Assessing the Performance of Different Time of Concentration Equations in Urban Ungauged Watersheds: Case Study of Cartagena de Indias, Colombia

In ungauged watersheds, the estimation of the time of concentration (Tc) is always a challenging task due to the intrinsic uncertainty involved when making assumptions. Given that Tc is one of the main inputs in a hydrological analysis for the design of hydraulic structures for stormwater management, ten equations (including one proposed in several local studies) and two Tc methodologies (overland flow time plus channel flow time) were used to compute the Tc in fifteen urban ungauged watersheds, located in Cartagena de Indias (Colombia), with different area sizes and slopes to statistically assess their performance against the value obtained via the Natural Resources Conservation Service (NRCS) velocity method (assumed to be the true value). According to the Nash–Sutcliffe efficiency index, none of the equations proved to be reliable in all watersheds as only four equations predicted the Tc value in 53% of the cases. In addition, based on the percent bias, all equations tended to significantly over- or underestimate the Tc, which affects the quantification of the runoff volume necessary for, among others, the implementation of best management practices for watershed management (e.g., conventional and/or sustainable drainage system design), flood-prone area delineation and flood risk analyses, urban planning, and stream restoration.

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Influence of basin connectivity on sediment source, transport, and storage within the Mkabela Basin, South Africa

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-9-10151-2012 ◽

2012 ◽

Vol 9 (9) ◽

pp. 10151-10204 ◽

Cited By ~ 2

Author(s):

J. R. Miller ◽

G. Mackin ◽

P. Lechler ◽

M. Lord ◽

S. Lorentz

Keyword(s):

South Africa ◽

Best Management Practices ◽

Management Practices ◽

Drainage System ◽

Sediment Source ◽

Riparian Wetlands ◽

Valley Bottom ◽

Sediment Size ◽

Catchment Areas ◽

And Storage

Abstract. The management of sediment and other non-point source (NPS) pollution has proven difficult, and requires a sound understanding of particle movement through the drainage system. The primary objective of this investigation was to obtain an understanding of NPS sediment source(s), transport, and storage within the Mkabela basin, a representative agricultural catchment within the KwaZulu-Natal Midlands of southeastern South Africa, by combining geomorphic, hydrologic and geochemical fingerprinting analyses. The Mkabela Basin can be subdivided into three distinct subcatchments that differ in their ability to transport and store sediment along the axial valley. Headwater (upper catchment) areas are characterized by extensive wetlands that act as significant sediment sinks. Mid-catchment areas, characterized by higher relief and valley gradients, exhibit few wetlands, but rather are dominated by a combination of alluvial and bedrock channels that are conducive to sediment transport. The lower catchment exhibits a low-gradient alluvial channel that is boarded by extensive riparian wetlands that accumulate large quantities of sediment (and NPS pollutants). Fingerprinting studies suggest that silt- and clay-rich layers found within wetland and reservoir deposits are derived from the erosion of fine-grained, valley bottom soils frequently utilized as vegetable fields. Coarser-grained deposits within both wetlands and reservoirs result from the erosion of sandier hillslope soils extensively utilized for sugar cane, during relatively high magnitude runoff events that are capable of transporting sand-sized sediment off the slopes. Thus, the source of sediment to the axial valley varies as a function of sediment size and runoff magnitude. Sediment export from the basin was limited until the early 1990s, in part because the upper catchment wetlands were hydrologically disconnected from lower parts of the watershed during low- to moderate flood events. The construction of a drainage ditch through a previously unchanneled wetland altered the hydrologic connectivity of the catchment, allowing sediment to be transported from the headwaters to the lower basin where much of it was deposited within the riparian wetlands. The axial drainage system is now geomorphically and hydrologically connected during most events throughout the study basin. The study indicates that increased valley connectivity partly negated the positive benefits of controlling sediment/nutrient exports from the catchment by means of upland based, best management practices.

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Overland Flow Time of Concentration on Very Flat Terrains

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/2060-15 ◽

2008 ◽

Vol 2060 (1) ◽

pp. 133-140 ◽

Cited By ~ 16

Author(s):

Ming-Han Li ◽

Paramjit Chibber

Keyword(s):

Regression Analysis ◽

Laboratory Experiments ◽

Overland Flow ◽

Flow Time ◽

Empirical Models ◽

The Other ◽

Tall Grass ◽

Antecedent Soil Moisture ◽

Time Of Concentration ◽

Artificial Rainfall

Two types of laboratory experiments were conducted to measure overland flow times on surfaces with very low slopes. One was a rainfall test using a mobile artificial rainfall simulator; the other was an impulse runoff test. Test plots were 6 ft (1.83 m) wide by 30 ft (9.14 m) long with slopes ranging from 0.24% to 0.48%. Surface types tested include bare clay, lawn (short grass), pasture (tall grass), asphalt, and concrete. A regression analysis was conducted to construct models for predicting flow times. Results predicted with regressed models were compared with those from empirical models in the literature. It was found that the slope variable in the regressed model from rainfall test data is less influential than that in existing models. Furthermore, the exponent for the slope variable in the regressed model for the impulse runoff condition is only 1/10th of those in existing models. Overall, most empirical models underestimate overland flow time for laboratory plots with very low slopes. The slope variable becomes insignificant in governing overland flow time when the slope is small. Antecedent soil moisture, not included in most empirical models, significantly affects time of concentration, which is included in the regressed models.

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Influence of basin connectivity on sediment source, transport, and storage within the Mkabela Basin, South Africa

Hydrology and Earth System Sciences ◽

10.5194/hess-17-761-2013 ◽

2013 ◽

Vol 17 (2) ◽

pp. 761-781 ◽

Cited By ~ 16

Author(s):

J. R. Miller ◽

G. Mackin ◽

P. Lechler ◽

M. Lord ◽

S. Lorentz

Keyword(s):

South Africa ◽

Best Management Practices ◽

Management Practices ◽

Drainage System ◽

Sediment Source ◽

Riparian Wetlands ◽

Valley Bottom ◽

Sediment Size ◽

Catchment Areas ◽

And Storage

Abstract. The management of sediment and other non-point source (NPS) pollution has proven difficult, and requires a sound understanding of particle movement through the drainage system. The primary objective of this investigation was to obtain an understanding of NPS sediment source(s), transport, and storage within the Mkabela Basin, a representative agricultural catchment within the KwaZulu–Natal Midlands of eastern South Africa, by combining geomorphic, hydrologic and geochemical fingerprinting analyses. The Mkabela Basin can be subdivided into three distinct subcatchments that differ in their ability to transport and store sediment along the axial valley. Headwater (upper catchment) areas are characterized by extensive wetlands that act as significant sediment sinks. Mid-catchment areas, characterized by higher relief and valley gradients, exhibit few wetlands, but rather are dominated by a combination of alluvial and bedrock channels that are conducive to sediment transport. The lower catchment exhibits a low-gradient alluvial channel that is boarded by extensive riparian wetlands that accumulate large quantities of sediment (and NPS pollutants). Fingerprinting studies suggest that silt- and clay-rich layers found within wetland and reservoir deposits of the upper and upper-mid subcatchments are derived from the erosion of fine-grained, valley bottom soils frequently utilized as vegetable fields. Coarser-grained deposits within these wetlands and reservoirs result from the erosion of sandier hillslope soils extensively utilized for sugar cane, during relatively high magnitude runoff events that are capable of transporting sand-sized sediment off the slopes. Thus, the source of sediment to the axial valley varies as a function of sediment size and runoff magnitude. Sediment export from upper to lower catchment areas was limited until the early 1990s, in part because the upper catchment wetlands were hydrologically disconnected from lower parts of the watershed during low to moderate flood events. The construction of a drainage ditch through a previously unchanneled wetland altered the hydrologic connectivity of the catchment, allowing sediment to be transported from the headwaters to the lower basin where much of it was deposited within riparian wetlands. The axial drainage system is now geomorphically and hydrologically connected during events capable of overflowing dams located throughout the study basin. The study indicates that increased valley connectivity partly negated the positive benefits of controlling sediment/nutrient exports from the catchment by means of upland based, best management practices.

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Developing a decision support tool for assessing land use change and BMPs in ungauged watersheds based on decision rules provided by SWAT simulation

Hydrology and Earth System Sciences ◽

10.5194/hess-22-3789-2018 ◽

2018 ◽

Vol 22 (7) ◽

pp. 3789-3806 ◽

Cited By ~ 12

Author(s):

Junyu Qi ◽

Sheng Li ◽

Charles P.-A. Bourque ◽

Zisheng Xing ◽

Fan-Rui Meng

Keyword(s):

Land Use ◽

Decision Support ◽

Land Use Change ◽

Best Management Practices ◽

Management Practices ◽

Hydrological Modeling ◽

Decision Support Tool ◽

Decision Makers ◽

Support Tool ◽

Ungauged Watersheds

Abstract. Decision making on water resources management at ungauged, especially large-scale watersheds relies on hydrological modeling. Physically based distributed hydrological models require complicated setup, calibration, and validation processes, which may delay their acceptance among decision makers. This study presents an approach to develop a simple decision support tool (DST) for decision makers and economists to evaluate multiyear impacts of land use change and best management practices (BMPs) on water quantity and quality for ungauged watersheds. The example DST developed in the present study was based on statistical equations derived from Soil and Water Assessment Tool (SWAT) simulations and applied to a small experimental watershed in northwest New Brunswick. The DST was subsequently tested against field measurements and SWAT simulations for a larger watershed. Results from DST could reproduce both field data and model simulations of annual stream discharge and sediment and nutrient loadings. The relative error of mean annual discharge and sediment, nitrate–nitrogen, and soluble-phosphorus loadings were −6, −52, 27, and −16 %, respectively, for long-term simulation. Compared with SWAT, DST has fewer input requirements and can be applied to multiple watersheds without additional calibration. Also, scenario analyses with DST can be directly conducted for different combinations of land use and BMPs without complex model setup procedures. The approach in developing DST can be applied to other regions of the world because of its flexible structure.

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RZ-TRADEOFF: A New Model to Estimate Riparian Water and Air Quality Functions

Water ◽

10.3390/w11040769 ◽

2019 ◽

Vol 11 (4) ◽

pp. 769 ◽

Cited By ~ 2

Author(s):

Hassanzadeh ◽

Vidon ◽

Gold ◽

Pradhanang ◽

Lowder

Keyword(s):

Land Use ◽

Air Quality ◽

Land Cover ◽

Water Table ◽

Best Management Practices ◽

Management Practices ◽

Overland Flow ◽

Subsurface Flow ◽

Riparian Zones ◽

The Impact

Riparian zones are often used as best management practices due to their ability to remove nitrate (NO3−) from subsurface flow. Research suggests that beyond local biogeochemical controls, the impact of riparian zones on nitrogen removal and other functions, such as phosphorus dynamics and greenhouse gas emissions, largely depends on land-use/land-cover, hydrogeomorphology, and weather. In this study, we therefore present RZ-TRADEOFF, a novel and easily applicable model that connects multiple riparian functions and characteristics (NO3− and phosphate (PO43−), concentration and removal in subsurface flow, total phosphorus (TP) removal in overland flow, nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) emissions, water table) to landscape hydrogeomorphic characteristics, weather, and land-cover/land-use. RZ-TRADEOFF was developed with data from past studies and digital databases, and validated with data collected from the literature. Three functions (water table, PO43− and CO2) were observed to be significantly influenced by climate/weather, while the others were primarily influenced by hydrogeomorphology and land use. The percent bias and normalized root mean square error respectively were −3.35% and 0.28 for water table, 16.00% and 0.34 for NO3− concentration, −7.83% and 20.82 for NO3− removal, 6.64% and 0.35 for PO43− concentration, 2.55% and 0.17 for TP removal, 40.33% and 0.23 for N2O, 72.68% and 0.18 for CH4, and −34.98% and 0.91 for CO2. From a management standpoint, RZ-TRADEOFF significantly advances our ability to predict multiple water and air quality riparian functions using easily accessible data over large areas of the landscape due to its scalability.

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Concepts about Forests and Water

Northern Journal of Applied Forestry ◽

10.1093/njaf/23.1.11 ◽

2006 ◽

Vol 23 (1) ◽

pp. 11-19 ◽

Cited By ~ 29

Author(s):

Gordon W. Stuart ◽

Pamela J. Edwards

Keyword(s):

Water Quality ◽

Best Management Practices ◽

Forest Canopy ◽

Management Practices ◽

Overland Flow ◽

Mineral Soil ◽

Wood Products ◽

Quality Water ◽

The Impact

Abstract Six concepts concerning forests, forestry, and water resources are discussed: (1) the role of the forest canopy in erosion control; (2) the impact of disturbance on soils; (3) the variability of natural water quality; (4) the impact of harvesting on water quality; (5) the role of extreme experiments; and (6) the effectiveness of forestry best management practices (BMP). The literature shows that the forest floor, not the canopy, protects soils from erosion. Harvesting can be conducted in ways that limit compaction and essentially confine overland flow to areas of exposed mineral soil on roads, trails, and log landings. Overland flow from these areas can be controlled and converted to subsurface flow before it reaches streams and lakes. Thus, effects to watershed hydrology are small. Undisturbed watersheds tend to have better quality water than highly disturbed watersheds, but the undisturbed character of a catchment does not assure high-quality water. Undisturbed forests vary greatly in sediment and chemical exports that are controlled by variables such as streamflow, soils, geology, air pollution, and land use history. Conversely, timber harvesting does not necessarily have measurable or biologically meaningful negative effects on water quality. Forestry BMP have proven effective in controlling adverse changes to in-stream sediment and water chemistry. Many studies that have reported large changes in water quality often represent extreme treatments not associated with typical forest operations, or they have not employed BMP. Properly and adequately used forestry BMP protect watershed resources while allowing the removal of wood products.

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