8.2: Streams and Stream Flow
- Page ID
- 34064
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)A stream is a body of flowing surface water of any size, ranging from a tiny trickle to a mighty river. The basic anatomy of a stream is such that the stream channel marks the area where water normally flows. On either side of the stream channel is the floodplain (Figure \(\PageIndex{1}\)). When the stream cannot hold all its water due to flooding, this area is covered by fast flowing water which usually carries a significant amount of sediment. When flooding ends, the floodplain is covered by a layer of sediment deposited when the water velocity slows, and the stream drops what it was carrying.
Figure \(\PageIndex{1}\): The stream channel has water in it in both images. The image on the left shows the stream flowing within its channel. The image on the right shows what happens when the stream floods as water covers the floodplain.
The area from which the water flows to form a stream is its drainage basin. Some of the precipitation (rain or snow) that falls within a drainage basin is returned to the atmosphere via evaporation or transpiration. The rest either flows across the surface and into a stream, or infiltrates to become groundwater and then slowly flows towards a stream (although it is possible that some of that groundwater will cross into an adjacent drainage basin via groundwater flow). An example of a drainage basin is shown in Figure \(\PageIndex{2}\).
The area in tan is the drainage basin as all precipitation which falls into this area will either infiltrate into the ground or make it to the Ashnola River using the tributaries, or smaller feeder streams, indicated with thin black lines. It is assumed the area is surrounded by high spots, or drainage divides, which separate this drainage basin from others nearby that feed water into other rivers.
Figure \(\PageIndex{3}\): shows part of the Ashnola River drainage basin. You can see the steep slope immediately ahead followed by a more gently sloped area where water is pooling.
The gradient, or steepness, of a stream can be tracked along its length using a hydrograph (Figure \(\PageIndex{4}\)). The upper and lower parts of the Ashnola River have quite steep gradients (in the order of 50 m/km, more in some areas) while the middle part and the part within the valley of the Similkameen River, are relatively flat (6 m/km, or less). The shape of the valley has been controlled first by tectonic uplift (related to plate convergence), then by pre-glacial stream erosion and mass wasting, then by several episodes of glacial erosion, and finally by post-glacial stream erosion and more mass wasting. The lowest elevation of the Ashnola River is 440 meters at the Similkameen River, and that is its base level. The Ashnola River cannot erode below that level unless the Similkameen River erodes deeper into its flood plain (the area that is inundated during a flood).
