‘Teflon Basin’ or Not? A High-Elevation Catchment Transit Time Modeling Approach

We determined the streamflow transit time and the subsurface water storage volume in the glacierized high-elevation catchment of the Rofenache (Oetztal Alps, Austria) with the lumped parameter transit time model TRANSEP. Therefore we enhanced the surface energy-balance model ESCIMO to simulate the ice melt, snowmelt and rain input to the catchment and associated δ18O values for 100 m elevation bands. We then optimized TRANSEP with streamflow volume and δ18O for a four-year period with input data from the modified version of ESCIMO at a daily resolution. The median of the 100 best TRANSEP runs revealed a catchment mean transit time of 9.5 years and a mobile storage of 13,846 mm. The interquartile ranges of the best 100 runs were large for both, the mean transit time (8.2–10.5 years) and the mobile storage (11,975–15,382 mm). The young water fraction estimated with the sinusoidal amplitude ratio of input and output δ18O values and delayed input of snow and ice melt was 47%. Our results indicate that streamflow is dominated by the release of water younger than 56 days. However, tracers also revealed a large water volume in the subsurface with a long transit time resulting to a strongly delayed exchange with streamflow and hence also to a certain portion of relatively old water: The median of the best 100 TRANSEP runs for streamflow fraction older than five years is 28%.

Download Full-text

Aggregation in environmental systems: seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-12-3059-2015 ◽

2015 ◽

Vol 12 (3) ◽

pp. 3059-3103 ◽

Cited By ~ 7

Author(s):

J. W. Kirchner

Keyword(s):

Transit Time ◽

Mean Transit Time ◽

Strong Nonlinearity ◽

Isotopic Tracers ◽

Water Fraction ◽

Benchmark Tests ◽

Environmental Systems ◽

Transit Times ◽

Event Based ◽

The Relationship

Abstract. Environmental heterogeneity is ubiquitous, but environmental systems are often analyzed as if they were homogeneous instead, resulting in aggregation errors that are rarely explored and almost never quantified. Here I use simple benchmark tests to explore this general problem in one specific context: the use of seasonal cycles in chemical or isotopic tracers (such as Cl−, δ18O, or δ2H) to estimate timescales of storage in catchments. Timescales of catchment storage are typically quantified by the mean transit time, meaning the average time that elapses between parcels of water entering as precipitation and leaving again as streamflow. Longer mean transit times imply greater damping of seasonal tracer cycles. Thus, the amplitudes of tracer cycles in precipitation and streamflow are commonly used to calculate catchment mean transit times. Here I show that these calculations will typically be wrong by several hundred percent, when applied to catchments with realistic degrees of spatial heterogeneity. This aggregation bias arises from the strong nonlinearity in the relationship between tracer cycle amplitude and mean travel time. I propose an alternative storage metric, the young water fraction in streamflow, defined as the fraction of runoff with transit times of less than roughly 0.2 years. I show that this young water fraction (not to be confused with event-based "new water" in hydrograph separations) is accurately predicted by seasonal tracer cycles within a precision of a few percent, across the entire range of mean transit times from almost zero to almost infinity. Importantly, this relationship is also virtually free from aggregation error. That is, seasonal tracer cycles also accurately predict the young water fraction in runoff from highly heterogeneous mixtures of subcatchments with strongly contrasting transit time distributions. Thus, although tracer cycle amplitudes yield biased and unreliable estimates of catchment mean travel times in heterogeneous catchments, they can be used reliably to estimate the fraction of young water in runoff.

Download Full-text

Assessment of hydrological pathways in East African montane catchments under different land use

Hydrology and Earth System Sciences ◽

10.5194/hess-22-4981-2018 ◽

2018 ◽

Vol 22 (9) ◽

pp. 4981-5000 ◽

Cited By ~ 12

Author(s):

Suzanne R. Jacobs ◽

Edison Timbe ◽

Björn Weeser ◽

Mariana C. Rufino ◽

Klaus Butterbach-Bahl ◽

...

Keyword(s):

Land Use ◽

Transit Time ◽

Stream Water ◽

Mean Transit Time ◽

Natural Forest ◽

Smallholder Agriculture ◽

Tea Plantation ◽

Water Fraction ◽

Transit Times ◽

Water Isotope

Abstract. Conversion of natural forest (NF) to other land uses could lead to significant changes in catchment hydrology, but the nature of these changes has been insufficiently investigated in tropical montane catchments, especially in Africa. To address this knowledge gap, we aimed to identify stream water (RV) sources and flow paths in three tropical montane sub-catchments (27–36 km2) with different land use (natural forest, NF; smallholder agriculture, SHA; and commercial tea and tree plantations, TTP) within a 1021 km2 catchment in the Mau Forest complex, Kenya. Weekly samples were collected from stream water, precipitation (PC) and mobile soil water for 75 weeks and analysed for stable isotopes of water (δ2H and δ18O) for mean transit time (MTT) estimation with two lumped parameter models (gamma model, GM; and exponential piston flow model, EPM) and for the calculation of the young water fraction. Weekly samples from stream water and potential endmembers were collected over a period of 55 weeks and analysed for Li, Na, Mg, K, Rb, Sr and Ba for endmember mixing analysis (EMMA). Solute concentrations in precipitation were lower than in stream water in all catchments (p < 0.05), whereas concentrations in springs, shallow wells and wetlands were generally more similar to stream water. The stream water isotope signal was considerably damped compared to the isotope signal in precipitation. Mean transit time analysis suggested long transit times for stream water (up to 4 years) in the three sub-catchments, but model efficiencies were very low. The young water fraction ranged from 13 % in the smallholder agriculture sub-catchment to 15 % in the tea plantation sub-catchment. Mean transit times of mobile soil water ranged from 3.2–3.3 weeks in forest soils and 4.5–7.9 weeks in pasture soils at 15 cm depth to 10.4–10.8 weeks in pasture soils at 50 cm depth. The contribution of springs and wetlands to stream discharge increased from a median of 16.5 (95 % confidence interval: 11.3–22.9), 2.1 (−3.0–24.2) and 50.2 (30.5–65.5) % during low flow to 20.7 (15.2–34.7), 53.0 (23.0–91.3) and 69.4 (43.0–123.9) % during high flow in the natural forest, smallholder agriculture and tea plantation sub-catchments, respectively. Our results indicate that groundwater is an important component of stream water, irrespective of land use. The results further suggest that the selected transit time models and tracers might not be appropriate in tropical catchments with highly damped stream water isotope signatures. A more in-depth investigation of the discharge dependence of the young water fraction and transit time estimation using other tracers, such as tritium, could therefore shed more light on potential land use effects on the hydrological behaviour of tropical montane catchments.

Download Full-text

An Evaluation of Catchment Transit Time Model Parameters: A Comparative Study between Two Stable Isotopes of Water

Geosciences ◽

10.3390/geosciences9070318 ◽

2019 ◽

Vol 9 (7) ◽

pp. 318

Author(s):

Samuel Bansah ◽

Samuel Ato Andam-Akorful ◽

Jonathan Quaye-Ballard ◽

Matthew Coffie Wilson ◽

Solomon Senyo Gidigasu ◽

...

Keyword(s):

Time Series ◽

Transit Time ◽

Mean Transit Time ◽

Model Parameters ◽

Flow Process ◽

Time Model ◽

Shallow Subsurface ◽

Behavioral Parameter ◽

Stable Isotopes Of Water ◽

Generalized Likelihood Uncertainty Estimation

Using δ18O and δ2H in mean transit time (MTT) modeling can ensure the verifiability of results across catchments. The main objectives of this study were to (i) evaluate the δ18O- and δ2H-based behavioral transit time distributions and (ii) assess if δ18O and δ2H-based MTTs can lead to similar conclusions about catchment hydrologic functioning. A volume weighted δ18O (or δ2H) time series of sampled precipitation was used as an input variable in a 50,000 Monte Carlo (MC) time-based convolution modeling process. An observed streamflow δ18O (or δ2H) time series was used to calibrate the model to obtain the simulated time series of δ18O (or δ2H) of the streamflow within a nested system of eight Prairie catchments in Canada. The model efficiency was assessed via a generalized likelihood uncertainty estimation by setting a minimum Nash–Sutcliffe Efficiency threshold of 0.3 for behavioral parameter sets. Results show that the percentage of behavioral parameter sets across both tracers were lower than 50 at the majority of the studied outlets; a phenomenon hypothesized to have resulted from the number of MC runs. Tracer-based verifiability of results could be achieved within five of the eight studied outlets during the model process. The flow process in those five outlets were mainly of a shallow subsurface flow as opposed to the other three outlets, which experienced other additional flow dynamics. The potential impacts of this study on the integrated use of δ18O and δ2H in catchment water storage and release dynamics must be further investigated in multiple catchments within various hydro-physiographic settings across the world.

Download Full-text

Insights into the water mean transit time in a high-elevation tropical ecosystem

Hydrology and Earth System Sciences ◽

10.5194/hess-20-2987-2016 ◽

2016 ◽

Vol 20 (7) ◽

pp. 2987-3004 ◽

Cited By ~ 26

Author(s):

Giovanny M. Mosquera ◽

Catalina Segura ◽

Kellie B. Vaché ◽

David Windhorst ◽

Lutz Breuer ◽

...

Keyword(s):

Transit Time ◽

Mean Transit Time ◽

High Elevation ◽

Lumped Parameter Model ◽

Data Set ◽

Shallow Subsurface ◽

Discharge Rates ◽

Lumped Parameter ◽

High Storage Capacity ◽

Specific Discharge

Abstract. This study focuses on the investigation of the mean transit time (MTT) of water and its spatial variability in a tropical high-elevation ecosystem (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53 km2) located in southern Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs under steady-state conditions (i.e., baseflow MTT). We used a unique data set of the δ18O isotopic composition of rainfall and streamflow water samples collected for 3 years (May 2011 to May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to explore controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15–0.73 years, 53–264 days). Regression analysis revealed a negative correlation between the catchment's average slope and MTT (R2 =  0.78, p < 0.05). MTT showed no significant correlation with hydrometric variables, whereas MEC increases with MTT (R2 =  0.89, p < 0.001). Overall, we conclude that (1) baseflow MTT confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; (2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and (3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.

Download Full-text

Water Age in Stormwater Management Ponds and Stormwater Management Pond Treated Catchments

10.32920/ryerson.14654427 ◽

2021 ◽

Author(s):

Kayla Wong

Keyword(s):

Transit Time ◽

Stormwater Management ◽

Damping Ratio ◽

Mean Transit Time ◽

Sine Wave ◽

Urban Stream ◽

Water Age ◽

Catchment Scale ◽

Water Fraction ◽

Hydrologic Responses

Increasing coverage of impervious surfaces in urban waterways result in 'flashy' hydrologic responses, elevated flood risk, and degraded water quality. Stormwater management ponds (SWMPs) are engineered into urban stream networks to mitigate this response. However, little is known about how SWMPs affect hydrological transit time at the catchment scale. This study aims to examine water age in SWMPs and catchments of varying SWMP control. Grab samples of ∂¹⁸O and ∂²H were collected bi-weekly from two SWMPs and five stream sites with varying land cover and stormwater control in their catchments. The damping ratio (DR), young water fraction (Fyw) and mean transit time (MTT) by sine-wave fitting were calculated for each sampled site. SWMP inlet water was consistently older than water arriving at SWMP outlets. MTT decreased as catchments SWMP control increased. Surficial geology was found to have the greatest influence on catchment MTT.

Download Full-text

Rainstorm Magnitude Likely Regulates Event Water Fraction and Its Transit Time in Mesoscale Mountainous Catchments: Implication for Modelling Parameterization

Water ◽

10.3390/w12041169 ◽

2020 ◽

Vol 12 (4) ◽

pp. 1169

Author(s):

Jun-Yi Lee ◽

Yu-Ting Shih ◽

Chiao-Ying Lan ◽

Tsung-Yu Lee ◽

Tsung-Ren Peng ◽

...

Keyword(s):

Sensitivity Analysis ◽

Transit Time ◽

Preferential Flow ◽

Mean Transit Time ◽

Time Estimation ◽

Parameter Sensitivity ◽

Hydrograph Separation ◽

Water Fraction ◽

Mountainous Catchments ◽

Time Invariant

Event water transit time estimation has rarely been done for violent rainstorms (e.g., typhoons) in steep and fractured mountainous catchments where the range of transit time, potential controlling factors, and the validity of time-invariant parametrization are unclear. Characterized by steep landscape and torrential typhoon rainfall, Taiwan provides great opportunities for inquiring into the above questions. In this study, the hydrometrics and δ18O in rainwater and streamwater were sampled with a ~3-h interval for six typhoon events in two mesoscale catchments. The TRANSEP (transfer function hydrograph separation) model and global sensitivity analysis were applied for estimating mean transit time (MTTew) and fraction (Few) of event water and identifying the chronosequent parameter sensitivity. Results showed that the MTTew and Few varied from 2.0 to 11.0 h and from 0.2 to 0.8, respectively. Our MTTew in the mesoscale catchments is comparable with that in microscale catchments, showing a fast rainfall-runoff transfer in our steep catchments. The average rainfall intensity is a predominant indicator, which negatively affects the MTTew and positively affects the Few, likely activating preferential flow-paths and quickly transferring event water to the stream. Sensitivity analysis among inter- and intra-events demonstrates that parameter sensitivity is event-dependent and time-variant. A quick and massive subsurface flow without distinct mixing with groundwater would be triggered during large rainstorms, suggesting that time-variant parameterization should be particularly considered when estimating the MTTew in steep and fractured catchments at rainstorm scale.

Download Full-text

Air temperature distribution and energy-balance modelling of a debris-covered glacier

Journal of Glaciology ◽

10.1017/jog.2016.31 ◽

2016 ◽

Vol 62 (231) ◽

pp. 185-198 ◽

Cited By ~ 15

Author(s):

THOMAS E. SHAW ◽

BEN W. BROCK ◽

CATRIONA L. FYFFE ◽

FRANCESCA PELLICCIOTTI ◽

NICK RUTTER ◽

...

Keyword(s):

Energy Balance ◽

Air Temperature ◽

Surface Air Temperature ◽

High Elevation ◽

Lapse Rate ◽

Balance Model ◽

Linear Temperature ◽

Near Surface ◽

Ice Melt ◽

Debris Cover

ABSTRACTNear-surface air temperature is an important determinant of the surface energy balance of glaciers and is often represented by a constant linear temperature gradients (TGs) in models. Spatio-temporal variability in 2 m air temperature was measured across the debris-covered Miage Glacier, Italy, over an 89 d period during the 2014 ablation season using a network of 19 stations. Air temperature was found to be strongly dependent upon elevation for most stations, even under varying meteorological conditions and at different times of day, and its spatial variability was well explained by a locally derived mean linear TG (MG–TG) of −0.0088°C m−1. However, local temperature depressions occurred over areas of very thin or patchy debris cover. The MG–TG, together with other air TGs, extrapolated from both on- and off-glacier sites, were applied in a distributed energy-balance model. Compared with piecewise air temperature extrapolation from all on-glacier stations, modelled ablation, using the MG–TG, increased by <1%, increasing to >4% using the environmental ‘lapse rate’. Ice melt under thick debris was relatively insensitive to air temperature, while the effects of different temperature extrapolation methods were strongest at high elevation sites of thin and patchy debris cover.

Download Full-text

Insights on the water mean transit time in a high-elevation tropical ecosystem

10.5194/hess-2015-546 ◽

2016 ◽

Author(s):

G. M. Mosquera ◽

C. Segura ◽

K. B. Vaché ◽

D. Windhorst ◽

L. Breuer ◽

...

Keyword(s):

Transit Time ◽

Mean Transit Time ◽

High Elevation ◽

Lumped Parameter Model ◽

Data Set ◽

Shallow Subsurface ◽

Discharge Rates ◽

Lumped Parameter ◽

High Storage Capacity ◽

Stream Waters

Abstract. This study focuses on the investigation of the yet unknown mean transit time (MTT) of stream waters and its spatial variability in tropical alpine ecosystems (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53 km2) located in south Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs. We used a unique data set of δ18O and δ2H isotopic composition of rainfall and streamflow water samples collected for three years (May 2011-May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to determine controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15-0.73 yr, 53-264 days). Regression analysis revealed negative correlation between the catchment’s average slope and MTT (R2 = 0.78, p < 0.05). MTT showed no significant correlation with hydrometric variables whereas MEC increases with MTT (R2 = 0.89 p < 0.001). Overall, we conclude that: 1) MTT of streams confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; 2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and 3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.

Download Full-text

Variability of Water Transit Time Distributions at the Strengbach Catchment (Vosges Mountains, France) Inferred Through Integrated Hydrological Modeling and Particle Tracking Algorithms

Water ◽

10.3390/w11122637 ◽

2019 ◽

Vol 11 (12) ◽

pp. 2637 ◽

Cited By ~ 3

Author(s):

Sylvain Weill ◽

Nolwenn Lesparre ◽

Benjamin Jeannot ◽

Frederick Delay

Keyword(s):

Transit Time ◽

Particle Tracking ◽

Temporal Variability ◽

Hydrological Modeling ◽

Mean Transit Time ◽

Subsurface Water ◽

Vosges Mountains ◽

Tracking Algorithms ◽

Magnetic Resonance Sounding ◽

Low Dimensional

The temporal variability of transit-time distributions (TTDs) and residence-time distributions (RTDs) has received particular attention recently, but such variability has barely been studied using distributed hydrological modeling. In this study, a low-dimensional integrated hydrological model is run in combination with particle-tracking algorithms to investigate the temporal variability of TTDs, RTDs, and StorAge Selection (SAS) functions in the small, mountainous Strengbach watershed belonging to the French network of critical-zone observatories. The particle-tracking algorithms employed rely upon both forward and backward formulations that are specifically developed to handle time-variable velocity fields and evaluate TTDs and RTDs under transient hydrological conditions. The model is calibrated using both traditional streamflow measurements and magnetic resonance sounding (MRS)—which is sensitive to the subsurface water content—and then verified over a ten-year period. The results show that the mean transit time is rather short, at 150–200 days, and that the TTDs and RTDs are not greatly influenced by water storage within the catchment. This specific behavior is mainly explained by the small size of the catchment and its small storage capacity, a rapid flow mainly controlled by gravity along steep slopes, and climatic features that keep the contributive zone around the stream wet all year long.

Download Full-text

Aggregation in environmental systems – Part 1: Seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments

Hydrology and Earth System Sciences ◽

10.5194/hess-20-279-2016 ◽

2016 ◽

Vol 20 (1) ◽

pp. 279-297 ◽

Cited By ~ 137

Author(s):

J. W. Kirchner

Keyword(s):

Transit Time ◽

Mean Transit Time ◽

Strong Nonlinearity ◽

Isotopic Tracers ◽

Water Fraction ◽

Benchmark Tests ◽

Environmental Systems ◽

Transit Times ◽

Event Based ◽

The Relationship

Abstract. Environmental heterogeneity is ubiquitous, but environmental systems are often analyzed as if they were homogeneous instead, resulting in aggregation errors that are rarely explored and almost never quantified. Here I use simple benchmark tests to explore this general problem in one specific context: the use of seasonal cycles in chemical or isotopic tracers (such as Cl−, δ18O, or δ2H) to estimate timescales of storage in catchments. Timescales of catchment storage are typically quantified by the mean transit time, meaning the average time that elapses between parcels of water entering as precipitation and leaving again as streamflow. Longer mean transit times imply greater damping of seasonal tracer cycles. Thus, the amplitudes of tracer cycles in precipitation and streamflow are commonly used to calculate catchment mean transit times. Here I show that these calculations will typically be wrong by several hundred percent, when applied to catchments with realistic degrees of spatial heterogeneity. This aggregation bias arises from the strong nonlinearity in the relationship between tracer cycle amplitude and mean travel time. I propose an alternative storage metric, the young water fraction in streamflow, defined as the fraction of runoff with transit times of less than roughly 0.2 years. I show that this young water fraction (not to be confused with event-based "new water" in hydrograph separations) is accurately predicted by seasonal tracer cycles within a precision of a few percent, across the entire range of mean transit times from almost zero to almost infinity. Importantly, this relationship is also virtually free from aggregation error. That is, seasonal tracer cycles also accurately predict the young water fraction in runoff from highly heterogeneous mixtures of subcatchments with strongly contrasting transit-time distributions. Thus, although tracer cycle amplitudes yield biased and unreliable estimates of catchment mean travel times in heterogeneous catchments, they can be used to reliably estimate the fraction of young water in runoff.

Download Full-text