Search

Entrance resistance occurs when water flows into a perforated subsurface drainage pipe, making the effective radius smaller than the real radius. Accurately calculating effective radius is essential for drainage calculation. No effective radius formulas for corrugated drains wrapped with thin geotextile are applicable. In this study, new effective radius formulas were proposed by dividing the entrance resistance into corrugation and perforation resistance. The accuracy of the formulas was verified by experiments. Sensitivity analysis was conducted, indicating that corrugation was the main factor affecting drainage efficiency. When the radius and structure of the drain wall were determined, the opening area exhibited high sensitivity with interactivity between it and drainage discharge. The effect of the opening area and position of the perforations on the effective radius was evaluated for different drainage discharges. Placing more rows of perforations on the lower half of the pipes was better for drainage efficiency. For small drainage discharge of less than 0.1 cm3 s−1 cm−1 , the opening area was not significant, and an opening area of 15 cm2 m−1 was sufficient. However, for greater drainage discharge, an opening area of 60 cm2 m−1 would be required. [ABSTRACT FROM AUTHOR]

The removal of nitrogen from water is a consequence of the synergistic action of plant uptake, sediment sorption, and microbial decomposition. However, there is a lack of long-term experimental studies on the effects of each component in the process of nitrogen removal. In this study, we investigated the effect of sediment, plants, and microorganisms on nitrogen removal by setting up three systems: water–sterilized sediment, water–sediment, and water–sediment–plant. The nitrogen removal effect followed the following rank order of effectiveness: the "water–sediment–plant" system > the "water–sediment" system > the "water–sterilized sediment" system. The ditch sediment had a strong enrichment effect for nitrogen. In addition, the migration rate of nitrogen in the sediment with different depths was different. The ammonia-nitrogen migration rate in the sediment showed an increasing trend with time and depth. The nitrate-nitrogen migration process in the sediment showed a trend of enrichment toward the middle layer (15.0–25.0 cm). Aquatic plants and microorganisms can promote the removal of nitrogen in water, with the average purification rates of 13.92% and 19.92%, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)