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Over the last century, afforestation in Ireland has increased from 1% of the land area to 10%, with most plantations on upland drained blanket peatlands. This land use change is considered to have altered the hydrological response and water balance of upland catchments with implications for water resources. Because of the difficulty of observing these long‐term changes in the field, the aim of this study was to utilize a hydrological model to simulate the rainfall runoff processes of an existing pristine blanket peatland and then to simulate the hydrology of the peatland if it were drained and afforested. The hydrological rainfall runoff model (GEOtop) was calibrated and validated for an existing small (76 ha) pristine blanket peatland in the southwest of Ireland for the 2‐year period, 2007–2008. The current hydrological response of the pristine blanket peatland catchment with regard to streamflow and water table (WT) levels was captured well in the simulations. Two land use change scenarios of afforestation were also examined, (A) a young 10‐year‐old and (B) a semi‐mature 15‐year‐old Sitka Spruce forest. Scenario A produced similar streamflow dynamics to the pristine peatland, whereas total annual streamflow from Scenario B was 20% lower. For Scenarios A and B, on an annual average basis, the WT was drawn down by 16 and 20 cm below that observed in the pristine peatland, respectively. The maximum WT draw down in Scenario B was 61 cm and occurred in the summer months, resulting in a significant decrease in summer streamflow. Occasionally in the winter (following rainfall), the WT for Scenario B was just 2 cm lower than the pristine peatland, which when coupled with the drainage networks associated with afforestation led to higher peak streamflows. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Spatial variability of hydraulic conductivity and bulk density along a blanket peatland hillslope 总被引：4，自引：0，他引：4
This article presents the results of a field investigation of saturated hydraulic conductivity Ksat and bulk density (ρbd) in an Atlantic blanket bog in the southwest of Ireland. Starting at a peatland stream and moving along an uphill transect toward the peatland interior, ρbd and Ksat were examined at regular intervals. Saturated horizontal hydraulic conductivity (Khsat) and vertical (Kvsat) was estimated at two depths: 10–20 and 30–40 cm below the peat surface, whereas ρbd was estimated for the full profile. We consider two separate zones, one a riparian zone extending 10 m from the stream and a second zone in the bog interior. We found that the Ksat was higher (~10–5 m s–1) in the bog interior than that in the riparian zone (~10–6 m s–1), whereas the converse applied to bulk density, with lowest density (~0.055 g cm–3) at the interior and highest (~0.11 g cm–3) at the riparian zone. In general, we found Khsat to be approximately twice the Kvsat. These results support the idea that the lower Ksat at the margins control the hydrology of blanket peatlands. It is therefore important that the spatial variation of these two key properties be accommodated in hydrological models if the correct rainfall runoff characteristics are to be correctly modelled. Stream flow analysis over 3 years at the peatland catchment outlet showed that the stream runoff was composed of 8% base flow and 92% flood flow, suggesting that this blanket peatland is a source rather than a sink for floodwaters. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Downstream variation of hydraulic geometry in rivers, characterized by fine textured banks and low width to depth ratios (7–25), is investigated in Victoria, Australia, with the aim of developing predictive models of channel geometry for large-scale spatial modeling applications. A one-dimensional hydraulic model is used to determine the mean bank-full geometry and discharge (Qbf) for 93 sites which are investigated in relation to discharge of fixed average recurrence interval (ARI). The median bank-full ARI is estimated at 0.8 years with 75% of sites between 0.5 and 2.5 years. Exponents in the downstream hydraulic geometry relations for width, depth and velocity are respectively 0.43, 0.40 and 0.18 (Q = Qbf) and 0.44, 0.38 and 0.03 (Q = Q2, i.e., 2-year ARI), falling near the mode of global values. Q2 and slope explain 66% of variance in Qbf, while Q2 explains 73% and 69% of the variance in width and depth relations, respectively: Q2 provides a reliable substitute for Qbf in spatial modeling applications. Spatial variation in hydraulic geometry relations within and between river basins remains largely unexplained. The W/D ratio characteristically decreases with increasing distance along the lower reaches of most rivers and this has contributed to the lower than expected value for the width exponent. 相似文献
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W. J. Tango J. Davis A. P. Jacob A. Mendez J. R. North J. W. O'Byrne E. B. Seneta P. G. Tuthill 《Monthly notices of the Royal Astronomical Society》2009,396(2):842-848
The binary star δ Sco (HD143275) underwent remarkable brightening in the visible in 2000, and continues to be irregularly variable. The system was observed with the Sydney University Stellar Interferometer (SUSI) in 1999, 2000, 2001, 2006 and 2007. The 1999 observations were consistent with predictions based on the previously published orbital elements. The subsequent observations can only be explained by assuming that an optically bright emission region with an angular size of ≳2 ± 1 mas formed around the primary in 2000. By 2006/2007 the size of this region grew to an estimated ≳4 mas.
We have determined a consistent set of orbital elements by simultaneously fitting all the published interferometric and spectroscopic data as well as the SUSI data reported here. The resulting elements and the brightness ratio for the system measured prior to the outburst in 2000 have been used to estimate the masses of the components. We find MA = 15 ± 7 M⊙ and MB = 8.0 ± 3.6 M⊙ . The dynamical parallax is estimated to be 7.03 ± 0.15 mas , which is in good agreement with the revised Hipparcos parallax. 相似文献
We have determined a consistent set of orbital elements by simultaneously fitting all the published interferometric and spectroscopic data as well as the SUSI data reported here. The resulting elements and the brightness ratio for the system measured prior to the outburst in 2000 have been used to estimate the masses of the components. We find M
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Bradford E. Prather Ciaran O'Byrne Carlos Pirmez Zoltán Sylvester 《Basin Research》2017,29(3):394-416
Deciphering the role slope topography plays in partitioning sediment on siliciclastic continental slope and base‐of‐slope systems helps our understanding of slope depositional processes in significant ways: (1) by validation of large‐scale depositional process models for continental margins, (2) by validation of numerical basin‐scale stratigraphic forward models used to test and deploy source‐to‐sink (S2S) concepts and (3) by creating models for setting reservoir presence and quality expectations in frontier areas poorly constrained by wells and seismic. A global database consisting of >700 km of drilled stratigraphy provide empirical rock data lacking from most S2S studies. Analysis of calibrated seismic stratigraphic units characterised using the contextual framework laid out in this paper show that both gross depositional environments (GDEs) and sand content occur across slope profiles in systematic ways. The challenge in using these observations to quantify reservoir risk and uncertainty lies with relating the observations to depositional processes that can be used to characterise frontier basins that lack calibration. Depositional process‐based understanding encoded in 3D stratigraphic forward models (SFM) can simulate both lithologies and GDEs providing broad predictions for exploration at the scale of an entire basin or slope system. Stratigraphic forward models allow the integration of S2S understanding and provide a framework for testing sediment‐partitioning hypotheses in frontier settings. Valid S2S models must balance sediment yield from the source catchments with sinks, and be consistent with basin specific observations. The proportions of GDEs across the slope provide additional validation criteria to ensure the models are plausible. 相似文献
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J. Davis A. Mendez E. B. Seneta † W. J. Tango A. J. Booth ‡ J. W. O'Byrne E. D. Thorvaldson § M. Ausseloos C. Aerts K. Uytterhoeven 《Monthly notices of the Royal Astronomical Society》2005,356(4):1362-1370
The bright southern binary star β Centauri (HR 5267) has been observed with the Sydney University Stellar Interferometer (SUSI) and spectroscopically with the European Southern Observatory Coude Auxiliary Telescope and Swiss Euler telescope at La Silla. The interferometric observations have confirmed the binary nature of the primary component and have enabled the determination of the orbital parameters of the system. At the observing wavelength of 442 nm the two components of the primary system have a magnitude difference of 0.15 ± 0.02 . The combination of interferometric and spectroscopic data gives the following results: orbital period 357.00 ± 0.07 d , semimajor axis 25.30 ± 0.19 mas , inclination 674 ± 03 , eccentricity 0.821 ± 0.003 , distance 102.3 ± 1.7 pc , primary and secondary masses M 1 = M 2 = 9.1 ± 0.3 M⊙ and absolute visual magnitudes of the primary and secondary M 1 V =−3.85 ± 0.05 and M 2 V =−3.70 ± 0.05 , respectively. The high degree of accuracy of the results offers a fruitful starting point for future asteroseismic modelling of the pulsating binary components. 相似文献
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The advance of a chemical weathering front into the bedrock of a hillslope is often limited by the rate weathering products that can be carried away, maintaining chemical disequilibrium. If the weathering front is within the saturated zone, groundwater flow downslope may affect the rate of transport and weathering—however, weathering also modifies the rock permeability and the subsurface potential gradient that drives lateral groundwater flow. This feedback may help explain why there tends to be neither “runaway weathering” to great depth nor exposed bedrock covering much of the earth and may provide a mechanism for weathering front advance to keep pace with incision of adjacent streams into bedrock. This is the second of a two‐part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low‐dimensional model based on hydraulic groundwater theory. Here, we show how a simplified kinetic model of 1‐D rock weathering can be extended to consider lateral flow in a 2‐D hillslope. Exact and approximate analytical solutions for the location and thickness of weathering within the hillslope are obtained for a number of cases. A location for the weathering front can be found such that lateral flow is able to export weathering products at the rate required to keep pace with stream incision at steady state. Three pathways of solute export are identified: “diffusing up,” where solutes diffuse up and away from the weathering front into the laterally flowing aquifer; “draining down,” where solutes are advected primarily downward into the unweathered bedrock; and “draining along,” where solutes travel laterally within the weathering zone. For each pathway, a different subsurface topography and overall relief of unweathered bedrock within the hillslope is needed to remove solutes at steady state. The relief each pathway requires depends on the rate of stream incision raised to a different power, such that at a given incision rate, one pathway requires minimal relief and, therefore, likely determines the steady‐state hillslope profile. 相似文献
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This is the first of a two‐part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low‐dimensional model based on hydraulic groundwater theory (also known as Dupuit or Boussinesq theory). Here, we examine the effect of lateral flow on the downward fluxes of water and solutes through perched groundwater at steady state. We derive analytical expressions describing the decline in the downward flux rate with depth. Using these, we obtain analytical expressions for water age in a number of cases. The results show that when the permeability field is homogeneous, the spatial structure of water age depends qualitatively on a single dimensionless number, Hi. This number captures the relative contributions to the lateral hydraulic potential gradient of the relief of the lower‐most impermeable boundary (which may be below the weathering front within permeable or incipiently weathered bedrock) and the water table. A “scaled lateral symmetry” exists when Hi is low: age varies primarily in the vertical dimension, and variations in the horizontal dimension x almost disappear when the vertical dimension z is expressed as a fraction z/H(x) of the laterally flowing system thickness H(x). Taking advantage of this symmetry, we show how the lateral dimension of the advection–diffusion‐reaction equation can be collapsed, yielding a 1‐D vertical equation in which the advective flux downward declines with depth. The equation holds even when the permeability field is not homogeneous, as long as the variations in permeability have the same scaled lateral symmetry structure. This new 1‐D approximation is used in the accompanying paper to extend chemical weathering models derived for 1‐D columns to hillslope domains. 相似文献
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J. R. North J. Davis J. G. Robertson T. R. Bedding H. Bruntt M. J. Ireland A. P. Jacob S. Lacour J. W. O'Byrne S. M. Owens D. Stello W. J. Tango P. G. Tuthill 《Monthly notices of the Royal Astronomical Society》2009,393(1):245-252
We have used the Sydney University Stellar Interferometer (SUSI) to measure the angular diameter of the F9 V star β Virginis (β Vir). After correcting for limb darkening and combining with the revised Hipparcos parallax, we derive a radius of 1.703 ± 0.022 R⊙ (1.3 per cent). We have also calculated the bolometric flux from published measurements which, combined with the angular diameter, implies an effective temperature of 6059 ± 49 K (0.8 per cent). We also derived the luminosity of β Vir to be L = 3.51 ± 0.08 L⊙ (2.1 per cent). Solar-like oscillations were measured in this star by Carrier et al. and using their value for the large frequency separation yields the mean stellar density with an uncertainty of about 2 per cent. Our constraints on the fundamental parameters of β Vir will be important to test the theoretical models of this star and its oscillations. 相似文献