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John A. Moody

Publications and source records attributed to John A. Moody.

At least 37 records · Page 2Linked to original sources
USGS2015

Relations between soil hydraulic properties and burn severity

Wildfire can affect soil hydraulic properties, often resulting in reduced infiltration. The magnitude of change in infiltration varies depending on the burn severity. Quantitative approaches to link burn severity with changes in infiltration are lacking. This study uses controlled laboratory measurements to determine relations between a remotely sensed burn severity metric ( dNBR , change in normalised burn ratio) and soil hydraulic properties (SHPs). SHPs were measured on soil cores collected from an area burned by the 2013 Black Forest fire in Colorado, USA. Six sites with the same soil type were selected across a range of burn severities, and 10 random soil cores were collected from each site within a 30-m diameter circle. Cumulative infiltration measurements were made in the laboratory using a tension infiltrometer to determine field-saturated hydraulic conductivity, K fs , and sorptivity, S . These measurements were correlated with dNBR for values ranging from 124 (low severity) to 886 (high severity). SHPs were related to dNBR by inverse functions for specific conditions of water repellency (at the time of sampling) and soil texture. Both functions had a threshold value for dNBR between 124 and 420, where K fs and S were unchanged and equal to values for soil unaffected by fire. For dNBR s >~420, the K fs was an exponentially decreasing function of dNBR and S was a linearly decreasing function of dNBR . These initial quantitative empirical relations provide a first step to link SHPs to burn severity, and can be used in quantitative infiltration models to predict post-wildfire infiltration and resulting runoff.

International Journal of Wildland Fire↗
USGS2013

Infiltration and runoff generation processes in fire-affected soils

Post-wildfire runoff was investigated by combining field measurements and modelling of infiltration into fire-affected soils to predict time-to-start of runoff and peak runoff rate at the plot scale (1 m 2 ). Time series of soil-water content, rainfall and runoff were measured on a hillslope burned by the 2010 Fourmile Canyon Fire west of Boulder, Colorado during cyclonic and convective rainstorms in the spring and summer of 2011. Some of the field measurements and measured soil physical properties were used to calibrate a one-dimensional post-wildfire numerical model, which was then used as a ‘virtual instrument’ to provide estimates of the saturated hydraulic conductivity and high-resolution (1 mm) estimates of the soil-water profile and water fluxes within the unsaturated zone. Field and model estimates of the wetting-front depth indicated that post-wildfire infiltration was on average confined to shallow depths less than 30 mm. Model estimates of the effective saturated hydraulic conductivity, K s , near the soil surface ranged from 0.1 to 5.2 mm h −1 . Because of the relatively small values of K s , the time-to-start of runoff (measured from the start of rainfall), t p , was found to depend only on the initial soil-water saturation deficit (predicted by the model) and a measured characteristic of the rainfall profile (referred to as the average rainfall acceleration, equal to the initial rate of change in rainfall intensity). An analytical model was developed from the combined results and explained 92–97% of the variance of t p , and the numerical infiltration model explained 74–91% of the variance of the peak runoff rates. These results are from one burned site, but they strongly suggest that t p in fire-affected soils (which often have low values of K s ) is probably controlled more by the storm profile and the initial soil-water saturation deficit than by soil hydraulic properties.

Hydrological Processes↗
USGS2013

Rethinking infiltration in wildfire-affected soils

Wildfires frequently result in natural hazards such as flash floods (Yates et al ., 2001) and debris flows (Cannon et a l., 2001a,b; Gabet and Sternberg, 2008). One of the principal causes of the increased risk of post-wildfire hydrologically driven hazards is reduced in filtration rates (e.g. Scott and van Wyk, 1990; Cerdà, 1998; Robichaud, 2000; Martin and Moody, 2001). Beyond the reduction in peak infiltration rate, there is mounting evidence that the fundamental physics of infiltration in wild fire-affected soils is different from unburned soils (e.g. Imeson et al. , 1992; Moody et al. , 2009; Moody and Ebel, 2012). Understanding post-wildfire hydrology is critical given the increasing wildfire incidence in the western USA (Westerling et al. , 2006) and elsewhere in the world (Kasischke and Turetsky, 2006; Holz and Veblen, 2011; Pausas and Fernández-Muñoz, 2012). Wildfire is a disturbance event with global distribution (Bowman et al. , 2009; Krawchuk et al. , 2009; Pechony and Shindell, 2010; Moritz et al. , 2012), and with increasing populations moving into fire-prone areas, understanding post-wildfire infiltration is of increasing importance for predicting post-wildfire consequences. Runoff is generally controlled by the infiltration-excess mechanism in fire-affected soils (e.g. Mayor et al ., 2007; Onda et al. , 2008; Kinner and Moody, 2010). It is essential that the fire community have conceptual models, physical equations and tools (i.e. numerical models) to predict infiltration and thus excess rainfall (after Horton, 1933), which can provide estimates of peak discharge, start of runoff, time to peak and total runoff for hydroclimatic scenarios after wildfires. Reductions in saturated hydraulic conductivity K sat [LT -1 ] are common for fire-affected soils, and the relatively low values observed explain the elevated flash flood hazards (e.g. K sat of 1–100 mm h -1 , Robichaud, 2000; Yates et al. , 2000; Martin and Moody, 2001; Robichaud et al. , 2007; Moody et al. , 2009; Neary, 2011; Nyman et al. , 2011).

Hydrological Processes↗
USGS2013

Current research issues related to post-wildfire runoff and erosion processes

Research into post-wildfire effects began in the United States more than 70 years ago and only later extended to other parts of the world. Post-wildfire responses are typically transient, episodic, variable in space and time, dependent on thresholds, and involve multiple processes measured by different methods. These characteristics tend to hinder research progress, but the large empirical knowledge base amassed in different regions of the world suggests that it should now be possible to synthesize the data and make a substantial improvement in the understanding of post-wildfire runoff and erosion response. Thus, it is important to identify and prioritize the research issues related to post-wildfire runoff and erosion. Priority research issues are the need to: (1) organize and synthesize similarities and differences in post-wildfire responses between different fire-prone regions of the world in order to determine common patterns and generalities that can explain cause and effect relations; (2) identify and quantify functional relations between metrics of fire effects and soil hydraulic properties that will better represent the dynamic and transient conditions after a wildfire; (3) determine the interaction between burned landscapes and temporally and spatially variable meso-scale precipitation, which is often the primary driver of post-wildfire runoff and erosion responses; (4) determine functional relations between precipitation, basin morphology, runoff connectivity, contributing area, surface roughness, depression storage, and soil characteristics required to predict the timing, magnitudes, and duration of floods and debris flows from ungaged burned basins; and (5) develop standard measurement methods that will ensure the collection of uniform and comparable runoff and erosion data. Resolution of these issues will help to improve conceptual and computer models of post-wildfire runoff and erosion processes.

Earth-Science Reviews↗
USGS2013

Variations in soil detachment rates after wildfire as a function of soil depth, flow properties, and root properties

Wildfire affects hillslope erosion through increased surface runoff and increased sediment availability, both of which contribute to large post-fire erosion events. Relations between soil detachment rate, soil depth, flow and root properties, and fire impacts are poorly understood and not represented explicitly in commonly used post-fire erosion models. Detachment rates were measured on intact soil cores using a modified tilting flume. The cores were mounted flush with the flume-bed and a measurement was made on the surface of the core. The core was extruded upward, cut off, and another measurement was repeated at a different depth below the original surface of the core. Intact cores were collected from one site burned by the 2010 Fourmile Canyon (FMC) fire in Colorado and from one site burned by the 2010 Pozo fire in California. Each site contained contrasting vegetation and soil types. Additional soil samples were collected alongside the intact cores and were analyzed in the laboratory for soil properties (organic matter, bulk density, particle-size distribution) and for root properties (root density and root-length density). Particle-size distribution and root properties were different between sites, but sites were similar in terms of bulk density and organic matter. Soil detachment rates had similar relations with non-uniform shear stress and non-uniform unit stream power. Detachment rates within single sampling units displayed a relatively weak and inconsistent relation to flow variables. When averaged across all clusters, the detachment rate displayed a linear relation to shear stress, but variability in soil properties meant that the shear stress accounted for only a small proportion of the overall variability in detachment rates (R 2 = 0.23; R 2 is the coefficient of determination). Detachment rate was related to root-length density in some clusters (R 2 values up to 0.91) and unrelated in others (R 2 values <0.1). The overall R 2 value improved and the range of exponents became narrower by applying a multivariate regression model where boundary shear stress and root-length density were included as explanatory variables. This suggests that an erodibility parameter which incorporates the effects of both flow and root properties on detachment could improve the representation of sediment availability after wildfire.

Scientific Investigations Report↗
USGS2013

Erosional and depositional changes wrought by the flood of May 1978 in the channels of Powder River, southeastern Montana

Powder River’s second largest flood of record (1919–2012) moved through northeastern Wyoming and southeastern Montana during May 1978. Within a ninety-kilometer reach of the channel in southeastern Montana, the most prominent planform effects of the flood were the growth of meander bends by bank erosion (this was most intense just downriver of bend apexes, causing 1–2 channel widths of lateral displacement) and the erosion of new cutoff channels through the necks of two large and two small meanders. Surveys of cross sections, made before and after the flood, show the responses of the channel to the flood waters, which ranged from minimal (bedrock control) to large (maximum channel curvature in unconsolidated bank and terrace deposits). Geomorphic work done during two weeks of extreme flooding in May 1978, as measured by cross-channel erosion and new sediment deposition, was approximately equal in magnitude to the work done during the two decades (1978–1998) that followed the flood.

Montana↗
USGS2012

Difference infiltrometer: a method to measure temporally variable infiltration rates during rainstorms

We developed a difference infiltrometer to measure time series of non-steady infiltration rates during rainstorms at the point scale. The infiltrometer uses two, tipping bucket rain gages. One gage measures rainfall onto, and the other measures runoff from, a small circular plot about 0.5-m in diameter. The small size allows the infiltration rate to be computed as the difference of the cumulative rainfall and cumulative runoff without having to route water through a large plot. Difference infiltrometers were deployed in an area burned by the 2010 Fourmile Canyon Fire near Boulder, Colorado, USA, and data were collected during the summer of 2011. The difference infiltrometer demonstrated the capability to capture different magnitudes of infiltration rates and temporal variability associated with convective (high intensity, short duration) and cyclonic (low intensity, long duration) rainstorms. Data from the difference infiltrometer were used to estimate saturated hydraulic conductivity of soil affected by the heat from a wildfire. The difference infiltrometer is portable and can be deployed in rugged, steep terrain and does not require the transport of water, as many rainfall simulators require, because it uses natural rainfall. It can be used to assess infiltration models, determine runoff coefficients, identify rainfall depth or rainfall intensity thresholds to initiate runoff, estimate parameters for infiltration models, and compare remediation treatments on disturbed landscapes. The difference infiltrometer can be linked with other types of soil monitoring equipment in long-term studies for detecting temporal and spatial variability at multiple time scales and in nested designs where it can be linked to hillslope and basin-scale runoff responses.

Hydrological Processes↗
USGS2012

Hydrologic conditions controlling runoff generation immediately after wildfire

We investigated the control of postwildfire runoff by physical and hydraulic properties of soil, hydrologic states, and an ash layer immediately following wildfire. The field site is within the area burned by the 2010 Fourmile Canyon Fire in Colorado, USA. Physical and hydraulic property characterization included ash thickness, particle size distribution, hydraulic conductivity, and soil water retention curves. Soil water content and matric potential were measured indirectly at several depths below the soil surface to document hydrologic states underneath the ash layer in the unsaturated zone, whereas precipitation and surface runoff were measured directly. Measurements of soil water content showed that almost no water infiltrated below the ash layer into the near-surface soil in the burned site at the storm time scale (i.e., minutes to hours). Runoff generation processes were controlled by and highly sensitive to ash thickness and ash hydraulic properties. The ash layer stored from 97% to 99% of rainfall, which was critical for reducing runoff amounts. The hydrologic response to two rain storms with different rainfall amounts, rainfall intensity, and durations, only ten days apart, indicated that runoff generation was predominantly by the saturation-excess mechanism perched at the ash-soil interface during the first storm and predominantly by the infiltration-excess mechanism at the ash surface during the second storm. Contributing area was not static for the two storms and was 4% (saturation excess) to 68% (infiltration excess) of the catchment area. Our results showed the importance of including hydrologic conditions and hydraulic properties of the ash layer in postwildfire runoff generation models.

Colorado↗
USGS2012

Hyper-dry conditions provide new insights into the cause of extreme floods after wildfire

A catastrophic wildfire in the foothills of the Rocky Mountains near Boulder, Colorado provided a unique opportunity to investigate soil conditions immediately after a wildfire and before alteration by rainfall. Measurements of near-surface (< 6 cm) soil properties (temperature, volumetric soil-water content, &theta; ; and matric suction, &psi; ), rainfall, and wind velocity were started 8 days after the wildfire began. These measurements established that hyper-dryconditions ( &theta; < ~ 0.02 cm 3 cm -3 ; &psi; > ~ 3 x 10 5 cm) existed and provided an in-situ retention curve for these conditions. These conditions exacerbate the effects of water repellency (natural and fire-induced) and limit the effectiveness of capillarity and gravity driven infiltration into fire-affected soils. The important consequence is that given hyper-dryconditions, the critical rewetting process before the first rain is restricted to the diffusion&ndash;adsorption of water-vapor. This process typically has a time scale of days to weeks (especially when the hydrologic effects of the ash layer are included) that is longer than the typical time scale (minutes to hours) of some rainstorms, such that under hyper-dryconditions essentially no rain infiltrates. The existence of hyper-dryconditions provides insight into why, frequently during the first rain storm after a wildfire, nearly all rainfall becomes runoff causing extremefloods and debris flows.

Colorado↗
USGS2012

An analytical method for predicting postwildfire peak discharges

An analytical method presented here that predicts postwildfire peak discharge was developed from analysis of paired rainfall and runoff measurements collected from selected burned basins. Data were collected from 19 mountainous basins burned by eight wildfires in different hydroclimatic regimes in the western United States (California, Colorado, Nevada, New Mexico, and South Dakota). Most of the data were collected for the year of the wildfire and for 3 to 4 years after the wildfire. These data provide some estimate of the changes with time of postwildfire peak discharges, which are known to be transient but have received little documentation. The only required inputs for the analytical method are the burned area and a quantitative measure of soil burn severity (change in the normalized burn ratio), which is derived from Landsat reflectance data and is available from either the U.S. Department of Agriculture Forest Service or the U.S. Geological Survey. The method predicts the postwildfire peak discharge per unit burned area for the year of a wildfire, the first year after a wildfire, and the second year after a wildfire. It can be used at three levels of information depending on the data available to the user; each subsequent level requires either more data or more processing of the data. Level 1 requires only the burned area. Level 2 requires the burned area and the basin average value of the change in the normalized burn ratio. Level 3 requires the burned area and the calculation of the hydraulic functional connectivity, which is a variable that incorporates the sequence of soil burn severity along hillslope flow paths within the burned basin. Measurements indicate that the unit peak discharge response increases abruptly when the 30-minute maximum rainfall intensity is greater than about 5 millimeters per hour (0.2 inches per hour). This threshold may relate to a change in runoff generation from saturated-excess to infiltration-excess overland flow. The threshold value was about 7.6 millimeters per hour for the year of the wildfire and the first year after the wildfire, and it was about 11.1 millimeters per hour for the second year after the wildfire.

California;Colorado;Nevada;New Mexico;South Dakota↗
USGS2010

Plot-scale sediment transport processes on a burned hillslope as a function of particle size

Soil moisture, rainfall, runoff, and sediment transport data were collected from four 1-m 2 hillslope plots after the 2000 Hi Meadow Fire in Colorado. Data were collected daily during three summers, two of which were affected by drought. Maximum 30-minute rainfall intensities, I 30 , were less than 20 mm h -1 and the average runoff volumes per plot were less than 4.7 L per storm. The data were separated into three sediment transport processes based on rainfall intensity and runoff magnitude: (1) dry ravel, (2) rainsplash, and (3) rainflow and then into eight different particle size classes ( D i ). For each class, dry ravel transport had a non-linear dependence on initial soil moisture, θ i , with a maximum at intermediate values of θ i (5-9 % cm 3 cm -3 ). Dry ravel transport rates were small for low θ i , which may be caused by a cementation process, and also small for high θ i , which may be caused by increased surface tension. Rainsplash transport was confined to the I 30 domain from 1-7 mm h -1 was proportional to D i ( I max 30 ) 0.63 . Rainflow transport ( I 30 > 7 mm h -1 ) in shallow flows ( h < 2 mm) was most likely dominated by particles rolling. It had a non-linear dependence on D i with maximum transport of sediment in the 2-4 mm size class. Transport also depended on stream power, but critical stream power was essentially zero, which may indicate that the rainsplash preceding runoff detached soil for transport by overland flow.

Conference Paper↗
USGS2009

Linking hydraulic properties of fire-affected soils to infiltration and water repellency

Heat from wildfires can produce a two-layer system composed of extremely dry soil covered by a layer of ash, which when subjected to rainfall, may produce extreme floods. To understand the soil physics controlling runoff for these initial conditions, we used a small, portable disk infiltrometer to measure two hydraulic properties: (1) near-saturated hydraulic conductivity, K f and (2) sorptivity, S ( θ i ), as a function of initial soil moisture content, θ i , ranging from extremely dry conditions ( θ i < 0.02 cm 3 cm −3 ) to near saturation. In the field and in the laboratory replicate measurements were made of ash, reference soils, soils unaffected by fire, and fire-affected soils. Each has a different degrees of water repellency that influences K f and S ( θ i ). Values of K f ranged from 4.5 × 10 −3 to 53 × 10 −3 cm s −1 for ash; from 0.93 × 10 −3 to 130 × 10 −3 cm s −1 for reference soils; and from 0.86 × 10 −3 to 3.0 × 10 −3 cm s −1 , for soil unaffected by fire, which had the lowest values of K f . Measurements indicated that S ( θ i ) could be represented by an empirical non-linear function of θ i with a sorptivity maximum of 0.18–0.20 cm s −0.5 , between 0.03 and 0.08 cm 3 cm −3 . This functional form differs from the monotonically decreasing non-linear functions often used to represent S ( θ i ) for rainfall–runoff modeling. The sorptivity maximum may represent the combined effects of gravity, capillarity, and adsorption in a transitional domain corresponding to extremely dry soil, and moreover, it may explain the observed non-linear behavior, and the critical soil-moisture threshold of water repellent soils. Laboratory measurements of K f and S ( θ i ) are the first for ash and fire-affected soil, but additional measurements are needed of these hydraulic properties for in situ fire-affected soils. They provide insight into water repellency behavior and infiltration under extremely dry conditions. Most importantly, they indicate how existing rainfall–runoff models can be modified to accommodate a possible two-layer system in extremely dry conditions. These modified models can be used to predict floods from burned watersheds under these initial conditions.

Journal of Hydrology↗
USGS2008

Infiltration and Runoff Measurements on Steep Burned Hillslopes Using a Rainfall Simulator with Variable Rain Intensities

Multiple rainfall intensities were used in rainfall-simulation experiments designed to investigate the infiltration and runoff from 1-square-meter plots on burned hillslopes covered by an ash layer of varying thickness. The 1-square-meter plots were on north- and south-facing hillslopes in an area burned by the Overland fire northwest of Boulder near Jamestown on the Front Range of Colorado. A single-nozzle, wide-angle, multi-intensity rain simulator was developed to investigate the infiltration and runoff on steep (30- to 40-percent gradient) burned hillslopes covered with ash. The simulated rainfall was evaluated for spatial variability, drop size, and kinetic energy. Fourteen rainfall simulations, at three intensities (about 20 millimeters per hour [mm/h], 35 mm/h, and 50 mm/h), were conducted on four plots. Measurements during and after the simulations included runoff, rainfall, suspended-sediment concentrations, surface ash layer thickness, soil moisture, soil grain size, soil lost on ignition, and plot topography. Runoff discharge reached a steady state within 7 to 26 minutes. Steady infiltration rates with the 50-mm/h application rainfall intensity approached 20?35 mm/h. If these rates are projected to rainfall application intensities used in many studies of burned area runoff production (about 80 mm/h), the steady discharge rates are on the lower end of measurements from other studies. Experiments using multiple rainfall intensities (three) suggest that runoff begins at rainfall intensities around 20 mm/h at the 1-square-meter scale, an observation consistent with a 10-mm/h rainfall intensity threshold needed for runoff initiation that has been reported in the literature.

Scientific Investigations Report↗
USGS2003

Lewis and Clark's observations and measurements of geomorphology and hydrology, and changes with time

Two VERY different men, Meriwether Lewis and William Clark, joined to J, ~ake the first recorded set of scientific observations and measurements of geomorphology and hydrology west of the Mississippi River. They did not limit themselves to these two scientific topics but were true naturalists, making observations and measurements related to astronomy (Large, 1979; Bedini, 1984; Plamondon, 1991; Bergantino, 1998), biology (Cutright, 1969), ecology, ethnology (Ronda, 1984a), geology (Bluemle, 2001; Bergantino, 1998), and phenology, as well as to the general geographical understanding of the arrangements of rivers and other topographical features of the trans-Mississippi West (Allen, 1975) .

Circular↗
USGS2001

Initial hydrologic and geomorphic response following a wildfire in the Colorado front range

A wildfire in May 1996 burned 4690 hectares in two watersheds forested by ponderosa pine and Douglas fir in a steep, mountainous landscape with a summer, convective thunderstorm precipitation regime. The wildfire lowered the erosion threshold in the watersheds, and consequently amplified the subsequent erosional response to shorter time interval episodic rainfall and created both erosional and depositional features in a complex pattern throughout the watersheds. The initial response during the first four years was an increase in runoff and erosion rates followed by decreases toward pre-fire rates. The maximum unit-area peak discharge was 24 m3 s-1 km-2 for a rainstorm in 1996 with a rain intensity of 90 mm h-1. Recovery to pre-fire conditions seems to have occurred by 2000 because for a maximum 30-min rainfall intensity of 50 mm h-1, the unit-area peak discharge in 1997 was 6.6 m3 s-1 km-2, while in 2000 a similar intensity produced only 0.11 m3 s-1 km-2. Rill erosion accounted for 6 per cent, interrill erosion for 14 per cent, and drainage erosion for 80 per cent of the initial erosion in 1996. This represents about a 200-fold increase in erosion rates on hillslopes which had a recovery or relaxation time of about three years. About 67 per cent of the initially eroded sediment is still stored in the watersheds after four years with an estimated residence time greater than 300 years. This residence time is much greater than the fire recurrence interval so erosional and depositional features may become legacies from the wildfire and may affect landscape evolution by acting as a new set of initial conditions for subsequent wildfire and flood sequences.

Colorado↗