Floodplains are composed of complex depositional patterns of ancient and recent stream sediments, and research is needed to address the manner in which coarse floodplain materials affect stream–groundwater exchange patterns. Efforts to understand the heterogeneity of aquifers have utilized numerous techniques typically focused on point-scale measurements; however, in highly heterogeneous settings, the ability to model heterogeneity is dependent on the data density and spatial distribution. The objective of this research was to investigate the correlation between broad-scale methodologies for detecting heterogeneity and the observed spatial variability in stream/groundwater interactions of gravel-dominated alluvial floodplains. More specifically, this study examined the correlation between electrical resistivity (ER) and alluvial groundwater patterns during a flood event at a site on Barren Fork Creek, in the Ozark ecoregion of Oklahoma, USA, where chert gravels were common both as streambed and as floodplain material. Water table elevations from groundwater monitoring wells for a flood event on 1–5 May 2009 were compared to ER maps at various elevations. Areas with high ER matched areas with lower water table slope at the same elevation. This research demonstrated that ER approaches were capable of indicating heterogeneity in surface water–groundwater interactions, and that these heterogeneities were present even in an aquifer matrix characterized as highly conductive. Portions of gravel-dominated floodplain vadose zones characterized by high hydraulic conductivity features can result in heterogeneous flow patterns when the vadose zone of alluvial floodplains activates during storm events. EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen
Streambank retreat is a complex cyclical process involving subaerial processes, fluvial erosion, seepage erosion, and geotechnical failures and is driven by several soil properties that themselves are temporally and spatially variable. Therefore, it can be extremely challenging to predict and model the erosion and consequent retreat of streambanks. However, modeling streambank retreat has many important applications, including the design and assessment of mitigation strategies for stream revitalization and stabilization. In order to highlight the current complexities of modeling streambank retreat and to suggest future research areas, this paper reviewed one of the most comprehensive streambank retreat models available, the Bank Stability and Toe Erosion Model (BSTEM), which has recently been integrated with several popular hydrodynamic and sediment transport models including the Hydrologic Engineering Centers River Analysis System (HEC-RAS). The objectives of this paper were to: (i) comprehensively review studies that have utilized BSTEM and report their findings, (ii) address the limitations of the model so that it can be applied appropriately in its current form, and (iii) suggest directions of research that will help make the model a more useful tool in future applications. The paper includes an extensive overview of peer reviewed studies to guide future users of BSTEM. The review demonstrated that the model needs further testing and evaluation outside of the central United States. Also, further development is needed in terms of accounting for spatial and temporal variability in geotechnical and fluvial erodibility parameters, incorporating subaerial processes, and accounting for the influence of riparian vegetation on streambank pore-water pressure dynamics, applied shear stress, and erodibility parameters.
Abstract Flume tests and in situ jet erosion tests (JETs) allow for the process‐based quantification of erodibility parameters of cohesive soils. In the excess shear stress model used to predict soil detachment, the critical shear stress (τ c ) corresponds to the stress at which fluvial forces can detach soil particles or aggregates and the erodibility coefficient ( k d ) governs the rate at which detachment occurs when the imposed shear exceeds τ c . The primary objective of this research was to derive and compare erodibility parameters from flume tests and JETs on various root‐permeated soil samples. Based on statistical analysis, erodibility coefficients from the flume tests were typically statistically similar to those derived with JETs. In order to further determine the capability of the JET to indicate differences in erodibility of root‐permeated soils, this research then performed JETs on side‐by‐side in situ soils. The JETs on root‐permeated soils estimated significantly higher τ c but insignificant differences in k d compared to JETs on adjacent bare soil. A significant correlation was observed between exposed root surface area (TRSA) and τ c , but no correlation between TRSA and k d or the equilibrium scour depth was observed. More flume and JET experiments are needed to clarify the relationship between root‐permeated soils and erodibility parameters, and address a wider range of average root diameters than was considered in this research.
The study region is the state of Oklahoma, USA, which has a varied climate. Precipitation increases west to east, and temperature decreases south to north across the state. Accordingly, Oklahoma has been divided into nine Climate Divisions, which reflect those climatic as well as regional differences in agricultural practices. Surface water is the dominant source for public water systems in Oklahoma and these supplies may be impacted by drought or climatic change. Hydrologic modeling is an important component of water resource planning, but may be beyond the budget of smaller communities. To create a freely available tool for initial assessment of drought streamflows, this study uses publicly available long-term precipitation records for climate divisions in Oklahoma to create flow duration curves (FDCs) from the drought-influenced subsets of streamflow records. The FDCs created from those subsets showed increased likelihood of reduced streamflows. The reduced flows were shown to increase water supply risk to run-of-river users. To eliminate the need for users to re-create these analytic steps, study results were compared to published FDCs and reasonable estimates of drought-influenced FDCs were produced by offsetting the expected exceedance by 10%.
The Ozark region of eastern Oklahoma is characterized by limestone and sandstone plateaus partitioned by steep-sided stream valleys and occupied by clear, gravel-bed streams. Alluvial floodplain soils are generally cherty with high hydraulic conductivities. Many areas have alluvial floodplains consisting of a mantle of alluvial soils overlying thick subsoil primarily consisting of gravel. Previous work at a site in eastern Oklahoma found preferential flow of a conservative tracer within the gravel subsoil with an estimated hydraulic conductivity of 140 to 230 m/d. Multi-electrode electrical resistivity imaging (ERI) was used as a non-invasive method to determine the nature and extent of the preferential flow path (PFP). The ERI two-dimensional profile found a highly resistive layer in the area of the PFP. The range of resistance for this area was similar to the resistance found in an ERI survey from the surface of a nearby gravel bar, which strongly suggested that the PFP consists of clean, coarse gravel. This study attempted to determine whether PFPs exist at two other alluvial floodplain sites in the Ozarks with differing catchment areas. Since the factors controlling resistivity are similar to the factors controlling hydraulic conductivity, an association between the two was expected. Borehole permeameter tests, using a system specifically designed for gravelly soils, were used to estimate saturated hydraulic conductivity. An equation was developed between the point-measured hydraulic conductivity and larger-scale electrical resistivity mapping. Limitations in current analytical solutions prevented the estimation of hydraulic conductivity for all tests, primarily due to the rates that were induced on the gravel subsoils.
The HF/DF cw chemical lasers have been stated to yield power levels exceeding 1 MW with acceptable beam quality.Based on these data, we estimate that even the least demanding strategic defense applications require power levels to be increased further by at least a factor of twenty while retaining beam quality.However, the laser geometry which achieved the above demonstration will have scaling problems to higher power levels; thus, the combination of power scaling and adequate beam quality must be explored for some different chemical laser design, yet to be demonstrated;A chemically pumped atomic iodine laser at 1.3 pm has been developed, although at this point only 5 kW of continuous wave power has been demonstrated.Because of atmospheric absorption, the HF laser (A, = 2. 8 p, m) would have to be deployed on space platforms, while the DF laser (A, = 3.8 pm) and the atomic iodine laser (A, = 1.3 p, m) could also operate on the ground.When based in space, chemical lasers face a special set of problems arising from vibrations and the exhaust of the burnt fuel (Section 3.2).We estimate that the pulse energy from excimer lasers for strategic defense applications needs improvement by at least four orders of magnitude over that currently achieved.Many advances are needed to achieve the required repetititve pulsing of these lasers at full scale.Free electron lasers suitable for strategic defense applications, operating riear 1 pm, require validation of several physical concepts. 4.Nuclear-explosion-pumpedx-ray lasers require validation of many of the physical concepts before their application to strategic defense can be evaluated.The free electron laser (FEL) is one of the newest laser technologies to be demonstrated.Peak powers of approximately 1 MW have been produced at a wavelength of 1 pm; peak powers of approximately 1 GW have been produced at a wavelength of 8 mm, demonstrating high gain and high efficiency at that wavelength.Scaling to short wavelengths at high powers is a more difficult technical problem than simply increasing average power.Obtaining high efficiency, high power free electron laser operation at 1 pm requires experimental verification of physical concepts which thus far are only theoretically developed, e.g. , optical guiding and transverse sextupole focusirig for the amplifier configuration, and sideband and harmonic control for the oscillator configuration.We estimate that for strategic defense applications, a groundbased free electron laser should produce an average power level of at least 1 GW at 1 pm wavelength, corresponding to peak powers of 0.1 -1.0 TW (Sections 3.4 and 6.3).The pulsed excimer lasers have demonstrated single pulse energies of about 10 kJ in 1 ps pulses from a single module (Section 3.3).This laser currently uses krypton ' provide a 99.7% availability.By going to seven climatically isolated locations in the continental U.S. , availability of 99.97% is possible.At each of these sites, local cloud cover conditions require further multiplicity of the large ground telescopes, separated by few km (Section 5.4).12. Ground-based laser systems require techniques for correcting atmospheric propagation aberrations.We estimate that these techniques must be extended by at least two orders of magnitude in resolution (number of actuators) than presently demonstrated.Phase correction techniques must be demonstrated at high powers.Ground-based laser systems will require either linear or nonlinear adaptive optics of a very sophisticated nature in order to precompensate the laser beam for Rev. Mod.Phys., Vol. 59, No. 3, Part ll, July 1987 vulnerability as any other space-based components (Section 9.3).shorter ranges than those required for boost phase intercepts (Sections 9.3 and 9.6).23. Survivability of ground-based facilities also raises serious issues.The relatively small number of large facilities associated with ground-based laser sites makes these facilities high-value targets.The ground-based laser B MD facilities must be successfully protected from direct attack from many threats (e.g. , cruise missiles, sabotage, etc.), in addition to ballistic missiles.Thus, any strategic defense system depending on ground-based lasers, or on other ground- based facilities which cannot be extensively proliferated, must be effective in defending against more threats than just ballistic missiles (Section 9.3).24. Directed energy weapons with capabilities below those needed for many ballistic missile defense applications can threaten space-based assets of a defensive system.25. X-ray lasers driven by nuclear explosions would constitute a special threat to space-based sensors, electronics, and optics.The high energy-to=weight ratio of nuclear explosive devices driving the directed energy beam weapons permits their use as "pop-up" devices.For this reason the x-ray laser, if successfully developed, would constitute a particularly serious threat against space- based assets of a BMD (Sections 3.5 and 9.3). CHARTER OF THE STUDYThe American Physical Society recognized that there were considerable uncertainties and differences of opinion among its members concerning the present state of the art of directed energy technologies, as well as the requirements for satisfying various ballistic missile defense missions (boost phase defense, mid-course discrimination, etc.).It, therefore, commissioned a study of the science and technology of directed energy weapons through its Council action on November 20, 1983.By November 1984, a Study Group comprising scientists and engineers from federal laboratories, industrial organizations, and universities had been constituted.Some members of the Ciroup were (and are) actively involved iri directed energy research.The Group was specifically chartered to examine the status of, and requirements for, directed energy weapon technologies, and to document its findings in an unclassified report.Responding to its charter, the Group has focused on the following central theme: perform an in-depth review of the several directed energy weapon technologies and estimate the parameter requirements necessary for accomplishing various future BMD missions.In light of this focus, we do not discuss KEW technologies nor do we address the complex issues associated with battle management and C'I (command, communications, control, and intelligence) including testability and reliability of the software.Also, this report does not address the related issues of arms control and strategic stability.Each of these issues is, however, suSciently important to merit a separate study.This study specifically does not evaluate the current SDI program, but rather establishes a framework which may be helpful to others interested in the evaluation of the DEW component of this program.The Group hopesthat the report which follows will serve as a useful technical reference for members of the APS, and for other scientists and engineers, as well as for a wider audience in order that discussions of the issues related to the Strategic Defense Initiative be better informed.Characteristics of photon beam propagation are described in Chapter 5 which includes the technology of beam control, delivery, and atmospheric beam propagation effects.The basic physical mechanisms by which photon beams and relativistic particle beams can damage targets are described in Chapter 6.The requirement of lethality, that the target be either destroyed or made inoperative, demands that a sum.cient amount of energy and/or power must be delivered to the target.The beams from DEWs must be directed at the targets, i.e. , they must intercept hostile ballistic missiles and/or their payloads.Acquisition, tracking, and discrimination of objects require sensor platforms, radars, and possibly laser and particIe beam tracking and discriminating devices in space.These problems are discussed in Chapter 7. The power requirements for space-based platforms present special problems which are examined in Chapter 8.The important issue of survivability of DEWs is discussed in Chapter 9.It depends sensitively on both device parameters and system architecture.The overall architecture of a defensive system depends heavily on considerations of many factors.These include command, control, communication, and intelligence (C I), hardware and software development and reliability for battle management,the possible inclusion of kinetic energy weapons, etc.The integration of aII these components and systems into an overall system presents extremely challenging problems, some of which are enumerated in Appendix A. A discussion of satellite constellations is presented in Appendix B. The combination of lethality, propagation, and range requirements determines the brightness required for directed energy weapons.For defense of the entire nation, including protection of population centers, via boost phase kill, the brightness requirements exceed by orders of magnitude the present state of the art of various types of lasers, particle beam devices, optical delivery systems, acquisition platforms, power supplies, etc.This is the main thrust of the detailed conclusions of this study which are presented in the Executive Summary. SCOPE OF THE STUDY Followingthis brief overview, the report first describes the targets at which the DEWs would be aimed.Thus, Chapter 2 deals with both the current and responsive missile threat.Next, all major candidates for laser DEWs are discussed in Chapter 3. Detailed technical information is presented for chemical lasers, excimer lasers, and free electron lasers, while only the principles of x-ray lasers are described because of classification restrictions.The state of the art of each and the requirements for DEW devices intended for BMD applications are given.The other category of DEW devices, the relativistic particle beams, is described in Chapter 4 along with their propagation characteristics. PERSPECTl YEThe Group notes that predicting the course of technological progress can be particularly dificult.Very optimistic predictions are often made for technologies or schemes which are at very early stages of development.Whenever orders of magnitude of improvement are necessary in operating parameters, it is likely that many new discoveries and inventions will have to be made.The discrepancy between the present state of the art of DEWs and the ultimate requirements is so large that major gaps in technical understanding must be closed before engineering technology verification could be productive.
