|What is a Watershed?|
|How Does a Watershed Work?|
|When Does the Water Flow?|
|How Does a Watershed Function?|
|Why Are Riparian Wetlands Important?|
|What is Groundwater?|
When Does The Water Flow?
Many of the world's streams do not flow year-round. In humid regions, streams and most tributaries are permanent, or perennial. In less well-watered regions many of the major streams and most tributaries carry water only part of the time, during the "wet season" or during and immediately after rains. These impermanent flows are called ephemeral if they carry water only during and immediately after a rain, or intermittent if they flow for only part of the year, although the term intermittent is sometimes used to apply to both cases. In desert areas, virtually all streams may be intermittent or ephemeral, with the notable exception of those that flow into the desert, bringing their water from somewhere else. These are called exotic streams.
Why Are Riparian Wetlands Important?
Riparian wetlands are found in low-lying regions adjacent to rivers and streams that are periodically subjected to overbank flooding. Since they are hydrologically connected to both the river (downstream) and surrounding watershed (upstream), riparian wetlands are of major importance in the watershed system. Riparian wetlands intercept surface and subsurface (groundwater) runoff from the upland regions of the wetland and thus function as buffers for the river systems. These wetlands also interact periodically with floodwaters originating from rivers and streams; these hydrologic interactions can have a significant effect on river water quality.
Riparian wetlands have been shown to be highly effective in the reduction of non-point source (NPS) loading of nutrients and sediments to rivers and streams. As a result, many agricultural (including forestry) Best Management Practices (BMPs) are based on the premise that riparian buffer zones, which include wetlands and non-wetland areas, are essential components of the watershed that should be preserved or restored. Of particular significance to downstream water quality are riparian wetlands associated with low-order (smaller) streams, because of the large hydrologic throughput in these wetlands relative to the flow in the river or stream. These wetlands generally occur in the upper reaches of watersheds. Although the riparian zone of a single low-order stream may seem insignificant to water quality in the watershed, the cumulative impact of the multitude of riparian wetlands along low-order streams can be extremely significant.