This book describes how groundwater is linked with surface water features such as rivers, lakes and wetlands and function as a continuous hydrologic system. The exchange of water is driven by differences in water levels, hydrogeologic properties of earth materials and the underlying geologic framework.
Challenges in documenting the locations and rates of water exchange include significant differences in flow paths and water residence times in connected groundwater and surface‑water systems. Nine Boxes, that are used to expand on concepts presented in the main text, present case studies as examples of water exchange. Six exercises and solutions are also provided.
Multiple conceptual models representing exchange of groundwater with streams, lakes and wetlands are presented in cross sections and map views. The types of exchange such as effluent, influent, flow‑though, zero exchange and mixed conditions are defined and used to describe groundwater‑surface water exchange. These conditions are linked to the terms gaining, losing, flow‑through and mixed, that are commonly used when the surface water feature is the focus, and to the terms upwelling and downwelling which are used by river ecologists.
The exchange process is discussed at multiple scales in landscapes of varying size such ranging from the watershed/basin to the channel bed scale.
Section 5 presents methods used to describe and quantify the location, magnitude and timing of groundwater-surface water exchange. These include the use of water budgets, geochemical budgets and heat budgets; stream‑gauging seepage runs; hydrograph separation; basin‑scale groundwater modeling; surface‑water stage and groundwater level monitoring; as well as the use of mini-piezometers, seepage meters, local‑ and remotely‑sensed water temperature; stream tracer tests, and geochemical methods. Each method is described and accompanied with figures. Methods include a number of general reference documents that are available on the internet, as well as additional references.
Those who understand the link between conceptual models and field measurements of groundwater-surface water exchange will be able to determine how natural and impacted streams, lakes and wetlands function, and which preservation or restoration actions can resolve issues and meet goals.