CIVE 633 - ENVIRONMENTAL HYDROLOGY

LARGE RIVER-FLOODPLAIN ECOSYSTEMS

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  • Natural functions of river-floodplain systems have disappeared.

  • River modifications have tended to prevent regular flooding.

  • Limnology usually presumes static water levels.

  • Use of rivers for bulk transportation, waste disposal and hydroelectricity has affected natural uses.

  • Productivity of natural resources has decreased due to drainage of wetlands.

  • Many countries are following the practices of developed countries to harness and modify rivers.
ECOLOGICAL BASIS

  • Dynamic interaction between water and land produces and maintains flood plains, and affects the biological adaptations that have evolved therein.

  • The flood pulse concept was developed to summarize these effects on the biota.

  • The flood pulse is not a disturbance; prevention of floods is a disturbance.

  • The flood pulse enhances biological productivity and maintains biodiversity.

  • In large systems like the Amazon, conditions are more lentic than lotic because the pulse has one seasonal recurrence.

  • The moving littoral during flooding provides excellent nursery grounds for fish and nearly optimal for invertebrates.

  • Fish need to grow quickly through the flood period to reach sufficient size to reduce predation losses when the water volume subsequently reduces to its minimum.

  • In the Upper Mississippi, the flood pulse now tends to occurs earlier and more briefly that it did last century.
BENEFITS

  • The benefit of maintaining genetic and species diversity are self evident.

  • The concept of flood pulse implies that biological production is enhanced through a variety of processes during the flood cycle.

  • There is a optimal rate of increase in water levels.

  • Flood pulse may increase biological productivity per unit water area compared to a lotic system.

  • All available data indicates that yields are higher in river-floodplain systems.

  • A restoration process requires a return to natural flooding conditions, and regular access of water and biota to previously isolated flood plains.

  • Physical alterations result in a highly unpredictable flood pulse and denial of access to water to much of the floodplain.

  • Tangible economic and recreational benefits are expected from restoration attempts.

  • Other benefits are increased biodiversity and decreased probability of catastrophic flooding.

RESEARCH STRATEGIES

  • Research must account for the effect of scale.

  • Studies should focus on large spatial and temporal scales.

  • Experiments should be designed paying attention to hydrology and geomorphology.

  • Landscaping of the floodplain requires accurate prediction of the dynamics of water and sediment transport, and on the effect of those dynamics on vascular plant colonization, and viceversa.

  • Understanding of these processes is necessary before landscaping is undertaken.

  • River restoration needs to begin with an experimental approach in which different hydrological alternatives are evaluated with respect to natural responses on the landscape and flora.

  • Detailed fisheries studies should be postponed until the vegetation has been stabilized.

CONCLUSIONS

  • There are some economic advantages from river restoration, including increased biodiversity and stability.

  • Cultural development has adversely affected river-floodplain ecosystems, and has destroyed our ability to study them in their pristine state.

  • Restoration of the natural hydrological regime is necessary to gain useful information about river-floodplain ecosystems.

  • Experimental restoration and evaluation should be preferred to conventional ecological research.

 
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