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Modeling Infiltration Behavior to Assess the Reliability of Surface Flow Generation in Forested and Deforested Watersheds.

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Title: Modeling Infiltration Behavior to Assess the Reliability of Surface Flow Generation in Forested and Deforested Watersheds.
Authors: Prajith, V.1 (AUTHOR) prajith@cwrdm.org, Rahman, Shamsur2 (AUTHOR), Narasimha, Kondra3 (AUTHOR), Gokul, T. S.4 (AUTHOR), Pillai, Ajeesh N.5 (AUTHOR), Das, N. Vishnu5 (AUTHOR), Ihjas, K.6 (AUTHOR)
Source: Journal of Hydrologic Engineering. Feb2025, Vol. 31 Issue 1, p1-13. 13p.
Subjects: Watersheds, Runoff, Absorption, Organic compound content of soils, Forest conservation, Climate change, Deforestation
Geographic Terms: Calicut (India), India
Abstract: Understanding differences in infiltration traits between forested and deforested watersheds is vital for evaluating the ecological and hydrological impacts of deforestation. This study addresses a notable research gap by investigating runoff generation in paired watersheds in Calicut, India, one forested and the other deforested, using a physical infiltration model integrated with a probabilistic framework. Infiltration dynamics are simulated with four classical models: Horton, Philip, Kostiakov, and Green–Ampt. The Green–Ampt model performs best, achieving the lowest root mean square error and percent bias and the highest Nash–Sutcliffe efficiency across sites. Runoff probabilities are assessed using the mean-value first-order second-moment method under five rainfall intensities (SR1–SR5, from light to extreme) based on Indian Meteorological Department classifications. Under low to moderate rainfall (SR1∶ 5 mm/h ; SR2∶ 21.55 mm/h), the forested watershed shows high reliability (β=16.36 , 12.86) and zero runoff probability. The deforested watershed also shows zero runoff probability but lower β values (8.67, 8.17), reflecting reduced resilience. Under higher intensities (SR3∶ 50 mm/h , SR4∶ 90 mm/h , SR5∶115.6 mm/h), the runoff probability rises sharply, reaching 84%–100% in forested and 79.5%–100% in deforested watersheds, despite antecedent rainfall being far greater in forested sites (119.5 versus 1.75 mm). At SR3–SR5, both watersheds are highly vulnerable to infiltration-excess runoff, but the deforested watershed responds more rapidly and severely, with more negative reliability indices (−0.82 to −38.5) compared to the forested watershed (−1.02 to −29.62). Soil organic matter is a principal factor, ranging from 2.1% to 2.3% in forested versus 0.9% to 1.8% in deforested sites. Higher organic matter enhances the soil structure, aggregation, and moisture retention, delaying runoff initiation. These findings highlight the critical role of forest vegetation in regulating runoff and emphasize forest conservation and restoration as strategies to mitigate flood risks and strengthen watershed resilience under climatic variability. Practical Applications: This study examines how land-cover changes, particularly deforestation, influence the ability of soil to absorb rainfall and reduce surface runoff. By conducting field-based infiltration tests in both forested and deforested watersheds, the research shows that forested areas are more effective at absorbing water, even when they are already moist from earlier rainfall. The analysis applies a simple reliability method to determine how likely it is for rainfall to exceed the soil's infiltration capacity under different storm conditions. Results show that forested areas remain more resilient to runoff during moderate rain events, while deforested areas become prone to runoff at much lower intensities. These findings emphasize the role of forest vegetation and organic-rich soils in managing flood risks and sustaining hydrological balance. The study offers practical insight for land-use planners, water resource managers, and policymakers by highlighting the benefits of preserving or restoring forest cover to enhance the natural water-absorbing capacity of landscapes and mitigate flooding risks, especially in the face of increasingly extreme rainfall events. [ABSTRACT FROM AUTHOR]
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Abstract:Understanding differences in infiltration traits between forested and deforested watersheds is vital for evaluating the ecological and hydrological impacts of deforestation. This study addresses a notable research gap by investigating runoff generation in paired watersheds in Calicut, India, one forested and the other deforested, using a physical infiltration model integrated with a probabilistic framework. Infiltration dynamics are simulated with four classical models: Horton, Philip, Kostiakov, and Green–Ampt. The Green–Ampt model performs best, achieving the lowest root mean square error and percent bias and the highest Nash–Sutcliffe efficiency across sites. Runoff probabilities are assessed using the mean-value first-order second-moment method under five rainfall intensities (SR1–SR5, from light to extreme) based on Indian Meteorological Department classifications. Under low to moderate rainfall (SR1∶ 5 mm/h ; SR2∶ 21.55 mm/h), the forested watershed shows high reliability (β=16.36 , 12.86) and zero runoff probability. The deforested watershed also shows zero runoff probability but lower β values (8.67, 8.17), reflecting reduced resilience. Under higher intensities (SR3∶ 50 mm/h , SR4∶ 90 mm/h , SR5∶115.6 mm/h), the runoff probability rises sharply, reaching 84%–100% in forested and 79.5%–100% in deforested watersheds, despite antecedent rainfall being far greater in forested sites (119.5 versus 1.75 mm). At SR3–SR5, both watersheds are highly vulnerable to infiltration-excess runoff, but the deforested watershed responds more rapidly and severely, with more negative reliability indices (−0.82 to −38.5) compared to the forested watershed (−1.02 to −29.62). Soil organic matter is a principal factor, ranging from 2.1% to 2.3% in forested versus 0.9% to 1.8% in deforested sites. Higher organic matter enhances the soil structure, aggregation, and moisture retention, delaying runoff initiation. These findings highlight the critical role of forest vegetation in regulating runoff and emphasize forest conservation and restoration as strategies to mitigate flood risks and strengthen watershed resilience under climatic variability. Practical Applications: This study examines how land-cover changes, particularly deforestation, influence the ability of soil to absorb rainfall and reduce surface runoff. By conducting field-based infiltration tests in both forested and deforested watersheds, the research shows that forested areas are more effective at absorbing water, even when they are already moist from earlier rainfall. The analysis applies a simple reliability method to determine how likely it is for rainfall to exceed the soil's infiltration capacity under different storm conditions. Results show that forested areas remain more resilient to runoff during moderate rain events, while deforested areas become prone to runoff at much lower intensities. These findings emphasize the role of forest vegetation and organic-rich soils in managing flood risks and sustaining hydrological balance. The study offers practical insight for land-use planners, water resource managers, and policymakers by highlighting the benefits of preserving or restoring forest cover to enhance the natural water-absorbing capacity of landscapes and mitigate flooding risks, especially in the face of increasingly extreme rainfall events. [ABSTRACT FROM AUTHOR]
ISSN:10840699
DOI:10.1061/JHYEFF.HEENG-6646