Browsing by Author "Kampf, Stephanie, advisor"
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Item Open Access Comparison of digital terrain and field-based channel derivation methods in a subalpine catchment, Front Range, Colorado(Colorado State University. Libraries, 2012) Hastings, Blaine, author; Kampf, Stephanie, advisor; Laituri, Melinda, committee member; Niemann, Jeffrey, committee memberUnderstanding the reliability of digitally derived channel networks for mountainous headwater catchments is important to many water resource and land-use management applications. Digital elevation models (DEMs) have become an essential tool for an increasing array of mountain runoff analyses. The purpose of this study is to investigate the influence of digitally-derived topographic variables on channel network formation for a high-elevation glaciated watershed. To accomplish this, our objectives were to (1) test how differences in gridded DEM resolution affect spatially distributed topographic parameters of local slope (tan β), specific contributing area (αs), and topographic wetness index (TWI) derived from both eight and infinite directional flow algorithms, (2) map the actual stream channel network at Loch Vale and examine the influence of surface variables on channel initiation, and (3) evaluate the performance of common methods for deriving channel networks from gridded topographic data by comparing to the observed network. We found that coarser DEM resolution leads to a loss of detail in spatial patterns of topographic parameters and an increase in the calculated mean values of ln(αs) and TWI. Grid cell sizes above 1m result in a substantial shift in the overall cumulative frequency distributions of ln(αs) and TWI towards higher values. A field survey at Loch Vale revealed a complex and disjointed channel network, with 242 channelized points and 30 channel heads. We found no predictable relationships between channel head locations and geomorphic process domains. Analysis of variance (ANOVA) showed no statistically significant difference in mean ln(αs) and TWI for channel head locations grouped by elevation, aspect, slope, formation process or upslope land cover type. For most DEM resolutions and flow partitioning algorithms, deriving channel networks with spatially constant flow accumulation and TWI thresholds provides poor network representation. The publicly available National Hydrography Dataset (NHD) layer oversimplifies the channel network by neglecting almost all first and second order channels. Many of the DEM-derived channel networks that use spatially constant flow accumulation and TWI thresholds also do not reproduce the locations of low order channels in the observed channel network well. Assumptions of topographic control on channel initiation are not shown to be valid at Loch Vale, likely due to their inability to capture subsurface processes and geologic features important to channel formation. However, if using these topographically dependent threshold methods to delineate channel networks, we suggest the use of field-based survey data to identify appropriate thresholds. With appropriate thresholds, both 1m and 10m DEMs can produce channel networks with similar drainage densities to the observed network, even if locations of low order channels are not predicted accurately. Performance degrades for 30m DEMs, so we suggest that DEMs with resolutions coarser than 10m should be avoided for channel network delineation.Item Open Access Effects of early snowmelt on plant phenophase timing and duration across an elevation gradient(Colorado State University. Libraries, 2021) Wilmer, Chelsea, author; Kampf, Stephanie, advisor; Steltzer, Heidi, advisor; Hufbauer, Ruth, committee memberPlant phenology is an important indicator of the effects of climate change, yet the relative importance of both the drivers of plant phenology and the importance of individual phenophases in how plants respond to climate change is not well understood. Here we assess the impact of early snowmelt, a critical climate perturbation in mountain regions, on the timing and duration of individual plant phenophases across an elevation gradient in Crested Butte, Colorado. We observed a sequence of plant phenophases, new leaves, full leaf expansion, first open flower, and full leaf color change at five sites at distinct elevations (2774 m, 2957 m, 3167 m, 3475 m, 3597 m) across three mountain life zones (montane, subalpine, and alpine) in 2017 and 2018. In the spring of 2018, we used solar radiation absorbing fabric to accelerate the timing of snowmelt and observed the differences in timing for early snowmelt plots relative to control plots. The two study years had different snowmelt timing with 2018 being much earlier than 2017, so we analyzed the data to evaluate the effect of year using unmanipulated plots only, and also, separately the snowmelt manipulation, on phenophase start dates and durations. Phenophase timing was advanced at nearly all sites in 2018 and was not clearly linked to shifts in duration, which were variable. The snowmelt manipulation did not shift the timing of phenophases at the lowest elevation in our elevation gradient and the effect of the experiment on the timing of phenophases decreased as elevation increased. Even though snowmelt was significantly accelerated in the manipulation plots in 2018 at the lowest elevation the timing of phenophases were not advanced. This may indicate a threshold beyond which early snowmelt no longer advanced leaf emergence. Earlier snowmelt in mountain regions can shift the timing and duration of plant growth, though not consistently, which will have consequences on how plants affect the movement of water and retention of nutrients and metals in mountain watersheds.Item Open Access Effects of post-fire mulch applications on hillslope-scale erosion(Colorado State University. Libraries, 2023) Geller, Jordyn, author; Kampf, Stephanie, advisor; Barnard, David, advisor; Nelson, Peter, committee memberWildfires are increasing in frequency and intensity, greatly altering the landscape and increasing risk of erosion. Mulching is a common restoration technique used after wildfire to enhance protective ground cover and reduce erosion, yet most studies are conducted at the plot-scale. This study applies an experimental approach to evaluate the impact of mulch treatments at the hillslope-scale using varying mulch levels. Similar adjacent hillslopes were chosen to minimize variability in landscape features. The objectives of this research are to 1) examine the effectiveness of post-fire mulching in reducing erosion at the hillslope-scale, and 2) identify landscape features and precipitation factors contributing to the occurrence and magnitude of sediment yield. Sediment fences were installed in convergent swales and planar hillslopes to quantify sediment yields before and after aerial wood mulch application. Rain gauges were installed to compute rainfall amount (mm), duration (hr), and maximum intensities (mm/hr) by storm event. Field observations, coupled with game camera footage, were utilized to evaluate whether each storm produced sediment in the fences. Surface cover surveys were conducted to assess cover changes over the season. Collectively these data were used to 1) identify rainfall intensity thresholds for erosion, 2) examine controls on sediment generation occurrence with a binomial distribution mixed-effects model, 3) examine controls on the magnitude of sediment yield using a gamma distribution mixed-effect model, and 4) assess relative importance of variables relating to sediment yield using random forest models. Threshold rainfall intensities for generating erosion at the study sites were 32-38 mm/hr for MI5, 11-18 mm/hr for MI15, 7-13 mm/hr for MI30, and 5-8 mm/hr for MI60. Across all models of erosion occurrence and magnitude of sediment yield, maximum rainfall intensity and total precipitation were primary drivers of erosion. There was no evidence of a mulch treatment effect on sediment occurrence or magnitude, likely resulting from insufficient initial mulch cover and a high-intensity storm that removed much of the mulch shortly after it was dropped on the hillslopes. Contributing area, slope mean, and slope length showed no influence on sediment yield, likely due to limited variation in these variables between hillslopes. These results highlight the importance of mulch cover that will stay in place under extreme rainfall. Future hillslope-scale studies should consider dropping mulch during a time period that is unlikely to have high intensity rainfall and explore mulch materials and application methods that will better ensure adequate initial cover for reducing hillslope-scale erosion.Item Open Access Effects of snow persistence on soil water nitrogen across an elevation gradient(Colorado State University. Libraries, 2019) Anenberg, Alyssa Nicole, author; Kampf, Stephanie, advisor; Baron, Jill, advisor; Borch, Thomas, committee memberIn the western United States, the timing and magnitude of snowmelt is an important control on soil water and nutrient availability. Warming trends can alter the timing of snowmelt, directly impacting snow cover and soil freeze-thaw cycles, as well as available water for downstream use. While prior research relating snow to soil water nitrogen has focused on areas with persistent winter snow, the snow and soil water dynamics in lower elevation areas with intermittent snowpack are not as well documented. The broad goal of this study is to understand how the duration of snow persistence affects soil moisture and soil water nitrogen concentrations. The specific objectives are to address (1) how the duration of snow persistence affects soil moisture across an elevation gradient, from areas where the snowpack ranges from shallow and intermittent to deep and persistent throughout the winter and (2) how this gradient in snowpack affects soil water nitrogen. Three study sites that span a 1500m elevation gradient were established in the Colorado Front Range to monitor snow, soil moisture, and soil water nitrogen. The highest elevation site, Michigan River, is located in the persistent snow zone; the middle elevation site, Dry Creek, is in the transitional snow zone; and the lowest elevation site, Mill Creek, lies in the intermittent snow zone. Each site was equipped with soil moisture probes at 5 and 20cm depth, soil temperature probes, snow depth poles monitored by time-lapse cameras, and ion exchange resin probes. The Mill Creek research site also contained nine snow manipulation chambers and twenty-seven tension lysimeters to sample soil water nitrogen. Snow cover persisted for longer periods of time as elevation increased and soil temperatures decreased. Lower elevation sites were consistently warmer and drier than the higher elevation site. At the highest elevation site, soil moisture increased after a large pulse of snowmelt in the late spring, while the lower elevations experienced multiple smaller pulses of soil moisture following individual snow events. In the snow manipulation chambers, plots with increased snow depth experienced increased soil moisture, however plots with decreased snow depth did not always produce the lowest soil moisture. Additionally, soil moisture in the control snow plots and in plots with increased snow depth consistently increased throughout the melt season, whereas plots with decreased snow depth briefly increased after each snowmelt event then declined to pre-event levels. NO₃– and NH₄+ were correlated with soil moisture, and large increases in soil moisture were associated with a flushing signal of NO₃–. This suggests that soil water nitrogen is regulated by the amount of soil water available, and that nitrogen can be impacted when changes in snow alter soil moisture timing and magnitude.Item Open Access Evaluating and correcting sensor change artifacts in the SNOTEL temperature records, southern Rocky Mountains, Colorado(Colorado State University. Libraries, 2017) Ma, Chenchen, author; Fassnacht, Steven, advisor; Kampf, Stephanie, advisor; Wei, Yu, committee memberIn many high elevation mountain regions, documented warming rates have been greater than the global surface average. These warming rates directly affect the snowpack, runoff, ecosystems, agriculture and species that rely on a high elevation snowpack. Temperature records from the snow telemetry (SNOTEL) network across the Southern Rocky Mountains in the western United States have high warming rates, which may have been affected by systematic inhomogeneities in the temperature data caused by sensor changes. This study evaluates the maximum, average, and minimum temperature trends from 68 long-term SNOTEL stations across Colorado for the period from the 1980s through 2015 using the non-parametric Mann-Kendall/Theil-Sen's analyses before and after the temperature records were corrected for the sensor-caused inhomogeneities. Three homogenization methods were tested using a simple temperature index snow accumulation and melt model. Results show that the significant warming trends found in the original datasets, especially in minimum temperature (average increase of 1.2 °C per decade), decreased (to an average of 0.5 °C per decade) after homogenization. Step-like shifts in temperature datasets were observed in SNOTEL temperature records at the time of temperature sensor change, which created a discontinuity in the temperature dataset. The temperature-index snow model simulated snow water equivalent (SWE) well (more than 93% of the calibrated stations within the "good" and "very good" performance category for all three statistical-evaluation periods based on the Nash-Sutcliffe coefficient of efficiency, NSCE) using the new temperature sensor dataset. However, these models did not perform as well when using the original (pre-sensor change) and homogenized temperatures, with 23% of stations for the original temperature data and 44-69% of stations for two homogenized temperature datasets within the "good" and "very good"temperature data, but they did not fully correct for the effects of sensor change on the temperature records. The NSCE and bias statistics from SWE modeling using the original and homogenized datasets suggest that the homogenization methods evaluated in this study are applicable for many of the SNOTEL stations in Colorado but not all, and need to be applied with caution. Potential users of temperature products from the SNOTEL network should also be very careful when choosing time periods for future climate change research and assessments. More long-term climate monitoring stations should be installed in high elevation mountain regions to document and investigate elevation-dependent warming.Item Open Access Evaluating post-fire woody mulch effects on soil and stream nitrogen(Colorado State University. Libraries, 2024) Richardson, Mikaela, author; Kampf, Stephanie, advisor; Rhoades, Chuck, advisor; Ross, Matt, committee member; Wilkins, Mike, committee memberSevere wildfires often increase nitrogen (N) loss from burned watersheds, impacting downstream water quality, water treatability, and aquatic habitat. Woody mulch is commonly applied to mitigate soil erosion and enhance revegetation post-fire, but it also provides a source of labile carbon (C) that may stimulate microbial immobilization and limit N release from soils. The objective of our study was to evaluate whether mulch application influenced turnover and loss of soil C and N in laboratory leaching trials and hillslope field settings, and then compared post-fire C and N in streams draining mulched and unmulched catchments. In the laboratory, we quantified C and N inputs and leaching outputs from mulched and unmulched soil columns. Within the Cameron Peak fire burn scar in northern Colorado, we compared soil N availability and potential leaching losses between mulched and unmulched hillslope plots. We also measured C, N, and other chemical constituents in streams draining three mulched and three unmulched catchments. In the laboratory leaching studies, mulch added high concentrations of dissolved organic carbon (> 500 mg L-1) and decreased nitrate leaching from soil columns by 27% during repeated simulated rainfall events. In hillslope plots, mulching also reduced soil nitrate, with greater impacts following spring snowmelt when N losses from soils to streams was highest. However, the effect of mulching was not measurable at the catchment scale due to low application rates and mulch extent, paired with high topographic and geomorphic variability amongst the catchments. Our findings show that C inputs from woody mulch can influence soil N retention in burned watersheds when applied at a minimum rate of 5 Mg ha-1; however practical constraints on aerial application may make it challenging to apply enough mulch for any downstream response to be detectable. Coupled with physical erosion protection, the biogeochemical impacts of mulching may facilitate soil and vegetation recovery following severe wildfire and reduce post-fire N losses to streams if sufficiently applied. Therefore, further post-fire rehabilitation efforts should optimize mulch operations by prioritizing sensitive watersheds and treating them with adequate mulch.Item Open Access Post-fire erosion response and recovery, High Park Fire, Colorado(Colorado State University. Libraries, 2014) Schmeer, Sarah R., author; Kampf, Stephanie, advisor; MacDonald, Lee, committee member; Rathburn, Sara, committee memberWildfires along the Colorado Front Range are increasing in extent, severity and frequency, and a better understanding of post-fire erosion processes is needed to manage burned lands. The objectives of this study were to: 1) document post-fire sediment production after the 2012 High Park Fire burn area, Colorado, 2) determine how sediment production relates to fire, rainfall, surface cover, soil and topographic characteristics, 3) model sediment yield at the study swales using the RUSLE and ERMiT erosion models and a site-specific multivariate regression (SSMR) model developed from the field measurements, and 4) assess how well the RUSLE and SSRM models performed when using remotely-sensed data in place of field-measured data. Sediment production, rainfall, surface cover, soil and topographic characteristics were measured for 29 swales in the High Park Fire burn area from August 2012 through September 2013. Eight of the swales were mulched with either wood shreds in October 2012 or straw in June 2013. Mean sediment yield from the unmulched swales in 2012 was 0.5 Mg ha-1 yr-1, increasing to 14.3 Mg ha-1 yr-1 in 2013. The increase in 2013 was largely due to above-average rainfall amounts. Mulched swales yielded 3.1 Mg ha-1 yr-1 in 2013. Precipitation thresholds for sediment production were best identified by rainfall erosivity. The erosivity threshold in 2012 was 3 MJ mm ha-1 hr-1 increasing to 22 MJ mm ha-1 hr-1 in 2013. Annual total sediment yield in 2013 was most closely correlated with rainfall erosivity whereas 2013 event sediment yield was more closely related by the thirty-minute maximum rainfall intensity. Independent variables with the strongest significant correlations to sediment yield were surface cover and topographic characteristics. Sediment yield was positively correlated with exposed bare soil in 2012 (Pearson's correlation coefficient [r] = 0.56) and negatively correlated with vegetation cover in 2013 (r = -0.46). Sediment yield was negatively correlated with percent cover by mulch (r = -0.97), but the type of mulch material did not affect sediment yield. Slope length was negatively correlated with sediment yield (r = -0.19), and narrower swales produced more sediment per unit area than wide swales. The best 2013 annual SSMR model used average percent bare soil in spring 2013, swale width-length ratio, summer erosivity, slope length and burn severity to predict sediment yield (R2 = 0.63). The two erosion models, ERMiT and RUSLE, did not accurately predict 2013 annual sediment yields. ERMiT under-predicted sediment yields for storms with maximum thirty-minute intensity recurrence intervals of 1.5-5 years, and over-predicted sediment yield for storms with precipitation depth recurrence intervals of 30-100 years. The RUSLE model run with field-measured independent variables similarly did not accurately predict sediment yield from the hillslopes (R2 = 0.05), and when the RUSLE variables were calculated with remotely sensed or GIS-derived data the correlation with measured values was even weaker (R2 = 0.02). The SSMR model developed from field-measured variables predicted sediment yield relatively well (R2 = 0.63), but declined when using remotely-derived data (R2 = 0.46). The results of this study show that rainfall erosivity and intensity, surface cover and topography are the dominant controls on post-fire sediment yield. The interactions of these controls is not captured in the existing erosion models ERMiT and RUSLE. Furthermore, the use of remote sensing and GIS to derive model inputs reduces the accuracy of these models.Item Open Access Snow persistence and hydrologic response across the intermittent-persistent snow transition(Colorado State University. Libraries, 2018) Hammond, John Christopher, author; Kampf, Stephanie, advisor; Covino, Tim, committee member; Denning, Scott, committee member; Fassnacht, Steven, committee memberIn mountainous regions and high latitudes, seasonal snow is a critical component of the surface energy balance and hydrologic cycle. Snowpacks have been declining in many mountain regions, but the hydrologic responses to snow loss have varied due to interactions of climatic, vegetative, topographic and edaphic factors. With continued climatic change, it remains uncertain whether the southwestern U.S. and other subtropical and mid-latitude dry areas may experience significant reductions in water yield. In this dissertation snow persistence and trends are mapped globally; relationships between snow persistence and annual water yield are examined in different climates, and snowmelt and rain partitioning in the critical zone are modelled to examine potential effects of snow loss on hydrologic response. Chapter 2 involves mapping the distribution of snow persistence (SP), the fraction of time that snow is present on the ground for a specific period, using MODIS snow cover data, classifying similar areas into snow zones, assessing how snow persistence relates to climatic variables and elevation, and testing for trends in annual SP. SP is most variable from year to year near the snow line, which has a relatively consistent decrease in elevation with increasing latitude across all continents. At lower elevations, SP is typically best correlated with temperature, whereas precipitation has greater relative importance for SP at high elevations. The largest areas of declining SP are in the seasonal snow zones of the Northern Hemisphere. Trend patterns vary within individual regions, with elevation, and on windward-leeward sides of mountain ranges. This analysis provides a framework for comparing snow between regions, highlights areas with snow changes, and can facilitate analyses of why snow changes vary within and between regions. In Chapter 3, SP is used to evaluate how water yield relates to snow patterns at the annual time scale across the western U.S. in different climates. I first compare snow cover variables derived from MODIS to more commonly utilized metrics (snow fraction and peak snow water equivalent (SWE)). I then evaluate how SP and SWE relate to annual streamflow (Q) for 119 USGS reference watersheds and examine whether these relationships vary for wet/warm (precipitation surplus) and dry/cold (precipitation deficit) watersheds. Results show high correlations between all snow variables, but the slopes of these relationships differ between climates. In dry/cold watersheds, both SP and SNODAS SWE correlate with Q spatially across all watersheds and over time within individual watersheds. I conclude that SP can be used to map spatial patterns of annual streamflow generation in dry/cold parts of the study region. In Chapter 4 of the dissertation, I use a series of one-dimensional simulations to study how snow loss may impact hydrologic response in mountain areas at event to annual time scales. I use Hydrus 1-D simulations with historical inputs from fifteen SNOTEL snow monitoring sites to investigate how inter-annual variability of water input type (snowmelt, rainfall) and timing affect soil saturation and deep drainage in different soil types and depths. Greater input rate and antecedent moisture are observed for snowmelt compared to rain events, resulting in greater runoff efficiencies. At the annual scale runoff efficiencies increase with snowmelt fraction and decrease when all input is rainfall. In contrast, deep drainage has no clear correlation to snowmelt fraction. Input that is concentrated in time leads to greater surface runoff and deep drainage. Soil texture and depth modify partitioning, but these effects are small compared to those caused by variability in climate. This dissertation's findings have direct implications for climate change impacts in cold dry areas globally. Through the synthesis of the chapters described above I highlight areas where hydrologic response to snow loss may be most sensitive, provide methods for comparing regional snow patterns, demonstrate how snow persistence can help estimate annual streamflow generation, and improve process-based knowledge of hydrologic response to rainfall and snowmelt in the western U.S. Collectively these findings indicate that annual water yield is not directly sensitive to whether input is snowmelt vs. rainfall; instead it is more dependent on the effect that snowpack accumulation has on input timing and rate. Loss of concentrated melt from persistent snowpacks may lead to lower streamflow and compromise deep drainage, and thus aquifer recharge, in semi-arid cold regions. The consequences of streamflow and groundwater recharge loss could be severe in regions already water-stressed, and this needs to be addressed in long-term water supply planning.Item Unknown Snowmelt and rainfall runoff in burned and unburned catchments at the intermittent-persistent snow transition, Colorado Front Range(Colorado State University. Libraries, 2016) Johnson, Adam, author; Kampf, Stephanie, advisor; Fassnacht, Steven, committee member; Niemann, Jeffrey, committee memberWinter snowmelt and summer monsoonal rains are the dominant sources for streamflow in the Colorado Front Range, and wildfire can greatly affect the hydrologic regime through which these inputs are delivered to the stream. However, the specific changes to the hydrologic processes that drive runoff production made by wildfire are not clearly understood. This research examines how wildfire affects the timing and magnitude of runoff production from snowmelt and rainfall by comparing four catchments in and near the High Park Fire area, two burned and two unburned, at the intermittent-persistent snow transition. Catchments were instrumented to monitor snow accumulation and ablation, rainfall, soil moisture, soil and air temperature, and streamflow response throughout water year 2015. These data were then utilized to determine the primary mechanisms of seasonal runoff generation and the magnitude of that runoff from each catchment. Runoff remained very low at all catchments during winter months. Spring snowmelt runoff in the form of lateral subsurface flow dominated catchment hydrographs for the water year. Following spring snowmelt, runoff production transitioned to a rainfall-dominated, drier summer period. During this time, limited infiltration excess overland flow was produced from high intensity rainfall events. Results of this research suggest that the loss of canopy cover due to wildfire may result in increased snowpack density and more intermittent snowpack throughout the winter months. Burned monitoring sites also maintained higher soil moisture than unburned sites, but this may be a function of site-specific variability rather than burning. Elevated soil moisture at burned sites did not translate to consistently higher runoff production. Both total runoff production and runoff ratios were highest in the high elevation unburned site with the highest snow persistence and the lowest elevation burned site with low snow persistence. During the one high intensity rain event that affected all catchments, burned catchments experienced an increase in discharge above baseflow of a greater magnitude than unburned sites. Overall, all catchments monitored showed site specific characteristics that defied easy classification but illustrated local variability in the hydrologic variables monitored.Item Open Access Spatial and temporal variability in channel surface flow across an elevation gradient on the Colorado Front Range(Colorado State University. Libraries, 2018) Martin, Caroline, author; Kampf, Stephanie, advisor; Rathburn, Sara, committee member; Falkowski, Michael, committee memberTopographic indices such as Upslope Accumulation Area (UAA) and the Topographic Wetness Index (TWI) are commonly used in watershed analyses to derive channel networks. These indices work well for large rivers and streams, but they do not always produce stream locations that match those observed in the field for headwater streams, where geology and soils affect locations of surface channels. This study maps the actively flowing drainage network of four headwater watersheds across an elevation gradient in the Colorado Front Range and examines how these locations of flow relate to topography, geology, climate, and soils. The objectives are to 1) document and digitize the active stream networks in the field, 2) delineate stream network with topographic indices and evaluate how index-derived channel networks compare with observations, and 3) evaluate how geology, climate, and soils affect surface water flow paths. Study sites are small headwater watersheds (1.7 – 15.5 km2) that vary in elevation from 1780 m up to 4190 m. At each watershed, surveys of surface water locations were conducted twice during the summer about a month apart in order to capture temporal variation. Stream densities documented during these surveys ranged from 5.09 * 10-4 m-1 at highest elevation site (3494 m – 4192 m) to 1.83 * 10-3 m-1 at lowest elevation site (1781 m – 2322 m). The lowest elevation site had the largest change in stream density between surveys, decreasing 84%. A middle elevation site that was affected by forest fire had the least change in stream density with only a 5% decrease between visits. TWI and UAA methods for deriving channel networks from topography performed well relative to field observations, ranging from 73% to 91% accuracy at low and middle elevation sites. At high elevation sites, these methods had the poorest performance, with accuracy between 21% and 74%. Also, at high elevation sites TWI performed slightly better than UAA, with 6-25% increased overall accuracy. Comparing channel networks at the four catchments, stream densities generally decreased with elevation, whereas streamflow magnitude and duration increased with elevation. Although stream density decreased with elevation, it had no apparent relationship with precipitation. The soil and bedrock geology were linked to streamflow location; in some cases, streamflow was discontinuous or dried up quickly in areas with high bedrock/soil hydraulic conductivity. Streams also followed shear zones, faults, and bedding contacts, where rocks are "weak", whereas they diverted around less erodible pegmatites. Results suggest that topography is the primary factor controlling streamflow location; however, geology and soils explained some of the cases where topographic predictions of flow location were inaccurate. Future channel delineation methods could add in a parameter based on the hydraulic conductivities of underlying soil and bedrock to improve stream channel mapping.Item Open Access Spatial and temporal variability of snow cover in the Andes Mountains and its influence on streamflow in snow dominant rivers(Colorado State University. Libraries, 2016) Pimentel, Freddy Alejandro Saavedra, author; Kampf, Stephanie, advisor; Sibold, Jason, advisor; Fassnacht, Steven, committee member; Niemann, Jeffrey, committee memberThe climate is changing, and snowmelt-dominated river basins are particularly sensitive to climate warming. In the Andes Mountains in South America climate measurements are sparse and unevenly distributed in snow-covered areas. Thus, remote sensing offers opportunities to improve understanding of the spatial and temporal snow patterns in this region and explore how these patterns relate to climate and hydrologic response. This study uses snow cover data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor to (1) identify snow climate regions across the Andes, (2) document trends in snow persistence and their relation to precipitation and temperature, and (3) develop statistical streamflow prediction models. The first chapter of the study identified five snow climate regions: two tropical and three mid-latitude regions. In the tropical regions, snow cover was present only over 5000m on both sides of the Andes. In the mid-latitude regions the elevation of the snow line varied with latitude, dropping from 4000m to 1000m from 23 to 36°S. In the mid-latitudes, particularly where mountain peaks are highest, snow cover accumulates at lower elevations on the west side than on the east side of the Andes. The second chapter quantifies trends in annual snow persistence (SP) from 2000-2014. In the northern part of the study region, limited snow cover is present, and few trends in snow persistence were detected. A large area (70,515 km2) south of 29°S is affected by a significant loss of snow cover (2-5 day less day of snow per year). In this latitude range, most of the land surface area with snow loss (62%) is on the east side of the Andes. The trends of snow persistence relate to both precipitation and temperature, but the relative importance of each parameter changes across elevation and latitude. Precipitation has greater relative importance at lower elevations, whereas temperature has greater relative importance at higher elevations. The final chapter explores the relationship between snow cover patterns and streamflow in snow-dominated rivers in the Chilean Andes (29-36° S). Snow covered area is correlated with water yield in snowmelt-dominated watersheds, but it is not as useful for water yield forecasts in watersheds with more limited snowmelt contributions. The snow cover information was combined with climatic variables (temperature and precipitation), and physiographic variables to develop statistical models of water yield (WY) and peak flow (PF). The final statistical model developed can forecast water year WY and PF in August using precipitation, snow cover, and area of watershed as predictors, with r2 values of 0.8 and 0.7 respectively. The approaches developed for applying snow cover information from remote sensing have led to important new findings about snow patterns in a large latitude range across the Andes Mountains. New tools developed for incorporating snow cover information into water yield and peak flow forecasts can aid water management under changing climate conditions.Item Open Access Streamflow generation across an elevation gradient after the 2020 Cameron Peak Fire(Colorado State University. Libraries, 2022) Miller, Quinn, author; Kampf, Stephanie, advisor; Nelson, Peter, committee member; Hammond, John, committee memberThe western United States is experiencing an increase in catastrophic wildfire in virtually all ecoregions. Many of these fires burn in forested headwaters that communities rely on for water supply, underscoring the need for a greater understanding of how wildfire impacts streamflow timing and magnitude. Though many studies have examined the hydrologic response to fire, the site-specific nature of this type of research has made it difficult to generalize findings. The 2020 Cameron Peak fire burned across a broad swathe of the Colorado Front Range, making it an ideal case study to examine the factors that affect post-fire runoff. The goal of this work is to identify how streamflow responses to rainfall vary from pre-to post-fire conditions and between mountain regions defined by seasonal snow cover and aridity. To this end, we selected three watersheds to compare fire effects on rainfall runoff between snow zones. These watersheds were unburned, moderately burned, and severely burned in each of two snow zones: the high-elevation persistent snow zone, and the mid-elevation intermittent snow zone. These watersheds were instrumented to monitor rainfall and stream discharge throughout water year 2021. To evaluate how wildfire affected runoff, we developed multi-variate statistical models and used Tukey's Honestly Significant Differences test to compare streamflow responses to rainfall between watersheds. Across all burn categories, the high elevation sites were more responsive to rainfall compared to streams at lower elevations; ~50% of rain events produced a streamflow response in the persistent snow zone, compared to ~25% in the intermittent snow zone. In both snow zones, the unburned sites were the least responsive to summer rainfall and had the highest summer baseflows. Although the high elevation streams were more responsive to rain, they did not exhibit evidence of infiltration excess overland flow. Lags between peak rainfall and peak discharge were 1.2-31.3 hr at these sites; in contrast, the low elevation severely burned site had a much more rapid rise to peak discharge (0.6 hr on average) that indicated infiltration excess overland flow. The rainfall intensity threshold necessary for runoff generation at this site was 4 mm hr-1, which agreed with thresholds reported in similar studies of burned areas in this region. We found no evidence that the moderately burned site in the intermittent snow zone generated rapid runoff, likely because that watershed did not experience enough moderate to high burn severity to promote widespread overland flow. Additionally, the flow response at burned sites was uniformly shorter than for the unburned sites in both snow zones. The magnitude of the flow response was higher in the persistent snow zone than in the intermittent snow zone; however, the effect of burn status on streamflow magnitude was difficult to ascertain. These results demonstrate that the streamflow responses to fire vary between snow zones, indicating a need to account for elevation and snow persistence in post-fire risk assessments. Future work in other regions could evaluate whether this snow zone effect is unique to the study area or a common cause of differences in post-fire streamflow.Item Open Access The frequency, magnitude and connectivity of post-wildfire rainfall-runoff and sediment transport(Colorado State University. Libraries, 2019) Wilson, Codie R., author; Kampf, Stephanie, advisor; Jones, Kelly, committee member; MacDonald, Lee, committee member; Ryan, Sandra, committee memberWildfire increases the likelihood of runoff, erosion, and downstream sedimentation in many of the watersheds that supply water for communities across the western U.S. The goal of this research was to examine the complex interactions between fire, rainfall and landscape properties (e.g., burn severity, topography) across scales from hillslopes to watersheds. The research combines both regional data analysis and field monitoring to examine the frequency, magnitude and connectivity of post-fire rainfall-runoff events and associated sediment delivery. In the first part of this study (chapter 2), the goal was to quantify rainfall thresholds that cause runoff and sediment delivery across multiple fires, years post-fire, spatial scales, and mulch treatments in the Colorado Front Range. Rain intensity thresholds were identified for plots, hillslopes, and watersheds across three Colorado Front Range fires. Thresholds did not significantly differ among fires for any year post-fire, but were significantly different between spatial scales and years post-fire. Thresholds increased with time since burn likely due to vegetation regrowth, litter accumulation and recovery of soil infiltration capacity. The frequency of storms exceeding thresholds for runoff and erosion was mapped across Colorado to provide a tool for identifying areas most vulnerable to post-fire runoff and sediment delivery and prioritizing post-fire treatments. In chapter three, the goal was to improve understanding of the catch efficiency of sediment fences commonly used to measure post-fire hillslope erosion. During post-fire year two (2014) of the 2012 High Park Fire four sediment fences were modified to collect and measure both the sediment deposited behind the fence and the amount of runoff and sediment that overtopped the fence. Sediment fence catch efficiency ranged from 28-100% for individual events and from 38-94% across the sampling season. Increasing rainfall intensities were correlated with greater runoff and total sediment loads and lower sediment fence catch efficiencies. Enrichment ratios indicate that the sediment behind the fence was significantly enriched in sand relative to the hillslope soil samples. These results indicate that sediment fences underestimate sediment yields and demonstrate how sediment particle sizes may be sorted en route to the stream network. In chapter four, the goal was to examine connectivity between hillslopes and channel networks. Runoff and sediment from nested hillslopes (n = 31) and catchments (n = 12) were assessed for two rainfall events with different duration and intensity during post-fire year three (2015) of the High Park Fire to determine the factors affecting connectivity. The first event had a return interval of <1 year with low intensity rainfall over an average of 11 hours, whereas the second event had high intensity rainfall that lasted for an average of 1 hour with a maximum return interval of 10 years. The lower intensity event led to low hillslope sediment yields and widespread channel incision. The higher intensity event led to infiltration excess overland flow, high sediment yields and in-stream sediment deposition and fining. During both events, the percent of a catchment that burned at high severity was positively correlated with sediment delivery ratios and area-normalized absolute channel change. Overall, this research demonstrated that the rainfall events and thresholds associated with the generation of post-fire runoff and sediment transport vary with spatial scale and time since burn. In addition, not every threshold-exceeding event will produce the same type of response due to the complex and transient nature of post-fire responses from hillslope to watershed scale. Increasing our understanding of post-fire responses and connectivity will therefore require nested multi-scale monitoring over time to determine how sediment moves to and through channel networks.Item Open Access Thresholds for runoff generation in ephemeral streams with varying morphology in the Sonoran Desert in Arizona, USA(Colorado State University. Libraries, 2015) Faulconer, Joshua D., author; Kampf, Stephanie, advisor; MacDonald, Lee, committee member; Ronayne, Michael, committee memberIn ephemeral streams, infrequent surface flow can be the main source of water that sustains plants throughout long dry periods. The objectives of this research are to: (1) explore seasonality of rainfall runoff in different channel types and (2) examine how runoff thresholds vary by channel type. The study area was two watersheds with areas of 188 km² and 323 km² on the Yuma Proving Grounds (YPG) in the Sonoran Desert near Yuma, Arizona. Eight tipping bucket rain gauges were installed to measure precipitation. Runoff was measured with 18 pressure transducers in five different channel types with different channel morphologies and contributing areas ranging from 0.002 km² to 225 km². Over approximately two years there were 11 to 48 rain events at the different rain gauges. Stream types with bedrock channels and small watershed areas between 0.005 km² and 0.015 km² produced runoff when the peak 60-minute precipitation intensity (I60) exceeded 4-6 mm hr⁻¹. At these sites, 17-25 percent of the rain storms generated runoff. I60 values of 5-9 mm hr⁻¹ produced runoff in streams with contributing areas of 0.021-0.061 km² on mid-Pleistocene piedmont surfaces covered by desert pavement. At these sites, 31-36 percent of rain events produced runoff. Streams incised into bedrock with some alluvium fill produced runoff at larger I60's of 13-18 mm hr⁻¹. Contributing areas for these sites were 0.8 km² to 2.2 km², and up to 10 percent of precipitation events at these sites produced flow. Precipitation thresholds for runoff generation in streams with contributing areas >3 km² were not clearly defined due to the influences of variable precipitation in upstream tributaries and transmission losses of streamflow through channel bed alluvium. For watersheds with <3km², rain intensity thresholds increased with the log of catchment area, and as a result flow frequency tended to decrease with increasing catchment area.