Analytical solutions to hillslope subsurface storm flow and saturation overland flow

The ongoing drought in the Western Cape of South Africa (2014 to present) has called for an urgent need to improve our understanding of water resources in the area. Rivers within the Western Cape are known to surge rapidly after rainfall events. Such storm-flow in natural river catchments in the Jonkershoek mountains has previously been shown to be driven by displaced groundwater, with less than 5% of rainfall appearing in the storm-flow. However, the origin of storm-flow surges within urban rivers in the region remains unknown. In this study, we used stable isotopes in water to illustrate that at least 90% of water in the Liesbeek River during a storm event was rainwater. There was a strong correlation between storm-flow and rainfall rates (P < 0.001, Pearson’s r = 0.86), as well as between the δ18O and δ2H values of river-water and rainwater (δ18O: Pearson’s r = 0.741 (P = 0.001), δ2H: Pearson’s r = 0.775 (P < 0.001)). Storm-flow within this urban river therefore appears to be driven by overland-flow over the hardened urban catchment, rather than piston-flow as seen in natural catchments. Our results support studies suggesting the Liesbeek River could be a target for stormwater harvesting to augment water resources in the city of Cape Town.

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Diverging Overland Flow

Hydrology Research ◽

10.2166/nh.1981.0007 ◽

1981 ◽

Vol 12 (2) ◽

pp. 81-98 ◽

Cited By ~ 7

Author(s):

V. P. Singh ◽

N. Agiralioglu

Keyword(s):

Free Boundary ◽

Boundary Problem ◽

Analytical Solutions ◽

Overland Flow ◽

Wave Theory ◽

Kinematic Wave ◽

Watershed Hydrology ◽

Proposed Model ◽

Natural Watersheds ◽

A Free Boundary Problem

Kinematic wave theory is utilized to investigate diverging overland flow which does not appear to have been previously investigated in watershed hydrology. This paper is the first in a sequel of two. It developes analytical solutions for a diverging geometry for two cases: (1) when infiltration is considered through rainfall-excess, and (2) when infiltration is treated concurrently with runoff; this gives rise to a free boundary problem. Part II discusses the application of the proposed model to natural watersheds.

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

Hydrology and Earth System Sciences ◽

10.5194/hess-2-65-1998 ◽

1998 ◽

Vol 2 (1) ◽

pp. 65-76 ◽

Cited By ~ 18

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.

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Phosphorus loss and speciation in overland flow from a plantation horticulture catchment and in an adjoining waterway in coastal Queensland, Australia

Soil Research ◽

10.1071/sr12042 ◽

2012 ◽

Vol 50 (6) ◽

pp. 515 ◽

Cited By ~ 2

Author(s):

Peter R. Stork ◽

David J. Lyons

Keyword(s):

Overland Flow ◽

Weighted Average ◽

Aquatic Organisms ◽

Molar Ratio ◽

Storm Events ◽

N Losses ◽

Marine Habitats ◽

Storm Flow ◽

High Concentrations ◽

Total P

Phosphorus (P) in overland flow from horticulture farms in coastal Queensland, Australia, could eutrophy coastal freshwater and marine habitats environments nearby. The potential for such eutrophication was investigated in a coastal macadamia plantation under commercial production. During the 13-month study, P losses in overland flow were quantified in a 0.24-ha farm catchment with a 3.1% gradient, during five consecutive storm events. These events were within expected short- and long-term episodic rainfall frequencies and intensities. Runoff occurred when such storms generated between 20–40 mm/h of rainfall for >9 min. Calculated annual losses of total P were 0.32 kg/ha.year, comprising dissolved inorganic P (DIP, 0.28 kg/ha.year), particulate P (0.03 kg/ha.year), and dissolved organic P (0.01 kg/ha.year). DIP represented 88% of all losses and this was attributed to excessive fertilisation and untimely applications. Losses of total P were generally higher than those reported in comparable studies. Concentrations of DIP in runoff were 20–200-fold higher than those found in other coastal catchments in Queensland. High concentrations of DIP were present in the topsoil of the non-fertilised, inter-row areas of the farm catchment and this was attributed to transfer and deposition of DIP from adjacent fertilised tree beds during storm flow. Therefore, it can be expected that farm runoff will be enriched with DIP from these areas for an indeterminate period despite any future remediation to fertiliser management. The weighted average of DIP in farm runoff was 2.01 mg/L, whereas it was 0.005 mg/L in a catchment stream bordering the farm, showing a steep concentration gradient between the two ecosystem compartments. Together with nitrogen (N) losses in runoff, reported previously, an N : P molar ratio of 2 : 1 was contained in the farm runoff. This was well below the growth-limiting threshold for aquatic organisms, as determined by the Redfield ratio of 16 : 1 (N : P). The entry of nutrient-enriched farm runoff, as detailed in this study, into the catchment stream and the proximity of such waterways (8 km) to the coastline may also have implications for the near-shore (oligotrophic) marine environment during periods of storm flow. Altogether, this work revealed the high risk of eutrophication from farming landscapes such as the one under study.

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Mixing Model Approaches to Estimate Storm Flow Sources in an Overland Flow-Dominated Tropical Rain Forest Catchment

Water Resources Research ◽

10.1029/95wr01651 ◽

1995 ◽

Vol 31 (9) ◽

pp. 2267-2278 ◽

Cited By ~ 73

Author(s):

Helmut Elsenbeer ◽

Daniel Lorieri ◽

Mike Bonell

Keyword(s):

Rain Forest ◽

Tropical Rain Forest ◽

Overland Flow ◽

Mixing Model ◽

Storm Flow ◽

Forest Catchment

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Water and soil quality in an Otago deer farm

Proceedings of the New Zealand Grassland Association ◽

10.33584/jnzg.2004.66.2534 ◽

2004 ◽

pp. 187-193 ◽

Cited By ~ 2

Author(s):

R.W. Mcdowell ◽

R.J. Paton

Keyword(s):

Water Quality ◽

Surface Water ◽

Overland Flow ◽

Surface Water Quality ◽

Mean Values ◽

E Coli ◽

Storm Flow ◽

Guideline Values ◽

Simulated Event ◽

Fence Line

This paper outlines findings for three experiments on the AgResearch Invermay deer farm that quantified soil and water quality via fence-line pacing and wallowing, and water quality in streams draining the farm. Five weeks after winter grazing (28 hinds/ha), fence-line pacing decreased soil macroporosity and saturated hydraulic conductivity, and increased suspended sediment (SS; 0.226 g/100ml), total phosphorus (P) (TP; 2.0 mg/l), mainly as particulate P (up to 90% of TP), and E. coli (3.52 log10 cfu/100ml) concentrations in a simulated overland flow 1 day after grazing had stopped compared to soils from the rest of the paddock (0.148 g/100ml, 0.86 mg/l and 2.86 log10/100ml). Six weeks following a first simulated rainfall event, and without interim grazing, concentrations in the second simulated event had decreased but losses of P, especially in fence-line paced soils, were still high and above recommended limits for surface water quality (TP = 0.033 mg/l). A survey of visible erosion in 6 deer paddocks with topography (2- 10o) yielded a mean erosion rate of 1.08 t/ha/yr (range, 0.41-2.01 t/ha/yr), 43% associated with fence-lines, troughs or gateways and 57% associated with wallows. Data from three waterways indicated that mean values for two sites that drain 100% deer farmed land, exceeded current lowland surface water limits for dissolved (0.01 mg/l) and TP (0.033 mg/l) and ammoniacal-nitrogen (N) (0.021 mg N/l). Limits for E. coli (126 E. coli/100ml) and nitrate-N (0.444 mg N/l) were also exceeded at another site, which drained a wallow. All guideline values were exceeded during storm flow when ephemeral streams, commonly draining wallows, were flowing to permanent waterways. However, loads of P, N and SS were below average for mixed-grazing pasture catchments in New Zealand. This was attributed to a dry year (rainfall

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