Year: 2020


We are excited to share a new Riverlab article, linked here, published this month in the Journal of Hydrology. This work advances current understanding of the controls on hydrological connectivity of impervious surfaces to downstream channels and storm-sewer networks and presents new methods of their estimation.

Connected impervious areas – those impervious surfaces that contribute directly to runoff in a storm network or stream – are a better indicator of hydrologic response, stream alteration, and water quality than total impervious area. Most methods for quantifying connected impervious areas require major assumptions regarding the definition of ‘connection’, potentially over-simplifying the role of variable climates, slope gradients, soils conditions, and heterogeneous flow paths on impervious surface connectivity.

In this study, we present a new metric, hydrologically connected impervious areas (HCIA), to refer to spatially explicit (mapped) estimates of the proportion of impervious surfaces that are hydrologically connected to the storm sewer system or stream network. HCIA is comprised of impervious surfaces that contribute directly to the storm-sewer network and are physically connected, Aphys, or those that contribute indirectly and are therefore variably connected (Avar) (see Figure 1). The degree to which Avar is “hydrologically connected” is represented with a coefficient, ϕvar, that ranges between 0 and 1, with 0 representing full connectivity (i.e. all runoff infiltrates downslope), and 1 representing no connectivity (i.e. no runoff infiltrates downslope).

Figure 1. Conceptual model of impervious surface categories: directly or physically connected (Aphys) and variably connected (Avar) (impervious that drains to pervious). The hydrological connectivity Aphys and Avar are given by ϕphys and ϕvar respectively.

Using a combination of hydrologic modeling in the PySWMM, a python interface for the EPA’s Stormwater Management Model, and machine-learning regression tree analysis, we evaluate the controls on ϕvar across varing soil types, slopes, rainfall scenarios, antecedent soil moisture conditions, as well as amounts of impervious and pervious areas. Figure 6 shows that of the factors tested, soil texture (panel A), fraction of downslope pervious area ϕperv (panel B), soil moisture (panel C), and precipitation (panel D) are sensitive, while total area (panel D), width of impervious area (panel F), and slope (panel G) are insensitive parameters.

Figure 6. Sensitivity of ϕvar to saturated soil texture and saturated hydraulic conductivity Ks (panel A), pervious fraction ϕperv (B), antecedent soil moisture conditions ASM (SAT = saturated, FC = field capacity, WP = wilting point) (C), total area A (D), precipitation depth P (E), width W (F), and slope S (%) (G).

To assist with dissemination of these methods in practice, we apply the regression tree in a geospatial tool for estimation of HCIA in ungauged urban catchments. We test the tool in a case study to an urban sewershed in Colorado, and find that the contribution of Avar to HCIA (compared to the contribution of Aphys) varied across the precipitation and soil moisture conditions. Avar contribution to HCIA was low at low precipitation depths and increased rapidly with increasing precipitation and initial soil moisture conditions (see Figure 9).

Overall, our results suggest that, for catchments consisting of highly impermeable soils, Avar contributes to HCIA such that HCIA approaches the total impervious area, but for catchments with highly permeable soils, Avar does not contribute significantly to HCIA, and thus the physically connected impervious area ( Aphys) could be used as a suitable surrogate for HCIA. In between these two extremes, however, lies a wide range of conditions that call for detailed and spatially explicit estimates of Avar connectivity.

References Cited

Sytsma, A., Bell, C., Eisenstein, W., Hogue, T., & Kondolf, G. M. (2020). A geospatial approach for estimating hydrological connectivity of impervious surfaces. Journal of Hydrology, 591, 125545. >>link to paper


With great regret, we cancel the 2020 shortcourse at Sagehen Creek Field Station, due to the many complications arising from the CVID-19 pandemic and the challenges in avoiding problems in holding the shortcourse at the station.  Those already registered are entitled to a full refund or may defer their participation to next year’s course offering, 16-20 August 2021.   We apologize for this very disappointing news, but look forward to better conditions under which we can once again hold the course next year.  We thank you for your understanding.


Matt Kondolf and the Sagehen Teaching Team

Geomorphic and Ecological Fundamentals for River and Stream Restoration

EPA Watershed Management Postgraduate Research Opportunity
DEADLINE: May 29, 2020
Office of Water | Washington, DC | Full-time | MONTHLY STIPEND PROVIDED

This opportunity will provide excellent exposure to the interface of watershed technical issues and environmental policy. It also offers exposure to the interaction between State and EPA CWA program practitioners in implementing their respective responsibilities under the CWA 303(d) program. Under the guidance of a mentor, the research participant will be involved in the activities above and will learn: (1)The respective roles of EPA, states and tribes in achieving the goals of the Clean Water Act (CWA) to achieve and maintain water quality; (2) Programmatic approaches and policy and technical tools to identify and develop restoration and protection plans for impaired or high quality waters, including those related to address nutrient impairments; (3) How states and EPA can continue to push the CWA 303(d) listing and TMDL program to better achieve environmental results in ways tailored to specific state priorities; (4) How to leverage different media to convey water quality information to a variety of audiences.

>>Job description


You may be interested in a new analysis of the effects of recently completed Xayaboury Dam (on the Mekong mainstem near Luang Prabang) and a cascade of dams upstream in China on flow patterns in the Lower Mekong River. The paper, Mekong River, Xayaboury Dam, and Mekong Delta in the first half dry season 2019-2020 by Nguyen Ngoc Tran was published in Vietnamese in TIA SANG, a scientific journal published by the Ministry of Science and Technology. The English version is now available here. As illustrated in excerpts of Figures 5 and 6 from the paper, the hydrologic analysis shows that flows this dry season have been significantly lower than in prior years’ dry seasons.

Riverlab members have contributed scientific papers on the cumulative effects of upstream dams on the sediment budget of the Mekong Delta and other threats to the sustainability of the Delta (Kondolf et al 2014, Kondolf et al 2018) and the potential for strategic dam planning to minimize impacts of dams on downstream sediment budgets and fish migration (Schmitt et al 2019).

Water levels in the Mekong River at Nakhon Phanom reflecting severe drought conditions in the current dry season of the 2019-2020 water year. (Source: Nguyen Ngoc Tran. 2020, Mekong River, Xayaboury Dam, and Mekong Delta in the first half dry season 2019-2020, Figure 5.)

View of the exposed bed of the Mekong River at Nakhon Phanom in late October 2019, reflecting severe drought conditions in this year’s dry season. (Source: Nguyen Ngoc Tran. 2020, Mekong River, Xayaboury Dam, and Mekong Delta in the first half dry season 2019-2020, Figure 6.)

References Cited

Kondolf, G.M., Z.K. Rubin, J.T. Minear. 2014. Dams on the Mekong: Cumulative sediment starvation.  Water Resources Research 50, doi:10.1002/2013WR014651. >>link to paper

Kondolf, GM, RJP Schmitt, P Carling, S Darby, M Arias, S Bizzi, A Castelletti, T Cochrane, S Gibson, M Kummu, C Oeurng, Z Rubin, and T Wild. 2018. Changing sediment budget of the Mekong: Cumulative threats and management strategies for a large river basin. Science of the Total Environment 625: 114-134. >>link to paper

Schmitt, R, S Bizzi, AF Castelletti, J Opperman, GM Kondolf. 2019. Planning dam portfolios for low sediment trapping shows limits on sustainable hydropower in the Mekong. Science Advances 5: eaaw2175 >>link to paper


The government of Cambodia announced on 16 March that it would postpone development of any of new dams on the mainstem Mekong River for 10 years, citing the need to develop alternative sources of energy for the country’s future development. While Cambodia has built a large dam on the SeSan-SrePok (important downstream tributaries), and left open the possibility it might build other tributary dams, the mainstem dams long-planned for Sambor and Stung Trang are on hold for the next decade. See story in the Guardian here.

Environmental Scientist: Regulatory Compliance Specialist – Pacific Watershed Associates

Pacific Watershed Associates is seeking applicants for the position of Environmental Scientist: Regulatory Compliance Specialist based in their office in McKinleyville, Humboldt County, California. Pacific Watershed Associates Inc., established in 1989, is a full service geological, hydrological, engineering, and biological consulting firm specializing in the development of technically sound management, restoration, and environmental solutions for watershed, forest, riverine, and coastal habitats. PWA is based in McKinleyville, California with an office in Petaluma (northern San Francisco Bay Area).

The application deadline is March 17. Click on the link bellow to view the job posting.

River Restoration: Fluvial-Geomorphic and Ecological Tools

22-26 June 2020, Beaumont du Ventoux, Provence FR

This shortcourse/workshop emphasizes understanding geomorphic process as a sound basis for planning and designing river restoration projects and programs, with specific applications and field visits to Mediterranean and mountain environments. The course draws heavily on innovative process based river restoration and management experiences in France and elsewhere in the EU, complemented by experiences in North America. Instruction includes lectures, field exercises, problem sets and workshops on approaches to planning and implementing process-based restoration, with instructors drawn from both sides of the Atlantic.


What’s Past is Present: A Re-Evaluation of Cerrito Creek

Matthew Sasaki, Mingyao Wang, Thea Yang


Post-Project Appraisal of Arroyo Viejo Improvement Project, Oakland, Californi

Jonathan McCall, Eric Garcia, Jill Dressler


Case Study: Pond and Plug Restoration at the Perazzo Meadows in the Northern Sierra Nevadas

Berenice Gonzalez, Daria Kieffer, Christopher Kingsley, Beatriz Stambuk-Torres, Erina Szeto


Post-Project Appraisal of Santa Rosa Creek Restoration

Charlie Yue, Elizabeth Hurley, Elyssa Lawrence, Zhiyao Shu


The Social Life of a Creek San Anselmo Creek Park Redesign

Yuling Chen, Arturo Fuentes-Ortiz, Celina Gu, Chenny Wang


Floodplain Restoration at the Old Orick Mill Site

Chandra Vogt, Eiji Jimbo, Jason Lin, Daniela Corvillon


Geomorphic and Hydraulic Controls on Coho Salmon Outmigration in the Russian River Watershed, California

Brian Kastl, Lukas Winklerprins, Kyle Leathers, Zack Dinh, and Shelby Witherby


Persistence and Effectiveness of Livewood as Large Wood in River Restoration

Danielle Charleston, Melissa Hassler, Kelsey Wilson

Student Presentations and Publications – 15th Annual River Restoration Symposium

Evaluating the effectiveness of restored side channel habitat, Lagunitas Creek
Chris Williams, Stephanie Clarke, Rachael Ryan, Jessie Moravek

Carbon emissions of a conventional restoration project vs a river’s restorative power
Timur Maraghe, Angadpreet Brar, Natan Johnson Lennon

Comparing Vermont stream corridors with Washington State’s channel migration zones
Will Pitkin

Urban river restoration on the Truckee: social vs ecological
Spencer Lacy, Faisal Ashraf, Gurjot Kohli, Yitao Li, James Hansen

Baxter Creek Gateway Park Restoration: a post-project appraisal
Yiwen Chen, Yuanshuo Pi

Cerrito Creek within Blake Garden: Opportunities for restoration
Moyan Chen, Nery Barrera Lopez, Tanner Howe, Sara Mahmoud, Tim Cole