Water Surface Height Research Articles

Combined Method for Measuring 3D Wave Spectra. II. Examples of Using the Basic Measurement Procedures and Analysis of the Obtained Results

UDC 551.466.3+551.46.086+004.932 In the second part of the work, which is dedicated to the methods of studying the wave characteristics, we present the results of measuring three-dimensional spectra of the water-surface height distributions in the closed sea- and lake-water areas with low-level waves. The data on the wave spectra is obtained on the basis of processing the wave video images using the energy and correlation approaches. On the whole, the obtained information on the multidimensional characteristics of the waves agrees with the theoretical concepts and the results of other studies.

Modeling tidal distortion in the Ogeechee Estuary

A 3D numerical model is used to simulate the distortion of tidal hydrodynamics in the Ogeechee Estuary, GA. The Ogeechee, like many estuaries found in the Southeastern US, consists of shallow channel networks and extensive intertidal storage in the form of wetlands. Such features are known to induce non-linear overtide generation and significant tidal distortion, otherwise known as tidal stage asymmetry. Simulations are run with varying parameters to assess their effects on modeling tidal distortion for the Ogeechee Estuary: bottom friction coefficients, enhanced wetland friction coefficients, and tidal flat elevations. To succinctly quantify the degree of distortion across the domain, the statistical parameters of skewness and asymmetry are calculated for time series of water surface heights and channel volume fluxes. The intertidal storage causes the peak flood flux to occur later and the peak ebb flux to occur earlier, thereby resulting in positive asymmetry for the volume flux for the full estuary. However, ebb dominance is a localized feature and varies throughout the estuary. Increasing the intertidal storage by lowering wetland elevation enhances the effects on high tide and volume flux magnitudes, decreasing the ebb-dominance and volume flux asymmetry typically associated with intertidal storage thereby indicating the importance of the wetland elevation over the total storage volume. Increased channel bottom friction reduces ebb-dominance by extending the duration of the falling tide. More interestingly, increased wetland friction reduces the influence of wetland intertidal storage on tidal distortion. The model suggests an increase in wetland friction does little to dampen wave propagation at high tide but rather impedes the lateral flooding of wetlands, reducing ebb dominance. Tidal flat elevation has the largest impact on distortion for the Ogeechee Estuary whereas enhanced wetland and bottom frictional influences on distortion are small, albeit not insignificant.

Observation of a local gravity potential isosurface by airborne lidar of Lake Balaton, Hungary

Abstract. Airborne lidar is a remote sensing method commonly used for mapping surface topography in high resolution. A water surface in hydrostatic equilibrium theoretically represents a gravity potential isosurface. Here we compare lidar-based ellipsoidal water surface height measurements all around the shore of a major lake with a local high-resolution quasi-geoid model. The ellipsoidal heights of the 87 km2 we sampled all around the shore of the 597 km2 lake surface vary by 0.8 m and strong spatial correlation with the quasi-geoid undulation was calculated (R2 = 0.91). After subtraction of the local geoid undulation from the measured ellipsoidal water surface heights, their variation was considerably reduced. Based on a network of water gauge measurements, dynamic water surface heights were also successfully corrected for. This demonstrates that the water surface heights of the lake were truly determined by the local gravity potential. We conclude that both the level of hydrostatic equilibrium of the lake and the accuracy of airborne lidar were sufficient for identifying the spatial variations of gravity potential.

Microwave-Photonic Sensor for Remote Water-Level Monitoring Based on Chaotic Laser

A microwave-photonic sensor for remote water-level monitoring based on chaotic laser is proposed and demonstrated. The probe chaotic signal with bandwidth of 18 GHz is generated in the central office and then transmitted at the remote antenna unit after a 24 km single-mode fiber transmission. And the monitoring data from the remote antenna unit is sent back to the central office over fiber. The water-level measuring is accomplished by cross-correlation between reference signal and probe signal at the central office. So the remote water-level monitoring system with a high spatial resolution of 2 cm is achieved and the height of water surface can be displayed in real time.

An integrated modelling framework of catchment‐scale ecohydrological processes: 1. Model description and tests over an energy‐limited watershed

ABSTRACTThe interactions between atmospheric, hydrological, and ecological processes at various spatial and temporal scales are not fully represented in most ecohydrological models. This first of a two‐part paper documents a fully integrated catchment‐scale ecohydrological model consisting of a three‐dimensional physically based hydrological model and a land surface model. This first part also presents a first application to test the model over an energy‐limited catchment (8.4 km2) of the Sleepers River watershed in Vermont.The physically based hydrological model (CATchment HYdrology, CATHY) describes three‐dimensional subsurface flow in variably saturated porous media and surface routing on hillslopes and in stream channels, whereas the land surface model (LSM), an augmented version of Noah LSM with multiple parameterization schemes (NoahMP), accounts for energy, water, and carbon flux exchanges between various land surface elements and the atmosphere. CATHY and NoahMP are coupled through exchanges of water fluxes and states. In the energy‐limited catchment of the Sleepers River watershed, where snowmelt runoff generation is the dominant hydrologic flux, the coupled CATHY/NoahMP model at both 90 and 30‐m surface grid resolutions, with minimal calibration, performs well in simulating the observed snow accumulation, and melt and subsequent snowmelt discharge. The Nash–Sutcliffe model efficiency of daily discharge is above 0.82 for both resolutions. The simulation at 90‐m resolution shows a marginal improvement over that at 30‐m resolution because of more elaborate calibration of model parameters. The coupled CATHY/NoahMP also shows a capability of simulating surface‐inundated area and distributed surface water height, although the accuracy of these simulations needs further evaluation. The CATHY/NoahMP model is thus also a potentially useful research tool for predicting flash flood and lake dynamics under climatic change. Copyright © 2013 John Wiley & Sons, Ltd.

Assessment of hydrokinetic energy near Rose Dhu Island, Georgia

The presented study reports on numerical simulations of flows in tidal channels near Rose Dhu Island, GA, which is used to identify hotspots of hydrokinetic energy and to assess the tidal stream energy potential at this site. The numerical simulations are complemented with field measurements of local current velocities and water surface heights, which are used to validate the simulations. Both velocity distributions and water surface heights as predicted by the numerical model are in good agreement with observed data. The simulations reveal a tidal asymmetry in the encompassing Ogeechee estuary with the ebb tide currents dominating over the flood tide ones. The model is able to successfully predict the distribution of discharge into the smaller creeks around Rose Dhu Island and thereby capturing the location of local hotspots of hydrokinetic energy. It is found that local hotspots do exist near the island, and the analysis suggests the maximum available annual power of 4.75 MW, with a peak estimated extraction surpassing 4 KW during Spring tides.

Nitrogen Removal Capacity in Horizon Subsurface Flow and Vertical Flow Constructed Wetland in Relation to Operational Mode

Two laboratory scale constructed wetlands were designed as horizon subsurface flow constructed wetland (HFCW) and vertical flow constructed wetland (VFCW) and were utilized to study the treatment capacity to reduce nitrogen. According to different inflow concentration and height of water surface, HFCW was analyzed in two operational modes and VFCW in four operational modes. The semi-submerged VFCW had the best capacity to remove nitrogen and the total nitrogen removal rate reached to 92% and the removal rate of HFCW was 90%. Moreover, the un-submerged VFCW could reduce 93% ammonia but nitrate removal rate just was 9%. And the removal rates of NH4+-N, NO3--N and TN respectively were 85%, 80% and 81% in submerged VFCW.

Flood flows and channel conveyance in the Athabasca River Delta, Canada

Channel conveyance, channel size and water levels in the Athabasca River Delta were investigated in detail during three summer seasons. The Athabasca Delta is between 58°N and 59°N, in Alberta, Canada, and is formed immediately upstream of where the river enters Lake Athabasca. Ice-free flow rates in the river and in the various distributary channels were measured by acoustic Doppler profiler, and water surface elevations by differential GPS and pressure transducer recorders. Approximate values were measured for river bank heights, and a profile of elevation for the river bank for a distance of 80 km upstream of the lake was established. Computed bankfull flows for cross-sections starting at the delta apex were found to reduce significantly in the downstream direction. High values for bankfull conveyance at the head of the delta, equivalent to 50-year return period flood flows, were noted. For medium Athabasca River flows (about 800–1100 m3/s), a comparison was made of water surface elevations at the delta apex during the survey, and data from 1971. A significant increase of water surface height for the same flow rate, by as much as 0.8 m, is apparent, indicating rapid channel aggradation.

Wetland hydrologic application of satellite altimetry – A case study in the Poyang Lake watershed

Hydrologic variation affects many functions of wetlands. Rapidly and accurately measuring hydrologic dynamics in a wetland watershed has become a fundamental need for estimating functional changes of wetlands. The satellite altimeters have become good data sources that can complement the measurements of gauge stations. As a case project applied in the Poyang Lake watershed, this study has developed a technical approach that integrates the altimeter measurements with the in situ water level data. The derived water surface heights with Envisat RA-2 data are compared with the daily observations of in situ water levels. The average absolute observation difference between the “altimeter station” and its nearest gauge station is 0.307 m, which is comparable to the average differences among the gauge stations. The results suggest that the derived water surface heights from the altimeter data have a good accuracy, which can be used along with the in situ observations as supplements to fill the ungauged area in Poyang Lake wetlands.

Triangulation methods for height profile measurements on instationary water surfaces

The precise measurement of water surface models or profiles plays an important role in experimental hydromechanics. Conventional gauge-based techniques often come with a large instrumental effort and a limited spatial resolution. The paper shows an e‰cient non-contact photogrammetric technique for the measurement of water-surface profiles, which is based on an extension of the well-known laser light sheet projection technique. While the original laser lightsheet triangulation technique is limited to surfaces with di¤use reflection properties, the developed technique is capable of measuring on reflecting instationary surfaces. This article presents the basic principle, potential and limitations of the method. Several evolution steps of the system with di¤erent applicability and di¤erent complexity are shown. A double projection plane system capable of simultaneously measuring water surface height and tilt profiles marks the ceiling of the development. Besides the geometrical models of different levels of complexity, system calibration procedures are described. The applicability of the techniques and their accuracy potential are shown in several practical tests.

Multi‐sensor analysis of water storage variations of the Caspian Sea

We perform a multi‐sensor analysis of water storage and surface height variations of the Caspian Sea, from mid‐2002 through 2006. Data from three satellite missions (GRACE, Jason‐1, and Aqua) are used to examine the relationship between changes in spatially averaged sea surface height (SSH) and water storage in and around the Caspian Sea. Two composite time series are constructed to represent the mass change signal, the first by removing a model of nearby hydrological signals from the GRACE time series, and the second by subtracting a MODIS SST‐based estimate of thermal expansion from the Jason‐1 time series. The composite time series agree well (rms difference = 5.2 cm), and a positive trend is seen in both the GRACE (4.5 ± 0.7 cm/yr) and Jason (3.2 ± 0.3 cm/yr) composite time series. This analysis provides an indirect means of validating these data at regional spatial and monthly temporal scales.

Mariotte Bottle with Side Openings

One of the applications of Bernoulli's equation studied in introductory physics courses is that of a liquid, such as water, flowing from an opening in the side of an open tank. The speed of the escaping water is variable: it depends on the height of the free water surface above the opening, and this speed will decrease as the water level drops.

A model of subaqueous sedimentation at the margin of the Late Midlandian Irish Ice Sheet, Connemara, Ireland, and its implications for regionally high isostatic sea-levels

The geomorphology and sedimentology of a series of Late Midlandian glacigenic sites in Connemara, western Ireland, are described and a set of commonly occurring sedimentary assemblages identified. These form components of a simple model of ice-contact subaqueous sedimentation involving progressive down current transition from subglacial esker tunnel fill, through proximal tunnel-mouth fans, proximal and distal subaqueous fans into basin floor sediments. In two of the sites aggradation to the water-line passes into fan-delta topsets and foresets. All sites abut into inferred water bodies to their west and imply minimum water-surface heights of between 35 and 65 m Irish OD or, in the case of the two deltaic sites, shoreline heights of between 75 and 80 m. These high water levels, very close to, and facing directly into, the immediately adjacent open Atlantic Ocean are difficult to explain as ice-dammed glaciolacustrine water bodies without invoking improbable ice-sheet marginal geometries. They may, however, be explained as a set of successive ‘fjord-head’ grounding-line depositional systems that trace temporary still-stands in the phased retreat of the Irish Ice Sheet from its offshore maximum. This possibility, not yet confirmed by the discovery of in situ marine fauna, implies a degree of Late Midlandian isostatic depression and subsequent response unexplained by currently applied crustal response models but supported by previously constructed glacio-sedimentary models.

Higher-order Boussinesq equations for two-way propagation of shallow water waves

Standard perturbation methods are applied to Euler's equations of motion governing the capillary-gravity shallow water waves to derive a general higher-order Boussinesq equation involving the small-amplitude parameter, α = a / h 0 , and long-wavelength parameter, β = ( h 0 / l ) 2 , where a and l are the actual amplitude and wavelength of the surface wave, and h 0 is the height of the undisturbed water surface from the flat bottom topography. This equation is also characterized by the surface tension parameter, namely the Bond number τ = Γ / ρ g h 0 2 , where Γ is the surface tension coefficient, ρ is the density of water, and g is the acceleration due to gravity. The general Boussinesq equation involving the above three parameters is used to recover the classical model equations of Boussinesq type under appropriate scaling in two specific cases: (1) | 1 3 − τ | ≫ β , and (2) | 1 3 − τ | = O ( β ) . Case 1 leads to the classical (ill-posed and well-posed) fourth-order Boussinesq equations whose dispersive terms vanish at τ = 1 3 . Case 2 leads to a sixth-order Boussinesq equation, which was originally introduced on a heuristic ground by Daripa and Hua [P. Daripa, W. Hua, A numerical method for solving an illposed Boussinesq equation arising in water waves and nonlinear lattices, Appl. Math. Comput. 101 (1999) 159–207] as a dispersive regularization of the ill-posed fourth-order Boussinesq equation. The relationship between the sixth-order Boussinesq equation and fifth-order KdV equation is also established in the limiting cases of the two small parameters α and β.

A105 水面反射光を用いた波面計測法

The reflected light image method has been developed to measure unsteady wave height distributions. In this method, the gradient vector distribution of water surface height can be obtained through image analysis. And the wave height distribution can be reconstructed from the measured gradient distribution and a known height at one point. In this paper, we made the following modifications to measure the waves around a model ship :(i) Formulation errors in calculating gradient are modified, (ii) Random pattern and grid pattern are used as the reference images, (iii) A new technique to reconstruct height from gradient is applied. Direct cross correlation method is applied to image tracking. But in the case of a wave having large surface curvature, a point in the reference pattern corresponds to several points in the deformed surface image, therefore we used grid pattern as a reference image and tracked the grid points manually.

Seasonal change in the extent of inundation on floodplains detected by JERS-1 Synthetic Aperture Radar data

Two sets of JERS-1 (Japanese Earth Resource Satellite–1) Synthetic Aperture Radar (SAR) data, coupled with ancillary datasets, were analysed in an effort to find a single algorithm to study the extent of inundation and its variation on floodplains at a regional scale. The SAR data were acquired on 14 January, 1993 and 9 August, 1994. The study area was ca 14 212 km2, covering the lower portions of the Cape Fear, Lumber, Little Pee Dee and Waccamaw river basins within the states of North Carolina and South Carolina, USA. The analysis was based on the decision tree classification that classifies the study area into three aquatic categories, water, marsh and flooded forest, and two upland classes, field and non-flooded forest. From January 1993 to August 1994, the aquatic extent varied from 4872 km2 to 3496 km2, and upland 9340 km2 to 10 717 km2. The decrease of the water, marsh and flooded forest categories and the increase of the field and non-flooded forest classes were mainly caused by falls in water surface heights and discharges of the rivers and their tributaries from January 1993 to August 1994. The overall classification accuracy was near to 90%. The search for the single algorithm ended with promising results and also prompted additional research.

Critical hydrologic conditions for overflow burst of moraine lake

Floodwater and debris flow caused by glacial lake burst is an important land process and a serious mountain disaster in glacial area of Xizang (Tibet) Autonomous Region, and the overflow burst is mainly caused by glacial landslide falling into moraine lake. On the premise that moraine lake is full, instantaneous burst in part of the lake bank happens, as flow velocity at burst mouth caused by overflow head is higher than threshold flow velocity of glacial till. Under some supposes, d(90) and d(10) of the glacial till in the hank were used as the threshold sizes of coarse and fine grains respectively. Thus, the formula of calculating threshold flow velocity of uniform sand was simplified, and threshold flow velocity of glacial till was calculated with the formula. Then, with synthesis formula calculating flow velocity of instantaneous part burst, flow velocity at overflow burst mouth was calculated, and calculation formula of critical height (H(0)) of overflow head was derived. Overflow head was caused by volume and surge of glacial landslide falling into moraine lake, calculation formulas of ascendant height (H(1)) of lake water surface and surge height (H(2)) on burst mouth caused by glacial landslide falling into moraine lake were derived. To sum up, critical hydrologic conditions of moraine lake burst with overflow form are: the burst is inevitable as H(1) > H(0); the burst is possible as H(1) H(0); the burst is impossible as (H(1)+H(2)) < H(0). In the factors influencing the burst critical conditions, it is advantageous for the burst that scale of the lake is 10(5)m(2) range; terminal glacial till is more fine and is even more uniform; the width of overflow mouth is even smaller than the length of the bank; the landslide has large scale and steep slip surface; and glacial end is close to the lake. With burst of Guangxiecuo Lake in Midui Valley of the Polongzangbu River in Xizang as an example, the burst critical conditions were tested.

Spatial and temporal analysis of vegetation mosaics for conservation: poor fen communities in a Cornish valley mire

AbstractAim Biogeographers increasingly realize the importance of seeing plant communities as spatial mosaics and understanding the spatial and temporal heterogeneity of a site is often a key to successful conservation. The aim of this paper is to examine the approaches to the description and analysis of spatial and temporal variation in sub‐communities within patch mosaics of vegetation in order to inform conservation management. The activities of the tin streaming industry in Cornwall over the last century have created a highly varied mosaic of poor fen vegetation on Goss Moor National Nature Reserve (NNR). The wetland mosaics comprise dry hummocks and different sized wet pools. The size and depth of the pools determines the rate and type of vegetation that develops, as does the nature of boundary or edge. The ergodic hypothesis is used to describe the various plant sub‐communities and their boundaries to identify pathways of hydroseral succession. A further aim was to test the use of Ellenberg Indicator (EI) values as a tool for the rapid description of spatial and temporal environmental change on wetland sites with a view to their management.Location Goss Moor National Nature Reserve, Cornwall, UK.Methods An extensive survey of the whole wetland complex was undertaken to identify patches of poor fen vegetation containing Potentilla palustris (L.) Scop. and Menyanthes trifoliata L. At each patch, species abundance data were collected as well as associated environmental information such as depth of the organic layer and standing water depth, patch location, patch size and boundary type. The plant sub‐communities present were defined using techniques of numerical classification [two‐way indicator species analysis (twinspan)] and ordination [detrended correspondence analysis (DCA)] and these were ordered using the ergodic hypothesis in order to characterize the stages of the hydrosere. Floristic and environmental relationships were examined using canonical correspondence analysis (CCA). Further environmental differences between the poor fen sub‐community types were characterized by weighted EI values for acidity (R), moisture (F), nitrogen (N) and light (L).Results and conclusions Twelve poor fen sub‐community types were described and found to be distributed along a primary environmental gradient of organic matter depth, surface water height and bare substrate. Separation of the poor fen communities by a moisture gradient was considered as spatial evidence for hydroseral succession, which begins with the colonization of open‐water pools created by tin excavations. High water levels were associated with the swamp communities, increased organic depth was associated with poor fen, and the type of boundary was shown to affect the resulting community composition. Weighted Community Ellenberg Indicator values for nitrogen, light, reaction and moisture are recommended as an effective tool for indicating differences between plant (sub‐)communities. The importance of examining sub‐community mosaics in the study of hydroseral development is stressed and the manner in which both sets of information may be used to underpin the conservation management of the site is demonstrated.

A class of model equations for bi-directional propagation of capillary–gravity waves

A class of model equations that describe the bi-directional propagation of small amplitude long waves on the surface of shallow water is derived from two-dimensional potential flow equations at various orders of approximation in two small parameters, namely the amplitude parameter α=a/h0 and wavelength parameter β=(h0/l)2, where a and l are the actual amplitude and wavelength of the surface wave, and h0 is the height of the undisturbed water surface from the flat bottom topography. These equations are also characterized by the surface tension parameter, namely the Bond number τ=Γ/ρgh02, where Γ is the surface tension coefficient, ρ is the density of water, and g is the acceleration due to gravity.The traveling solitary wave solutions are explicitly constructed for a class of lower order Boussinesq system. From the Boussinesq equation of higher order, the appropriate equations to model solitary waves are derived under appropriate scaling in two specific cases: (i) β≪(1/3−τ)⩽1/3 and (ii) (1/3−τ)=O(β). The case (i) leads to the classical Boussinesq equation whose fourth-order dispersive term vanishes for τ=1/3. This emphasizes the significance of the case (ii) that leads to a sixth-order Boussinesq equation, which was originally introduced on a heuristic ground by Daripa and Hua [Appl. Math. Comput. 101 (1999) 159] as a dispersive regularization of the ill-posed fourth-order Boussinesq equation.

Surface water dynamics in the Amazon Basin: Application of satellite radar altimetry

Satellite radar altimetry has the ability to monitor variations in surface water height (stage) for large wetlands, rivers, and associated floodplains. A clear advantage is the provision of data where traditional gauges are absent. As part of an international program, a complete altimetric analysis of the Amazon Basin is being undertaken. Here, an updated and more rigorous evaluation of the TOPEX/POSEIDON (T/P) data set is presented for the first ∼7.5 years of the mission. With an initial study group of 230 targets, height variability at many ungauged locations can be observed for 30–50%, the range reflecting the clarity of the variations in lieu of instrument limitations. An assessment of the instrument performance confirms that the minimum river width attainable is ∼1 km in the presence of some inundated floodplain. This constraint does allow observation of the main stem (Solimões/Amazon) and the larger tributaries, but rugged terrain in the vicinity of the target additionally places severe limitations on data retrieval. First‐order validation exercises with the deduced 1992–1999 time series of stage fluctuations reveal accuracies ranging from tens of centimeters to several meters (mean ∼1.1 m rms). Altimetric water levels in the Solimões and Amazon are particularly well defined with amplitudes &lt;13 m and variations in peak‐level timing from May to July. The water‐surface gradient of the main stem is found to vary both spatially and temporally, with values ranging from 1.5 cm/km downstream to 4.0 cm/km for more upstream reaches. In agreement with ground‐based estimates, the seasonal variability of the gradients reveals that the hysteresis characteristic of the flood wave varies along the main stem and the derived altimetric velocity of this flood wave is estimated to be ∼0.35 m/s. Overall, the altimetric results demonstrate that the T/P mission is successfully monitoring the transient flood waves of this continental‐scale river basin.