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• The proposed sediment connectivity framework integrates the rainfall regime. • Event-based sediment connectivity helps identify the sediment source contribution. • The mismatched area exists for erosion and sediment connectivity. • The overlay between erosion and connectivity is key to explaining sediment yield. Sediment connectivity quantifies the intermediate processes between initial erosion and the corresponding sediment yield. However, fully capturing the variations in sediment connectivity at the event scale and revealing their impact on watershed sediment sources remains challenging. Herein, we established an event-based model to assess sediment connectivity by integrating runoff factors. The spatiotemporal variability of sediment connectivity was evaluated for 58 rainfall events in three heterogeneous watersheds. The degree of sediment connectivity served as an indicator to quantify the proportion of potential sediment transport from units to the watershed outlet, with 1 indicating that the eroded sediment can be fully connected and 0 indicating that it cannot be transported. Moreover, the controls of sediment connectivity on watershed sediment sources and yield were determined. Our results indicated that the watersheds with poor vegetation and dense gullies were characterized by high sediment connectivity during all the rainfall events. The connectivity degree was below 0.5 in approximately 80 % of the watershed area, suggesting that most of the eroded sediment was deposited. Rainfall amount and duration dominated the degree of connectivity of the distal hillslopes, while rainfall intensity exerted a primary control on the transport of sediments from riverbanks to the outlet. In addition, the increase of mismatched area between sediment connectivity and erosion resulted in the decrease of sediment yield. The interaction between sediment connectivity and erosion effectively explained the spatial patterns of sediment sources (p < 0.05). Our work confirmed that the coupled erosion model and sediment connectivity predicted the sediment yield accurately. The predictions for different watersheds portrayed that the Nash-Sutcliffe efficiency and Willmott's agreement index were greater than 0.70 and 0.89, respectively. These findings revealed the role of sediment connectivity and are the critical basis to identify watershed-specific sediment management practices. [ABSTRACT FROM AUTHOR]

• The proposed sediment connectivity framework integrates the rainfall regime. • Event-based sediment connectivity helps identify the sediment source contribution. • The mismatched area exists for erosion and sediment connectivity. • The overlay between erosion and connectivity is key to explaining sediment yield. Sediment connectivity quantifies the intermediate processes between initial erosion and the corresponding sediment yield. However, fully capturing the variations in sediment connectivity at the event scale and revealing their impact on watershed sediment sources remains challenging. Herein, we established an event-based model to assess sediment connectivity by integrating runoff factors. The spatiotemporal variability of sediment connectivity was evaluated for 58 rainfall events in three heterogeneous watersheds. The degree of sediment connectivity served as an indicator to quantify the proportion of potential sediment transport from units to the watershed outlet, with 1 indicating that the eroded sediment can be fully connected and 0 indicating that it cannot be transported. Moreover, the controls of sediment connectivity on watershed sediment sources and yield were determined. Our results indicated that the watersheds with poor vegetation and dense gullies were characterized by high sediment connectivity during all the rainfall events. The connectivity degree was below 0.5 in approximately 80 % of the watershed area, suggesting that most of the eroded sediment was deposited. Rainfall amount and duration dominated the degree of connectivity of the distal hillslopes, while rainfall intensity exerted a primary control on the transport of sediments from riverbanks to the outlet. In addition, the increase of mismatched area between sediment connectivity and erosion resulted in the decrease of sediment yield. The interaction between sediment connectivity and erosion effectively explained the spatial patterns of sediment sources (p < 0.05). Our work confirmed that the coupled erosion model and sediment connectivity predicted the sediment yield accurately. The predictions for different watersheds portrayed that the Nash-Sutcliffe efficiency and Willmott's agreement index were greater than 0.70 and 0.89, respectively. These findings revealed the role of sediment connectivity and are the critical basis to identify watershed-specific sediment management practices. [ABSTRACT FROM AUTHOR]

• SWAT hydrological model has high potential in the assessment of watershed changes. • Land use changes caused by forest fires affect hydrological response of watershed. • Significant increase in surface runoff and sediment load in the post-fire scenario. • Sediment yield increased by 6.5 times with the highest fire spatial distribution. • Forest fire scenarios help to limit hydrological impacts of fire on sediment load. Forest fires profoundly affect the nature of watershed responses to precipitation, increases in runoff rate and volume, and post-fire sediment discharge. A post-fire watershed assessment to identify potential trouble spots for soil erosion and flooding can help land managers for decision-making on deploy mitigation, remediation measures, and restoration action plans. Predicting the potential impact of fires on runoff and soil erosion requires distributed hydrological modeling methods. This study used the Soil and Water Assessment Tool (SWAT), a rainfall-runoff model, to investigate the hydrological consequences of forest fires and their impact on sediment load under different burnt scenarios. For the pre-fire (baseline) scenario, the watershed is calibrated by using the measured discharge and suspended sediment concentration data from the weather station during the time step to estimate post-fire changes at the sub-catchment scale. The total water and sediment yield for the selected sub-catchment in the post-fire scenario with the highest spatial distribution of forest fire, due to the excessive surface runoff (an increase of 14.5%) increased significantly, resulted in 6.5 times increase in sediment yield. The results obtained from the study indicate a significant increase in sediment transport into the stream in the post-fire scenario. A large volume of soil losses occurred during the time step. In contrast, due to removing trees and vegetation from the ground, less evapotranspiration and infiltration occurred in selected sub-catchment areas after forest fires. In terms of watershed management, understanding the consequences of forest fires on hydrological services will be an effective method for sediment budget control. Therefore, applying the rainfall-runoff and erosion models for the watershed with developing plausible forest fire scenarios can be a productive method to deal with the threats and hydrological risks such as soil erosion and sediment transfer to the downstream environment. [ABSTRACT FROM AUTHOR]

Abstract: Pinpointing erosional ‘hot spots’ or sediment source areas within a watershed can be difficult because of the highly non-linear and episodic nature of effective runoff and sediment transport. Continuous monitoring of stream networks can provide insight into sediment source areas not possible from routine sampling by capturing episodic events and integrating entire storm events. This paper presents the results of a three-year study of spring snowmelt runoff in watersheds of Lake Tahoe, California, USA, using a network of nine nephelometric turbidometers. We estimate that montane badlands, comprising 1.2% of the Ward Creek watershed (25 km2), contributed 10–39% of snowmelt-derived suspended sediment load. The badlands are comprised of poorly-vegetated and deeply-incised gullies formed in parent material of Miocene volcanic mudflow breccia. The larger (29.5 km2) Blackwood Creek watershed also showed high relative erosion rates from volcanic terrain. Tributaries draining forested granitic and metasedimentary headwater regions had minimal sediment loads. Monitoring networks indicated that temporary main channel storage regulated release of fine sediment eroded from steep headwater slopes. This lag between erosion and delivery may lead to underestimation of gully erosion contribution to sediment budgets. [Copyright &y& Elsevier]