Download Now. Start networking and exchanging professional insights Register now or log in to join your professional community. Follow What is the difference between catchment, water shed and basin? Upvote 0 Views Followers 2. Write an Answer Register now or log in to answer. Upvote 2 Downvote 0 Reply 0. Watersheds can be as small as a footprint or large enough to encompass all the land that drains water into rivers that drain into Chesapeake Bay, where it enters the Atlantic Ocean.
This map shows one set of watershed boundaries in the continental United States; these are known as National hydrologic units watersheds. The word "watershed" is sometimes used interchangeably with drainage basin or catchment. Ridges and hills that separate two watersheds are called the drainage divide. The watershed consists of surface water --lakes, streams, reservoirs, and wetlands --and all the underlying groundwater. Larger watersheds contain many smaller watersheds. It all depends on the outflow point; all of the land that drains water to the outflow point is the watershed for that outflow location.
Watersheds are important because the streamflow and the water quality of a river are affected by things, human-induced or not, happening in the land area "above" the river-outflow point. This picture gives a good representation of a watershed. It only shows a part of the Agashoshok watershed, but you can see how precipitation that falls on the near side of the ridges will move down-gradient to flow into the river in the picture.
Most of the precipitation that falls within the drainage area of a stream's USGS monitoring site collects in the stream and eventually flows by the monitoring site. Many factors, some listed below, determine how much of the streamflow will flow by the monitoring site. Imagine that the whole basin is covered with a big and strong plastic sheet. Then if it rained one inch, all of that rain would fall on the plastic, run downslope into gulleys and small creeks and then drain into main stream.
Ignoring evaporation and any other losses, and using a 1-square mile example watershed, then all of the approximately 17,, gallons of water that fell as rainfall would eventually flow by the watershed-outflow point. To picture a watershed as a plastic-covered area of land that collects precipitation is overly simplistic and not at all like a real-world watershed.
A career could be built on trying to model a watershed water budget correlating water coming into a watershed to water leaving a watershed. There are many factors that determine how much water flows in a stream these factors are universal in nature and not particular to a single stream :.
Precipitation : The greatest factor controlling streamflow, by far, is the amount of precipitation that falls in the watershed as rain or snow. However, not all precipitation that falls in a watershed flows out, and a stream will often continue to flow where there is no direct runoff from recent precipitation. Infiltration : When rain falls on dry ground, some of the water soaks in, or infiltrates the soil.
Some water that infiltrates will remain in the shallow soil layer, where it will gradually move downhill, through the soil, and eventually enters the stream by seepage into the stream bank.
Some of the water may infiltrate much deeper, recharging groundwater aquifers. Water may travel long distances or remain in storage for long periods before returning to the surface. The amount of water that will soak in over time depends on several characteristics of the watershed:. Evaporation : Water from rainfall returns to the atmosphere largely through evaporation.
The amount of evaporation depends on temperature, solar radiation, wind, atmospheric pressure, and other factors. Most of this water moves through the plant and escapes into the atmosphere through the leaves. Transpiration is controlled by the same factors as evaporation, and by the characteristics and density of the vegetation.
Vegetation slows runoff and allows water to seep into the ground. I've heard of the gridded pattern issue and experienced it one time when I had to expand the DEM I have with a neighboring county's larger sized grid DEM.
I don't recall that it caused any problems. I've seen threads relating to the issue, but haven't had much experience with it, so I'm not sure I can give you solid advice. I searched and found these threads using the search words: DEM "grid pattern".
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