Rapid Water-level Fluctuations Research Articles

Spatial-temporal variations of stage-area hysteretic relationships in large heterogeneous lake–floodplain systems

The hysteretic relationship between the water level and the inundated area is one of the basic non-linear characteristics of lake hydrology. However, it is difficult to obtain this relationship accurately, especially for large floodplain lakes that exhibit time-varying boundaries with rapid water-level fluctuations. Taking the largest lake-floodplain system of the Yangtze River basin – Poyang Lake and its extremely productive wetland – as an example, we investigated the spatial–temporal variation of the stage-area hysteretic relationship in large heterogeneous lake-floodplain systems by adopting the Enhanced Spatial and Temporal Adaptive Reflection Fusion Model (ESTARFM) based on the observed water levels and reconstructed high spatial–temporal resolution inundation datasets using multi-source remote sensing data. The major results indicate that the inundation dynamics in the regions of the main lake and seasonal floodplain lakes are remarkably inconsistent. Concerning the inundation behavior of the river and lake-floodplain, a conceptual model was established to explain the formation mechanism of the counter-clockwise and clockwise stage-area hysteretic relationships in the Poyang lake–floodplain system. Further investigation revealed that seasonal lakes exist widely in floodplain settings and have a crucial impact on increasing the hysteresis of upstream stations and decreasing that of downstream stations. The magnitude and direction of the stage-area hysteretic relationships varied with time in a changingenvironment. This study extends the understanding of the complexity of hydrological behavior in large heterogeneous lake-floodplain systems, which is of vital importance for lake water resources and ecological management.

Impact of Accumulated Temperature on Wetland Vegetation Area in燩oyang燣ake

Accumulated temperature, which is now widely used in agronomy, is an important ecological factor to the growth of plants, but few relative studies have been found on the vegetation area of floodplain grasslands in Poyang Lake. This research used the classification and regression tree (CART) to classify normalized vegetation area index derived from MODIS LAI (Moderate Resolution Imaging Spectroradiometer Leaf Area Index) images from 2008 to 2014, according to different climate indexes, such as mean daily air temperature (n), accumulated temperature (jw), daily maximum temperature (g), daily minimum temperature (d), accumulative precipitation (j), water level (s) and average water level for 20 days preceding (a). The results showed that: (1) The accumulated temperature and the 20-day average WL (water level) were found to have the greatest impact on variation in wetland vegetation area, and they both dominated the classification process twice; (2) Two classification thresholds of accumulated temperature were 790°C and 1784°C, approximately corresponding to the beginning of April and mid-May; (3) 790°C could also be used as a threshold to select remote sensing images to analysis the annual variability of vegetation, i.e. while accumulated temperature is lower than 790°C, remote sensing images of similar accumulated temperature rather than similar date should be selected from different years for comparison. We also found that, effects of different hydrological factors on area of floodplain grasslands showed stage characteristics: (1) From January to March, water level changes slowly with less rainfall, as a result, the 20-day average WL which can interpret the hydrologic characteristics smoothly showed significant importance in this stage; (2) While entering April, intense rainfall make accumulative precipitation to be the dominating factor of classification; (3) From late April to mid-May, in condition of accumulative precipitation higher than 405 mm, daily water level is of most importance, because to the flood recession process as well as rapid water level fluctuations.

Effects of Rapid Water-Level Fluctuations on the Stability of an Unsaturated Reservoir Bank Slope

The instability of reservoir slope is likely to cause some severe natural hazards such as surge and barrier lake. In this study, the changes in seepage field and the distribution of the unsaturated zone of a reservoir bank slope subjected to rapid water-level fluctuations are investigated using the finite element method. The stability analysis of a reservoir slope under water-level fluctuation with a rate of 2 m/day is performed. The stability analysis is based on the theory of unsaturated soil mechanics and saturated-unsaturated seepage and accounts for the hydromechanical coupling effect. The changes in shear stress and strain as well as pore water pressure due to rapid water-level fluctuations are explicitly examined. Furthermore, the stability factor of safety, the underlying failure mechanism, and relevant influence factors are discussed. Based on the finite element analysis, it is found that the rapid loss of matrix suction would give rise to the surface landslide near the slope toe.

A submerged Mesolithic lagoonal landscape in the Baltic Sea, south-eastern Sweden – Early Holocene environmental reconstruction and shore-level displacement based on a multiproxy approach

Remains of a submerged landscape around the mouth of a small river are preserved off the Baltic Sea coast at Haväng in south-eastern Sweden. Organic-rich sediment ridges with abundant wood remains and archaeological artefacts extend 3 km from the modern coast to depths of at least 20 m below the present sea level. This exceptionally well-preserved material gives evidence of a lagoonal environment surrounded by a pine-dominated forest, which was inhabited by Mesolithic humans during two low-stand phases of the Baltic Basin, from the Yoldia Sea stage to the Initial Littorina Sea stage (c. 11,700–8000 cal BP). As part of ongoing efforts to reconstruct the local landscape development and to refine the shore-level displacement history during the Early Holocene, a 3-m sediment sequence was collected at 8 m b.s.l. and dated by radiocarbon analysis. A multi-proxy stratigraphic approach was applied to the sediment record, including pollen, diatom, organic and inorganic elemental analyses. This stratigraphic dataset is explored in the context of detailed bathymetry of the area based on multibeam echo sounding and surveillance and sampling of artefacts by divers. The investigated sediment sequence reflects a stable, highly productive lagoonal environment with an unusually high sediment accumulation rate at c. 9100–8600 cal BP. The uppermost 1-m part of the sequence represents a destabilized depositional environment interpreted as reflecting an increased influence of brackish water due to the approaching coastline during the Littorina transgression. The shore-level displacement in the area is characterized by rapid water-level fluctuations. Following a regression to around 22 m b.s.l. during the Yoldia Sea stage, the Ancylus transgression reached a maximum of 2 m b.s.l., followed by a second regression to a low-stand at 12 m b.s.l. during the Initial Littorina Sea stage. Several unprecedented archaeological findings made in the study area are presented and discussed, including stationary fishing constructions, dated to c.9100–8400 cal BP. These constructions, the oldest known in Northern Europe, indicate extensive riverine and lagoonal fishing, previously not recorded during the Mesolithic in Sweden. Furthermore, bones and antlers of red deer with slaughter marks and a unique pick axe made of elk antler provide evidence of human exploitation of terrestrial resources. The Haväng site shows the strong potential of submerged landscapes as palaeoecological source materials, and demonstrates the importance of resources at coastal settings near river mouths for Mesolithic communities.

Edaphic and geomorphic evidences of water level fluctuations in Gallocanta Lake, NE Spain

The pedological implications of lake water level fluctuations are complex, especially in lake margin, where topographical, hydrological, and sedimentary conditions are most variable. Lake water level fluctuations generate landscape elements, which provide insights into the processes involved in soil development and the extent of the zones affected by flooding/desiccation. Coupling information from detailed geomorphological inspections in the field, the mapping of the lakeshore, and the pedogenesis of each landscape element can provide a better understanding of these relationships, which was used to study the saline Gallocanta Lake, NE Spain, a semiarid intramontane lacustrine system that undergoes significant and rapid water level fluctuations. Geomorphic classification of the lake margin forms and environments served as a guide for soil sampling. The geomorphological survey revealed high diversity and contrast in the lake margin environment, from shores affected by coastal erosion to zones characterized by progradation/aggradation. Two soil toposequences and 11 pedons that were on different geomorphic units were studied on two margins of the lake. Following gradients in elevation, moisture, and salinity, soils showed a succession of Inceptisols to Aridisols, with Mollisols developed at intermediate positions and Aquic soils at the lake floor and southern shore. Soils had a sandy, loamy texture and a predominantly carbonatic composition, high variation in CCE (mean=37%), texture, and coarse fragments throughout the soil profiles. Soil salinity was the highest at the lowest topographic position and in the upper soil horizons, where mean ECe=188.6dSm−1 at 25°C. In addition, the highest organic matter (6%) and gypsum (34%) content occurred at the lake floor. Soil color characteristics and concentrations, and depletions of Fe and Mn indicated redox changes associated with soil water saturation under carbonate and or saline conditions. Macro and micromorphological features of oxidized and reduced horizons indicated the alternation between palustrine (reduced) and non-palustrine (detrital, emerged, oxidized) events at different geomorphic and topographic positions, from the lake floor up to 7m above it. Pedogenesis inferred and the littoral/submerged forms located at permanently emerged areas confirmed the past and present trend towards the desiccation of the lake. This study has improved our understanding of how soils form and develop within the context of geomorphic units, and can be used in making land-use decisions in the protected reserve and agricultural surroundings of the lake.

Hydrological constraints of paleo-Lake Suguta in the Northern Kenya Rift during the African Humid Period (15–5 ka BP)

During the African Humid Period (AHP, 15–5kaBP) an almost 300m deep paleo-lake covering 2200km2 developed in the Suguta Valley, in the Northern Kenya Rift. Data from lacustrine sediments and paleo-shorelines indicate that a large paleo-lake already existed by 13.9kaBP, and record rapid water level fluctuations of up to 100m within periods of 100years or less, and a final lowstand at the end of the AHP (5kaBP). We used a hydro-balance model to assess the abruptness of these water level fluctuations and identify their causes. We observed that fluctuations within the AHP were caused by abrupt changes in precipitation of 26–40%. Despite the absence of continuous lacustrine data documenting the onset of the AHP in the Suguta Valley, we conclude from the hydro-balance model that only an abrupt onset to the AHP, prior to 14.8kaBP, could have led to high water levels recorded. The modeling results suggest that the sudden increase in rainfall was the direct consequence of an eastward migration of the Congo Air Boundary (CAB), caused by an enhanced atmospheric pressure gradient between East Africa and southern Asia during a northern hemisphere (NH) summer insolation maximum. In contrast, the end of the AHP must have been gradual despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the study area. This abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during September–October. This change would have meant that the only rain source was the Intertropical Convergence Zone (ITCZ), which would have carried a greater amount of moisture during the short rainy season thus slowing the fall in water level over a period of about 1000years in association with the reduction in insolation. The results of this study provide an indication of the amount of time available for humans in north-eastern Africa to adapt in response to a changing climate, from hunting and gathering to farming and herding.

Observations and Impacts from the 2010 Chilean and 2011 Japanese Tsunamis in California (USA)

The coast of California was significantly impacted by two recent teletsunami events, one originating off the coast of Chile on February 27, 2010 and the other off Japan on March 11, 2011. These tsunamis caused extensive inundation and damage along the coast of their respective source regions. For the 2010 tsunami, the NOAA West Coast/Alaska Tsunami Warning Center issued a state-wide Tsunami Advisory based on forecasted tsunami amplitudes ranging from 0.18 to 1.43 m with the highest amplitudes predicted for central and southern California. For the 2011 tsunami, a Tsunami Warning was issued north of Point Conception and a Tsunami Advisory south of that location, with forecasted amplitudes ranging from 0.3 to 2.5 m, the highest expected for Crescent City. Because both teletsunamis arrived during low tide, the potential for significant inundation of dry land was greatly reduced during both events. However, both events created rapid water-level fluctuations and strong currents within harbors and along beaches, causing extensive damage in a number of harbors and challenging emergency managers in coastal jurisdictions. Field personnel were deployed prior to each tsunami to observe and measure physical effects at the coast. Post-event survey teams and questionnaires were used to gather information from both a physical effects and emergency response perspective. During the 2010 tsunami, a maximum tsunami amplitude of 1.2 m was observed at Pismo Beach, and over $3-million worth of damage to boats and docks occurred in nearly a dozen harbors, most significantly in Santa Cruz, Ventura, Mission Bay, and northern Shelter Island in San Diego Bay. During the 2011 tsunami, the maximum amplitude was measured at 2.47 m in Crescent City Harbor with over $50-million in damage to two dozen harbors. Those most significantly affected were Crescent City, Noyo River, Santa Cruz, Moss Landing, and southern Shelter Island. During both events, people on docks and near the ocean became at risk to injury with one fatality occurring during the 2011 tsunami at the mouth of the Klamath River. Evaluations of maximum forecasted tsunami amplitudes indicate that the average percent error was 38 and 28 % for the 2010 and 2011 events, respectively. Due to these recent events, the California tsunami program is developing products that will help: (1) the maritime community better understand tsunami hazards within their harbors, as well as if and where boats should go offshore to be safe, and (2) emergency managers develop evacuation plans for relatively small “Warning” level events where extensive evacuation is not required. Because tsunami-induced currents were responsible for most of the damage in these two events, modeled current velocity estimates should be incorporated into future forecast products from the warning centers.

Comparison of the hydrological and hydrochemical evolution of Lake Naivasha (Kenya) during three highstands between 175 and 60 kyr BP

Three diatomite beds exposed in the Ol Njorowa Gorge south of Lake Naivasha, Central Kenya Rift, document three major lake-level highstands between 175 and 60 kyr BP. Diatom transfer-function estimates of hydrological and hydrochemical parameters suggest that a deep and large freshwater lake existed during the highstands at ∼135 and ∼80 kyr BP. In contrast, a shallower but more expanded freshwater lake existed at ∼110 kyr BP. The best analog for the most extreme highstand at ∼135 kyr BP is the highstand during the Early Holocene humid period from 10 to 6 kyr BP. The environmental conditions as reconstructed from diatom assemblages suggest long-lasting episodes of increased humidity during the high lake periods. This contrasts to the modern situation with a relatively shallow Lake Naivasha characterized by rapid water level fluctuations within a few decades. The most likely cause for the variable hydrological conditions since 175 kyr BP is orbitally driven insolation changes on the equator and increased lateral moisture transport from the ocean.

Comparison of the hydrological and hydrochemical evolution of Lake Naivasha (Kenya) during three highstands between 175 and 60 kyr BP

Three diatomite beds exposed in the Ol Njorowa Gorge south of Lake Naivasha, Central Kenya Rift, document three major lake-level highstands between 175 and 60 kyr BP. Diatom transfer-function estimates of hydrological and hydrochemical parameters suggest that a deep and large freshwater lake existed during the highstands at ∼135 and ∼80 kyr BP. In contrast, a shallower but more expanded freshwater lake existed at ∼110 kyr BP. The best analog for the most extreme highstand at ∼135 kyr BP is the highstand during the Early Holocene humid period from 10 to 6 kyr BP. The environmental conditions as reconstructed from diatom assemblages suggest long-lasting episodes of increased humidity during the high lake periods. This contrasts to the modern situation with a relatively shallow Lake Naivasha characterized by rapid water level fluctuations within a few decades. The most likely cause for the variable hydrological conditions since 175 kyr BP is orbitally driven insolation changes on the equator and increased lateral moisture transport from the ocean.

The record of jökulhlaups from Summit Lake, northwestern British Columbia

Summit Lake, which is impounded by Salmon Glacier, is the largest self-draining, ice-dammed lake in Canada. Until 1961, it contained few icebergs and was stable, overflowing to the north into me Bowser River valley. The first jökulhlaup occurred in December 1961, after a lengthy period of thinning and retreat of Salmon Glacier, when a subglacial runnel developed in the weakened ice dam, allowing the lake to drain suddenly. This flood and two others in 1965 and 1967 caused major damage to the road system in the Salmon River valley south of the lake. Since 1965, with three exceptions, Summit Lake has drained annually; minor floods along Salmon River in 1966, 1969, and 1973 may record partial drainings of the lake, although other explanations are possible. Jökulhlaups in recent years have been smaller and have occurred earlier in the year than most of the early floods. Rapid water-level fluctuations associated with the annual emptying and refilling of Summit Lake have generated large numbers of icebergs, derived from the Salmon Glacier dam; these icebergs presently choke the surface of the lake. The present jökulhlaup cycle is likely to continue either until the glacier readvances or until it retreats to the point that it no longer forms an effective seal.

Observations and implications of water well and creepmeter anomalies in the Mojave segment of the San Andreas fault zone

Four years of continuous water level data from a 1,900 m deep well near the San Andreas fault in southern California show a 21-month period of unusual rapid fluctuations. The anomalous water level activity ceases with the occurrence of the 8 July 1986, ML = 5.6 North Palm Springs earthquake on the San Andreas fault, approximately 120 km southeast of the well site. The water level data correlate with signals from two San Andreas fault zone strain sensors. The long-term water level variations are similar in shape to those recorded by a borehole dilatometer 30 km from the well site, while the rapid water level fluctuations correlate in time with anomalies in the record of a fault zone creepmeter located 35 km from the water level monitor. The observations are interpreted in terms of strain occurring in a horizontally and vertically heterogeneous crust. Tectonic deformation is concentrated along weak block-bounding fault zones. The blocks are sufficiently rigid to generate correlated displacement phenomena along their weak boundaries. As a consequence, fault zone strain events can be related over large distances as in the case of the North Palm Springs earthquake and the coincident creep and water level anomalies. The observed creep and water level events occur in a weak aseismic shallow (<3 km) material overlying stronger asperities along which the fault is locked and regional strain loading occurs. Local failure of the fault within the weak shallow material has no far-field effects and is not important in the crustal stress budget, but may signal accelerated strain accumulation at depth. In this context, the reported observations demonstrate the possibility of joint detection of fault zone anomalies that relate to, and possibly anticipate, major tectonic strain events on large faults.

A quantitative survey of Culicoides variipennis (Diptera: Ceratopogonidae) in dairy wastewater ponds in southern California.

Culicoides variipennis (Coquillett) larvae were sampled five times over a 10-wk period in late summer in each of 26 dairy wastewater ponds in western Riverside County, Calif. Slope, degree of cattle access, prevalence of visible manure solids, salinity, chemical oxygen demand, plankton volume, and whether the ponds were pumped for irrigation were determined concurrently. Larvae of C. variipennis were associated positively with plankton volume, degree of animal access, and salinity, and negatively with slope and the pumping of the ponds for irrigation. High densities of larvae were found in shoreline mud in shallow, "evaporation bed" type ponds that were not pumped (means = 106 larvae per 30 ml). In contrast, pumped ponds were deeper, had steeper slopes, and supported lower densities of C. variipennis (means = 52 larvae per 30 ml). The pumped ponds tended to hold water continuously (more stable in time), and to have lower phytoplankton volumes and lower values of chemical oxygen demand. Rapid water level fluctuations in the pumped ponds also may have reduced C. variipennis density.

Observations of rapid water-level fluctuations in ice sink-hale lakes, Martin River Glacier, Alaska

Observations of rapid water-level fluctuations in ice sink-hale lakes, Martin River Glacier, Alaska

Observations of rapid water-level fluctuations in ice sink-hale lakes, Martin River Glacier, Alaska

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