However, difference in magnitude of ET during summer 2009 yielded a statistical difference. During the peak growing season in July and August, the Kc values were greater in the SSD field due to healthy crops. / USDA (Grants CSREES NRI 2008-35102-19253) / USDA NRCS / North Dakota Agricultural Experiment Station / North Dakota State Water Commission / North Dakota Water Resource Research Institute / North Dakota Department of Health

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