scholarly journals Use of deuterium to understand runoff generation in a headwater catchment containing a dambo

1998 ◽  
Vol 2 (1) ◽  
pp. 65-76 ◽  
Author(s):  
M. P. McCartney ◽  
C. Neal ◽  
M. Neal
Keyword(s):  
Overland Flow ◽  
Hydrological Cycle ◽  
Hydrograph Separation ◽  
Runoff Generation ◽  
Rainfall Characteristics ◽  
Headwater Catchments ◽  
Antecedent Conditions ◽  
Storm Flow ◽  
Total Proportion ◽  
Made In

Abstract. Dambos, seasonally saturated wetlands, are widespread in headwater catchments in southern Africa and play an important role in the regional hydrological cycle. However, the processes influencing runoff from these catchments are poorly understood. This paper reports an isotopic investigation of runoff-generating mechanisms within a Zimbabwean catchment containing a dambo. Hydrograph separation using deuterium reveals that, once the dambo is saturated, up to 70% of total storm flow can be considered "new" water (i.e. derived directly from rainfall generating the runoff event). However, both the total proportion and the instantaneous maximum amount of "new" water in hydrographs are sensitive to rainfall characteristics and antecedent conditions. These results are (1) compatible with observations made in catchments in temperate climates when wetlands are present, and contrast with results obtained when wetlands are absent and (2) consistent with saturation overland flow, generated in saturated regions of the dambo, being the major storm runoff mechanism. To reconcile these observations with past perceptions that dambos attenuate flood flows, a dual role for dambos in storm flow production is postulated.

scholarly journals Identifying Flow Pathways for Phosphorus Transport Using Observed Event Forensics and the CRAFT (Catchment Runoff Attenuation Flux Tool)

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 1081 ◽  
Author(s):  
Russell Adams ◽  
Paul Quinn ◽  
Nick Barber ◽  
Sean Burke
Keyword(s):  
Overland Flow ◽  
Forensic Analysis ◽  
Frequency Resolution ◽  
Storm Event ◽  
Hydrograph Separation ◽  
Near Surface ◽  
Headwater Catchments ◽  
Additional Tool ◽  
Flow Pathways ◽  
Catchment Runoff

Identifying key flow pathways is critical in order to understand the transport of Phosphorus (P) from agricultural headwater catchments. High frequency/resolution datasets from two such catchments in Northwest England enabled individual events to be examined to identify the flow (Q) and Total P (TP) and Total Reactive P (TRP) dynamics (forensics). Detailed analysis of multiple flow and water quality parameters is referred to here as the event forensics. Are there more flow pathways than just surface runoff (dominated by overland flow) and baseflow (mainly groundwater) contributing at the outlet of these catchments? If so, hydrograph separation alone will not be sufficient. This forensic analysis gives a classification of four storm event response types. Three classes are based on the balance of old and new water giving enrichment and dilution of TRP pattern in the subsurface flow. A fourth type was observed where a plume of nutrient is lost to the channel when there is no observed flow. Modelling is also essential when used in combination with the event forensics as this additional tool can identify distinct flow pathways in a robust form. A case study will apply the Catchment Runoff Attenuation Flux Tool (CRAFT) to two contrasting small headwater catchments in Northwest England, which formed part of the Demonstration Test Catchments (DTC) Programme. The model will use data collected during a series of events observed in the two catchments between the period 2012 and 2014. It has the ability to simulate fast near surface (that can represent flow in the upper soil horizons and field drains) and event subsurface soil flow, plus slower groundwater discharge. The model can capture P enrichment, dilution and the role that displacement of “old” P rich water has during events by mixing these flows. CRAFT captures the dominant flow and P fluxes as seen in the forensic analysis and can create outputs including smart export coefficients (based on flow pathways) that can be conveyed to policy makers to better underpin decision making.

scholarly journals The influence of soil moisture on threshold runoff generation processes in an alpine headwater catchment

2010 ◽  
Vol 7 (5) ◽  
pp. 8091-8124 ◽  
Author(s):  
D. Penna ◽  
H. J. Tromp-van Meerveld ◽  
A. Gobbi ◽  
M. Borga ◽  
G. Dalla Fontana
Keyword(s):  
Soil Moisture ◽  
Overland Flow ◽  
Riparian Zone ◽  
Temporal Dynamics ◽  
Runoff Generation ◽  
Antecedent Conditions ◽  
Antecedent Moisture ◽  
Dry Conditions ◽  
Strong Control ◽  
Headwater Catchment

Abstract. This study investigates the role of soil moisture on the threshold runoff response in a small headwater catchment in the Italian Alps that is characterised by steep hillslopes and a distinct riparian zone. This study focuses on: (i) the threshold soil moisture-runoff relationship and the influence of catchment topography on this relation; (ii) the temporal dynamics of soil moisture, streamflow and groundwater that characterize the catchment's response to rainfall during dry and wet periods; and (iii) the combined effect of antecedent wetness conditions and rainfall amount on hillslope and riparian runoff. Our results highlight the strong control exerted by soil moisture on runoff in this catchment: a sharp threshold exists in the relationship between soil water content and runoff coefficient, streamflow, and hillslope-averaged depth to water table. Low runoff ratios were related to the response of the riparian zone, which was always close to saturation. High runoff ratios occurred during wet antecedent conditions, when the soil moisture threshold was exceeded. In these cases, subsurface flow was activated on hillslopes, which became major contributors to runoff. Antecedent wetness conditions also controlled the catchment's response time: during dry periods, streamflow reacted and peaked prior to hillslope soil moisture whereas during wet conditions the opposite occurred. This difference resulted in a hysteretic behaviour in the soil moisture-streamflow relationship. Finally, the influence of antecedent moisture conditions on runoff was also evident in the relation between cumulative rainfall and total stormflow. Small storms during dry conditions produced low runoff amounts, mainly from overland flow from the near saturated riparian zone. Conversely, for rainfall events during wet conditions, hillslopes contributed to streamflow and higher runoff values were observed.

Young water fractions at diverse time scales are driven by varying runoff generation processes in a Mediterranean small research catchment

2020 ◽  
Author(s):  
Francesc Gallart ◽  
Pilar Llorens ◽  
Carles Cayuela ◽  
Matthias Sprenger ◽  
Jérôme Latron ◽  
...  
Keyword(s):  
Overland Flow ◽  
Stream Water ◽  
Special Role ◽  
Hydrograph Separation ◽  
Runoff Generation ◽  
Time Intervals ◽  
Water Fraction ◽  
Early Results ◽  
Generation Mechanisms ◽  
Large Discharge

<p>The time water resides within a catchment has important implications for the water availability and quality for both ecosystem and human use. Here, we look at the short-term water transport using the concept of young water fraction (<em>F<sub>yw</sub></em>), defined as the proportion of water that is younger than 2-3 months. The study was conducted for the 0.56 Km<sup>2</sup> sub-humid Can Vila catchment (Vallcebre Research Catchments). During a period of over 58 months, the isotope ratios (<sup>2</sup>H and <sup>18</sup>O) of rainwater was sampled at 5-mm rainfall intervals and stream water was sampled at variable time intervals (30 minutes to 1 week) depending on flow.</p><p>The early results of this research revealed intense dynamics of<em> F<sub>yw</sub></em> in relationship with discharge: <em>F<sub>yw</sub></em> had values between 0 for low flows and around 1 for the highest flows. Yet, the high variability of discharge and flashy response behaviour in this catchment along with the relatively large discharge sensitivity (<em>S<sub>d</sub></em>) of <em>F<sub>yw</sub></em> implied that even if the maximum sampled discharges were exceeded by only 0.01% of time, about 25% of the <em>F<sub>yw</sub></em> associated to the highest flows were estimated to be missed by the stream water sampling. This behaviour may be associated with a response dominated by saturation runoff generation mechanisms during wet episodes, which are known to drive the main hydrological response of this catchment.</p><p>Nevertheless, these results are obtained when all the samples are lumped for the whole 58 month period, but when different 12-month windows are investigated, the behaviour of <em>F<sub>yw</sub></em> becomes more intricate. Indeed, the wetter year was associated with the largest <em>F<sub>yw</sub></em> and <em>S<sub>d</sub></em> values, but drier years had irregularly varying values poorly correlated to precipitation or runoff statistics. Thus, other runoff generation mechanisms previously identified, including Hortonian-type overland flow in small degraded areas, that lead to runoff of new (and hence young) waters for low to moderate flows, will play a special role.</p><p>Current research is comparing <em>F<sub>yw</sub></em> analyses for groups of events of the same class, supported by hydrograph separation analyses and hydrometric indicators, for better understanding the dynamic and complex response of <em>F<sub>yw</sub></em> in this catchment. Our work further advances the understanding of limitations and opportunities of the <em>F<sub>y</sub><sub>w</sub></em> approach.</p>

scholarly journals The influence of soil moisture on threshold runoff generation processes in an alpine headwater catchment

2011 ◽  
Vol 15 (3) ◽  
pp. 689-702 ◽  
Author(s):  
D. Penna ◽  
H. J. Tromp-van Meerveld ◽  
A. Gobbi ◽  
M. Borga ◽  
G. Dalla Fontana
Keyword(s):  
Soil Moisture ◽  
Overland Flow ◽  
Riparian Zone ◽  
Temporal Dynamics ◽  
Runoff Generation ◽  
Antecedent Conditions ◽  
Antecedent Moisture ◽  
Dry Conditions ◽  
Strong Control ◽  
Headwater Catchment

Abstract. This study investigates the role of soil moisture on the threshold runoff response in a small headwater catchment in the Italian Alps that is characterised by steep hillslopes and a distinct riparian zone. This study focuses on: (i) the threshold soil moisture-runoff relationship and the influence of catchment topography on this relation; (ii) the temporal dynamics of soil moisture, streamflow and groundwater that characterize the catchment's response to rainfall during dry and wet periods; and (iii) the combined effect of antecedent wetness conditions and rainfall amount on hillslope and riparian runoff. Our results highlight the strong control exerted by soil moisture on runoff in this catchment: a sharp threshold exists in the relationship between soil water content and runoff coefficient, streamflow, and hillslope-averaged depth to water table. Low runoff ratios were likely related to the response of the riparian zone, which was almost always close to saturation. High runoff ratios occurred during wet antecedent conditions, when the soil moisture threshold was exceeded. In these cases, subsurface flow was activated on hillslopes, which became a major contributor to runoff. Antecedent wetness conditions also controlled the catchment's response time: during dry periods, streamflow reacted and peaked prior to hillslope soil moisture whereas during wet conditions the opposite occurred. This difference resulted in a hysteretic behaviour in the soil moisture-streamflow relationship. Finally, the influence of antecedent moisture conditions on runoff was also evident in the relation between cumulative rainfall and total stormflow. Small storms during dry conditions produced low stormflow amounts, likely mainly from overland flow from the near saturated riparian zone. Conversely, for rainfall events during wet conditions, higher stormflow values were observed and hillslopes must have contributed to streamflow.

Controls on streamwater age in a saturation overland flow-dominated catchment

2021 ◽  
Author(s):  
Dana Lapides ◽  
David Dralle ◽  
Daniella Rempe ◽  
William Dietrich ◽  
W. Jesse Hahm
Keyword(s):  
Overland Flow ◽  
Return Flow ◽  
Field Observations ◽  
Hydrograph Separation ◽  
Storm Events ◽  
Runoff Generation ◽  
Water Age ◽  
Flow Pathways ◽  
Generation Mechanisms ◽  
California Coast Ranges

<p>Water age and flow pathways should be related; however, it is still generally unclear how integrated catchment runoff generation mechanisms result in streamflow age distributions at the outlet. Here, we combine field observations of runoff generation at the Dry Creek catchment with StorAge Selection (SAS) age models to explore the relationship between streamwater age and runoff pathways. Dry Creek is an intensively monitored catchment in the northern California Coast Ranges with a Mediterranean climate and thin subsurface critical zone. Due to limited storage capacity, runoff response is rapid (~1-2 hours), and total annual streamflow consists predominantly of saturation overland flow, based on field mapping of saturated extents and runoff thresholds. Even though SAS modeling reveals that streamflow is younger at higher wetness states, flow is still typically older than one day and thus older than event water. Because streamflow is mostly overland flow, this means that a significant portion of overland flow must derive from groundwater returning to the surface, consistent with field observations of exfiltrating head gradients, return flow through macropores, and extensive saturation days after storm events. We conclude that even in a landscape with widespread overland flow, runoff pathways may be longer than anticipated, with implications for contaminant delivery and biogeochemical reactions. Our findings have implications for the assumptions built into classic hydrograph separation inferences, namely, that overland flow is not all new water.</p>

Isotopic hydrograph separation in a small agricultural catchment

2021 ◽  
Author(s):  
Borbála Széles ◽  
Juraj Parajka ◽  
Ladislav Holko ◽  
Stefan Wyhlidal ◽  
Katharina Schott ◽  
...  
Keyword(s):  
Overland Flow ◽  
Agricultural Land ◽  
Drainage System ◽  
Time Lapse ◽  
Tile Drainage ◽  
Hydrograph Separation ◽  
Runoff Generation ◽  
Agricultural Catchments ◽  
Two Component ◽  
Generation Mechanisms

<p>Exploring the isotopic composition of precipitation and streamflow in small catchments and the event and pre-event components of precipitation events using two-component isotopic hydrograph separation may better explain the overall catchment behaviour, more specifically the sources of water origin. This study’s main objective is to investigate the origin of water for different streamflow gauges in a small agricultural catchment, which represent different runoff generation mechanisms. The analysis will be performed in the Hydrological Open Air Laboratory (HOAL) in Austria, a 66 ha experimental catchment dominated by agricultural land use (Blöschl et al., 2016). One of the main specialities of this research catchment is that several tributaries of the catchment representing different runoff generation mechanisms are gauged, such as tile drainage flow or saturation excess runoff from erosion gullies. Two-component isotopic hydrograph separation (for both <sup>18</sup>O and <sup>2</sup>H) will be conducted for five streamflow gauges (catchment inlet and outlet, two erosion gullies and a tile drainage system) for multiple events in the period 2013-2018. The results will be linked and interpreted using additional observations such as time-lapse images of overland flow, electric conductivity measurements, groundwater level changes, evapotranspiration measurements, etc. The aim is to explain and discuss the processes of rainfall-runoff generation in small agricultural catchments.</p><p> </p><p>Reference:</p><p>Blöschl, G., et al. (2016). The Hydrological Open Air Laboratory (HOAL) in Petzenkirchen: A hypothesis‐driven observatory. Hydrol. Earth Syst. Sci., 20(1), 227–255. doi: 10.5194/hess‐20‐227‐2016.</p>

scholarly journals Modified Richards’ Equation to Improve Estimates of Soil Moisture in Two-Layered Soils after Infiltration

Water ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 1174 ◽  
Author(s):  
Honglin Zhu ◽  
Tingxi Liu ◽  
Baolin Xue ◽  
Yinglan A. ◽  
Guoqiang Wang
Keyword(s):  
Soil Moisture ◽  
Overland Flow ◽  
Hydrological Cycle ◽  
Soil Depth ◽  
Controlling Factors ◽  
Moisture Distribution ◽  
Richards Equation ◽  
Infiltration Process ◽  
Soil Moisture Distribution

Soil moisture distribution plays a significant role in soil erosion, evapotranspiration, and overland flow. Infiltration is a main component of the hydrological cycle, and simulations of soil moisture can improve infiltration process modeling. Different environmental factors affect soil moisture distribution in different soil layers. Soil moisture distribution is influenced mainly by soil properties (e.g., porosity) in the upper layer (10 cm), but by gravity-related factors (e.g., slope) in the deeper layer (50 cm). Richards’ equation is a widely used infiltration equation in hydrological models, but its homogeneous assumptions simplify the pattern of soil moisture distribution, leading to overestimates. Here, we present a modified Richards’ equation to predict soil moisture distribution in different layers along vertical infiltration. Two formulae considering different controlling factors were used to estimate soil moisture distribution at a given time and depth. Data for factors including slope, soil depth, porosity, and hydraulic conductivity were obtained from the literature and in situ measurements and used as prior information. Simulations were compared between the modified and the original Richards’ equations and with measurements taken at different times and depths. Comparisons with soil moisture data measured in situ indicated that the modified Richards’ equation still had limitations in terms of reproducing soil moisture in different slope positions and rainfall periods. However, compared with the original Richards’ equation, the modified equation estimated soil moisture with spatial diversity in the infiltration process more accurately. The equation may benefit from further solutions that consider various controlling factors in layers. Our results show that the proposed modified Richards’ equation provides a more effective approach to predict soil moisture in the vertical infiltration process.

scholarly journals Physically-based modelling of hydrological processes in a tropical headwater catchment (West Africa) – process representation and multi-criteria validation

2006 ◽  
Vol 10 (6) ◽  
pp. 829-847 ◽  
Author(s):  
S. Giertz ◽  
B. Diekkrüger ◽  
G. Steup
Keyword(s):  
Soil Moisture ◽  
Rainy Season ◽  
Overland Flow ◽  
Soil Layer ◽  
Hydrological Processes ◽  
Runoff Generation ◽  
Field Investigations ◽  
Physically Based ◽  
In The Beginning ◽  
Headwater Catchment

Abstract. The aim of the study was to test the applicability of a physically-based model to simulate the hydrological processes in a headwater catchment in Benin. Field investigations in the catchment have shown that lateral processes such as surface runoff and interflow are most important. Therefore, the 1-D SVAT-model SIMULAT was modified to a semi-distributed hillslope version (SIMULAT-H). Based on a good database, the model was evaluated in a multi-criteria validation using discharge, discharge components and soil moisture data. For the validation of discharge, good results were achieved for dry and wet years. The main differences were observable in the beginning of the rainy season. A comparison of the discharge components determined by hydro-chemical measurements with the simulation revealed that the model simulated the ratio of groundwater fluxes and fast runoff components correctly. For the validation of the discharge components of single events, larger differences were observable, which was partly caused by uncertainties in the precipitation data. The representation of the soil moisture dynamics by the model was good for the top soil layer. For deeper soil horizons, which are characterized by higher gravel content, the differences between simulated and measured soil moisture were larger. A good agreement of simulation results and field investigations was achieved for the runoff generation processes. Interflow is the predominant process on the upper and the middle slopes, while at the bottom of the hillslope groundwater recharge and – during the rainy season – saturated overland flow are important processes.

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