Understanding River Landscapes
Lowland Open Floodplain Rivers These are meandering rivers with unconfined, extensive floodplains. They are typical of the major rivers of the Murray-Darling
Basin, the top end, and larger rivers on the coastal plain. Typical rivers are the Murray River at Swan Hill, the lower Clarence
River in NSW and the South Alligator River in the NT. They are usually of relatively low energy with sandy to muddy beds, and can be
turbid in times of moderate to high flow. Their
defining feature is the extensive floodplains containing billabongs, wetlands, alluvial flats, and flood channels.
Riparian vegetation is a crucial contributor to several elements of these rivers. Click on the diagram below to discover more about these elements:
<![CDATA[<table border='0' cellspacing='0' cellpadding='0'>
<tr valign='top'><td><img height="220" width="393" src="graphics/map4_lib.gif" alt="Lowland Open Floodplain River" border="0">
<ul>
<li><a href="#woodydebris">woody debris</a>, and
<li><a href="#floodplainhabitats">floodplain habitats</a>.
</ul>
<p>Other distinctive processes are:</p>
<ul>
<li>control of <a href="#stockaccess">stock access,
<li><a href="#erosioncontrol">erosion control</a>,
<li><a href="#shading">shading</a>, and
<li><a href="#in-streamprocessing">in-stream processing</a>.
</ul>
<p>Other riparian management aims along these rivers include:</p>
<ul>
<li><a href="floodcontrol.htm">Flood control</a>
</ul>
<p><a name="woodydebris"> </a></p>
<h3>Woody Debris</h3>
<p><a class='glossaryitem' href="glossary.htm#Large%20Woody%20Debris" onMouseover='showTerm(event,"The sticks, branches, trunks and whole trees that fall into rivers and streams.")' onmouseOut='hideTerm();'>Woody debris</a> provides one of the few stable substrates on which micro-organisms can grow in lowland rivers, as the bed and banks
are composed of finer unstable material. Woody debris is also important habitat for shelter and breeding as these rivers are more
open and have smoother beds than headwater streams.</p>
<p><table border='0' cellpadding='0' cellspacing='0' align='none'><tr><td width="200"><a onClick="popImageWindow('woodydebris1.jpg');return false;" href="showimage.htm_6BD9C00F"><img src='images/medium/woodydebris1.jpg' width='200' height='143' border='0' style='border:1px solid black;' alt="Woody debris, Lachlan River, NSW"></a><br><span class='photocaption'>Woody debris, Lachlan River, NSW<br><a onClick="popImageWindow('woodydebris1.jpg');return false;" href="showimage.htm_6BD9C00F"><img src="graphics/zoom.gif" height="17" width="49" alt="Zoom Image" border="0" /></a></span></td></tr>
</table>
<p><a href="woodydebris.htm">Click for more about the process of woody debris.</a></p>
<p><a name="floodplainhabitats"> </a></p>
<h3>Floodplain Stream Interaction</h3>
<p>These river landscapes contain extensive floodplain environments that support diverse and distinctive animal and plant communities. For example, the red gum forests of the Murray River, and the <a class='glossaryitem' href="glossary.htm#Phragmites" onMouseover='showTerm(event,"Also known as 'common reed' Phragmites australis is a grass species that occurs in slow moving water. It has a worldwide distribution but occurs naturally in Australia.")' onmouseOut='hideTerm();'>phragmites</a> dominated wetlands that support water bird colonies through large breeding events. Maintaining the natural pattern of flooding and inundation is essential to keep these environments healthy. Many of these floodplain environments are linked to highly regulated rivers with levees, weirs and gates that control flows - in some cases specific environmental flows are now being released to ensure that floodplains receive the inundation events they require.</p>
<p><table border='0' cellpadding='0' cellspacing='0' align='none'><tr><td width="200"><a onClick="popImageWindow('blandcktemora2.jpg');return false;" href="showimage.htm_0A185185"><img src='images/medium/blandcktemora2.jpg' width='200' height='137' border='0' style='border:1px solid black;' alt="Bland Creek near Temora, NSW"></a><br><span class='photocaption'>Bland Creek near Temora, NSW<br><a onClick="popImageWindow('blandcktemora2.jpg');return false;" href="showimage.htm_0A185185"><img src="graphics/zoom.gif" height="17" width="49" alt="Zoom Image" border="0" /></a></span></td></tr>
</table>
<p><a href="floodplainstreaminteractions.htm">Click for more about floodplain processes.</a></p>
<p><a name="stockaccess"> </a></p>
<h3>Stock Access</h3>
<p>Control of stock access along these rivers is important for maintaining the health of the floodplain environment. Stock also damage river banks and contribute to erosion. Uncontrolled stock access into the wetlands, billabongs, and floodplain creeks can cause more damage than the impact they have on streams because of the infrequent flushing and renewal of these environments.</p>
<p><a href="stockaccess.htm">Click for other benefits of controlling stock access.</a></p>
<p><a name="erosioncontrol"> </a></p>
<h3>Erosion Control</h3>
<p>Because of their relatively low energy, erosion control is less of an issue in these rivers than in the higher energy coastal
streams or the more numerous headwater streams. Trees can still prevent
<a class='glossaryitem' href="glossary.htm#Mass%20Failure" onMouseover='showTerm(event,"A form of bank erosion where large blocks of material slide or topple into the water.")' onmouseOut='hideTerm();'>mass failure</a> of
banks though, and macrophytes such as
<a class='glossaryitem' href="glossary.htm#Phragmites" onMouseover='showTerm(event,"Also known as 'common reed' Phragmites australis is a grass species that occurs in slow moving water. It has a worldwide distribution but occurs naturally in Australia.")' onmouseOut='hideTerm();'>phragmites</a> can prevent fluvial scour,
which is sometimes worsened by flow regulation. Much of the sediment in these streams is
supplied from upstream rather than locally but
<a class='glossaryitem' href="glossary.htm#Nutrients" onMouseover='showTerm(event,"Natural elements (usually nitrogen and phosphorus) that are essential for plant and animal growth.")' onmouseOut='hideTerm();'>nutrients</a> from the floodplains,
<a class='glossaryitem' href="glossary.htm#Groundwater" onMouseover='showTerm(event,"Water flowing through a saturated zone of soil or rock. The water is derived from rainfall that infiltrates into and through the soil. The water then emerges back at the surface downslope or downstream. It is the main contribution to river flow between storms and floods.")' onmouseOut='hideTerm();'>groundwater</a> and banks can be important.</p>
<p><table border='0' cellpadding='0' cellspacing='0' align='none'><tr><td width="200"><a onClick="popImageWindow('murraywahgunyahphragmites.jpg');return false;" href="showimage.htm_CEB264FB"><img src='images/medium/murraywahgunyahphragmites.jpg' width='200' height='133' border='0' style='border:1px solid black;' alt="Phragmites, Murray River, Wargunyah, VIC"></a><br><span class='photocaption'>Phragmites, Murray River, Wargunyah, VIC<br><a onClick="popImageWindow('murraywahgunyahphragmites.jpg');return false;" href="showimage.htm_CEB264FB"><img src="graphics/zoom.gif" height="17" width="49" alt="Zoom Image" border="0" /></a></span></td></tr>
</table>
<p><a href="erosioncontrol.htm">Click for other benefits of erosion control.</a></p>
<p><a name="shading"> </a></p>
<h3>Shading</h3>
<p>Tree canopies do not extend far over these large rivers, so shade is not significant for control of algal growth, temperature or
light. Overhanging trees and vegetation along the side of the banks are still important for fish habitat, cover from predators and food for instream organisms.</p>
<p><table border='0' cellpadding='0' cellspacing='0' align='none'><tr><td width="200"><a onClick="popImageWindow('darlingtreeavoca.jpg');return false;" href="showimage.htm_CA846FBD"><img src='images/medium/darlingtreeavoca.jpg' width='200' height='150' border='0' style='border:1px solid black;' alt="Darling River at Avoca Station, NSW"></a><br><span class='photocaption'>Darling River at Avoca Station, NSW<br><a onClick="popImageWindow('darlingtreeavoca.jpg');return false;" href="showimage.htm_CA846FBD"><img src="graphics/zoom.gif" height="17" width="49" alt="Zoom Image" border="0" /></a></span></td></tr>
</table>
<p><a href="shading.htm">Click for other benefits of shading.</a></p>
<p><a name="in-streamprocessing"> </a></p>
<h3>In-Stream Processing</h3>
<p>The sandy beds of these streams can be important sites for
<a class='glossaryitem' href="glossary.htm#Biofilm" onMouseover='showTerm(event,"An organic matrix comprised of microscopic algae, bacteria and other microorganisms that grow on stable surfaces in water bodies (eg. submerged logs, rocks or large vascular plants).")' onmouseOut='hideTerm();'>biofilm</a> growth which can scavenge significant quantities of nitrogen,
particularly in low flow.</p>
<p><a href="instreamprocessing.htm">Click for more about in-stream processes.</a></p>
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Erosion control |
Stock access | Floodplain habitat | Woody debris | Shading | In-stream processing
See also chapters 2 and 3 of Rivers as Ecological Systems
and sections 3, 4, and 7 of Running Down: Water in a Changing Land .
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