H31B-01
Hydro-Geomorphologic Effects Of Large Wood Jams On A Third-Order Stream (Tierra Del Fuego, Argentina)
Dead wood pieces, especially when organized in jams, play an important geomorphic role in streams because of the effects on flow hydraulics, pool formation and sediments storage. The increase of stream morphological diversity and complexity also exerts also an important ecological role. This work reports on geomorphic role of large wood pieces and jams in a third order mountain stream located in the Southern Tierra del Fuego (Argentina), and draining an old-growth nothofagus forested basin not influenced by the beavers damming activity. Even if the in-stream number of wood pieces (length > 1m; diameter > 0.1 m) is comparable to what observed in other climatic areas, the slow growth of the nothofagus forest causes a lower wood abundance in terms of volumetric load. Since the relatively small dimensions of the surveyed large wood pieces, almost the 70% of them demonstrated to have been fluvial transported and the also wood jams reflect the apparent dynamic of wood in the channel. Wood jams exert a significant influence on the channel morphology, representing almost the half of the drop caused by steps and being responsible for the creation of 30% of the pools. The LW-forced pool volume is strongly and positively correlated to the height of the LW jam, and a significant inverse relationship between pool spacing and wood density within is evident if only the LW-forced pools are considered. The geomorphic influence of LW jams is also exerted by a considerable sediment storing capacity.
H31B-02
Geomorphic Effect of Wood in Southern Andes Streams: Evidences From Three Mountain Basins
This study analyses large wood (LW) storage and the associated effects on channel morphology and flow hydraulics in three third-order mountain basins (drainage area 9-12 km2) covered in old-growth nothofagus forests, ranging from the temperate warm Chilean Andean Cordillera to the subantarctic Tierra del Fuego (Argentina). Amount, characteristics and dimensions of large wood (>10 cm large, > 1 m long) were recorded, as well as their effects on stream morphology, hydraulics and on sediment storage. Also, wood transport over a 1 year time period was assessed. Results show that major differences in LW abundance exist even between adjacent basins, due to the basins' disturbance history (fire). Massive LW volumes (i.e. > 1,000 m3ha-1) can be reached in basins disturbed by fires followed by mass movements and debris flows. However, wood mobility at bankfull conditions appears quite scarce (<4% of the logs moved), with travel distances inversely related to the piece length/channel width ratio. Potential energy dissipation due to wood dams is about a quarter of the total elevation drop in two streams, with a the gross sediment volume stored behind wood dams of around 1,000 m3km-1, which appears to be of the same order of the annual sediment yield. Finally, the presence of wood dams may increase flow resistance up to one order of magnitude.
H31B-03
Morphological Changes in a Braided River of the Italian Alps During the Last Two Centuries and the Related Dynamics of Riparian Vegetation
This study aims to determine the timing and the extent of the morphological changes occurred in a 30-km long reach of a gravel bed river of the Eastern Italian Alps (the Piave river, in the Val Belluna synclinal), now covered with abundant riparian vegetation and forested islands that may represent important source of wood during floods. The Piave river (drainage area 3,300 km2 at the exit of the montane district) was once characterised by a wide, braided active channel confined by climatic terraces formed during the last glacial retreat (Holocene). It underwent a strong narrowing during the last century that led to a wandering/single-thread morphology, leaving large areas available to the establishment of riparian forests (genus Populus, Salix, Robinia). It is notable that some of these woodlands are now most valuable under an ecological perspective, in particular they represent important nesting sites for avifauna (EC BIRDS Directive). Nine sets of historical maps and aerial photos (from 1805 to 2003) were used to determine changes in the Piave river corridor (active channel width, vegetation cover, island areas and number), georeferencing and editing maps by a GIS software. Two series of cross-sections (1935-2003) allowed to get insights into the vertical evolution of the streambed. Discharge data (from 1926) permitted to assess the possible effect of flow regulation on formative discharge. Results indicate that average channel width (i.e. channel area/channel length) dropped from about 600 m during the XIX century to 200 m in the 1991, and increased thereafter up to 300 m in the 2003. The dynamics of riparian vegetation follows a clear complementary trend. Such a pattern reflects the different human impacts on the river system, particularly the gravel mining activity intensely carried out in the '70-'80. Large forested islands were already present at the early XIX century, but their extension relative to channel area was much smaller (3 times) than in 1991. However, present island areas are back to early XX century values. Also, island erosion is clearly linked to flood events having recurrence intervals R.I. > 10 yr. Magnitude-frequency analysis of discharge data allowed to rule out the effect of flow regulation on channel forming discharges (R.I. 2-3 yr), thus suggesting that sediment starvation - due to lower basin supply earlier and in-channel mining later - is the primary reason for the observed channel adjustments. Finally, a map showing the location of likely wood sources in case of intense flood events was derived by intersecting the channel migration corridor with present riparian forest areas. These areas may then be subjected to specific management in order to reduce flood hazards for downstream sections.
H31B-04
MR2K: A Program to Calculate Drawdown, Velocity, Storage and Capture Response Functions
A program, MR2K, used for calculating drawdown, velocity, storage loss, and capture response functions for multi-aquifer groundwater flow systems was developed. Capture is defined as the sum of the increase in aquifer recharge and decrease in aquifer discharge as a result of an applied stress from groundwater pumping. The capture phenomena treated are stream-aquifer leakance, reduction of evapotranspiration losses, flows to and from prescribed head boundaries, and increases or decreases in natural recharge or discharge from head- dependent boundaries. The response functions are independent of the magnitude of the pumping stresses, and are dependent on the type of partial differential equation, boundary and initial conditions and the parameters thereof, and the spatial and temporal locations of stresses. The aquifers modeled may have irregular-shaped boundaries and non- homogeneous transmissive and storage qualities. The stresses are groundwater withdrawals from wells. The utility of response functions arises from their capacity to be embedded in management models such as decision support systems. The response functions are incorporated into the objective function or constraints that couple the hydrologic system with the management system. Three response-function examples are presented for a hypothetic basin.
H31B-05
Water Diagnosis in Shrimp Aquaculture based on Neural Network
In many countries, the shrimp aquaculture has not advanced computational systems to supervise the artificial
habitat of the farms and laboratories. A computational system of this type helps significantly to improve the
environmental conditions and to elevate the production and its quality. The main idea of this study is the creation
of a system using an artificial neural network (ANN), which can help to recognize patterns of problems and their
evolution in shrimp aquaculture, and thus to respond with greater rapidity against the negative effects. Bad control
on the shrimp artificial habitat produces organisms with high stress and as consequence losses in their
defenses. It generate low nutrition, low reproduction or worse still, they prearrange to acquire lethal diseases.
The proposed system helps to control this problem.
Environmental variables as pH, temperature, salinity, dissolved oxygen and turbidity have an important effect in
the suitable growth of the shrimps and influence in their health. However, the exact mathematical model of this
relationship is unspecified; an ANN is useful for establishing a relationship between these variables and to
classify a status that describes a problem into the farm.
The data classification is made to recognize and to quantify two states within the pool:
a) Normal: Everything is well.
b) Risk: One, some or all environmental variables are outside of the allowed interval, which generates problems.
The neural network will have to recognize the state and to quantify it, in others words, how normal or risky it is,
which allows finding trend of the water quality.
A study was developed for designing a software tool that allows recognizing the status of the water quality and
control problems for the environment into the pond.
http:www.cic.ipn.mx
H31B-06
Mountains Micro Basin Degradation Indicators based in Duration Curves Analysis as a Basis for Establishment Policy Briefs to Achieve Hydrological Forestry Regeneration
Based on the research results of 4 disturbed micro catchments with different soil uses and different degradation degree, and of 3 undisturbed micro catchments as a comparison statement, some action lines were defined in order to formulate policy briefs to achieve hydrological forestry regeneration and potential soil use. The flow duration curves and Base Flow Index analysis, which demonstrate quantitatively the degree of degradation at catchment scale, formed the basis on which this preliminary policy briefs were elaborated. This should be the key factor in order to have a better understanding and to help authorities to do their work appropriately. The flow duration curves for the non depredated areas are characterized by good flow regulation characteristics in a drought period, related with the degree of conservation, in comparison with a low regulation capacity observed in the degraded micro catchments.
H31B-07
The Importance of the Nothofagus Forest on Snowmelt Process linked to floods in Mountain Basins of Tierra del Fuego, Argentina as Input for Land Use Policies.
The conception and application of policies and best practices for the appropriate land use from the view point of
extreme floods attenuation, must be based on scientist acknowledge of the basin response, reaching each one
of the hydrological cycle's components. That condition is necessary as a start point for an integrated intersectoral
management of water and forest resources at the basin scale, especially when forest logging or forest
urbanization appear as land use alternatives with socioeconomic importance, confronting the natural roll of the
forest in the basin.
Within this framework, this article analyzes the forest importance on the seasonal snow-pack and snow-melting
process in the mountain basin environment of Tierra del Fuego Island, Argentina, where a mixed rain-snow
hydrological regimen and a canopy of native Nothofagus forest are basic features considered.
Extreme floods events are related to heavy rain and snow-melting combination. In theory, the worst scenario is
the exceptional rain occurrence at the moment of the maximum snow storage, air temperature higher than 0ºC in
the whole basin, and previous wet conditions. On this scenario we analyze aspects that indicate forest influences
on the snow pack distribution and evolution which are favorable to the attenuation of the intensity of melting
process which are induced by rain and temperate air mass. Results were obtained in the context of the EPIC
FORCE (EU) Project.
http:www.ceg.ncl.ac.uk/epicforce/
H31B-08
Coastal Flooding Induced by Surcharging Storm Sewer Systems at Low Elevations
While conventional stormwater sewer systems are intended to prevent flooding, these same systems installed at low elevations actually facilitate flooding. This flood hazard merits further investigation as the potential for economic damages on the low elevation bay side of developed barrier islands is significant. The potential for damages caused by elevated water levels in back bay systems separating barrier islands from the mainland has been largely overlooked in the recent study of coastal flooding hazards. This research addresses the challenge of identifying and documenting adverse consequences attributed to the common practice of allowing storm sewers to surcharge. One such region which suffers from chronic flooding facilitated by the stormwater sewer system is Seaside Park, NJ located on the Barnegat Barrier Island. There are large floods (up to .6 m) 3 to 4 times each year and minor floods (up to .2 m) 1 to 2 times each month. This study focuses on a .40 km stretch of Bayview Avenue which runs parallel to the bay and is protected by a bulkhead .76m high. A pressure transducer was installed to record time-series data of flood levels on the roadway. Comparing flood level time-series data with rainfall records and United States Geological Survey (USGS) tide gage readings, it is shown that surcharging storm sewers from elevated water levels in the bay is the primary mechanism causing flooding along Bayview Avenue. The contribution of surface runoff is shown to be minor in comparison with floods occurring even in the absence of rainfall. The critical water level for which flooding can be expected is determined for the Barnegat Bay USGS tide gage at Seaside Heights. Based on the real-time tide gage readings it is possible to predict when flooding will occur at to what level it will reach. This value is then used to sort historical records from the tide gage to determine that the frequency of flooding over time is increasing. Several hypotheses for this increase are presented. This study further investigates the effectiveness of the existing bulkhead installed to prevent flooding. A solution is purposed that retrofits the storm sewers to prevent surcharging thus increasing the effectiveness of the bulkhead structure and reducing the magnitude and frequency of flooding.
H31B-09
The Accessibility and Reliability of Water Sources in Benin City Metropolis :A Case Study of Uselu Quaters, Nigeria
A study of the accessibility and reliability of water sources in Benin City Metropolis was carried out using data collected from the analysis of a questionnaire survey, analysis of water samplefrom Ikpoba River,newspaper reports and information from the Edo State Public Utilities Board, Benin City,Nigeria. Results indicate great difficulty in obtaining water from the various water sources, a heavy dependence on borehole water sources and poor quality of the tap water whenever the taps flow in some localities in the metropolis. The major difficulties encountered and the options adopted by the communities are highlighted. Keywords: Water sources, quality and supply strategies.
H31B-10
The Center for Natural Hazards Research at East Carolina University
The Center for Natural Hazards Research (CNHR) in the Thomas Harriot College of Arts and Sciences at East Carolina University (ECU) was established in 2004 to foster a multidisciplinary research community that seeks to understand and, thereby, improve our ability to withstand and recover from adverse events caused by natural processes. In keeping with its mission "to promote research and analysis that ultimately reduces the harm caused by forces of nature to life, business, and the environment" the CNHR has 15 core faculty and faculty associates and supports graduate student research. Projects range from examining the economic impact and rebuilding plans in the wake of Hurricane Katrina to analyzing global precipitation extremes.
H31B-11 INVITED
Regeneration of Native Trees and Wetlands: Results of an Unplanned, Twenty Year Experiment in the Colorado River Delta, Mexico
Historically, cottonwood and willow trees were common on the Lower Colorado River, although quantitative estimates of their former abundance are not available. During the past hundred years, dams and flow regulation have altered the riparian habitat to favor dominance by exotic saltcedar and other salt-tolerant shrubs over the floodplain. It is widely assumed that, once established, saltcedar competitively excludes native trees, and that removal of saltcedar will be necessary as part of restoration programs. We studied the regeneration of cottonwood and willow trees in the presence of saltcedar in the delta of the Colorado River in Mexico from 1992 to 2002 in response to flood releases from the U.S. Flood releases of 50 cms to 750 cms in El Nino years of 1993, 1997-1998 and 2000 each germinated cohorts of trees amidst saltcedar stands and in bare soil scoured by the floods. During their establishment year, these trees rooted into the shallow aquifer under the river channel, and became dominant age classes of trees in subsequent years. Low-volume administrative spills (water ordered by irrigators but not used) provided a nearly perennial run of water in the river in non-flood years. The large and small flows created a rich avian habitat, containing backwaters, marsh areas, and a multi-stored canopy of native trees, saltcedar and other shrubs. Bird density and diversity in this river stretch are higher than has been reported anywhere else on the Lower Colorado River. The acreage of cottonwood and willow trees in the delta might be as high today as was reported in a 1904 timber survey before the era of dams and agriculture. The main threats to the ecosystem are fires, many deliberately set, timber harvesting, and vegetation clearing projects. Although surface flows are needed to wash salts from the riverbanks, germinate seeds, and enhance avian habitat, the main water source for the trees is the regional aquifer maintained by irrigation of the surrounding agricultural fields in the valley. In this agro-ecosystem, riparian and wetland habitats benefit greatly from agricultural inefficiencies and the vagaries of climate related to El Nino cycles.
H31B-12
DEVELOPMENT OF REPRESENTATIVE HYDROLOGIC INDICATORS FOR STREAMFLOW ALTERATION
To study the impact of river regulation due to dams and to design optimal reservoir operation policies, hydrologic indicators, which describe the overall health of the river and the degree of hydrological alteration caused by a particular reservoir operation policy, are needed. Currently over 170 hydrologic indicators have been recommended to describe various aspects of streamflow regimes. Many of these indicators are redundant or correlated, including many of the Indicators of Hydrological Alteration (IHA), which is a set of 67 commonly used indicators. This has made environmental flow management difficult. Hence, there is an increasing need to develop a smaller set of independent, representative indicators. The objective of this research is to develop a small set of representative hydrologic indicators that best characterize hydrologic alteration caused by reservoirs. To compute the values of the above-mentioned indicators, simulated streamflow data generated from a software tool called Water Evaluation And Planning (WEAP) and real pre- and post-dam streamflow data measured at 200 US Geological Survey sites are used. Principal component analysis (PCA) is performed to evaluate the ability of the proposed hydrologic indicators to represent the complete variability expressed using the IHA parameters. Preliminary results of the PCA indicate that "ecodeficit", which is the area below the pre-impact flow duration curve (FDC) and above the post-impact FDC of a site, is one good candidate of such hydrologic indicators.