ABSTRACT Unpaved roads are usually the largest anthropogenic sediment source in forested watershe... more ABSTRACT Unpaved roads are usually the largest anthropogenic sediment source in forested watersheds. Road sediment production, road-stream connectivity, and road sediment delivery should each be affected by climate change, but there are no field data that have directly measured the differences in road sediment production and delivery in areas with similar geology but varying climates, or varying geology in areas with similar climates. In this paper we: 1) summarize the differences in road sediment production and road-stream connectivity in rain- vs. snow-dominated environments and different geologic terranes in California's Sierra Nevada; 2) use these field data to predict the potential effects of climate change on road sediment production and delivery. Road sediment production was measured with sediment fences at up to 67 different segments for 2-5 years in California's southern and central Sierra Nevada. In the southern Sierra simultaneous data were collected from the rain-dominated Jose Basin and the snow-dominated Kings River Experimental Watersheds. Road drainage features and road-stream connectivity were measured by detailed surveys along 40 km of unpaved roads in the southern, central, and northern Sierra Nevada. Road sediment production averaged nearly 2 kg m-2 yr-1 in the rain-dominated study area in the southern Sierra, and this was an order of magnitude higher than the erosion rates in the higher, snowmelt-dominated areas. Mean sediment production rates in the mixed rain-snow regime in the central Sierra were intermediate at 0.2-0.8 kg m-2 yr-1, but sediment production rates declined above 1200 m due to the reduction in rainfall. Thirty percent of the native surface roads in the lower elevation Jose Basin were connected to the stream as compared to only 3% in the higher-elevation watersheds; in the mixed rain-snow regime in the central Sierra Nevada 25% of the roads were connected. Road-stream connectivity is expected to be lower in the volcanic terrane in the northern Sierra where there is more groundwater flow and a lower stream density. A warming climate and the resulting shift from rain to snow can sharply increase road erosion rates, and may increase road-stream connectivity by increasing runoff and erosion rates as well as increasing stream densities. The effects of a warming climate may be substantially less in more permeable geologic terranes where there are fewer streams and less road runoff.
Unpaved roads are a major source of sediment in many forested watersheds, but there are relativel... more Unpaved roads are a major source of sediment in many forested watersheds, but there are relatively few data on road sediment production rates and the factors controlling sediment production. The primary goals of this study are to: (1) quantify sediment production rates from different road surfaces; (2) determine the key controls on road sediment production rates and develop an empirical predictive model; and (3) to better understand road erosion and transport processes by comparing the particle size distribution of sediment sources and sinks. The study is part of the Kings River Experimental Watershed study (KREW) in the southern Sierra Nevada Mountains in east-central California. Elevations range from 1485 m to 2420 m, and most of the precipitation falls as snow. Sediment production was measured with sediment fences from 36 road segments and 9 undisturbed swales over the 2003-2004 wet season, and from 41 road segments and 18 undisturbed swales over the 2004-2005 wet season. The roa...
Wildfire increases the potential connectivity of runoff and sediment throughout watersheds due to... more Wildfire increases the potential connectivity of runoff and sediment throughout watersheds due to greater bare soil, runoff and erosion as compared to pre‐fire conditions. This research examines the connectivity of post‐fire runoff and sediment from hillslopes (<1.5 ha; n = 31) and catchments (<1000 ha; n = 10) within two watersheds (<1500 ha) burned by the 2012 High Park Fire in northcentral Colorado, USA. Our objectives were to: (1) identify sources and quantify magnitudes of post‐fire runoff and erosion at nested hillslopes and watersheds for two rain storms with varied duration, intensity and antecedent precipitation; and (2) assess the factors affecting the magnitude and connectivity of runoff and sediment across spatial scales for these two rain storms. The two summer storms that are the focus of this research occurred during the third summer after burning. The first storm had low intensity rainfall over 11 hours (return interval <1–2 years), whereas the second eve...
Concerns over wildfire impacts to water supplies have motivated efforts to mitigate risk by reduc... more Concerns over wildfire impacts to water supplies have motivated efforts to mitigate risk by reducing forest fuels. Methods to assess fuel treatment effects and prioritise their placement are needed to guide risk mitigation efforts. We present a fuel treatment optimisation model to minimise risk to multiple water supplies based on constraints for treatment feasibility and cost. Risk is quantified as the expected sediment impact costs to water supplies by combining measures of fire likelihood and behaviour, erosion, sediment transport and water supply vulnerability. We demonstrate the model’s utility for prioritising fuel treatments in two large watersheds in Colorado, USA, that are critical for municipal water supply. Our results indicate that wildfire risk to water supplies can be substantially reduced by treating a small portion of the watersheds that have dense, fire-prone forests on steep slopes that drain to water supply infrastructure. Our results also show that the cost of fue...
Post-wildfire landscapes are highly susceptible to rapid geomorphic changes at both the hillslope... more Post-wildfire landscapes are highly susceptible to rapid geomorphic changes at both the hillslope and watershed scales due to increases in hillslope runoff and erosion, and the resulting downstream effects. Numerous studies have documented these changes at the hillslope scale, but relatively few studies have documented larger-scale post-fire geomorphic changes over time. In this study we used five airborne laser scanning (ALS) datasets collected over four years to quantify valley bottom changes in two ∼15 km 2 watersheds, Skin Gulch and Hill Gulch, after the June 2012 High Park fire in northern Colorado and a large mesoscale flood 15 months later. The objectives were to: 1) quantify spatial and temporal patterns of erosion and deposition throughout the channel network following the wildfire and including the mesoscale flood; and 2) evaluate whether these changes are correlated to precipitation metrics, burn severity, or morphologic variables. Geomorphic changes were calculated using a DEMs of difference (DoD) approach for the channel network segmented into 50-m lengths. The results showed net sediment accumulation after the wildfire in the valley bottoms of both watersheds, with the greatest accumulations in the first two years after burning in wider and flatter valley bottoms. In contrast, the mesoscale flood caused large net erosion, with the greatest erosion in the areas with the greatest post-fire deposition. Volume changes for the different time periods were weakly but significantly correlated to, in order of decreasing correlation, contributing area, channel width, percent burned at high and/or moderate severity, channel slope, confinement ratio, maximum 30-minute rainfall, and total rainfall. These results suggest that morphometric characteristics, when combined with burn severity and a specified storm, can indicate the relative likelihood and locations for post-fire erosion and deposition. This information can help assess downstream risks and prioritize areas for post-fire hillslope rehabilitation treatments.
A review of past efforts to monitor water quality reveals that success or failure depends on four... more A review of past efforts to monitor water quality reveals that success or failure depends on four components: monitoring design (asking the right question); making the right measurements; managing the data; and analyzing the data to answer the question. A failure of any one of these components will doom the monitoring study. (1) Monitoring design. What is the question or hypothesis that is to be tested? • A clear and detailed statement of the monitoring objective, including a precise description of what will be measured, where it will be measured, why it will be measured, how it will be measured, and when and how long it will be measured – including a detailed discussion of how these measurements will be used to address (solve) the stated monitoring objective. (2) Making measurements. • Selection of appropriate locations, instrumentation, data timing, frequency, and duration required to adequately address the objectives described in (1). • Ability to successfully collect the appropr...
Forests account for 33 percent of the U.S. land area, process nearly two-thirds of the fresh wate... more Forests account for 33 percent of the U.S. land area, process nearly two-thirds of the fresh water supply, and provide water to 40 percent of all municipalities or about 180 million people. Water supply management is becoming more difficult given the increasing demand for water, climate change, increasing development, changing forest ownership, and increasingly fragmented laws governing forest and watershed
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2014
Post-fire flooding and erosion can pose a serious threat to life, property, and municipal water s... more Post-fire flooding and erosion can pose a serious threat to life, property, and municipal water supplies. Increased peak flows and sediment delivery due to the loss of surface cover and fire-induced changes in soil properties are of great concern to both resource managers and the public. To respond to this threat, interdisciplinary Burned Area Emergency Response (BAER) Teams are formed to assess potential erosion and flood risks. These teams are under tight deadlines as remediation plans and treatments must be developed and implemented before the first major storms in order to be effective. One of the primary sources of information for making these decisions is a burn severity map derived from remote sensing data (typically Landsat) that reflects fire induced changes in vegetative cover and soil properties. Slope, soils, land cover, and climate are also important parameters that need to be considered when accessing risk. Many modeling tools and datasets have been developed to assist BAER teams, but process-based and spatially explicit empirical models are currently under-utilized compared to simpler, lumped models because they are both more difficult to set up and require spatially explicit inputs such as digital elevation models, soils, and land cover. We are working to facilitate the use of models by preparing spatial datasets within a web-based tool that rapidly modifies model inputs using burn severity maps derived from earth observation data. Automating the creation of model inputs facilitates the wider use of more accurate, process-based models for spatially explicit predictions of post-fire erosion and runoff.
Land managers often need to predict watershed-scale erosion rates after disturbance or other land... more Land managers often need to predict watershed-scale erosion rates after disturbance or other land cover changes. This study compared commonly used hillslope erosion models to simulate post-fire sediment yields (SY) at both hillslope and watershed scales within the High Park Fire, Colorado, U.S.A. At hillslope scale, simulated SY from four models-RUSLE, AGWA/KINEROS2, WEPP, and a site-specific regression model-were compared to observed SY at 29 hillslopes. At the watershed scale, RUSLE, AGWA/KINEROS2, and WEPP were applied to simulate spatial patterns of SY for two 14-16 km 2 watersheds using different scales (0.5-25 ha) of hillslope discretization. Simulated spatial patterns were compared between models and to densities of channel heads across the watersheds. Three additional erosion algorithms were implemented within a land surface model to evaluate effects of parameter uncertainty. At the hillslope scale, SY was only significantly correlated to observed SY for the empirical model, but at the watershed scale, sediment loads were significantly correlated to observed channel head densities for all models. Watershed sediment load increased with the size of the hillslope sub-units due to the nonlinear effects of hillslope length on simulated erosion. SY's were closest in magnitude to expected watershed-scale SY when models were divided into the smallest hillslopes. These findings demonstrate that current erosion models are fairly consistent at identifying areas with low and high erosion potential, but the wide range of predicted SY and poor fit to observed SY highlight the need for better field observations and model calibration to obtain more accurate simulations.
Slope wetlands generally occur at breaks in slope where discharging ground water maintains moist ... more Slope wetlands generally occur at breaks in slope where discharging ground water maintains moist soil conditions. They often are found on the perimeter of highly permeable alluvial fans, but there have been no detailed hydrologic studies of these particular wetlands. We combined stream and spring flow measurements with five years of water-level and piezometric data to understand the hydrology of a 1.6 ha slope wetland at the base of a 5.2 ha alluvial fan in the central Rocky Mountains of Colorado. Step changes in streamflow inputs resulting from an upstream water diversion helped confirm the linkages inferred from the hydrometric data. Nearly 30% of the streamflow along a 180-m reach on the alluvial fan was lost to seepage. Discharge from two springs at the toe of the alluvial fan was eliminated and the piezometric head in the toe of the fan decreased by more than 80 cm within 1-2 days after the stream was diverted, indicating that stream seepage is the primary source of groundwater recharge for the alluvial fan. Streamflow and ground water discharging at the base of the alluvial fan were the primary wetland inflows, with summer precipitation playing a relatively minor role. Consequently, wetland water levels declined by up to 75 cm after the diversion began operating. The largest declines were in the lower part of the wetland, where surface sheet flow from the stream was the main water source. Continuing groundwater discharge into the upper part of the wetland limited the water level declines to less than 40 cm. The importance of streamflow as a water source distinguishes slope wetlands adjacent to alluvial fans from those found in other settings and makes them particularly vulnerable to upstream water diversions.
Ecosystem Dynamics in a Polar Desert: the Mcmurdo Dry Valleys, Antarctica, 2013
In the McMurdo Dry Valleys, glacial meltwater streams are a critical linkage between the glaciers... more In the McMurdo Dry Valleys, glacial meltwater streams are a critical linkage between the glaciers and the lakes in the valley bottoms. This paper analyzes the physiographic characteristics and six years of discharge data from five streams in order to better characterize the dynamic inputs into Lake Fryxell, a closed basin in Taylor Valley. These feeder streams typically flow only for six to eight weeks during the summer, and streamflow is highly variable on an interannual as well as daily basis. During low flow years, the shorter streams contributed a higher proportion of the total annual inflow into the lake; this pattern may reflect the greater losses to wetting the hyporheic zone. Comparisons of the period of direct sun on the glacier faces with the time of peak flow suggested that solar position and melt from the glacier faces are the dominant controls on the diurnal fluctuations in streamflow. An analysis of streamflow recession showed considerable variability between streams and in some cases, over time. For example, recession coefficients for Canada Stream, a short stream with an incised channel, were fairly invariant with streamflow. In contrast, the recession coefficients for Lost Seal Stream, an unconfined, low gradient stream, increased significantly with increasing discharge. These observations lead to hypotheses for the control of streamflow dynamics in the McMurdo Dry Valleys by climate, solar position, and geomotphic factors.
Characteristics of streams and rivers reflect variations in local geomorphology, climatic gradien... more Characteristics of streams and rivers reflect variations in local geomorphology, climatic gradients, spatial and temporal scales of natural disturbances, and the dynamic features of the riparian forest. This results in a variety of stream types which, when coupled with the many human uses of the Pacific Northwest coastal ecoregion, presents a difficult challenge in identifying and evaluating fundamental, system-level components of ecologically healthy watersheds. Over 20 types of streams are found in western Oregon, Washington, and British Columbia and in southeastern Alaska, a region where extractive forest, agricultural, fishing, and mining industries and a rapidly increasing urban population are severely altering the landscape. Yet stream characteristics remain the best indicators of watershed vitality, provided the fundamental characteristics of healthy streams are accurately known. The premise of this article is that the delivery and routing of water, sediment, and woody debris to streams are the key processes regulating the vitality of watersheds and their drainage networks in the Pacific Northwest coastal ecoregion. Five fundamental components of stream corridors are examined: basin geomorphology, hydrologic patterns, water quality, riparian forest characteristics, and habitat characteristics. Ecologically healthy watersheds require the preservation of lateral, longitudinal, and vertical connections between system components as well as the natural spatial and temporal variability of those components. The timing and mode of interdependencies between fundamental components are as important as the magnitude of individual components themselves.
Big Meadows. a 63-ha fen in Rocky Mountain National Park (RMNP). was ditched for agricultural pur... more Big Meadows. a 63-ha fen in Rocky Mountain National Park (RMNP). was ditched for agricultural purposes in the early part of this century. Although use of the ditch ceased after the establishment of RMNP in 1915. it continued to intercept sheet flows in the central and southern portions of the fen. causing the groundwater level to decrease and aerobic soil conditions to develop in the mid-to late-summer of most years. In 1990. the ditch was blocked in an attempt to restore the hydrologic regime in the central and southern portions of the fen. Water-level data from three years prior to restoration and four years after restoration show that blocking the ditch successfully restored surface sheet flow. high late-summer watertable levels. and anaerobic soil conditions in much of the central and southern portions of the fen. Conditions in these areas are now similar to those in the northern portion of the fen. The long-term data from this site also indicate that summer rainfall has a greater influence on the magnitude of late-summer drying than the size of the winter snowpack. In a post-restoration year with extremely low rainfall in July and August. water levels throughout the fen decreased to levels similar to those observed throughout most of the pre-restoration period. The study suggests that this and other fens in the southern Rocky Mountains are extremely sensitive to summer precipitation and the hydrologic changes created by even small ditches or water diversions.
The water drop penetration time (WDPT) technique was applied in 2018 to check persistence of soil... more The water drop penetration time (WDPT) technique was applied in 2018 to check persistence of soil water repellency (SWR) in a Sicilian mountain area affected by a wildfire on June 2016. A total of four sites, that were severely water repellent immediately after burning, were sampled. Depending on the site, wettable soil conditions, less SWR and maintenance of a noticeable SWR were detected two years later. At the site showing a near-constant SWR, WDPTs were particularly high in the top soil layer (0-0.03 m) and they appreciably decreased more in depth. Signs of decreasing SWR in drier soil conditions and in association with coarser soil particles were also detected at this site. High gradients of the WDPT can occur at very small vertical distances and a depth increment of approximately 0.01 m should be appropriate to capture small-scale vertical changes in SWR, especially close to the soil surface. Occurrence of SWR phenomena is easily perceivable and explainable if an inverse relationship between WDPTs and antecedent soil water content is obtained. A direct relationship between these two variables is more difficult to interpret because infiltration times that increase in wetter soil are expected according to the classical infiltration theory. A hypothesis that should be tested in the future is to verify if WDPTs that decrease in drier soil conditions signal less SWR as a consequence of a reduced biological activity of the soil. Finally, long-term monitoring projects on longevity of fire effects on SWR should be developed, even because an in depth knowledge of the involved processes is relevant for the civil protection system.
Wildfires have become a recurrent threat for many Mediterranean forest ecosystems. The characteri... more Wildfires have become a recurrent threat for many Mediterranean forest ecosystems. The characteristics of the Mediterranean climate, with its warm and dry summers and mild and wet winters, make this a region prone to wildfire occurrence as well as to post-fire soil erosion. This threat is expected to be aggravated in the future due to climate change and land management practices and planning. The wide recognition of wildfires as a driver for runoff and erosion in burnt forest areas has created a strong demand for model-based tools for predicting the post-fire hydrological and erosion response and, in particular, for predicting the effectiveness of post-fire management operations to mitigate these responses. In this study, the effectiveness of two post-fire treatments (hydromulch and natural pine needle mulch) in reducing post-fire runoff and soil erosion was evaluated against control conditions (i.e. untreated conditions), at different spatial scales. The main objective of this study was to use field data to evaluate the ability of different erosion models: (i) empirical (RUSLE), (ii) semi-empirical (MMF), and (iii) physically-based (PESERA), to predict the hydrological and erosive response as well as the effectiveness of different mulching techniques in fire-affected areas. The results of this study showed that all three models were reasonably able to reproduce the hydrological and erosive processes occurring in burned forest areas. In addition, it was demonstrated that the models can be calibrated at a small spatial scale (0.5 m 2) but provide accurate results at greater spatial scales (10 m 2). From this work, the RUSLE model seems to be ideal for fast and simple applications (i.e. prioritization of areas-at-risk) mainly due to its simplicity and reduced data requirements. On the other hand, the more complex MMF and PESERA models would be valuable as a base of a possible tool for assessing the risk of water contamination in fire-affected water bodies and for testing different land management scenarios.
Post-fire rehabilitation treatments are commonly implemented after high-severity wildfires, but f... more Post-fire rehabilitation treatments are commonly implemented after high-severity wildfires, but few data are available about the efficacy of these treatments. This study assessed post-fire erosion rates and the effectiveness of seeding, straw mulching, and contour felling in reducing erosion after a June 2000 wildfire northwest of Loveland, Colorado. Site characteristics and sediment yields were measured on 12 burned and untreated control plots and 22 burned and treated plots from 2000 to 2003. The size of the hillslope plots ranged from 0Ð015 to 0Ð86 ha. Sediment yields varied significantly by treatment and were most closely correlated with the amount of ground cover. On the control plots the mean sediment yield declined from 6-10 Mg ha 1 in the first two years after burning to 1Ð2 Mg ha 1 in 2002 and 0Ð7 Mg ha 1 in 2003. Natural regrowth caused the amount of ground cover on the control plots to increase progressively from 33% in fall 2000 to 88% in fall 2003. Seeding had no effect on either the amount of ground cover or sediment yields. Mulching reduced sediment yields by at least 95% relative to the control plots in 2001, 2002, and 2003, and the lower sediment yields are attributed to an immediate increase in the amount of ground cover in the mulched plots. The contour-felling treatments varied considerably in the quality of installation, and sediment storage capacities ranged from 7 to 32 m 3 ha 1. The initial contour-felling treatment did not reduce sediment yields when subjected to a very large storm event, but sediment yields were significantly reduced by a contour-felling treatment installed after this large storm. The results indicate that contour felling may be able to store much of the sediment generated in an average year, but will not reduce sediment yields from larger storms. Copyright
ABSTRACT Unpaved roads are usually the largest anthropogenic sediment source in forested watershe... more ABSTRACT Unpaved roads are usually the largest anthropogenic sediment source in forested watersheds. Road sediment production, road-stream connectivity, and road sediment delivery should each be affected by climate change, but there are no field data that have directly measured the differences in road sediment production and delivery in areas with similar geology but varying climates, or varying geology in areas with similar climates. In this paper we: 1) summarize the differences in road sediment production and road-stream connectivity in rain- vs. snow-dominated environments and different geologic terranes in California&#39;s Sierra Nevada; 2) use these field data to predict the potential effects of climate change on road sediment production and delivery. Road sediment production was measured with sediment fences at up to 67 different segments for 2-5 years in California&#39;s southern and central Sierra Nevada. In the southern Sierra simultaneous data were collected from the rain-dominated Jose Basin and the snow-dominated Kings River Experimental Watersheds. Road drainage features and road-stream connectivity were measured by detailed surveys along 40 km of unpaved roads in the southern, central, and northern Sierra Nevada. Road sediment production averaged nearly 2 kg m-2 yr-1 in the rain-dominated study area in the southern Sierra, and this was an order of magnitude higher than the erosion rates in the higher, snowmelt-dominated areas. Mean sediment production rates in the mixed rain-snow regime in the central Sierra were intermediate at 0.2-0.8 kg m-2 yr-1, but sediment production rates declined above 1200 m due to the reduction in rainfall. Thirty percent of the native surface roads in the lower elevation Jose Basin were connected to the stream as compared to only 3% in the higher-elevation watersheds; in the mixed rain-snow regime in the central Sierra Nevada 25% of the roads were connected. Road-stream connectivity is expected to be lower in the volcanic terrane in the northern Sierra where there is more groundwater flow and a lower stream density. A warming climate and the resulting shift from rain to snow can sharply increase road erosion rates, and may increase road-stream connectivity by increasing runoff and erosion rates as well as increasing stream densities. The effects of a warming climate may be substantially less in more permeable geologic terranes where there are fewer streams and less road runoff.
Unpaved roads are a major source of sediment in many forested watersheds, but there are relativel... more Unpaved roads are a major source of sediment in many forested watersheds, but there are relatively few data on road sediment production rates and the factors controlling sediment production. The primary goals of this study are to: (1) quantify sediment production rates from different road surfaces; (2) determine the key controls on road sediment production rates and develop an empirical predictive model; and (3) to better understand road erosion and transport processes by comparing the particle size distribution of sediment sources and sinks. The study is part of the Kings River Experimental Watershed study (KREW) in the southern Sierra Nevada Mountains in east-central California. Elevations range from 1485 m to 2420 m, and most of the precipitation falls as snow. Sediment production was measured with sediment fences from 36 road segments and 9 undisturbed swales over the 2003-2004 wet season, and from 41 road segments and 18 undisturbed swales over the 2004-2005 wet season. The roa...
Wildfire increases the potential connectivity of runoff and sediment throughout watersheds due to... more Wildfire increases the potential connectivity of runoff and sediment throughout watersheds due to greater bare soil, runoff and erosion as compared to pre‐fire conditions. This research examines the connectivity of post‐fire runoff and sediment from hillslopes (<1.5 ha; n = 31) and catchments (<1000 ha; n = 10) within two watersheds (<1500 ha) burned by the 2012 High Park Fire in northcentral Colorado, USA. Our objectives were to: (1) identify sources and quantify magnitudes of post‐fire runoff and erosion at nested hillslopes and watersheds for two rain storms with varied duration, intensity and antecedent precipitation; and (2) assess the factors affecting the magnitude and connectivity of runoff and sediment across spatial scales for these two rain storms. The two summer storms that are the focus of this research occurred during the third summer after burning. The first storm had low intensity rainfall over 11 hours (return interval <1–2 years), whereas the second eve...
Concerns over wildfire impacts to water supplies have motivated efforts to mitigate risk by reduc... more Concerns over wildfire impacts to water supplies have motivated efforts to mitigate risk by reducing forest fuels. Methods to assess fuel treatment effects and prioritise their placement are needed to guide risk mitigation efforts. We present a fuel treatment optimisation model to minimise risk to multiple water supplies based on constraints for treatment feasibility and cost. Risk is quantified as the expected sediment impact costs to water supplies by combining measures of fire likelihood and behaviour, erosion, sediment transport and water supply vulnerability. We demonstrate the model’s utility for prioritising fuel treatments in two large watersheds in Colorado, USA, that are critical for municipal water supply. Our results indicate that wildfire risk to water supplies can be substantially reduced by treating a small portion of the watersheds that have dense, fire-prone forests on steep slopes that drain to water supply infrastructure. Our results also show that the cost of fue...
Post-wildfire landscapes are highly susceptible to rapid geomorphic changes at both the hillslope... more Post-wildfire landscapes are highly susceptible to rapid geomorphic changes at both the hillslope and watershed scales due to increases in hillslope runoff and erosion, and the resulting downstream effects. Numerous studies have documented these changes at the hillslope scale, but relatively few studies have documented larger-scale post-fire geomorphic changes over time. In this study we used five airborne laser scanning (ALS) datasets collected over four years to quantify valley bottom changes in two ∼15 km 2 watersheds, Skin Gulch and Hill Gulch, after the June 2012 High Park fire in northern Colorado and a large mesoscale flood 15 months later. The objectives were to: 1) quantify spatial and temporal patterns of erosion and deposition throughout the channel network following the wildfire and including the mesoscale flood; and 2) evaluate whether these changes are correlated to precipitation metrics, burn severity, or morphologic variables. Geomorphic changes were calculated using a DEMs of difference (DoD) approach for the channel network segmented into 50-m lengths. The results showed net sediment accumulation after the wildfire in the valley bottoms of both watersheds, with the greatest accumulations in the first two years after burning in wider and flatter valley bottoms. In contrast, the mesoscale flood caused large net erosion, with the greatest erosion in the areas with the greatest post-fire deposition. Volume changes for the different time periods were weakly but significantly correlated to, in order of decreasing correlation, contributing area, channel width, percent burned at high and/or moderate severity, channel slope, confinement ratio, maximum 30-minute rainfall, and total rainfall. These results suggest that morphometric characteristics, when combined with burn severity and a specified storm, can indicate the relative likelihood and locations for post-fire erosion and deposition. This information can help assess downstream risks and prioritize areas for post-fire hillslope rehabilitation treatments.
A review of past efforts to monitor water quality reveals that success or failure depends on four... more A review of past efforts to monitor water quality reveals that success or failure depends on four components: monitoring design (asking the right question); making the right measurements; managing the data; and analyzing the data to answer the question. A failure of any one of these components will doom the monitoring study. (1) Monitoring design. What is the question or hypothesis that is to be tested? • A clear and detailed statement of the monitoring objective, including a precise description of what will be measured, where it will be measured, why it will be measured, how it will be measured, and when and how long it will be measured – including a detailed discussion of how these measurements will be used to address (solve) the stated monitoring objective. (2) Making measurements. • Selection of appropriate locations, instrumentation, data timing, frequency, and duration required to adequately address the objectives described in (1). • Ability to successfully collect the appropr...
Forests account for 33 percent of the U.S. land area, process nearly two-thirds of the fresh wate... more Forests account for 33 percent of the U.S. land area, process nearly two-thirds of the fresh water supply, and provide water to 40 percent of all municipalities or about 180 million people. Water supply management is becoming more difficult given the increasing demand for water, climate change, increasing development, changing forest ownership, and increasingly fragmented laws governing forest and watershed
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2014
Post-fire flooding and erosion can pose a serious threat to life, property, and municipal water s... more Post-fire flooding and erosion can pose a serious threat to life, property, and municipal water supplies. Increased peak flows and sediment delivery due to the loss of surface cover and fire-induced changes in soil properties are of great concern to both resource managers and the public. To respond to this threat, interdisciplinary Burned Area Emergency Response (BAER) Teams are formed to assess potential erosion and flood risks. These teams are under tight deadlines as remediation plans and treatments must be developed and implemented before the first major storms in order to be effective. One of the primary sources of information for making these decisions is a burn severity map derived from remote sensing data (typically Landsat) that reflects fire induced changes in vegetative cover and soil properties. Slope, soils, land cover, and climate are also important parameters that need to be considered when accessing risk. Many modeling tools and datasets have been developed to assist BAER teams, but process-based and spatially explicit empirical models are currently under-utilized compared to simpler, lumped models because they are both more difficult to set up and require spatially explicit inputs such as digital elevation models, soils, and land cover. We are working to facilitate the use of models by preparing spatial datasets within a web-based tool that rapidly modifies model inputs using burn severity maps derived from earth observation data. Automating the creation of model inputs facilitates the wider use of more accurate, process-based models for spatially explicit predictions of post-fire erosion and runoff.
Land managers often need to predict watershed-scale erosion rates after disturbance or other land... more Land managers often need to predict watershed-scale erosion rates after disturbance or other land cover changes. This study compared commonly used hillslope erosion models to simulate post-fire sediment yields (SY) at both hillslope and watershed scales within the High Park Fire, Colorado, U.S.A. At hillslope scale, simulated SY from four models-RUSLE, AGWA/KINEROS2, WEPP, and a site-specific regression model-were compared to observed SY at 29 hillslopes. At the watershed scale, RUSLE, AGWA/KINEROS2, and WEPP were applied to simulate spatial patterns of SY for two 14-16 km 2 watersheds using different scales (0.5-25 ha) of hillslope discretization. Simulated spatial patterns were compared between models and to densities of channel heads across the watersheds. Three additional erosion algorithms were implemented within a land surface model to evaluate effects of parameter uncertainty. At the hillslope scale, SY was only significantly correlated to observed SY for the empirical model, but at the watershed scale, sediment loads were significantly correlated to observed channel head densities for all models. Watershed sediment load increased with the size of the hillslope sub-units due to the nonlinear effects of hillslope length on simulated erosion. SY's were closest in magnitude to expected watershed-scale SY when models were divided into the smallest hillslopes. These findings demonstrate that current erosion models are fairly consistent at identifying areas with low and high erosion potential, but the wide range of predicted SY and poor fit to observed SY highlight the need for better field observations and model calibration to obtain more accurate simulations.
Slope wetlands generally occur at breaks in slope where discharging ground water maintains moist ... more Slope wetlands generally occur at breaks in slope where discharging ground water maintains moist soil conditions. They often are found on the perimeter of highly permeable alluvial fans, but there have been no detailed hydrologic studies of these particular wetlands. We combined stream and spring flow measurements with five years of water-level and piezometric data to understand the hydrology of a 1.6 ha slope wetland at the base of a 5.2 ha alluvial fan in the central Rocky Mountains of Colorado. Step changes in streamflow inputs resulting from an upstream water diversion helped confirm the linkages inferred from the hydrometric data. Nearly 30% of the streamflow along a 180-m reach on the alluvial fan was lost to seepage. Discharge from two springs at the toe of the alluvial fan was eliminated and the piezometric head in the toe of the fan decreased by more than 80 cm within 1-2 days after the stream was diverted, indicating that stream seepage is the primary source of groundwater recharge for the alluvial fan. Streamflow and ground water discharging at the base of the alluvial fan were the primary wetland inflows, with summer precipitation playing a relatively minor role. Consequently, wetland water levels declined by up to 75 cm after the diversion began operating. The largest declines were in the lower part of the wetland, where surface sheet flow from the stream was the main water source. Continuing groundwater discharge into the upper part of the wetland limited the water level declines to less than 40 cm. The importance of streamflow as a water source distinguishes slope wetlands adjacent to alluvial fans from those found in other settings and makes them particularly vulnerable to upstream water diversions.
Ecosystem Dynamics in a Polar Desert: the Mcmurdo Dry Valleys, Antarctica, 2013
In the McMurdo Dry Valleys, glacial meltwater streams are a critical linkage between the glaciers... more In the McMurdo Dry Valleys, glacial meltwater streams are a critical linkage between the glaciers and the lakes in the valley bottoms. This paper analyzes the physiographic characteristics and six years of discharge data from five streams in order to better characterize the dynamic inputs into Lake Fryxell, a closed basin in Taylor Valley. These feeder streams typically flow only for six to eight weeks during the summer, and streamflow is highly variable on an interannual as well as daily basis. During low flow years, the shorter streams contributed a higher proportion of the total annual inflow into the lake; this pattern may reflect the greater losses to wetting the hyporheic zone. Comparisons of the period of direct sun on the glacier faces with the time of peak flow suggested that solar position and melt from the glacier faces are the dominant controls on the diurnal fluctuations in streamflow. An analysis of streamflow recession showed considerable variability between streams and in some cases, over time. For example, recession coefficients for Canada Stream, a short stream with an incised channel, were fairly invariant with streamflow. In contrast, the recession coefficients for Lost Seal Stream, an unconfined, low gradient stream, increased significantly with increasing discharge. These observations lead to hypotheses for the control of streamflow dynamics in the McMurdo Dry Valleys by climate, solar position, and geomotphic factors.
Characteristics of streams and rivers reflect variations in local geomorphology, climatic gradien... more Characteristics of streams and rivers reflect variations in local geomorphology, climatic gradients, spatial and temporal scales of natural disturbances, and the dynamic features of the riparian forest. This results in a variety of stream types which, when coupled with the many human uses of the Pacific Northwest coastal ecoregion, presents a difficult challenge in identifying and evaluating fundamental, system-level components of ecologically healthy watersheds. Over 20 types of streams are found in western Oregon, Washington, and British Columbia and in southeastern Alaska, a region where extractive forest, agricultural, fishing, and mining industries and a rapidly increasing urban population are severely altering the landscape. Yet stream characteristics remain the best indicators of watershed vitality, provided the fundamental characteristics of healthy streams are accurately known. The premise of this article is that the delivery and routing of water, sediment, and woody debris to streams are the key processes regulating the vitality of watersheds and their drainage networks in the Pacific Northwest coastal ecoregion. Five fundamental components of stream corridors are examined: basin geomorphology, hydrologic patterns, water quality, riparian forest characteristics, and habitat characteristics. Ecologically healthy watersheds require the preservation of lateral, longitudinal, and vertical connections between system components as well as the natural spatial and temporal variability of those components. The timing and mode of interdependencies between fundamental components are as important as the magnitude of individual components themselves.
Big Meadows. a 63-ha fen in Rocky Mountain National Park (RMNP). was ditched for agricultural pur... more Big Meadows. a 63-ha fen in Rocky Mountain National Park (RMNP). was ditched for agricultural purposes in the early part of this century. Although use of the ditch ceased after the establishment of RMNP in 1915. it continued to intercept sheet flows in the central and southern portions of the fen. causing the groundwater level to decrease and aerobic soil conditions to develop in the mid-to late-summer of most years. In 1990. the ditch was blocked in an attempt to restore the hydrologic regime in the central and southern portions of the fen. Water-level data from three years prior to restoration and four years after restoration show that blocking the ditch successfully restored surface sheet flow. high late-summer watertable levels. and anaerobic soil conditions in much of the central and southern portions of the fen. Conditions in these areas are now similar to those in the northern portion of the fen. The long-term data from this site also indicate that summer rainfall has a greater influence on the magnitude of late-summer drying than the size of the winter snowpack. In a post-restoration year with extremely low rainfall in July and August. water levels throughout the fen decreased to levels similar to those observed throughout most of the pre-restoration period. The study suggests that this and other fens in the southern Rocky Mountains are extremely sensitive to summer precipitation and the hydrologic changes created by even small ditches or water diversions.
The water drop penetration time (WDPT) technique was applied in 2018 to check persistence of soil... more The water drop penetration time (WDPT) technique was applied in 2018 to check persistence of soil water repellency (SWR) in a Sicilian mountain area affected by a wildfire on June 2016. A total of four sites, that were severely water repellent immediately after burning, were sampled. Depending on the site, wettable soil conditions, less SWR and maintenance of a noticeable SWR were detected two years later. At the site showing a near-constant SWR, WDPTs were particularly high in the top soil layer (0-0.03 m) and they appreciably decreased more in depth. Signs of decreasing SWR in drier soil conditions and in association with coarser soil particles were also detected at this site. High gradients of the WDPT can occur at very small vertical distances and a depth increment of approximately 0.01 m should be appropriate to capture small-scale vertical changes in SWR, especially close to the soil surface. Occurrence of SWR phenomena is easily perceivable and explainable if an inverse relationship between WDPTs and antecedent soil water content is obtained. A direct relationship between these two variables is more difficult to interpret because infiltration times that increase in wetter soil are expected according to the classical infiltration theory. A hypothesis that should be tested in the future is to verify if WDPTs that decrease in drier soil conditions signal less SWR as a consequence of a reduced biological activity of the soil. Finally, long-term monitoring projects on longevity of fire effects on SWR should be developed, even because an in depth knowledge of the involved processes is relevant for the civil protection system.
Wildfires have become a recurrent threat for many Mediterranean forest ecosystems. The characteri... more Wildfires have become a recurrent threat for many Mediterranean forest ecosystems. The characteristics of the Mediterranean climate, with its warm and dry summers and mild and wet winters, make this a region prone to wildfire occurrence as well as to post-fire soil erosion. This threat is expected to be aggravated in the future due to climate change and land management practices and planning. The wide recognition of wildfires as a driver for runoff and erosion in burnt forest areas has created a strong demand for model-based tools for predicting the post-fire hydrological and erosion response and, in particular, for predicting the effectiveness of post-fire management operations to mitigate these responses. In this study, the effectiveness of two post-fire treatments (hydromulch and natural pine needle mulch) in reducing post-fire runoff and soil erosion was evaluated against control conditions (i.e. untreated conditions), at different spatial scales. The main objective of this study was to use field data to evaluate the ability of different erosion models: (i) empirical (RUSLE), (ii) semi-empirical (MMF), and (iii) physically-based (PESERA), to predict the hydrological and erosive response as well as the effectiveness of different mulching techniques in fire-affected areas. The results of this study showed that all three models were reasonably able to reproduce the hydrological and erosive processes occurring in burned forest areas. In addition, it was demonstrated that the models can be calibrated at a small spatial scale (0.5 m 2) but provide accurate results at greater spatial scales (10 m 2). From this work, the RUSLE model seems to be ideal for fast and simple applications (i.e. prioritization of areas-at-risk) mainly due to its simplicity and reduced data requirements. On the other hand, the more complex MMF and PESERA models would be valuable as a base of a possible tool for assessing the risk of water contamination in fire-affected water bodies and for testing different land management scenarios.
Post-fire rehabilitation treatments are commonly implemented after high-severity wildfires, but f... more Post-fire rehabilitation treatments are commonly implemented after high-severity wildfires, but few data are available about the efficacy of these treatments. This study assessed post-fire erosion rates and the effectiveness of seeding, straw mulching, and contour felling in reducing erosion after a June 2000 wildfire northwest of Loveland, Colorado. Site characteristics and sediment yields were measured on 12 burned and untreated control plots and 22 burned and treated plots from 2000 to 2003. The size of the hillslope plots ranged from 0Ð015 to 0Ð86 ha. Sediment yields varied significantly by treatment and were most closely correlated with the amount of ground cover. On the control plots the mean sediment yield declined from 6-10 Mg ha 1 in the first two years after burning to 1Ð2 Mg ha 1 in 2002 and 0Ð7 Mg ha 1 in 2003. Natural regrowth caused the amount of ground cover on the control plots to increase progressively from 33% in fall 2000 to 88% in fall 2003. Seeding had no effect on either the amount of ground cover or sediment yields. Mulching reduced sediment yields by at least 95% relative to the control plots in 2001, 2002, and 2003, and the lower sediment yields are attributed to an immediate increase in the amount of ground cover in the mulched plots. The contour-felling treatments varied considerably in the quality of installation, and sediment storage capacities ranged from 7 to 32 m 3 ha 1. The initial contour-felling treatment did not reduce sediment yields when subjected to a very large storm event, but sediment yields were significantly reduced by a contour-felling treatment installed after this large storm. The results indicate that contour felling may be able to store much of the sediment generated in an average year, but will not reduce sediment yields from larger storms. Copyright
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