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Geology topics

John A. Moody

Publications and source records attributed to John A. Moody.

At least 19 recordsLinked to original sources
USGS2026

Thickness and other characteristics of overbank sediment deposited during an extreme flood in May 1978 along the Powder River, Montana

An extreme flood on the Powder River in southeastern Montana in May 1978 inundated its valley and deposited sediment on the floodplains and terraces at multiple heights. The recurrence interval for this flood was less than 1 percent in the reach between Moorhead and Broadus, Montana. Peak discharges at the U.S. Geological Survey streamgages at Moorhead and Broadus were 779 and 711 cubic meters per second (m 3 /s), respectively, the difference reflecting the water and sediment stored on the valley surfaces. Bankfull discharge depended on the height of the bank at the start of the valley transect and varied from 243 to 713 m 3 /s. Sediment-thickness and particle-size data were collected and analyzed in the autumn of 1978 by U.S. Geological Survey scientists at about 900 sites along 20 valley transects between Moorhead and Broadus, Mont. These transects were approximately orthogonal to the floodflow across the floodplain from near the edge of the channel to the high-water mark. Estimated maximum flood depths along these transects ranged from 0.9 to 4.2 meters. Contrary to theory and controlled laboratory experiments, the distribution of sediment thickness and particle sizes along valley transects did not decrease systematically with distance from the main channel but were affected by the distribution of vegetation. Additionally, some water and sediment—primarily muds and silts—were conveyed by subsidiary channels (often connected to the main channel downriver from the valley transect) during the early stages of the flood before water overtopped the banks at the start of the valley transect. The vegetation created natural sediment traps in the recirculation and wake zones in the lee of trees and shrubs. Sediment that accumulated in these traps formed dunes and thus an undulating surface with many local maximums and minimums in sediment thicknesses. Sediment in the traps are referred to as lee dunes, which recorded flow conditions and a predominance of coarsening-upward sequence of particle sizes (mud to silt to sands) starting at the preflood surface. These sequences were associated with the rising limb of the hydrograph, and later as the flood began to recede, the lee dunes recorded a fining-upward sequence associated with the falling limb of the hydrograph.

Montana↗
USGS2024

Rainfall as a driver of post-wildfire flooding and debris flows: A review and synthesis

The increasing threat of post-wildfire hazards creates an imperative for improved post-wildfire flooding and debris flow prediction capabilities. Because rainfall is a primary driver of predictive hydrology and debris flow initiation and inundation models, recent efforts have emphasized the need for interdisciplinary collaboration between meteorology and post-wildfire hazard science that develops more accurate rainfall estimates with longer lead times. In this work, we identified critical knowledge gaps for developing rainfall estimates and filled those gaps by reviewing recent literature and synthesizing pre-existing datasets. Gap areas were organized into the following general topics: a) rainfall intensity-duration-frequency relations, b) time-varying rainfall, c) spatially varying rainfall, and d) rainfall regimes. Recent key research advances include the increasing availability of gridded quantitative rainfall estimates, the expanded use of distributed hydrologic and erosion models that incorporate spatial and temporal variability in rainfall, and the linking of concepts and modeling from the atmospheric and climate sciences with post-wildfire hazard science. We prototype a rainfall regime regionalization schema that captures self-similar properties of rainfall intensity ( k , the maximum rainfall intensity) and temporal scaling ( n , the decay rate). Our k - n relations schema could serve as a framework for organizing, interpreting, and predicting post-wildfire hydrologic and erosional responses. Finally, we summarize salient gaps for implementing spatiotemporally varying rainfall as the driver of post-wildfire hydrologic models designed to improve the prediction of flooding and debris flow hazards to the built environment for emergency managers.

Earth-Science Reviews↗
USGS2023

Ecogeomorphic interactions of Russian olives (Elaeagnus angustifolia) and point-bar morphology along Powder River, Montana, USA

Point bars are crucial alluvial features that help sustain meandering river ecosystems. They are influenced by interactions among physical processes and biological components, such as riparian vegetation. Understanding the mechanisms underlying these interactions can inform management decisions. The meandering Powder River in southeastern Montana, USA, provides a valuable study system for fluvial interactions because it has no major human alterations. Riparian stands of non-native Russian olive trees ( Elaeagnus angustifolia ) became noticeable after ~50-year flood in 1978. Fortuitously, 20 channel cross-sections had been established in 1975 and 1977 and have been surveyed periodically ever since. This temporally extensive dataset was coupled with a spatially extensive dataset of 85 point-bar cross-sections derived from high-resolution LiDAR that enabled evaluation of interactions between Russian olives and point-bar morphology through time and space. Based on published literature and field observations, we hypothesised that an increase in the width of Russian olive stands would result in (1) a decrease in the overall point-bar slope, (2) an increase in point-bar heights and (3) in point-bar toe-slopes. The results indicated that point-bar slopes did decrease with an increase in stand width, supporting the first hypothesis ( R 2 = 0.87). However, point-bar heights decreased with an increase in stand width ( R 2 = 0.63), contradicting the second hypothesis and there was no relation between point-bar toe-slopes and stand width ( R 2 < 0.1). The reverse hypothesis that point-bar morphology controls Russian olive stand widths makes more biophysical sense. Thus, Russian olive stand width increases as the point-bar slope and height decrease ( R 2 = 0.79 and 0.50), which provide a greater area of inundation for colonisation. This study demonstrates that geomorphology is controlling non-native vegetation colonisation along Powder River, but that the subsequent stabilisation associated with Russian oliveexpansion may in turn upset the critical geomorphic balance between bank erosion and point-bar aggradation necessary for a stable meandering system.

Montana↗
USGS2022

The effects of discharge and bank orientation on the annual riverbank erosion along Powder River in Montana, USA

Annual bank erosion was measured at multiple cross sections along the free-flowing meandering Powder River in the western United States from 1979 through 2019. Bank erosion was separated into two components—above water and underwater erosion. Above water erosion was measured as the annual bank retreat rate (0–15.4 m y −1 ). Underwater erosion rate (0–47 m 3 m −1 y −1 ) was calculated as the volume eroded below the water level corresponding to the dominant annual peak discharge, Q p . This paper focuses primarily on the underwater erosion. A total of 491 annual erosion rates were calculated for 23 bank sites along a 90-km study reach in southeastern Montana. Sites were not just hotspots for bank erosion but represent the spectra of variables such as the radius of curvature divided by channel width, R / w (2–86), the peak discharge, Q p (22.7–314 m 3 s −1 ), and the bank orientation (0–360°). Local annual bank erosion was extremely variable in time and space. It was episodic and unsynchronized along the study reach with the maximum annual bank erosion occurring in different years at different bank sites. The composite probability distribution of all 491 annual bank erosion rates was best modeled by a zero-adjusted Weibull distribution. Individual probability distributions for each of the 23 sites were all different from each other and from the composite distribution highlighting the extreme variability. The correlation of the annual underwater erosion with channel geometry and bank variables was low (R 2 < 0.31) but the correlation was higher for peak discharge with 25% of the sites having R 2 > 0.50. Time-averaging reduced the variability at each site and when grouped into five peak-discharge classes each class was correlated with R / w as a power law with an exponent of about −1. Reach-averaging also reduced the variability for each year, and when grouped by bank orientation (north-, east-, south-, and west-facing), bank erosion was linearly related to Q p with south- and west-facing orientations having about twice as much erosion per unit discharge (0.030 m 3 m −1 y −1 /m 3 s −1 ) than north- and east-facing orientations. Bank erosion was found to be not just a multi-variate complex process with little correlation and high variability that suggests randomness, but also a process that was a function of a different combinations of variables at different sites at the same time. However, this high variability was reduced by time- and reach-averaging, which produced predictable results analogous to the central limit theorem.

Montana↗
USGS2022

Post-fire temporal trends in soil-physical and -hydraulic properties and simulated runoff generation: Insights from different burn severities in the 2013 Black Forest Fire, CO, USA

Burn severity influences on post-fire recovery of soil-hydraulic properties controlling runoff generation are poorly understood despite the importance for parameterizing infiltration models. We measured soil-hydraulic properties of field-saturated hydraulic conductivity (Kfs), sorptivity (S), and wetting front potential (ψf) for four years after the 2013 Black Forest Fire, Colorado, USA at six sites across a gradient of initial remotely sensed burn severity using the change in the normalized burn ratio (dNBR). These measurements were correlated with soil-physical property measurements of bulk density (ρb), loss on ignition (LOI, a measure of soil organic matter), and ground cover composition to provide insight into causal factors for temporal changes in Kfs, S, and ψf . Modeled infiltration using the Smith-Parlange approach parameterized with measured Kfs, S, and ψf further discerned the role of precipitation intensity on runoff generation. Temporal trends of soil-physical properties and ground cover showed influences from initial burn severity. Trends in soil-hydraulic properties , surprisingly, were not strongly influenced by initial burn severity despite inferred effects of ρb, LOI, and ground cover on trends in Kfs and S. Calculations of dNBR at the time of sampling showed strong correlations with Kfs and S, demonstrating a new approach for estimating long-unburned Kfs and S values, infiltration model parameters after fire, and assessing the time of return to pre-fire values. Simulated infiltration-excess runoff, in contrast, did depend on initial burn severity. Time series of the ratio S2/Kfs ≈ ψf tended to converge between 1 to 10 mm four years after wildfire, potentially (i) defining a long-unburned forest domain of S2/Kfs and ψf from 1 to 10 mm with relatively high Kfs values, and (ii) providing a new post-fire soil-hydraulic property recovery metric (i.e. S2/Kfs ≈ ψf in the range of 1 to 10 mm) for sites in the Rocky Mountains of the USA.

Colorado↗
USGS2021

Reconstruction of an extreme flood hydrograph and morphodynamics of a meander bend in a high-peak discharge variability river (Powder River, USA)

Understanding of morphodynamic processes associated with large-scale floods has recently improved following significant advances of modern technologies. Nevertheless, a clear link between flood discharge and in-channel sedimentation processes remains to be resolved. The hydrological and geomorphological data available for the meandering Powder River (Montana, USA) since 1977 makes it a perfect laboratory to investigate connections between flood discharge and point-bar sedimentation processes. This study focuses on a point-bar that accreted laterally ca 70 m during a 50-year recurrence flood, which lasted about 14 days in May 1978. In September 2018, a trench ca 2 m deep and 70 m long was excavated through the axial point-bar deposits, and the 1978 flood deposits were delineated based on georeferenced pre-flood and post-flood cross-section surveys. Sedimentological data show that point-bar deposits accumulated at the early and late flood stages, when the flow was confined to the channel, and have similarities with classical facies models in terms of palaeocurrent patterns and vertical grain-size trend. However, during high-stage flood conditions, when the flow overtopped the bar, cross-cutting of the bar and armouring were typical processes. Integration of sedimentological and palaeo-hydrological data highlight that the relation between channel cross-sectional area and flood discharge play a key role in preserving bar deposits. The integrated approach adopted here provides a basis for advancing palaeoflood hydrology beyond the stage of estimating peak discharges to the next stage of estimating palaeoflood hydrographs.

Montana↗
USGS2020

Parameter estimation for multiple post-wildfire hydrologic models

Predictions of post‐wildfire flooding and debris flows are needed, typically with short lead times. Measurements of soil‐hydraulic properties necessary for model parameterization are, however, seldom available. This study quantified soil‐hydraulic properties, soil‐water retention, and selected soil physical properties within the perimeter of the 2017 Thomas Fire in California. The Thomas Fire burn scar produced catastrophic debris flows in January 2018, highlighting the need for improved prediction capability. Soil‐hydraulic properties were also indirectly estimated using relations tied to soil‐water retention. These measurements and estimates are examined in the context of parameterizing post‐wildfire hydrologic models. Tension infiltrometer measurements showed significant decreases ( p < .05) in field‐saturated hydraulic conductivity ( K fs ) and sorptivity ( S ) in burned areas relative to unburned areas. Wildfire effects on soil water‐retention were dominated by significant decreases in saturated soil‐water content ( θ S ). The van Genuchten parameters α , N , and residual water content did not show significant wildfire effects. The impacts of the wildfire on hydraulic and physical soil properties were greatest in the top 1 cm, emphasizing that measurements of post‐fire soil properties should focus on the near‐surface. Reductions in K fs , θ s , and soil‐water retention in burned soils were attributed to fire‐induced decreases in soil structure evidenced by increases in dry bulk density. Sorptivity reductions in burned soils were attributed to increases in soil‐water repellency. Rapid post‐fire assessments of flash flood and debris flow hazards using physically‐based hydrologic models are facilitated by similarities between K fs , S , and the Green–Ampt wetting front potential ( ψ f ) with measurements at other southern CA burned sites. We suggest that ratios of burned to unburned K fs (0.37), S (0.36), and ψ f (0.66) could be used to scale unburned values for model parameterization. Alternatively, typical burned values ( K fs = 20 mm hr −1 ; S = 6 mm hr −0.5 ; ψ f = 1.6 mm) could be used for model parameterization.

California↗
USGS2019

Sources of inherent infiltration variability in postwildfire soils

An automated disc infiltrometer was developed to improve the measurements of soil hydraulic properties (saturated hydraulic conductivity and sorptivity) of soils affected by wildfire. Guidelines are given for interpreting curves showing cumulative infiltration as a function of time measured by the autodisc. The autodisc was used to measure the variability of these soil hydraulic properties in three different sample sets: (a) a reference soil consisting of a nonrepellent, uniform, fine sand; (b) soils with the same soil textural classification derived from the same bedrock geology but having different initial burn severities; and (c) soils from different bedrock geology but having the same burn severity. The autodisc infiltrometer had greater sampling rates and volume resolution when compared with the visual minidisc infiltrometer from previous studies. There was no statistical difference in the mean values measured using the autodisc and visual minidisc, but the variability of the autodisc measurements was significantly less than the visual minidisc for a given set of samples. The greatest variability of soil hydraulic properties in reference samples with uniform particle size was attributed to different pore geometries (coefficient of variation [COV] = 0.28–0.34). Unburned field samples (same soil type) with heterogeneous particle sizes had greater variability (COV = 0.57–0.78) than the reference samples. However, this basic variability decreased or remained constant in these field samples as burn severity increased. Additional sources of variability (COV = 0.53–1.99) were attributed to multiple layers resulting from ash or sediment deposition. Results indicate that resolving differences in soil hydraulic properties from different sites requires more than the common 10 random samples because of the multiple sources of variability.

Hydrological Processes↗
USGS2019

Dynamic relations for the deposition of sediment on floodplains and point bars of a freely-meandering river

Fluvial features such as floodplains and point bars are built by sediment deposition and sculpted by erosion. Long-term measurements (38 yr) of the cross-section topography of active floodplains and point bars along the freely-meandering Powder River in southeastern Montana, USA (mean daily discharge of 12.5 m 3 s −1 ), were used to develop dynamic relations between annual sediment deposition and peak-flood discharge. Five floodplain sections and five point-bar sections were selected from 24 cross sections along a 90-km study reach. At each cross section the sediment deposition volume per unit streamwise distance was computed as the difference between two topographic surveys made in consecutive years. Snowmelt floods were found to be the dominant annual process. However, other processes such as flash floods, ice breakup floods, and autumnal floods were important episodically. The dynamic relations were linear for both fluvial features. The snowmelt deposition-discharge relations showed, in general, that point bars were about two times more efficient at trapping sediment than floodplains. Each relation had a discharge threshold that must be exceeded before sediment was deposited. Although these discharge thresholds for floodplains and point bars had essentially the same mean value (69 and 71 m 3 s −1 , respectively), they represented different processes. Thresholds for other rivers will probably differ from those for Powder River because of different channel geometry and sediment characteristics.

Montana↗
USGS2018

Influence of extreme and annual floods on point-bar sedimentation: Inferences from Powder River, Montana, USA

Effects of discharge variability on point-bar sedimentation are not well documented, although resulting changes in flow patterns are well known. This paper focuses on a meander of Powder River in Montana (USA). In May 1978, Powder River had a 50-year recurrence flood, which caused outer bank retreat of ∼70 m. This bank continued to retreat over ∼40 m in response to annual floods between 1979 and 2016. A trench, up to 2 m deep and 60 m long, was excavated in 2016 through the axial point-bar deposits accumulated during and since the 1978 flood. Deposits from the extreme 1978 flood consisted of stratified, coarsening-upward pebbles with subordinate sand, and show paleoflow toward the outer bank. Deposits accreted during subsequent annual floods consist of fining-upward, medium to fine sand with subordinate mud and gravel. These deposits contain sedimentary structures indicating transport from the channel up the bar. Field observations indicate that during extreme floods, the axial part of the bar was armored by coarsening-upward gravels and not affected by secondary helical circulation. In contrast, during annual floods, armoring was not observed and most of the flow was directed up the sloping point-bar surface, indicating secondary circulation near the bend apex. This paper shows that the area affected by the secondary helical circulation shifts downstream and upstream of the bend apex during extreme and annual floods, respectively. This causes significant changes in grain size and sedimentary facies distribution in point-bar deposits, which should be considered when analyzing meandering-river deposits in the ancient sedimentary record.

Montana↗
USGS2018

Decadal changes in channel morphology of a freely meandering river—Powder River, Montana, 1975–2016

Few studies exist on the long-term geomorphic effects of floods. However, the U.S. Geological Survey (USGS) was able to begin such a study after a 50-year recurrence interval flood in 1978 because 20 channel cross sections along a 100-kilometer reach of river were established in 1975 and 1977 as part of a study for a proposed dam on Powder River in southeastern Montana. These cross-section measurements (data for each channel cross section are available at the USGS ScienceBase website) have been repeated about 30 times during four decades (1975–2016) and provide a unique dataset for understanding long-term changes in channel morphology caused by an extreme flood and a spectrum of annual floods. Changes in channel morphology of a 100-kilometer reach of Powder River are documented in a series of narratives for each channel cross section that include a time series of photographs as a record of these changes. The primary change during the first decade (1975–85) was the rapid vertical growth of a new inset flood plain within the flood-widened channel. Changes during the second decade (1985–95) were characterized by slower growth of the flood plain, and the effects of ice-jam floods typical of a northward-flowing river. Changes during the third decade (1995–2005) showed little vertical growth of the inset flood plain, which had reached a height that limited overbank deposition. And changes during the final decade (2005–16) covered in this report showed that, because the new inset flood plain had reached a limiting height, the effects of the large annual flood of 2008 (largest flood since 1978) were relatively small compared to smaller floods in previous decades. Throughout these four decades, the riparian vegetation, which interacts with the river, has undergone a gradual but substantial change that may have lasting effects on the channel morphology.

Montana↗
USGS2017

Description of chronostratigraphic units preserved as channel deposits and geomorphic processes following a basin-scale disturbance by a wildfire in Colorado

The consequence of a 1996 wildfire disturbance and a subsequent high-intensity summer convective rain storm (about 110 millimeters per hour) was the deposition of a sediment superslug in the Spring Creek basin (26.8 square kilometers) of the Front Range Mountains in Colorado. Spring Creek is a tributary to the South Platte River upstream from Strontia Springs Reservoir, which supplies domestic water for the cities of Denver and Aurora. Changes in a superslug were monitored over the course of 18 years (1996–2014) by repeat surveys at 18 channel cross sections spaced at nearly equal intervals along a 1,500-meter study reach and by a time series of photographs of each cross section. Surveys were not repeated at regular time intervals but after major changes caused by different geomorphic processes. The focus of this long-term study was to understand the evolution and internal alluvial architecture of chronostratigraphic units (defined as the volume of sediment deposited between two successive surveys), and the preservation or storage of these units in the superslug. The data are presented as a series of 18 narratives (one for each cross section) that summarize the changes, illustrate these changes with photographs, and provide a preservation plot showing the amount of each chronostratigraphic unit still remaining in June 2014. The most significant hydrologic change after the wildfire was an exponential decrease in peak discharge of flash floods caused by summer convective rain storms. In response to these hydrologic changes, all 18 locations went through an aggradation phase, an incision phase, and finally a stabilization phase. However, the architecture of the chronostratigraphic units differs from cross section to cross section, and units are characterized by either a laminar, fragmented, or hybrid alluvial architecture. In response to the decrease in peak-flood discharge and the increase in hillslope and riparian vegetation, Spring Creek abandoned many of the nearly horizontal erosional and depositional surfaces and left a landscape consisting of a series of cut-and-fill terraces as a legacy of this wildfire disturbance.

Colorado↗
USGS2017

Residence times and alluvial architecture of a sediment superslug in response to different flow regimes

A superslug was deposited in a basin in the Colorado Front Range Mountains as a consequence of an extreme flood following a wildfire disturbance in 1996. The subsequent evolution of this superslug was measured by repeat topographic surveys (31 surveys from 1996 through 2014) of 18 cross sections approximately uniformly spaced over 1500 m immediately above the basin outlet. These surveys allowed the identification within the superslug of chronostratigraphic units deposited and eroded by different geomorphic processes in response to different flow regimes. Over the time period of the study, the superslug went through aggradation, incision, and stabilization phases that were controlled by a shift in geomorphic processes from generally short-duration, episodic, large-magnitude floods that deposited new chronostratigraphic units to long-duration processes that eroded units. These phases were not contemporaneous at each channel cross section, which resulted in a complex response that preserved different chronostratigraphic units at each channel cross section having, in general, two dominant types of alluvial architecture—laminar and fragmented. Age and transit-time distributions for these two alluvial architectures evolved with time since the extreme flood. Because of the complex shape of the distributions they were best modeled by two-parameter Weibull functions. The Weibull scale parameter approximated the median age of the distributions, and the Weibull shape parameter generally had a linear relation that increased with time since the extreme flood. Additional results indicated that deposition of new chronostratigraphic units can be represented by a power-law frequency distribution, and that the erosion of units decreases with depth of burial to a limiting depth. These relations can be used to model other situations with different flow regimes where vertical aggradation and incision are dominant processes, to predict the residence time of possible contaminated sediment stored in channels or on floodplains, and to provide insight into the interpretation of recent or ancient fluvial deposits.

Geomorphology↗
USGS2016

Synthesis of soil-hydraulic properties and infiltration timescales in wildfire-affected soils

We collected soil-hydraulic property data from the literature for wildfire-affected soils, ash, and unburned soils. These data were used to calculate metrics and timescales of hydrologic response related to infiltration and surface runoff generation. Sorptivity ( S ) and wetting front potential (Ψ f ) were significantly different (lower) in burned soils compared with unburned soils, whereas field-saturated hydraulic conductivity ( K fs ) was not significantly different. The magnitude and duration of the influence of capillarity during infiltration was greatly reduced in burned soils, causing faster ponding times in response to rainfall. Ash had large values of S and K fs but moderate values of Ψ f , compared with unburned and burned soils, indicating ash has long ponding times in response to rainfall. The ratio of S 2 /K fs was nearly constant (~100 mm) for unburned soils but more variable in burned soils, suggesting that unburned soils have a balance between gravity and capillarity contributions to infiltration that may depend on soil organic matter, whereas in burned soils the gravity contribution to infiltration is greater. Changes in S and K fs in burned soils act synergistically to reduce infiltration and accelerate and amplify surface runoff generation. Synthesis of these findings identifies three key areas for future research. First, short timescales of capillary influences on infiltration indicate the need for better measurements of infiltration at times less than 1 min to accurately characterize S in burned soils. Second, using parameter values, such as Ψ f , from unburned areas could produce substantial errors in hydrologic modeling when used without adjustment for wildfire effects, causing parameter compensation and resulting underestimation of K fs . Third, more thorough measurement campaigns that capture soil-structural changes, organic matter impacts, quantitative water repellency trends, and soil-water content along with soil-hydraulic properties could drive the development of better techniques for numerically simulating infiltration in burned areas.

Hydrological Processes↗
USGS2016

Estimates of peak flood discharge for 21 sites in the Front Range in Colorado in response to extreme rainfall in September 2013

Extreme rainfall in September 2013 caused destructive floods in part of the Front Range in Boulder County, Colorado. Erosion from these floods cut roads and isolated mountain communities for several weeks, and large volumes of eroded sediment were deposited downstream, which caused further damage of property and infrastructures. Estimates of peak discharge for these floods and the associated rainfall characteristics will aid land and emergency managers in the future. Several methods (an ensemble) were used to estimate peak discharge at 21 measurement sites, and the ensemble average and standard deviation provided a final estimate of peak discharge and its uncertainty. Because of the substantial erosion and deposition of sediment, an additional estimate of peak discharge was made based on the flow resistance caused by sediment transport effects. Although the synoptic-scale rainfall was extreme (annual exceedance probability greater than 1,000 years, about 450 millimeters in 7 days) for these mountains, the resulting peak discharges were not. Ensemble average peak discharges per unit drainage area (unit peak discharge, [ Q u ]) for the floods were 1–2 orders of magnitude less than those for the maximum worldwide floods with similar drainage areas and had a wide range of values (0.21–16.2 cubic meters per second per square kilometer [m 3 s -1 km -2 ]). One possible explanation for these differences was that the band of high-accumulation, high-intensity rainfall was narrow (about 50 kilometers wide), oriented nearly perpendicular to the predominant drainage pattern of the mountains, and therefore entire drainage areas were not subjected to the same range of extreme rainfall. A linear relation (coefficient of determination [ R 2 ]=0.69) between Q u and the rainfall intensity ( I Tc , computed for a time interval equal to the time-of-concentration for the drainage area upstream from each site), had the form: Q u =0.26( I Tc -8.6), where the coefficient 0.26 can be considered to be an area-averaged peak runoff coefficient for the September 2013 rain storms in Boulder County, and the 8.6 millimeters per hour to be the rainfall intensity corresponding to a soil moisture threshold that controls the soil infiltration rate. Peak discharge estimates based on the sediment transport effects were generally less than the ensemble average and indicated that sediment transport may be a mechanism that limits velocities in these types of mountain streams such that the Froude number fluctuates about 1 suggesting that this type of floodflow can be approximated as critical flow.

Colorado↗
USGS2015

Measurements of the initiation of post-wildfire runoff during rainstorms using in situ overland flow detectors

Overland flow detectors (OFDs) were deployed in 2012 on a hillslope burned by the 2010 Fourmile Canyon fire near Boulder, Colorado, USA. These detectors were simple, electrical resistor-type instruments that output a voltage (0–2·5 V) and were designed to measure and record the time of runoff initiation, a signal proportional to water depth, and the runoff hydrograph during natural convective rainstorms. Initiation of runoff was found to be spatially complex and began at different times in different locations on the hillslope. Runoff started first at upstream detectors 56% of the time, at the mid-stream detectors 6%, and at the downstream detectors 38% of the time. Initiation of post-wildfire runoff depended on the time-to-ponding, travel time between points, and the time to fill surface depression storage. These times ranged from 0·5–54, 0·4–1·1, and 0·2–14 minutes, respectively, indicating the importance of the ponding process in controlling the initiation of runoff at this site. Time-to-ponding was modeled as a function of the rainfall acceleration (i.e. the rate of change of rainfall intensity) and either the cumulative rainfall at the start of runoff or the soil–water deficit. Measurements made by the OFDs provided physical insight into the spatial and temporal initiation of post-wildfire runoff during unsteady flow in response to time varying natural rainfall. They also provided data that can be telemetered and used to determine critical input parameters for hydrologic rainfall–runoff models.

Earth Surface Processes and Landforms↗
USGS2015

Preserving geomorphic data records of flood disturbances

No central database or repository is currently available in the USA to preserve long-term, spatially extensive records of fluvial geomorphic data or to provide future accessibility. Yet, because of their length and continuity these data are valuable for future research. Therefore, we built a public accessible website to preserve data records of two examples of long-term monitoring (40 and 18 years) of the fluvial geomorphic response to natural disturbances. One disturbance was ∼50-year flood on Powder River in Montana in 1978, and the second disturbance was a catastrophic flood on Spring Creek following a ∼100-year rainstorm after a wildfire in Colorado in 1996. Two critical issues arise relative to preserving fluvial geomorphic data. The first is preserving the data themselves, but the second, and just as important, is preserving information about the location of the field research sites where the data were collected so the sites can be re-located and re-surveyed in the future. The latter allows long-term datasets to be extended into the future and to provide critical background data for interpreting future landscape changes. Data were preserved on a website to allow world-wide accessibility and to upload new data to the website as they become available. We describe the architecture of the website, lessons learned in developing the website, future improvements, and recommendations on how also to preserve information about the location of field research sites.

GeoResJ↗