b.) Some ephemeral channels begin to flow quickly during most events, at least those with some minimum amount of precipitation or melt, while others flow only rarely, such as when soil moisture is saturated or nearly saturated – this is the essence of the non‐uniformity of moisture delivery at the heart of the variable source area concept (Figure 6). Whenever there is little rainfall, most of it is absorbed by the porous soil, some of it evaporates, and the remaining runs off only to be soaked in during its journey. Due to snow melt, water yield is significant even during spring and summer, which can be used for water supply. The drainage system includes the geographic area surrounding the stream
Identification of ephemeral channels that flow rarely, especially those that flow once or less per year can be difficult because they may look more like swales than actual channels. guidance of interest to local and state health departments. When liquid precipitation is involved, individual throughfall droplets often coalesce into larger droplets on leaf, twig, or branch surfaces, and their larger masses help ensure their successful delivery through the layered leaf canopy. Page path. Penn State Cooperative Extension has urban and community forestry
cause profound groundwater changes. However, many of the processes and management principles that are discussed for forests also have relevance to other types of ecosystems, although the degree or importance of specific hydrologic processes or components in these other ecosystems may differ from that in forested ecosystems. Consequently, water may be transferred laterally by subsurface flow at a relatively rapid rate, so precipitation becomes streamflow quickly. In addition to these human‐engineered trans‐basin diversions, there are also natural transfers of water between watersheds. channels and meet at the bottom, where water flows out of the watershed,
The
graph above illustrates that the risks of severe flooding and flood
Science in Your Watershed General Introduction and Hydrologic Definitions W. B. LANGBEIN and KATHLEEN T.ISERI Manual of Hydrology: Part 1. The hydrograph variables stormflow volume before peak, stormflow volume after peak, total stormflow volume, peakflow, time to peak, time after peak, and total event length are defined from the general components and can be quantified for comparison between different time periods or to other watersheds. URBANIZATION
and deposition patterns on a meandering stream are shown at right. In
For hardwoods, transpiration declines during leaf senescence (i.e., the final stage of leaf development) and terminates once leaf fall occurs. an interactive CD-ROM. upland locations. In the winter, interception losses of snow also can occur by sublimation, which is the transformation of solid precipitation (snow or ice) directly to a gas. If you do not receive an email within 10 minutes, your email address may not be registered, Baseflow exists because the water table intersects the bed of local stream or river channels. leads to great increases in flooding during and immediately
A higher water
Under
After
sensitive hydrologic areas like the streambank riparian buffers and
The standard project flood (SPF) limit is the brown area
By and large, such watersheds have substantial vegetation, such that in some cases, these could be considered as forest watersheds also. precipitation that falls onto it. Ephemeral streams are the final type of stream. Respectively, each of these is termed a storm hydrograph (Figure 7), daily hydrograph, weekly hydrograph, monthly hydrograph, seasonal hydrograph, and annual hydrograph. The term watershed describes an area of land that drains downslope to the lowest point. Such transfers typically involve conveyance of streamflow via pipelines or aqueducts from one watershed to another where water is less available. Although urbanization
Consequently, for a watershed with a total of 750 mm of streamflow for a year, that water would be 750 mm deep if it was spread over the surface of the watershed. Local
After a rain when the rivers are full, they recharge the
seek out priority pollutant reduction opportunities, then protect
DEFINITION |
watershed, and small watersheds join to become larger watersheds. of the floodplain. Even greater annual totals are recorded in some areas of southeastern Alaska and portions of the Hawaiian Islands. You are currently using guest access . A small watershed in Wyoming. stabilize the stream banks. Stemflow, which usually constitutes only about 2 to 5 percent of precipitation that reaches the ground (Chang 2006), is more efficiently delivered on smooth‐barked trees (e.g., maple and beech) than on rough‐barked trees (e.g., oak and conifers).