Understanding groundwater recharge is essential for successful management of water resources and modeling fluid and contaminant transport within the subsurface. This book provides a critical evaluation of the theory and assumptions that underlie methods for estimating rates of groundwater recharge. Detailed explanations of the methods are provided - allowing readers to apply many of the techniques themselves without needing to consult additional references. Numerous practical examples highlight benefits and limitations of each method. Approximately 900 references allow advanced practitioners to pursue additional information on any method. For the first time, theoretical and practical considerations for selecting and applying methods for estimating groundwater recharge are covered in a single volume with uniform presentation. Hydrogeologists, water-resource specialists, civil and agricultural engineers, Earth and environmental scientists and agronomists will benefit from this informative and practical book. It can serve as the primary text for a graduate-level course on groundwater recharge or as an adjunct text for courses on groundwater hydrology or hydrogeology. For the benefit of students and instructors, problem sets of varying difficulty are available at http://wwwbrr.cr.usgs.gov/projects/GW_Unsat/Recharge_Book/

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Estimating groundwater recharge

Although the study of plants (botany) is one of the oldest sciences, relatively detailed quantitative theories of water transport in plant tissue have lagged behind those describing water transport in soils and other geologic materials which constitute the saturated and unsaturated zones. Many existing texts deal with various aspects of water transport in these earth materials, but little or nothing is devoted to the analogous transport of water in plant roots and tissue at a similar quantitative level. Yet the soil-root-stem water pathway is a major component of the subsurface hydrologic system. Evidently there is a need for both engineering and agricultural hydrologists to further develop their quantitative understanding of water movement in plant and soil-plant systems. Modern quantitative theories of water transport in plants can be traced to concepts developed and disseminated effectively in landmark papers by Gradmann and van den Honert in 1928 and 1948 respectively. The material reviewed in this paper, while more advanced, is based on these concepts. Emphasis is placed on water movement in soil containing roots and on a general approach to water transport in living plant tissue. Detailed quantitative studies of water extraction by plant roots date back to studies by Gardner published in 1960. Many contemporary models are built around extraction functions in the Darcy-Richards equation. Several such functions are listed in a table, and their applications, relative advantages, and limitations are discussed in the text. In a series of papers published in 1958, Philip developed the first detailed quantitative description of water transport in plant tissue. His approach resulted in a diffusion equation which could be written with water potential as the dependent variable. Philip's derivation assumed that water movement was primarily from vacuole to vacuole. Subsequent workers have refined and extended Philip's development to include water movement in cell walls and plasmodesmata. The development, interpretation, and application of these models over the past decade is presented in some detail. It can be argued that contemporary models of water transport in plant tissue are oversimplified. However, they have been subjected to some successful testing and they provide a framework within which to devise experiments. Moreover, the recent development of sophisticated experimental techniques should result in more detailed model testing during the 1980's.

Models of water transport in the soil‐plant system: A review

Publisher Summary This chapter focuses on the role of the soil structure (the soil–pore system) through which both water and roots move. The principle reason for concentrating on soil structure is that, of the soil's intrinsic physical properties, it is the one most easily, frequently, and widely altered, particularly by cultivation. The transmission porosity is responsible for rapid water movement and provides pre-existing channels for root growth. Disruption or lack of, transmission pores is common in cultivated soil. This leads to impeded water flow and root growth within the profile. Structural instability is frequently encountered at the surface of tilled soils. It gives rise to crusting and translocation of clay into the subsoil. Crusting can reduce the infiltration rate by up to two orders of magnitude. Organic matter accumulation at the soil surface, by conservation tillage practices, provides the most cost-effective remedy. Crop roots have been studied less than crop canopies, but it appears that considerable inter-and intra-specific variation exists in such properties as maximum rooting depth, lateral branch production, xylem vessel diameter, and root hair length. Mechanical impedance and transient waterlogging are structurally related causes of restriction to root development in arable soils. There is evidence that loosening of zones of high strength improves crop–water relations.

The influence of soil structure on water movement, crop root growth, and water uptake

A simple empirical model of root water uptake

Advances and challenges in predicting agricultural management effects on soil hydraulic properties

A Field Study of Soil Water Depletion Patterns in Presence of Growing Soybean Roots: I. Determination of Hydraulic Properties of the Soil1

A Field Study of Soil Water Depletion Patterns in Presence of Growing Soybean Roots: III. Rooting Characteristics and Root Extraction of Soil Water1

A Field Study of Soil Water Depletion Patterns in Presence of Growing Soybean Roots: II. Effect of Plant Growth on Soil Water Pressure and Water Loss Patterns1

D. A. Farrell

Papers

A Field Study of Soil Water Depletion Patterns in Presence of Growing Soybean Roots: I. Determination of Hydraulic Properties of the Soil1

A Field Study of Soil Water Depletion Patterns in Presence of Growing Soybean Roots: III. Rooting Characteristics and Root Extraction of Soil Water1

A Field Study of Soil Water Depletion Patterns in Presence of Growing Soybean Roots: II. Effect of Plant Growth on Soil Water Pressure and Water Loss Patterns1