Land and Watershed Management - Practices of Irrigation and On-farm Water Management - page 198

6.3.2 How the Watershed Functions
Because they convey the water that runs over the land and into the ground, water-
sheds provide many vital ecological and hydrological functions. Hydrologically,
watersheds collect water from rainfall and snowmelt, storing some of this precip-
itation in wetlands, soils, trees, and other vegetation, and underground in aquifers.
The floodplain along the banks of a river also serves as an important storage site
for water during periods of heavy runoff. These natural storage sites help eliminate
contaminants as suspended particles settle out and as water infiltrates into the soil
where biological and chemical reactions can break down impurities. Some of this
stored water eventually flows into streams, rivers, and lakes as runoff.
Ecologically, watersheds provide critical habitat for many plant and animal
species, as well as transport paths for sediment, nutrients, minerals, and a variety
of chemicals. Watersheds also provide water to human communities for drinking,
cleaning, recreation, navigation, hydroelectric power, and manufacturing.
6.3.3 Factors Affecting Watershed Functions
Like all organisms, humans are an integral part of the watersheds in which they
live. Therefore, human activities, both in the water and on the land, can have a great
impact on the watershed functions described previously. The creation of buildings,
parking lots, and roads; the draining of wetlands; mining; deforestation; and agri-
cultural activities can all alter the quality and quantity of water that flows over and
infiltrates into the ground. These changes can alter watershed functions by eliminat-
ing critical water storage sites (e.g., wetlands and floodplains) and by contributing
additional sediments and chemicals to runoff. Human activities can also eliminate
critical natural habitat sites, thereby limiting biodiversity in the watershed.
6.3.4 Importance of Watershed Management
People and wildlife require healthy watersheds. Everyone lives in a watershed and
each person's actions in turn affect their neighbors and the land and water “down-
stream.” For managing water effectively, the most appropriate land unit is the
watershed.
Activities of all land uses within watersheds impact the water quality of down
gradient water bodies. Point and nonpoint sources of pollution in a watershed con-
tribute nutrients, bacteria, and chemical contaminants to waterways. Watershed
management encompasses all the activities aimed at identifying sources and min-
imizing contaminants to a water body from its watershed.
6.3.5 Addressing/Naming a Watershed
We may refer to watersheds by their proper name as well as by a grouping of num-
bers. This set of numbers is called the watershed's Hydrologic Unit Code (HUC),
also known as the watershed address. The HUC can range from 2 to 16 digits in
length.