8: Redistribution and Drainage
- Page ID
- 38739
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)We have considered how water inputs are modified by the process of interception and then partitioned between infiltration and runoff. Now, we will tum our attention to the fate of the infiltrated water. The process of continued movement of soil water after infiltration ends is called redistribution. In this chapter, we will focus on some fundamental aspects of the redistribution process such as:
• its rate decreases over time
• it influences the availability of water to plants
• it drives solute transport in soil
We will also examine the process of drainage, which is the loss of water from below the root zone or from the bottom of the soil profile. We will learn a relatively simple method for estimating drainage rates and will also think about artificial (or man-made) soil drainage systems and their impact on agriculture and the environment. Please take a few minutes to listen to the audio overview to help begin your study of this chapter [website].
- 8.1: Redistribution within partially wetted profiles
- The process of soil water redistribution creates a dynamic situation where the infiltration-wetted part of the soil profile is getting drier while the neighboring parts of the soil are getting wetter. For this reason, the redistribution process is sensitive to hysteresis in the water retention curve. As you may recall from Section 3.3.3, the water content for any given matric potential is higher.....
- 8.2: Drainage from the soil profile
- The strong forcings imposed at the soil surface by rainfall or irrigation events and by diurnal and annual cycles of solar radiation are typically moderated as we move deeper in the soil profile. As a result, the gradients in pressure potential are often smaller in magnitude at depth than they are near the soil surface. As a result, the gradients in pressure potential are often smaller in magnitude at depth than they are near the soil surface...
- 8.3: Field capacity
- Procedures have been developed for estimating field capacity in the field and in the laboratory. The most common way to estimate field capacity is to assume that it is equal to the water content retained in the soil at a specific matric potential. Research has proven repeatedly that there is not any one matric potential value which universally represents field capacity, but the convenience of this approach to estimating field capacity...
- 8.4: Artificial drainage
- In some situations, the natural drainage capability of the soil is inadequate to meet the requirements of the intended agricultural or engineering uses for the land. Therefore, people invest substantial time, money, and resources to increase soil drainage rates by installing artificial drainage systems. One widespread type of artificial drainage is subsurface drainage...
- 8.5: Problem set
- Use the unit - gradient approach and Campbell’s hydraulic conductivity model What is the value of θ when the drainage rate drops to How many mm of water have drained from the soil profile when that value of θ is reached?
- 8.6: References
- Staple, W.J., Comparison of Computed and Measured Moisture Redistribution Following Infiltration1. Soil Science Society of America Journal, 1969. 33(6): p. 840-847. Rubin, J., Numerical Method for Analyzing Hysteresis-Affected, Post-Infiltration Redistribution of Soil Moisture1. Soil Science Society of America Journal, 1967. 31(1): p. 13-20.