Browsing by Subject "Agricultural drainage"

Now showing 1 - 3 of 3
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    An Assessment of land use impacts on channel morphology in a Western Minnesota watershed.
    (2009-12) Christner Jr., William Thomas
    This research is a comprehensive investigation encompassing land use changes in an agricultural watershed and corresponding changes to the rainfall-runoff relationship and stream channel morphology. The Lac qui Parle (LqP) watershed is one of eleven major watersheds within the Minnesota River Basin (MRB). Agriculture is the dominant land use within the MRB occurring on more than 90-percent of the landscape. This research investigates the spatial and temporal changes in channel morphology and land use between 1965/66 and 2002/03. Historical data were obtained from the US Army Corps of Engineers for the South Fork Lac qui Parle (SF LqP) River. Sixty-five cross-section sites were re-surveyed and evaluated. Current channel morphology was assessed through a second year of data collection. Additional data were collected and analyzed for crop history, riparian vegetation, agricultural drainage, annual discharge, annual peak discharge, and monthly and annual precipitation. Results indicate crop diversity within the SF LqP River has diminished and is currently dominated by corn and soybean. Surface and subsurface drainage of agricultural lands was documented on 37-percent of the sub-watershed area evaluated. Analysis of the discharge and precipitation records indicates an increase in the Q/P ratio and average annual runoff volume post-1960. The analysis indicates land use changes within the SF LqP watershed have impacted the channel morphology of the SF LqP River post-1965/66. Significant changes in channel cross-sectional area were noted in the Middle and Upper watersheds. Results corresponds to a channel enlargement ratio (CER) of 1.02 - 1.30. Changes in cultivation practices and drainage activities correspond with higher CER of 2.32 - 2.6. Similar increases were noted for peak discharge (1.30 - 1.35). CERs match values developed for storm sewered streets in urbanized areas. All changes were significant at the 95-% confidence level. A separate investigation evaluated the use of natural channel design for agricultural ditches. Results indicate natural channel design provides more efficient sediment transport, increased channel diversity/complexity, and may reduce channel maintenance costs.
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    Design, construction, and assessment of a self-Sustaining drainage ditch.
    (2011-08) Kramer, Geoffrie
    Agricultural drainage is a double-edged sword: helping farmers achieve everincreasing crop yields to meet consumers’ demands, while providing a short-circuit through the soil profile for excess water and nutrients. Drainage ditches are an important pathway as water moves downstream in headwater landscapes. As low order streams, ditches have the potential to remove and assimilate nutrients. In order to operate at their maximum nutrient removal potential, ditches should be healthy, self-sustaining ecosystems that function similarly to natural streams. The two-stage agricultural drainage ditch is an innovative solution for creating drainage ditches that behave more like natural streams. A low-flow channel provides sediment transport during low-flow periods, while benches within the ditch allow for overbank flow and energy dissipation during high-flow periods. The larger crosssectional area increases surface contact between water and the ditch at certain flow depths, which likely enhances nutrient removal. In this study, a two-stage agricultural drainage ditch was designed and then constructed in southern Minnesota, USA in the autumn of 2009. Extensive monitoring of the ditch has been conducted following construction; efforts have focused on establishing an understanding of the geomorphic, water source, and water quality aspects of the ditch. Analysis of field measurements from August 2010 show that between 10 and 15 percent of nitrate N entering the ditch was removed within the ditch reach. A slight increase in average channel thalweg elevation has been measured, while increased pool-riffle sequencing has also been observed. Channel cross-sectional surveys have showed slight changes in low-flow channel dimensions. Economic analyses have been performed to measure the feasibility of two-stage ditch construction. There are situations where predicted cost reductions in periodic ditch maintenance provide enough savings to offset two-stage channel construction costs. In other cases, subsidies may be required to economically justify a two-stage system. An analysis was performed to estimate the cost of additional nitrogen (N) removal ($/kg N removed) in two-stage ditches, using increased N removal as a basis for subsidies. Results show situations where N removal costs is less than $3 to $4 kg-1 of N removed, which is competitive with other Best Management Practices.
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    The Varying Effects of Climate And Landscape Changes on Increased River Flows In Minnesota Watersheds
    (2023-05) Ulrich, Jason
    Minnesota has experienced increases in precipitation and river flows, particularly in its southern, heavily agricultural region, since 1940. However, these areas have also experienced significant increases in the extent of corn/soybean cropping and artificial drainage. Currently, the relative contributions of these factors to increased flows are not well understood. There is also some indication that intense rain events have increased across this region and may coincide with increased flood events. However, most climate studies have not considered the roles of watershed antecedent moisture conditions and runoff storage in their proxies of potential flood impact, nor explored any direct observational evidence of intense rain event links with flooding. Therefore, to better understand the relationships between these complicating factors, this study pursued the following three objectives: (1) Apportion the relative contributions of increases in climate, corn/soybean agriculture, and artificial drainage to increased river flows in 21 agricultural watersheds in southern Minnesota, (2) Analyze trends in intense rainfall, antecedent moisture conditions and predicted runoff at 132 climate stations across Minnesota to estimate potential flooding hotspots and, (3) Apportion the relative contributions of intense rain events of different magnitudes, snowmelt, and antecedent moisture conditions to flooding in the Cottonwood River watershed -- a heavily agricultural watershed that has seen exceptional increases in intense rain events and flooding since 1950.To apportion the relative contributions of increases in climate, corn/soybean agriculture, and artificial drainage to increased river flows, trends in precipitation, crop conversions, and extent of drained depressional area in 21 Minnesota watersheds were compared from 1940-2009. Watersheds with large land-use changes had increases in seasonal and annual water yields of >50% since 1940. On average, changes in precipitation and crop evapotranspiration explained less than one-half of the increase, with the remainder highly correlated with artificial drainage and loss of depressional areas. Trends for intense rain events, antecedent moisture conditions and watershed storage were analyzed in 132 precipitation stations within 65 major watersheds in Minnesota. Resulting runoff was predicted using a simplified rainfall-runoff model. Results show widespread increases in intense rain events across southern Minnesota since 1950, but markedly fewer trends in antecedent moisture conditions and predicted runoff. However, exceptional intense rain events, antecedent moisture conditions, and predicted runoff increases are concentrated in and around specific hotspot watersheds in Minnesota. The study shows the importance of considering watershed hydrology when diagnosing potential impacts of intense rain event increases. Relative contributions of intense rain and antecedent moisture conditions to flooding in the Cottonwood watershed were determined using an empirical, data-driven approach which apportioned the roles of snowmelt, intense rain events and antecedent moisture conditions in each every flow (and flood) event 1950-2021. Results suggest that recent major flooding in the Cottonwood has been driven by intense rain events (≥ 75/mm/day), and to a lesser degree by event antecedent baseflow, which reduces channel storage and increases flood stage. Less severe flooding is driven roughly equally by (less) intense rain events (≥ 25mm/day & <75/mm/day) and both antecedent base- and quickflows.