ABSTRACT
Without at least a frequently occurring extended period of water on or near the soil surface, there would be no wetlands-an obvious conclusion that anyone could reach. What factors promote this degree of wetness to form wetlands? An overview of wetland formation and hydrology provides some answers to this seminal question. This chapter serves as an introduction to these topics*; readers should consult the references cited for more detailed discussions as well as hydrology and hydrogeology textbooks, especially for basic principles of hydrology and modeling. The last two parts of the chapter deal with indicators of wetland hydrology and other short-term assessments that can be employed to evaluate site wetness, including a brief introduction to hydrology monitoring. How to address sites with altered hydrology in making wetland determinations is discussed in Chapter 7. While other factors such as water chemistry (pH and salinity), natural disturbances, and human actions influence plant composition, soil development, and wetland functions, hydrology is the driving force that creates and maintains wetlands on the landscape-it is the foundation upon which other factors operate to produce the diversity of wetland types on Earth.
