Water Level Conditions Research Articles

Monitoring Model for Dam Seepage Based on Lag Effect

The traditional dam seepage monitoring model is based on the relationship of seepage elements with the upstream reservoir water level and rainfall, which includes the impact of base value, this model will weaken the effects of reservoir water level variation and rainfall on the variation of seepage elements, especially under the condition of high reservoir water level and smaller head fluctuation, so components separated by this model are not normally the practical. Based on the theory of unsteady seepage, the lag effect function has been introduced into the seepage monitoring model to take the lag effect of reservoir water level variation and rainfall into account, and the daily variation monitoring model of dam seepage elements is established. Case studies are in good agreement with original observations, so the proposed model can be used in the daily variation monitoring and forecasting of dam seepage elements.

The Analysis about Seepage of the Bank Slope under the Cycle Rising and Drawdown of Reservoir Water Level

Bank slope seepage field is analyzed by saturated-unsaturated seepage theory under the three times cycle conditions of water level rising and drawdown . The pore water pressure distribution laws of the water level rising period, the stabilization period, the period of decline and decline stable period for every cycle are researched. The result shows soil near slope region is saturated easily after many rounds of water level rising and drawdown, and saturation region gradually increases. Soil phreatic line near slope falls fastly in the drawdown period, away from the slope, phreatic line declines slowly.

Modeling wetland vegetation community response to water-level change at Long Point, Ontario

Three spatially-explicit wetland models were developed in a geographic information system (GIS) to simulate wetland vegetation response to water-level fluctuations at the Long Point, Ontario wetland complex. They included: a rule-based model that used a series of if-then statements related to pre-existing vegetation, water depth and wetland vegetation community tolerance ranges; a vegetation state probability model based on likelihood of certain wetland vegetation communities occurring at specific water depths; and a vegetation transition probability model based on likelihood of wetland communities changing to another community under declining or rising water level conditions. The accuracy of the models was evaluated by comparing area and spatial distribution of the simulated wetland landscape to digital historical wetland vegetation data from air photo interpretation. The accuracy of the models ranged from over 80% of the cells correctly classified by the vegetation transition probability model and rule-based model to about 55% correctly classified by the vegetation state probability model. The vegetation transition probability model was marginally more accurate than the rule-based model when assessed on a cell-by-cell basis, but the rule-based model replicated the spatial distribution of vegetation communities more accurately and may be more broadly applicable. Recommended improvements include: additional environmental factors (wave exposure and substrate) incorporated in the decision rules and more detailed input data for the digital elevation model (DEM). Spatially-explicit modeling such as the rule-based model can explore management issues related to climate change and water-level regulation impacts on wetlands in the Great Lakes basin and elsewhere.

완도 해역의 해수면 조건에 따른 파랑 변형 특성

The aim of this study was estimated the characteristics of the wave propagation by the water level conditions using a numerical modeling method at the Wando sea area. For three cases numerical simulation on the condition of incident and incoming of the deepwater design wave and the season normal wave, the spatial distribution of the incident wave at study area were investigated. And the calculated numerical modeling results were compared with measured field wave data. According to on-site wave data measured for 18 days, the range of the significant wave height and period were 0.10~1.14 m, 4.35~8.74 sec, respectively, and the maximum wave height were 0.15~1.66 m. From the results of numerical model for offshore design wave incident, the wave height attacked from Southern-East direction at this study area were over maximum 10.5 m because of rapidly change of water depth. Numerical modeling by three water level conditions of Approxmate Lowest Low Water Level(Approx. L.L.W), Mean Sea Level(M.S.L) and Approximate Highest High Water Level(Approx. H.H.W) were practiced. From the results for the case of Approx. H.W.L, variations of wave height at the back area of islands were about 1.6 m at maximum value for the case of deepwater design wave incoming. The significant wave heights of winter season were bigger than summer under normal wave condition, the incident wave height over 5.5 m decreased by shielding effect of islands. The change of maximum wave height at summer season were distinct than winter and was about 1.2 m and 0.8 m, respectively.

Stability Analysis on the Slope Located in Embankment Dam Downstream under Seepage Action

A embankment dam model was established in this paper, and the steady seepage field of the embankment dam in the normal water level conditions was solved based on FEM, then the corresponding seepage force was calculated and the seepage force for each earth stripe was obtained. The slope stability in embankment dam downstream was analyzed with the help of simplified Bishop method which is based on rigid body limit equilibrium coupled with seepage force, and the seepage field’s influence on the slope’s stability was explored, a theoretical basis for the embankment dam engineering design was provided in this paper.

Coastal sand barrier hydrology – observations from the BARDEX II prototype-scale laboratory experiment

Turner, I.L., Rau, G.C., Andersen, M.S., Austin, M.J, Puleo, J. and Masselink, G. 2013. Coastal sand barrier hydrology – observations from the BARDEX II prototype-scale laboratory experiment In: Conley, D.C., Masselink, G., Russell, P.E. and O’Hare, T.J. (eds.), Proceedings 12 th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1886-1891, ISSN 0749-0208. The dynamics of groundwater at the land-ocean boundary has important implications to the exchange of water, nutrients and pollutants between the ocean and coastal aquifers, and varying groundwater levels may induce differing morphological response (erosion versus accretion) at the beachface. As a component of the Barrier Dynamics Experiment BARDEX II (Hydrolab IV) completed during June-July 2012 in the Delta Flume (The Netherlands), an extensive test program was undertaken to acquire a comprehensive data set of groundwater levels, pressure fluctuations, flow paths and tracer dispersion beneath the beachface and across the width of a prototype-scale sand barrier (D50 = 0.42mm). A particular feature of the experiment was the inclusion of a landward ‘lagoon’ and pump system that enabled the water levels on both the seaward and landward side of the barrier to be independently varied. The completion of these experiments complimented the previous BARDEX test program undertaken in the same test facility in 2008, where a gravel barrier (D50 = 10mm) was subjected to similar wave and lagoon-sea water-level conditions. An overview of the barrier hydrology instrumentation deployed and data obtained is provided here.

Growth and Yield Response of Shallots (Allium Ascalonicum) to Various Water Height from Soil Surface

The research was conducted from May to October 2008 in Payakumbuh Agriculture Polytechnic.The objective of the research was to get appropriate level of water surface from ground and suitable for optimal shallot yield and growth. This research was arrange in Randomized Block Design with three treatment. The treatment was the water surface level (W) with three water level (10, 25 and 40 cm from soil surface). Statistical analysis was performed with SAS System for Windows v6.12. The result showed that water surface level significantly affecting the plant height, relative growth rate, number of leaf, number of tuber, and tuber yield (t ha-1) due to water availablity. Water surface level that significantly increase the yield of shallot was water level condition at 25 cm from soil surface.

极端干旱区多枝柽柳幼苗对人工水分干扰的形态及生理响应

PDF HTML阅读 XML下载 导出引用 引用提醒 极端干旱区多枝柽柳幼苗对人工水分干扰的形态及生理响应 DOI: 10.5846/stxb201305091000 作者: 作者单位: 新疆师范大学生命科学学院,新疆师范大学生命科学学院,荒漠与绿洲生态国家重点实验室,新疆师范大学生命科学学院,新疆师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(41261103);新疆维吾尔自治区自然科学基金资助项目(2012211B18) The morphological and physiological responses of Tamarix ramosissima seedling to different irrigation methods in the extremely arid area Author: Affiliation: Xinjiang Normal University,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在塔里木河下游断流河道人工生态输水的大背景下,多枝柽柳(Tamarix ramosissima )作为当地优势物种,其更新恢复研究对下游荒漠河岸林的恢复尤为重要。通过研究多枝柽柳幼苗形态、水分和光合生理对不同灌溉处理的响应,分析不同人工水分干扰模式对柽柳幼苗生长发育的影响。实验设计了侧渗分层(LSI)和地表灌溉(AGI)两种给水方式,以及高灌(W1,50 L/株)、中灌(W2,25 L/株)、低灌(W3,12.5 L/株)3 个给水水平,并在整个生长季定期监测幼苗的形态参数变化、生物量、水势和光合速率。结果显示:(1)侧渗分层灌溉方式对幼苗基径、株高、冠幅以及前期生长速率都有促进作用;(2)在侧渗分层灌溉高灌下,幼苗地下及总生物量都显著高于地表灌溉(P < 0.05),且地表灌溉下根冠比(R/S:Root shoot ratio)明显高于侧渗分层灌溉;(3)侧渗分层灌溉下,幼苗茎水势高于地表漫灌,且在中灌和低灌下达到显著水平(P < 0.05),表明侧渗分层灌溉下幼苗的水分吸收效率更高;(4)在侧渗分层高灌及中灌下,实际光化学光量子产量值高于地表灌溉处理,并在高灌时差异极显著(P < 0.01)。研究表明,侧渗分层灌溉方式对多枝柽柳幼苗早期生长及水分和光合生理都具有显著促进作用。 Abstract:Water shortages are not only the main limiting factor of plant survival and growth in many habitats, but also are the direct cause for vegetation degradation in arid regions. The lower reaches of Tarim River are located in an extremely arid climate in northwestern China. The vegetation structure along the river banks of the lower reaches of the Tarim River is relatively simple, with only a few plant species present. Major plant species include such trees as Populus euphratica and shrubs such as Tamarix ramosissima, and Tamarix hispida. During the past 50 years, intense human activities effects in this region have led to the nearly complete interception of water in 321 km of the watercourse in the lower reaches of the Tarim River; as a result, the groundwater table has dropped considerably and natural vegetation which depends on that groundwater has become severely degraded. To preserve the endangered desert river bank forest vegetation and restore the damaged ecological system, an Ecological Water Conveyance Project was initiated in 2000. Artificially planting native dominant plant species including Tamarix spp. to initiate rapid rehabilitation of the plant community has become an important research subject in this area. However, the increased river flow from this project has produced very limited results in increasing both the amount of intermittent water flow in the river and in raising the downstream ground water table. As a result, the water demands of the T. ramosissima seedlings in the early growth stage could not be met. Therefore, irrigating field transplanted seedlings during the early stage of growth has been very important. T. ramosissima was once widely distributed in the desert plains and in the sandy and alkaline lands in northwestern China. It was also a dominant shrub in the desert riparian forest in the lower reaches of the Tarim River and played a key role in ecological rehabilitation and maintenance of the stability of the riparian forest in this area. The objective of this study was to test the growth and physiological responses of T. ramosissima seedling to different irrigation methods, i.e. layered side irrigation (LSI) and aboveground irrigation (AGI), using three water levels, i.e. high (W1, 50 L plant-1 repetition-1), medium (W2, 25 L plant-1 repetition-1) and low (W3, 12.5 L plant-1 repetition-1) water levels. The results showed that LSI increased basal diameter, stem length, crown width and growth rate of the seedling; LSI also increased soil moisture under the same water level conditions when compared with the AGI method. LSI significantly increased belowground biomass, total biomass and the root shoot ratio (R/S) of the seedling under W1 (P < 0.05). LSI significantly increased stem water potential under W1 and W2 (P < 0.05). The findings show that LSI can be used to increase water use efficiency of the seedlings. LSI increased photochemical quantum yield of PSⅡ in the light (Yield) of the seedlings under W1 and W2, and this increase was statistically significant under W1 (P < 0.05). Our results suggest that LSI caused rapid and large amounts of growth and biomass production in T. ramosissima seedlings, as well as had a valuable positive effect on water potential and photosynthesis which benefited the seedling's survival rates during the early stage of growth. 参考文献 相似文献 引证文献

An accurate record of volcanic ash fall deposition as characterized by dispersed organic matter in a lower Permian tonstein layer (Faxinal Coalfield, Paraná Basin, Brazil)

For the first time, the dispersed organic matter in the tonstein layer interbedded with a coal seam in the Faxinal Coalfield (Sakmarian, Southern Parana Basin, Brazil) is characterized. The deposition of clusters of pollen grains was highly influenced by the intense ash fall process that probably occurred during seasonal dehiscence of reproductive structures. The well-preserved phytoclasts with their upper and lower leaf cuticles stuck together indicate that the rapid fall of ash on this material hindered organic biodegradation. The preservation of seemingly autochthonous Botryococcus colonies at the top of the tonstein layer is evidence of the subaqueous deposition of this layer. The darkening in cuticles and xylem phytoclasts can be attributed to different causes: the thermal influence of ash fall during deposition, chemical effects of the ash, prolonged oxidation of organic matter in low water level conditions or the burning of plant organs by wildfires. Analyses of dispersed organic matter along the tonstein layer showed that the organic matter succession reflects the composition of different plant strata (herbaceous pteridophytes and arboreal glossopterids-cordaitaleans) around the deposition site.

A comparative study of macrophyte species richness in differently managed shore stretches of Lake Peipsi

We have compared the floristic composition of managed (M) and wild (W) shore areas in the northwestern, eutrophic part of Lake Peipsi (3555 km 2 , with unregulated water levels). Management techniques include uprooting or cutting of reeds and willows, building a terraced area between the dunes and the water edge and frequent mowing. In 2006 and 2008, macrophyte species richness was registered summarily for different shore stretches; in 2009–2010, a study on 12 transects, each with 10–15 quadrats of 0.5 m × 0.5 m, was carried out in the same area. In parallel to this, the vegetation in an overgrown inlet near the lake was studied. The aims were: (1) to estimate species richness on managed and wild shore areas and to determine the suitability of managed areas for maintaining declining species and (2) to study the impact of terrace building and duration of management on the vegetation. In total, 116 herbaceous species were found during the study period. Xero-, meso- and hygrophilous apophytes were characteristic for M (managed) stretches and hydrophilous apophytes for W (wild) stretches. Small threatened amphibious plants and hygrophytes such as Alisma gramineum , Ranunculus reptans , Sagina nodosa , Cyperus fuscus , Eleocharis spp., Juncus spp. were characteristic for the M stretches. The number of species was the highest (average per quadrat 11) in the mowed intermediate zone between the terrace and open water. In the inlet area the number of protected plants was highest in the first study year (2006) and then declined from 5 to 2. The highest total number of species was found in areas under ownership with diverse M and W habitats. Jaccard's similarity coefficients (JSCs) for the whole study area between the years were 0.30–0.50. The calculation of 462 JSCs among all ownerships and transects for the study period yielded floristic similarities of 0–0.59. The year along with style of management seemed to have strongest relationship with higher JSCs, and the yearly changing water levels the most obvious reason for the changes. This study has revealed the contribution of active management towards the support of persistent species richness in conditions of changing water levels, but probably not supporting richness at the more stable water edge.

Wave-induced extreme water levels in the Puerto Morelos fringing reef lagoon

Abstract. Wave-induced extreme water levels in the Puerto Morelos fringing reef lagoon are investigated by means of a phase-resolving non-hydrostatic wave model (SWASH). This model solves the nonlinear shallow water equations including non-hydrostatic pressure. The one-dimensional version of the model is implemented in order to investigate wave transformation in fringing reefs. Firstly, the numerical model is validated with (i) laboratory experiments conducted on a physical model (Demirbilek et al., 2007)and (ii) field observations (Coronado et al., 2007). Numerical results show good agreement with both experimental and field data. The comparison against the physical model results, for energetic wave conditions, indicates that high- and low-frequency wave transformation is well reproduced. Moreover, extreme water-level conditions measured during the passage of Hurricane Ivan in Puerto Morelos are also estimated by the numerical tool. Subsequently, the model is implemented at different along-reef locations in Puerto Morelos. Extreme water levels, wave-induced setup, and infragravity wave energy are estimated inside the reef lagoon for different storm wave conditions (Hs &gt;2 m). The numerical results revealed a strong correlation between the offshore sea-swell wave energy and the setup. In contrast, infragravity waves are shown to be the result of a more complex pattern which heavily relies on the reef geometry. Indeed, the southern end of the reef lagoon provides evidence of resonance excitation, suggesting that the reef barrier may act as either a natural flood protection morphological feature, or as an inundation hazard enhancer depending on the incident wave conditions.

모형실험에 의한 트러스형 리프트 게이트의 진동 특성

본 연구에서는 4대강 사업으로 건설중인 트러스형 리프트의 진동특성을 검토하기 위하여 모형실험이 수행된다. 경간 40 m, 높이 9 m의 트러스형 리프트게이트를 축척 1/25로 모형이론에 따라 아크릴과 납으로 모형을 제작하고, 폭 1.6 m, 길이 25 m, 높이 0.8 m의 수로에서 실험된다. 먼저 모형의 고유진동수가 측정되고 모형을 검증하기 위하여 유한요소 해석결과와 비교된다. 검증된 모형에서 상하류 수위와 문비 개방고에 따른 진동가속도 진폭이 측정된다. 또한 문비의 진동을 줄 일수 있는 하부형상을 검토하기 위하여 문비 최하부의 각도가 <TEX>$20^{\circ}$</TEX>, <TEX>$35^{\circ}$</TEX>, <TEX>$50^{\circ}$</TEX>인 모형을 제작하고 실험결과를 서로 비교한다. 실험 결과는 수문 조작 시 유지관리지침의 기본 자료를 제공하고, 수문의 진동특성과 진동을 줄일 수 있는 수문의 하부형상을 검토한다. A model test is performed to investigate the dynamic behavior of truss type lift gate which is being constructed by the four major rivers project. The gate dimensioned 40 m in width, 9m in height is scaled with the ratio of 1:25 and is made of acryl panel and supplemented weight by lead in the concrete test flume dimensioned 1.2 m in width, 0.5 m in height and 30m in length. Firstly natural frequencies of the model gate are measured and compared with the numerical results for the calibration. The amplitudes of the vibration are measured under the different gate opening, upstream water level conditions. Also models with bottom angle <TEX>$20^{\circ}$</TEX>, <TEX>$35^{\circ}$</TEX> and <TEX>$50^{\circ}$</TEX> are tested and compared to find out a proper shape of bottom structure which minimizes the gate vibration. These test results presents a basic data for the guide manuals of gate management and a design method to reduce the gate vibration of truss type lift gate.

Three-Dimensional Slope Stability Analysis Methods Based on GIS Technology

By using imbalance thrust force method, the slope stability factor based on three-dimensional slide block was deduced. According to the borehole data of highway, the TIN data layer and grid data layer for three-dimensional slope stability analysis were carried out by use of ArcMap. The value of each gird cell of different layers are picked up as slide block, it makes convenience in the slope stability analysis. Considering the property of bedding landslide, the three-dimensional slope stability analysis program based on VBA of ArcGIS is put forward in this paper. Taking one of the large rocky landslides as an example, the results of the three-dimensional stability analysis with slope before and after excavation, as well as the different water level conditions are compared. Furthermore, the directive significance of the three-dimensional method in landslide harness engineering was discussed.

Barrier Island Geomorphology, Hydrodynamic Modelling, and Historical Shoreline Changes: An Example from South Uist and Benbecula, Scottish Outer Hebrides

Dawson, A.G.; Gómez, C.; Ritchie, W.; Batstone, C.; Lawless, M.; Rowan, J.S.; Dawson, S.; Mcilveny, J.; Bates, R., and Muir, D., 2012. Barrier island geomorphology, hydrodynamic modelling, and historical shoreline changes: an example from South Uist and Benbecula, Scottish Outer Hebrides.A partly quantitative reconstruction is provided of the evolution of Gualan Island, a barrier island located between South Uist and Benbecula in the Scottish Outer Hebrides, using historical maps, aerial photographs, and Lidar (light detection and ranging) data. Geomorphological changes over the last approximately 200 years are described together with quantitative changes in the dimension of the barrier island, including rates of shoreline retreat. A series of digital terrain models (DTMs) provided the boundary conditions for a two-dimensional (2D) ocean circulation tide-surge model simulating water level and wave conditions associated with a highly destructive storm that took place during January 2005. During this storm event, the central part of the barrier island was overtopped by waves. Validating the hydrodynamic model against eye-witness and field evidence obtained after the 2005 storm allowed simulation of a range of potential future breaching scenarios. Thus with the same storm conditions a large barrier breach 500 m wide would result in wave heights rising by 0.8–0.9 m on hitherto sheltered shorelines.

Analysis on Stability of Powerhouse Slope under the Operation Water Level Condition of Tianhuaban Hydropower Station

Through numerical calculation on the stability of powerhouse slope by the coupling fluid-solid model of ABAQUS software, stability of powerhouse slope under the operation water level of Tianhuaban hydropower station has been evaluated. The results show that influence of pore pressure and the pore fluid effective velocity vector under the operation water level of Tianhuaban hydropower station has been limited on the scope of powerhouse slope from elevation 971m to 990m; the displacement concentration phenomenon has been existed on the scope of powerhouse slope from elevation 971m to 1010m, but the value of total displacement is smaller; influence on the stability of powerhouse slope under the operation water level is weaker; and on the scope of powerhouse slope from elevation 971m to 990m, the seepage phenomenon may be happened, and the waterproofing measures on this area must be strengthened. The achieved results can provide a research foundation for the stability of hydropower station slope on the periodic pore pressure disturbance.

EXPERIMENTAL STUDY ON THE DISCHARGE CHARACTERISTICS OF SLUICE FOR TIDAL POWER PLANT

The discharge characteristics of sluice caisson for tidal power plant were investigated by carrying out a physical experiment in a planar open channel. The experiment was performed by installing 10 sluice models whose scale was 1/70 of the prototype in the planar open channel, where apron sections were made in front of and behind the sluice models to reproduce the field condition. The locations and method of measuring water levels were carefully determined so as to accurately estimate the discharge coefficient, an index of representing the discharge performance of the sluice caisson. The experimental results for various conditions of flow rates and water levels showed that the discharge coefficient of the sluice caisson was in the range of 1.3 to 1.47. These values were substantially smaller than those obtained from the previous study performed in a two-dimensional open channel (Lee et al., 2010). As the previous study had some limitations in reproducing the bathymetric and flow conditions in the field, it is more recommended to use the results acquired in the present experiment.

Stability Evaluation for Cut-Off Wall of Daning Reservoir during Operation Period

The stress and deformation of cut-off wall will be changed as the water level cyclical varying during reservoir's operation. Therefore, the prediction is important to the safety and stability of reservoir. In this paper, the seepage characteristics of the highest and the lowest water level condition have been predicted, and the variation of horizontal displacement is discussed under the vehicle load of road and cyclical fluid load. Meanwhile, the displacement distribution and stress state in junction area of the upper wall and the lower wall are obtained. The results show that the Cut-off wall is less affected by the vehicle load of road, and its stress and deformation will gradually stabilize after the second water store-discharge cycle. The upper reinforced concrete wall will tilt towards outside of reservoir, but the deformation is very small at lower plastic concrete wall. The guide wall has a good effect on preventing the upper wall's inclining and improving the lower wall's stress environment. Besides, the maximum principle stress of cut-off wall is too small to course plastic failure.

Three-Dimensional Numerical Modeling of Cavitation and Aeration System in Dam Outlets

Abstract Preservation of the live storage of reservoirs is a serious challenge for most of the countries that encounter drought. Flushing of deposited sediments through bottom outlets in a dam is one of the suitable means to transport sediments toward downstream of the dam. Due to complicated conditions of flow through bottom outlets, we are facing a lack of accurate information about the various phenomena that occurs in bottom outlets such as cavitation, corrosion, and abrasion. Cavitation is the most important problem that causes remarkable damages on the lining of these tunnels. A numerical model based on the finite volume method for fully three-dimensional (3D) open channel flow equations is incorporated into a modeling cavitation and aeration system along the dam outlets. In this study, complex two-phase turbulent flow is simulated using the K-ɛ model. The pressure and velocity distribution under different conditions of gate opening and reservoir water level are computed along the tunnel and validation of the work has been obtained by comparison with measurements of a laboratory model. For both nonaerated and aerated flow, cavitation index in flow direction have been estimated and compared with each other.

Water Level Variations in Fractured, Semi-Confined Aquifers of Anantapur District, Southern India

Abstract The study on water level conditions of fractured aquifer system in northeastern part of Anantapur district is of immense importance as the area is covered by varied geological formations and has different irrigation patterns. The monthly groundwater level data of 154 observation wells for five year period (2001-06) is analyzed to decipher the behavior of water levels in different seasons and geo-environments. The hydrographs of the average water level data of each Mandal (group of villages) indicate steady declining trend ranging from 0.50 to 2.91m/yr. Yellanuru Mandal has both the shallowest and the deepest water levels among eight Mandals, highly undulating terrain could be one of the reasons for this contrasting condition. The pre-monsoon water levels show decline of 8.22 m in one year from May 2002 to 2003. A negative seasonal fluctuation of -1.49m has occurred in the year 2002 during which the area received 32% less than normal rainfall. The mean water levels are deeper by 42% in areas covered by sedimentary formations than those of granite terrain. Raise in water levels is significant where monthly rainfall is more than 200 mm. Due to erratic rainfall in space and time, deeper water levels are noticed even in post-monsoon period and shallow in February month at some locations. The water levels in command areas are deep and exhibit falling trend as the area forms the tail end part of the Tunga Bhadra High Level Canal. The deeper water level conditions and its declining feature is directly related to groundwater development in the form of increased agriculture activity, reduced area under rain-fed crops, high horticulture development. Arid climatic conditions, low precipitation and continuous exploitation of groundwater resources could be other factors contributing for steady decline in water levels in the area. The wide variations in groundwater levels could be due to uneven topography, heterogeneous and anisotropic conditions of granites and poor porosity - permeability of shales, lack of vegetation, and increased groundwater extraction.

Determination of mangrove forest performance in reducing tsunami run-up using physical models

Coastal ecosystems such as mangroves fringing tropical coastlines have been recognized as natural protectors of the coastal areas against destructive attack of a tsunami. In this paper, the authors aim to investigate the interaction of a tsunami wave on a typical mangrove forest and to determine its performance in reducing the run-up. A laboratory experiment using a hydraulic flume with a mangrove forest model was carried out in which tests were conducted by varying the vegetation widths of 0, 1, 2 and 3 m and average densities of 8, 6 and 4 trees per 100 cm2 using a scale ratio of 1:100. Two conditions of water levels were considered in the experiments at several tsunami wave heights between 2.4 and 14 cm. The dam break method used in the experiments produced two types of waves. At low water condition, a bore was developed and subsequently, a solitary wave was produced during high water. The results of the experiments showed that in general, vegetation widths and densities demonstrate a dampening effect on tsunami run-up. A larger vegetation width was found to be more effective in dissipating the wave energy. The first 1 m width of mangrove forest could reduce 23–32 % during high water and 31–36 % during low water. Increasing the mangrove forest width to 2 and 3 m could further increase the average percentage of run-up reduction by 39–50 % during high water and 34–41 % during low water condition. It was also observed that densities of the mangrove forest do not influence the run-up reduction as significantly as the forest widths. For mangrove forest densities to be significantly enough to reduce more tsunami run-up, an additional density of 4 trees/100 m2 needs to be provided. The experiments also showed that mangrove roots are more effective in reducing the run-up compared to the trunks and canopies. The experiments managed to compare and present the usefulness of mangrove forests in dissipating wave energy and results produced are beneficial for initiating design guidelines in determining setback limits or buffer zones for development projects in mangrove areas.