<p>Controlled drainage is a management strategy designed to
mitigate water quality issues caused by subsurface drainage. To improve
controlled drainage system management and better understand its hydrological
and environmental effects, this study analyzed water table recession rate, as
well as drain flow, nitrate and phosphorus loads of both free and controlled
drainage systems, and simulated the hydrology of a free drainage system to
evaluate surface runoff and ponding at the Davis Purdue Agricultural Center
located in Eastern Indiana. </p>
<p>Statistical analyses, including paired
watershed approach and paired t-test, indicated that controlled drainage
had a statistically significant effect (<i>p</i>-value <0.01) on the rate of water table fall and
reduced the water table recession rate by 29% to 62%. The slower recession rate
caused by controlled drainage can have negative impacts on crop growth and trafficability by causing the water table
to remain at a detrimental level for longer. This finding can be used by
farmers and other
decision-makers to improve the management of controlled drainage systems
by actively managing the system during storm events. </p>
<p>A method was developed to estimate drain flow during missing
periods using the Hooghoudt equation and continuous water table observations.
Estimated drain flow was combined with nutrient concentrations to show that
controlled drainage decreased annual nitrate loads significantly (p<0.05) by
25% and 39% in two paired plots, while annual soluble reactive phosphorus (SRP)
and total phosphorus (TP) loads were not significantly different. These results
underscore the potential of controlled drainage to reduce nitrate losses from
drained landscapes with the higher level of
outlet control during the non-growing season (winter) providing about
70% of annual water quality benefits and the
lower level used during the growing season (summer) providing about 30%.
</p>
<p>Three different methods including monitored water table depth,
a digital photo time series and the DRAINMOD model simulations were used to determine the generation process of surface
ponding and runoff and the frequency of incidence. The estimated annual water balance indicated that
only 7% of annual precipitation contributed to surface
runoff. Results from both simulations and
observations indicated that all of the ponding events were generated as a
result of saturation excess process rather than infiltration excess.</p>
<p>Overall, nitrate transport
through controlled drainage was lower than free drainage, indicating the
drainage water quality benefits of controlled drainage, but water table remained at a higher
level for longer when drainage was controlled. This can have negative impacts
on crop yields, when water table is above a detrimental level, and can also increase the potential of nutrient transport through
surface runoff since
the saturation excess was the main reason
for generating runoff at this field.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/7438976 |
| Date | 16 January 2019 |
| Creators | Samaneh Saadat (5930210) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/EVALUATION_OF_HYDROLOGICAL_PROCESSES_AND_ENVIRONMENTAL_IMPACTS_OF_FREE_AND_CONTROLLED_SUBSURFACE_DRAINAGE/7438976 |
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