Levee Height Research Articles

Retracted: Levee Layouts and Design Optimization in Protection of Flood Areas

This paper addresses a possible decrease in flood damages by using structural methods and determines proper locations (layout) to construct protective levees and height of levees (design of levees) in high-risk areas. Because of discontinuity of the objective function and a large number of decision variables, the optimization uses the genetic algorithm (GA). The simulation of the region is carried out with the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) model. The GA is employed to maximize the benefit of flood control and also to minimize the cost of protective levees’ construction. Thus, the fitness function of the algorithm maximizes the net benefit of the project. After a sensitivity analysis, mutation and crossover probability are assumed to be 0.03 and 0.7, respectively. Thus, 1,000 generations and 98 chromosomes for each run are considered. The optimization model is run 5 times for floods with return periods of 50 and 100 years. Furthermore, the algorithm is used to evaluate flood damages in the Sarm and Khoor Abad River, located in the Qom province of Iran. Project net benefits resulting from the optimization model for rivers using 100-year flood exceed those for a 50-year flood. Results indicate that construction of protective levees reduces the rate of damages up to 99% in comparison with a nonconstruction of levees scenario. By taking into account the construction cost of levees, net benefits decrease by 0.97% and 1.1% for floods with 50-year and 100-year return periods, respectively.

Continuous deep-seated slope failure recycles sediments and limits levee height in submarine channels

Channel-levee systems are responsible for constructing deep sea fans, among the largest sedimentary deposits on Earth. Levee height plays a key role in defining the volume and texture of the material that is deposited in the bounding levees, and thus the morphology of submarine fans. Models of channel formation and evolution generally assume that the levees aggrade in response to the cumulative overspill of turbidity flows, and that their height is controlled by these flows. In contrast, we show that levee growth in the Ursa Basin (Gulf of Mexico) is limited by the mechanical strength of the levee, not the flow behavior. While many studies document sidewall failures in levee systems, our poro-mechanical model is the first to demonstrate that collapse of levees is a large-scale, deep-seated process driven by the interaction of levee formation and high fluid pressure. Rapid deposition of a regional sand unit induced large fluid overpressure in the underlying mud, which preconditioned the system for levee failure, which then fed a large volume of sediment back into the channel-levee system. Long-lived levee failures continually reintroduced previously deposited levee material back into the channel system. This implies that a large volume of sediment is continuously recycled, which has not been previously understood. Turbidite flow models generally assume that flows progressively lose their fine-grained component due to levee overspill as they traverse the channel. In contrast, we show a mechanism by which fine-grained material can re-enter the system in large quantities, and this has significant and broad importance for models of channel and fan evolution. We also show that that levee failure introduces significant unconformities, in contrast with the common assumption that levees offer complete and high-resolution records of climate, tectonics, and sea level.

홍수범람지도 작성을 위한 GIS기반 1차원 동역학적 해석 기법

홍수는 한 국가의 발전에 영향을 미칠 수 있는 주요 자연재해 중 하나이다. 세계 각국에서는 댐, 저류지, 제방 등과 같은 수공 구조물의 설계빈도를 초과하는 이상 홍수가 발생할 경우에 대비하여 비구조적 대책의 일환으로 홍수범람지도를 작성하고 있다. 본 연구는 댐 붕괴에 대한 1차원 하천수리해석 모형(DAMBRK)과 GIS를 연계한 홍수범람지도 작성 방법에 관해 보여준다. 이를 위해 여러 가지의 댐 붕괴 시나리오에 따라 붕괴유출량을 산정하고, 이 중 가장 극한조건에 대한 하류부 홍수추적을 통해 하류부 주요지점별 첨두유량, 최고홍수위, 홍수파 도달시간, 최고홍수위 도달시간을 산정하고 최고홍수위와 좌 우 제방고도 비교한다. 그리고 이러한 하천수리해석 결과를 GIS를 연계하여 수심별 홍수범람지도를 작성하는 방법에 관해 상세하게 보여준다. 본 연구에서 제안한 홍수범람지도 작성방법은 홍수터 해석에 대해 1차원 하천수리해석 모형이 가지는 한계점을 보완할 수 있다. Flooding as one of the major natural disasters affects country's economy. Most country is establishing a flood inundation maps as a non-structural measures to prevent damages from an abnormal flooding over the design criteria of hydraulic structures such as dams, storages, and levees et al. This study suggests method to establish GIS based inundation map induced by dam-break flood simulated by 1D hydrodynamic model(DAMBRK). In this study, the dam-break hydrograph were simulated by various scenario events and especially for the extreme event, peak discharge, peak water surface elevation, arrival time of flood wave and peak water surface elevation are calculated by flood routing at the control points and peak water surface elevation was compared with levee height to detect inundation. In addition, the detailed flood inundation mapping processes at each water level linking with GIS are presented in this study. The proposed method to establish a flood inundation map is able to complement the limitation of 1D hydrodynamic model in analyses of flood plains.

Flash flood routing modeling for levee-breaks and overbank flows due to typhoon events in a complicated river system

There has been a yearly increase in precipitation in Taiwan, consistent with trends seen across the world. In the summer and fall, typhoons or tropical cyclones with torrential rainfall frequently occur as a result of Taiwan’s subtropical climate. Flash floods may cause a levee-break and/or the overtopping of banks at narrow neck locations in a river system, which may in turn produce inundation in urban areas. Therefore, a model that predicts flash floods is of vital importance for river management. The present study is based on a flash flood routing model, which incorporates levee-break and overbank functions to calculate the discharge hydrographs in the complicated Danshuei River system of northern Taiwan. The numerical model was calibrated and verified against observed water stages using three typhoon events. The results indicate reasonable agreement between the model simulations and the observed data. The model was then used to calculate the levee-break and overbank flow hydrographs due to Typhoon Talim (2005) and Typhoon Nari (2001), respectively. The simulated results indicate that several parameters significantly affect the flow hydrograph during a levee-break and should be carefully monitored when levee-break events occur in the river system. The simulated water stages at several stations are consistent with observed data from Typhoon Nari. The simulated overbank flow results quantitatively agree with reported information. The data also confirm that most of the overbank events occurred at the upper reaches of the Keelung River, consistent with the low levee height protection.

Turbiditic levee deposition in response to climate changes: The Var Sedimentary Ridge (Ligurian Sea)

The Var turbiditic system located in the Ligurian Sea (SE France) is an intermediate mud/sand-rich system. The particularity of the Var deep-sea fan is its single channel with abrupt bends and its asymmetric and hyper-developed levee on the right hand side: the Var Sedimentary Ridge. Long-term sediment accumulation on the Var Sedimentary Ridge makes this an ideal target for studying the link between onshore climate change and deep-sea turbidite stratigraphy. This paper focuses on the establishment of the first detailed stratigraphy of the levee, which is used to analyze the timing of overbank deposition throughout the last deglaciation. Main results indicate that high variability in turbidite frequencies and deposition rates along the Var Sedimentary Ridge are determined by two main parameters: 1) the progressive decrease of the levee height controlling the ability of turbidity currents to spill out from the channel onto the levee, and 2) climatic variations affecting the drainage basin, in particular changes in glacial condition since late Last Glacial Maximum to early Holocene. Compared to other deep-water areas, this study confirms the ability of turbiditic systems to record past climatic events on millennial timescales, and underlines the influence of European deglaciation on the observed decrease in turbidite activity in the Var canyon. The presence of a very narrow continental shelf and a single, large channel-levee system makes the Var Sedimentary Ridge a unique example of climate-controlled turbiditic accumulations.

Case Study: Flood Mitigation of the Muda River, Malaysia

The 2003 flood of the Muda River reached 1,340 m3/s at Ladang Victoria and adversely impacted 45,000 people in Malaysia. A flood control remediation plan proposed a levee height based on a 50-year discharge of 1,815 m3/s obtained from hydrologic models. This design discharge falls outside the 95% confidence intervals of the flood frequency analysis based on field measurements. Instream sand and gravel mining operations also caused excessive riverbed degradation, which largely off sets apparent benefits for flood control. Pumping stations have been systematically required at irrigation canal intakes. Several bridge piers have also been severely undermined and emergency abutment protection works were needed in several places. Instream sand and gravel mining activities should be replaced with offstream mining in the future.

Formation and maintenance of single‐thread tie channels entering floodplain lakes: Observations from three diverse river systems

Tie channels connect rivers to floodplain lakes on many lowland rivers and thereby play a central role in floodplain sedimentology and ecology; yet they are generally unrecognized and little studied. Here we report the results of field studies focused on tie channel origin and morphodynamics in the following three contrasting systems: the Middle Fly River (Papua New Guinea), the Lower Mississippi River, and Birch Creek in Alaska. Across these river systems, tie channels vary by an order of magnitude in size but exhibit the same characteristic morphology and appear to develop and evolve by a similar set of processes. In all three systems, the channels are characterized by a narrow, leveed, single‐thread morphology with maximum width approximately one tenth the width of the mainstem river. The channels typically have a V‐shaped cross section, unlike most fluvial channels. These channels develop as lakes become isolated from the river by sedimentation. Narrowing of the connection between river and lake causes a sediment‐laden jet to develop. Levees develop along the margins of the jet leading to channel emergence and eventual levee aggradation to the height of the mainstem levees. Bidirectional flow in these channels is common. Outflows from the lake scour sediment and prevent channel blockage. We propose that channel geometry and size are then controlled by a dynamic balance between channel narrowing by suspended sediment deposition and incision and widening by mass failure of banks during outflows. Tie channels are laterally stable and may convey flow for hundreds to a few thousand of years.

Construction dynamics of a lava channel

We use a kinematic GPS and laser range finder survey of a 200 m-long section of the Muliwai a Pele lava channel (Mauna Ulu, Kilauea) to examine the construction processes and flow dynamics responsible for the channel–levee structure. The levees comprise three packages. The basal package comprises an 80–150 m wide ′a′a flow in which a ∼2 m deep and ∼11 m wide channel became centred. This is capped by a second package of thin (<45 cm thick) sheets of pahoehoe extending no more than 50 m from the channel. The upper-most package comprises localised ′a′a overflows. The channel itself contains two blockages located 130 m apart and composed of levee chunks veneered with overflow lava. The channel was emplaced over 50 h, spanning 30 May–2 June, 1974, with the flow front arriving at our section (4.4 km from the vent) 8 h after the eruption began. The basal ′a′a flow thickness yields effusion rates of 35 m3 s−1 for the opening phase, with the initial flow advancing across the mapped section at ∼10 m/min. Short-lived overflows of fluid pahoehoe then built the levee cap, increasing the apparent channel depth to 4.8 m. There were at least six pulses at 90–420 m3 s−1, causing overflow of limited extent lasting no more than 5 min. Brim-full flow conditions were thus extremely short-lived. During a dominant period of below-bank flow, flow depth was ∼2 m with an effusion rate of ∼35 m3 s−1, consistent with the mean output rate (obtained from the total flow bulk volume) of 23–54 m3 s−1. During pulses, levee chunks were plucked and floated down channel to form blockages. In a final low effusion rate phase, lava ponded behind the lower blockage to form a syn-channel pond that fed ′a′a overflow. After the end of the eruption the roofed-over pond continued to drain through the lower blockage, causing the roof to founder. Drainage emplaced inflated flows on the channel floor below the lower blockage for a further ∼10 h. The complex processes involved in levee–channel construction of this short-lived case show that care must be taken when using channel dimensions to infer flow dynamics. In our case, the full channel depth is not exposed. Instead the channel floor morphology reflects late stage pond filling and drainage rather than true channel-contained flow. Components of the compound levee relate to different flow regimes operating at different times during the eruption and associated with different effusion rates, flow dynamics and time scales. For example, although high effusion rate, brim-full flow was maintained for a small fraction of the channel lifetime, it emplaced a pile of pahoehoe overflow units that account for 60% of the total levee height. We show how time-varying volume flux is an important parameter in controlling channel construction dynamics. Because the complex history of lava delivery to a channel system is recorded by the final channel morphology, time-varying flow dynamics can be determined from the channel morphology. Developing methods for quantifying detailed flux histories for effusive events from the evidence in outcrop is therefore highly valuable. We here achieve this by using high-resolution spatial data for a channel system at Kilauea. This study not only indicates those physical and dynamic characteristics that are typical for basaltic lava flows on Hawaiian volcanoes, but also a methodology that can be widely applied to effusive basaltic eruptions.

Up or Out?—Economic-Engineering Theory of Flood Levee Height and Setback

Levee setback location and height are important issues in flood levee system design and modification. This paper derives an economic-engineering theory of the optimal trade-off of levee setback for height both for original and redesigned flood levees, demon- strating the interconnection of levee setback, height, costs and risks, and economically optimal design. These analyses assume stationary flood hydrology and static ratios among damageable property value, unit construction cost, and land price. The economic trade-off of levee setback for height depends on economic cost and benefit and hydraulic parameters, and only indirectly on flood frequency and economic damage parameters. The redesign rules derived in this paper indicate conditions where existing levees should be raised or moved in response to changes in conditions. Numerical examples illustrate the results. This paper demonstrates several ideas and theory for economic flood levee system planning and policy rather than providing guidelines for direct design practice.

The shape of submarine levees: exponential or power law?

Field observations indicate that the height of submarine levees decays with distance from the channel either exponentially or according to a power law. This investigation clarifies the flow conditions that lead to these respective shapes, via a shallow water model for the overflow currents that govern the levee formation. The model is based on a steady state balance of sediment supply by the turbidity current, and sediment deposition onto the levee, with the settling velocity and the entrainment rate appearing as parameters. It demonstrates that entrainment of ambient fluid is the determining factor for the levee shape. For negligible entrainment rates, levee shapes tend to exhibit exponential profiles, while constant rates of entrainment or detrainment result in power law shapes. Interestingly, whether a levee has an exponential or a power law shape is determined by kinematic considerations only, viz. the balance laws for sediment mass and fluid volume. We find that the respective coefficients governing the exponential or power law decay depend on the settling speeds of the sediment grains, which in turn is a function of the grain size. Two-dimensional, unsteady Navier–Stokes simulations confirm the emergence of a quasi-steady state. The depositional behaviour of this quasi-steady state is consistent with the predictions of the shallow water model, thus validating the assumptions underlying the model, and demonstrating its predictive abilities.

Evaluation of paddy water storage dynamics during flood period in South Korea

A daily paddy water balance model was developed using four years (1996–1997 and 2001–2002) field experimentals data of two locations. The model could simulate the actual daily ponding depth of paddy pretty well by treating paddy levee height and threshold ponding depth indicating irrigation time as ten days average parameters of the model with 0.76 four year average Nash-Sutcliffe efficiency. The amount ranging from 425.1 mm in 1996 to 850.8 mm in 2002. The storage ratio (amount of storage divided by rainfall) linearly decreased as total rainfall amount increased within the range of observed rainfall. From the model application, direct seeding type was more favorable to store rainfall than transplanting type.

A two‐dimensional hydrodynamic model for flood inundation simulation: a case study in the lower Mekong river basin

AbstractThe lower Mekong basin is frequently affected by floods. Prolonged floods disrupt daily activities and cause huge socio‐economic damage almost every year. An advanced flood warning system could provide achievable non‐structural measures for reducing such damages. With a view to developing an advanced flood warning system, a distributed hydrodynamic modelling approach has been adopted for simulating a flood inundation phenomenon in the lower Mekong basin. A modelling system with a one‐dimensional (1‐D) river flow model and a two‐dimensional (2‐D) surface flow model has been used for simulating flood inundation. In the model, exchange of flows between the river and surface floodplain is calculated through established links, which determine the overflow from river nodes to surface grids or vice versa. These occur due to overtopping or failure of the levee when water height surpasses levee height. The model has incorporated detailed information about urban terrain features like embankments, roads, bridges, culverts, etc. in the simulation. A geographical information system (GIS)‐based comprehensive raster database of different spatial data layers is prepared and used in the model development. An explicit solution scheme is used for numerical computation, which considerably reduces the run time and makes the model suitable for use as a flood warning system in a large river basin. The model simulated results in the lower Mekong basin have shown close alignment with the observed data in terms of water level and discharge in various river gauging stations and flood extents in the floodplain and from the results it can be inferred that the model can predict the magnitude and duration of flood inundation to a reasonable level of accuracy. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Raising the Bar for Levees

Engineers have worked for millennia to control natural flooding through dams and levees. While the fundamental principles and challenges of holding back water have not changed, the tools brought to the task continue to evolve. Among other tools being tested and implemented today are elaborate sensors to detect stresses and strains within structures, and impermeable lining materials known as geomembranes, which are laid underneath the structure before it is built to prevent water seepage.

Morphology of basaltic lava channels during the Mt. Etna September 2004 eruption from airborne laser altimeter data

The morphological features of active lava channels acquired over Mt. Etna by means of airborne laser altimeter data are presented. The data were acquired on 16th September 2004, using an Optech ALTM 3033 laser altimeter. The flight height was about 2000 m above ground. During the flight, the lava, erupted from the eastern part of the Mt. Etna summit area, flowed into the Valle del Bove. The measured morphologic features are: channel width (Wc), flow width (Wf), levee height (Hl), flow thickness (Tf), and channel depth (Dc). The main lava flow shows a well‐developed channel with levees. The average measured values for the morphologic features of this flow are: Wc = 16 m, Wf = 52 m, Hl = 7 m, Tf = 5 m and Dc = 2 m. The Wc parameter shows linear increase from about 7 m near the vent up to about 25 m close to the front (∼1600 m in length).

扇状地水田におけるカエル類の生息量と畦畔環境との対応関係

The research was conducted to clarify relationships between frogs abundance and environments such as arrangement, grass height, and grass coverage of levees around paddy fields in an alluvial fan. Target species ware Rana porosa porosa adults, yearlings, and Hyla japonica yearlings that were widely distributed in study region. Walking on the levees, frogs abundance and the condition of levees were recorded. When a ditch was adjacent to the levees, the environments of ditch were investigated. R. porosa porosa adults were abundant levees where the earth ditch was adjacent, whereas R. porosa porosa yearlings were abundant levees where plant height was low. On the other hand, H. japonica yearlings were abundant levees where a concrete ditch and the woods are adjacent or plant height was high. In the agricultural landscape, It is important to conserve the habitat for R. porosa porosa whose range of environmental preference is narrower than that of H. japonica. We should be conserved the good ditch environments such as the earth ditch with high grass coverage, and clarified the best management practices of levees for frogs.

홍수기 논의 저류량 산정모형 개발 및 적용

논의 수문학적인 거동은 물관리에 따른 담수심 상태, 벼의 생육시기별 물꼬관리에 크게 지배 받는다. 강우사상에 의한 논에서의 저류 및 배수량은 하천유량에 적지 않은 영향을 준다. 본 연구에서는 홍수기 논의 저류효과를 정량적으로 파악하기 위하여 논의 저류량을 모의할 수 있는 일별 물수지 모형을 개발하고, 수원과 여주의 논을 대상으로 4년간(1996, 1997, 2001, 2002) 측정한 자료를 이용하여 모형의 적용성을 검토하였다. 모형에서 물꼬높이와 기준 담수심(관개를 해야하는 한계 달수심)을 10일 단위의 매개변수로 처리하여 일별 담수심을 재현할 수 있었다. 홍수기 논의 저류량은 425.1 mm - 850.8 mm의 강우량 변동폭에 대하여 305.9 mm - 343.6 mm의 상대적으로 작은 저류량 변동폭을 보였다. The hydrologic behavior of paddy field depends largely on the irrigation and levee height management by farmers. The storage and drainage amount of paddy for storm events certainly influences the stream discharge. To understand the paddy storage effect during storm periods, a daily paddy water balance model embedding farmer's water management was developed by using 4 years (1996, 1997, 2001, 2002) field experimental data at 2 locations (Suwon and Yeoju) From the modeling, it was possible to simulate the daily ponding depth of paddy by treating paddy levee height and threshold pending depth indicating irrigation time as 10 days average parameters of the model. The storage amount(306.9 mm to 343.6 mm) showed little deviation to rainfall amount(425.1 mm to 850.8 mm).

STREAM DISCHARGE PREDICTION VIA A GRID BASED SOIL WATER ROUTING WITH PADDY FIELDS1

ABSTRACT: A grid based daily hydrologic model for a watershed with paddy fields was developed to predict the stream discharge. ASCII formatted elevation, soil, and land use data supported by the GRASS Geographic Information System are used to generate distributed results such as surface runoff and subsurface flow, soil water content, and evapotranspiration. The model uses a single flow path algorithm and simulates a water balance at each grid element. A linear reservoir assumption was used to predict subsurface runoff components. The model was applied to a 75.6 km2 watershed located in the middle of South Korea, and observed stream flow hydrographs from 1995 and 1996 were compared to model predictions. The stream flow predictions of 1995 and 1996 generally agreed with the observed flow, resulting in a Nash‐Sutcliffe efficiency R2 of 0.60 and 0.62, respectively. The hydraulic conductivity for percolating water through the saturated layer affected baseflow generation. The levee height of the paddy influenced the time and magnitude of the surface runoff, depending on irrigation management. The model will be used for making low flow management decisions by evaluating the role of each land use to stream flow, especially in case of paddy decrease by gradual urbanization of a watershed.

Local- and watershed-scale controls on the spatial variability of natural levee deposits in a large fine-grained floodplain: Lower Pánuco Basin, Mexico

This study examines spatial variations in natural levee deposits within the lower reaches of a large coastal plain drainage system. The Pánuco basin (98,227 km 2) drains east-central Mexico, and is an excellent setting to examine the influence of watershed and local controls on the morphology and sedimentology of natural levees. Although many fluvial systems in the U.S. Gulf Coastal Plain have been investigated, the rivers in the Mexican Gulf Coastal Plain have received comparatively little attention. Lateral and downstream characteristics of natural levee morphology and sediment texture are considered within the context of meandering river floodplain deposits. Data sources include total-stations surveying, sediment samples of surficial levee deposits, topographic maps (1:50,000), and aerial photographs (1:40,000). The slope of natural levees average 0.0049 m/m, whereas the texture ( D 84) of levee deposits averages 0.12 mm. Natural levee characteristics vary due to local- and watershed-scale controls. The lateral reduction in levee height displays a curvilinear pattern that coincides with an abrupt change in sediment texture. The downstream pattern of natural levee texture exhibits the influence of local-scale perturbations superimposed upon a larger watershed-scale trend. Disruption to the fining trend, either by tributary inputs of sediment or reworking of Tertiary valley deposits, is retained for a limited distance. The influence of the channel planform geometry on levee morphology is examined by consideration of the radius of curvature ( R c) of meander bends, and is inversely related to natural levee width. This suggests that the planform geometry of river channels exerts a control on the dispersal of flood sediments, and is responsible for considerable local variability in the floodplain topography. The average width of natural levees increases with drainage area, from an average of 747 m in the Moctezuma to an average of 894 m in the Pánuco. However, in the lower reaches of the Pánuco valley the width of natural levees rapidly decreases, which is associated with fining of the suspended sediment load. Thus, the reduction in natural levee width signifies an abrupt change in the directionality of cause–effect relationships at the watershed-scale. Findings from this study elucidate linkages between meandering river channels and floodplains for a large lowland alluvial valley.

Potential benefits of increased application of water to paddy fields in Taiwan

AbstractThe potential benefits of increased application of water to paddy fields in Taiwan are investigated in this paper. A conceptual model is used to represent the hydrological system of the paddy field. A technique is presented to estimate the parameters of the model. Field experiments also are performed for parameter estimation and model verification. The simulated results are in good agreement with the observed during model verification. With parameters estimated from the field data, the model is used to simulate the effects of applying water beyond current practice. The simulation results show that the downward percolation increases when the irrigation water increases. However, the percolation reaches a capacity rate no matter how large the amount of water applied. This phenomenon results from the existence of a hard layer below the paddy field. The effects of raising the height of levees around paddy fields are also studied. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Interpreting avulsion process from ancient alluvial sequences: Guadalope-Matarranya system (northern Spain) and Wasatch Formation (western Colorado)

Alluvial deposits of the Guadalope-Matarranya system (Oligocene, Ebro basin, Spain) and the Wasatch Formation (Eocene, western Colorado), provide time-integrated records of the process of river-channel avulsion. These sequences consist of isolated channel-belt sandstones incised into, and abruptly overlain by, flood-plain siltstones, indicating deposition by avulsive river systems. The geometry and distribution of channel incisions suggest that avulsion was not controlled by tectonics, climate, or base-level changes, but formed by autocyclic processes. Measurements from 221 channel fills in the Guadalope-Matarranya system and 38 from the Wasatch Formation allow us to statistically characterize channel geometries we infer to be associated with establishment and abandonment of individual river avulsions. Paleoflow depths in both systems average 1.4 to 1.6 m. Aggradation height (superelevation) of channel margin levees are, on average, 0.6 and 1.1 times paleoflow depth in the Guadalope-Matarranya and Wasatch systems, respectively. These results are consistent with values from recently avulsed modern rivers and suggest that (1) flow depth is the appropriate parameter against which to scale the critical superelevation necessary for channel avulsion; and (2) the increase in potential energy due to channel perching drives the lateral instability that is needed for avulsion to be successful. Numerous stacked channel fills indicate repeated reoccupation of the same site by avulsing channels. These reoccupation channels indicate that inherited flood-plain topography, here abandoned channel forms, was an important control on the arrival site of newly avulsed channels. Comparison of our results to others suggests two end-member types of avulsion can take place. Incisional avulsion, seen here, is characterized by an early incision phase followed by infilling by migrating bar forms. Aggradational avulsion begins with aggradation followed in time by stream integration into a single downcutting channel. We suggest that the type of avulsion is strongly influenced by whether or not the adjacent flood plain is well or poorly drained. In both cases subsequent aggradation and channel perching increase the chances that some triggering event will lead to avulsion.