Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2011
Publication Date: 5/31/2011
Publication URL: http://handle.nal.usda.gov/10113/54527
Citation: He, J., Dougherty, M., Shaw, J., Fulton, J., Arriaga, F.J. 2011. Hydraulic management in a soil moisture controlled SDI wastewater dispersal system in an Alabama black belt soil. Journal of Environmental Management. 92:2479-2485. Interpretive Summary: The Black Belt region of Alabama is characterized by dark soils that expand and contract considerably, depending on their moisture content. This creates significant problems for traditional home septic water treatment systems that can lead to environmental degradation due to untreated water escapes from the system. An experimental water delivery system was designed to control water delivery using soil moisture content. The system was installed in one location of the Black Belt region and tested for two years. The system was designed to start water application under the soil surface before the soil dried too much and cracks were formed. Results showed that this system delivered more water during drier times of the year, such as in the summer, and less water was delivered in the wet winter months. The lower water application in winter creates the need for at least a two-month wastewater storage, which creates a great challenge for rural homeowners in this economically suppressed region. An estimated 30% of applied water infiltrated below 1.5 ft depth during the first summer which included a 30-year historic drought. This result was probably caused by cracks in the soil due to the extremely dry weather. The water loss indicated that this experimental system is not able to effectively control soil moisture during extreme dry weather events. Overall findings of this study indicated that the soil moisture controlled wastewater delivery system is not suitable as a standalone system in these soils. However, it may help supplement other wastewater disposal methods.
Technical Abstract: An experimental field moisture controlled subsurface drip irrigation (SDI) system was designed and installed as a field trial in a Vertisol in the Alabama Black Belt region for two years. The system was designed to start hydraulic dosing only when field moisture was below field capacity. Results showed that system hydraulic dosing rates fluctuated as expected with higher dosing rates during warm seasons and with near zero or zero dosing rates during cold seasons. The lower hydraulic dosing in winter creates the need for at least a two-month wastewater storage which is an insurmountable challenge for rural homeowners. An estimated 30% of dosed water percolated below 45 cm depth during the first summer which included a 30-year historic drought. This result was presumably caused by preferential flows stimulated by dry weather clay soil cracking. This massive water percolation loss indicated that this experimental system is not able to effective control soil moisture within its monitoring zone as designed. Overall findings of this study indicated that soil moisture controlled SDI wastewater dosing is not suitable as a standalone system in these Vertisols. However, it may find application as a supplement to other wastewater disposal methods that can function during cold seasons.