Brett F. Sanders

Taking the “Waste” Out of “Wastewater” for Human Water Security and Ecosystem Sustainability

Humans create vast quantities of wastewater through inefficiencies and poor management of water systems. The wasting of water poses sustainability challenges, depletes energy reserves, and undermines human water security and ecosystem health. Here we review emerging approaches for reusing wastewater and minimizing its generation. These complementary options make the most of scarce freshwater resources, serve the varying water needs of both developed and developing countries, and confer a variety of environmental benefits. Their widespread adoption will require changing how freshwater is sourced, used, managed, and priced.

Environmental Fate and Transport Modeling for Perfluorooctanoic Acid Emitted from the Washington Works Facility in West Virginia

Perfluorooctanoic acid (PFOA) has been detected in environmental samples in Ohio and West Virginia near the Washington Works Plant in Parkersburg, West Virginia. This paper describes retrospective fate and transport modeling of PFOA concentrations in local air, surface water, groundwater, and six municipal water systems based on estimates of historic emission rates from the facility, physicochemical properties of PFOA, and local geologic and meteorological data beginning in 1951. We linked several environmental fate and transport modeling systems to model PFOA air dispersion, transit through the vadose zone, surface water transport, and groundwater flow and transport. These include AERMOD, PRZM-3, BreZo, MODFLOW, and MT3DMS. Several thousand PFOA measurements in municipal well water have been collected in this region since 1998. Our linked modeling system performs better than expected, predicting water concentrations within a factor of 2.1 of the average observed water concentration for each of the six municipal water districts after adjusting the organic carbon partition coefficient to fit the observed data. After model calibration, the Spearmans rank correlation coefficient for predicted versus observed water concentrations is 0.87. These models may be useful for estimating past and future public well water PFOA concentrations in this region.

Integration of a shallow water model with a local time step

A Local Time Stepping (LTS) scheme was applied to an explicit Godunov–type shallow–water model to improve run–time efficiency. Using LTS, the solution in each cell is advanced with the largest power of two multiple of the global time step required for stability, δt, that satisfies the local criterion for stability.A careful sequencing of flux calculations and solution updates ensures conservation. Test problems including practical applications show that LTS achieves run–time reductions ranging from 50 to 70% without loss of accuracy. In addition, a four level scheme that coordinates time steps of δt, 2δt, 4δt, and 8δt performs best in idealized and practical test problems considered for this study. Additional levels achieve no further reduction in run time, and in some cases cause instability and deteriorate conservation.

Australia's Drought: Lessons for California

COMMENTARY Refl ective scientifi c treatises Strengthening citizen science LETTERS I BOOKS I POLICY FORUM I EDUCATION FORUM I PERSPECTIVES LETTERS edited by Jennifer Sills 28 MARCH 2014 sumptive activities—such as daytime lawn watering and car washing—to rules promot- ing efficient water use—such as require- ments for shutoff valves on hoses. Out of those temporary restrictions, permanent restrictions grew. Some areas in Australia still restrict daytime sprinkler use. Perhaps most relevant for worried Californians is how the Australian public received these changes. Studies cite an overall spirit of goodwill and cooperation fostered by the stress of drought (6). The Millennium Drought brought about profound changes in Australians’ concep- tion of the environment, climate change, and water. The sticking power of those les- sons and the success of the resulting policies and strategies will be tested by the next big drought. One lesson California can glean from the Australian experience is empower- ment. Individuals making frugal water deci- sions can make a big difference in urban areas. Water markets and other measures that increase the fl exibility of irrigation farmers in their response to drought can have big payoffs. Sustaining critical environmental water requirements will provide the basis for postdrought environmental recovery. A spirit of cooperation rather than contention can prevail even when tough decisions are made to address the needs of farmers and city residents. AMIR AGHAKOUCHAK, 1 * DAVID FELDMAN, 1 MICHAEL J. STEWARDSON, 2 JEAN-DANIEL SAPHORES, 1 STANLEY GRANT, 1,2 BRETT SANDERS 1 The Henry Samueli School of Engineering, University of California, Irvine, Irvine, CA 92697, USA. 2 Melbourne School of Engineering, The University of Melbourne, Parkville, VIC 3010, Australia. *Corresponding author. E-mail: amir.a@uci.edu References 1. A. I. Dijk et al., Water Resources Res. 49, 1040 (2013). 2. Z. Hao et al., Sci. Data 1, 1 (2014). 3. S. Dolnicar, A. I. Schafer, J. Environ. Manage. 90, 888 VOL 343 SCIENCE www.sciencemag.org Published by AAAS Downloaded from www.sciencemag.org on March 27, 2014 MOST OF CALIFORNIA IS SUFFERING FROM AN extreme drought, and storage levels in the major reservoirs are well below historic lev- els. For the past several months, an unusually stubborn ridge of high pressure off the West Coast of the United States has been blocking normal winter storms and the rain they carry. California’s history of drought has led to state- wide strategies to save water, but Californian residents and policy-makers can do even more: They can look to the story of Australia’s experi- ence with a drought so intense and long-lasting that it was dramatically dubbed the Millennium Drought (1). The Millennium Drought lasted from 1997 until late 2009 (2). Australia’s economy and environment were hit hard. The drought accel- erated the same trends facing farmers in devel- oping countries worldwide: Small farms were squeezed out. Midsized farms were most vul- nerable because they could neither achieve the economies of scale available to larger produc- ers nor buffer losses with off-farm employ- ment like the smallest farms could. Amazingly, despite blows to crop yields and Dried out. As of February 2014, most of California is in Extreme to Exceptional Drought (see red and livestock numbers, Australia’s rate of growth in dark red areas on map). agricultural production has quickly returned to predrought trends. The impacts of this major drought on irrigation communities were buffered by some critical water reforms. These included: (i) well-developed water markets that allowed water trade to farmers in the greatest need; (ii) modernization of irrigation infrastructure that increased the effi ciency of water delivery; and (iii) establishment of clear water entitlements for the environment that protected critical refuge habitats and populations as water availability declined. The use of water markets was particularly critical. More than 40% of annual water alloca- tions were traded at the height of the drought in 2007. For example, increased water prices allowed dairy farmers to sell their allocation and purchase fodder with the proceeds rather than irrigate pasture. Fruit growers and other producers who needed to maintain irrigation through- out the drought could purchase the dairy farmers’ water to keep their operations viable. In urban areas, strategies to increase supply and decrease demand were brought to bear. Expensive desalination and water recycling plants were built. Australians were more comfort- able with the desalinated water (3, 4), despite the recycled water’s safety and the desalination plants’ greater cost and large carbon and environmental footprints (4). Between 2002 and 2009, per capita municipal water use in southeast Australia decreased by nearly 50% (5). Water use restrictions ranged from outright bans of conspicuously con- CREDIT: DATA FROM THE GLOBAL INTEGRATED DROUGHT MONITORING AND PREDICTION SYSTEM (GIDMAPS) (2) Australia’s Drought: Lessons for California

From Rain Tanks to Catchments: Use of Low-Impact Development To Address Hydrologic Symptoms of the Urban Stream Syndrome

Catchment urbanization perturbs the water and sediment budgets of streams, degrades stream health and function, and causes a constellation of flow, water quality, and ecological symptoms collectively known as the urban stream syndrome. Low-impact development (LID) technologies address the hydrologic symptoms of the urban stream syndrome by mimicking natural flow paths and restoring a natural water balance. Over annual time scales, the volumes of stormwater that should be infiltrated and harvested can be estimated from a catchment-scale water-balance given local climate conditions and preurban land cover. For all but the wettest regions of the world, a much larger volume of stormwater runoff should be harvested than infiltrated to maintain stream hydrology in a preurban state. Efforts to prevent or reverse hydrologic symptoms associated with the urban stream syndrome will therefore require: (1) selecting the right mix of LID technologies that provide regionally tailored ratios of stormwater harvesting and infiltration; (2) integrating these LID technologies into next-generation drainage systems; (3) maximizing potential cobenefits including water supply augmentation, flood protection, improved water quality, and urban amenities; and (4) long-term hydrologic monitoring to evaluate the efficacy of LID interventions.

Non-reflecting boundary flux function for finite volume shallow-water models

An approach to implement non-reflecting boundary conditions in finite-volume based shallow-water models is presented. Shallow-water models are routinely applied to sections of rivers, estuaries, and coastal zones, introducing computational boundaries where no physical control is present, and necessitating a condition that supplies information to the model while it simultaneously allows disturbances from the interior to pass out unhampered. The approach presented here builds upon the finite-volume convention of constructing a Riemann problem at the interface between cells and then solving it with a flux function. Hence, non-reflecting boundary conditions are achieved using a non-reflecting flux function on cell faces aligned with open boundaries. Numerical tests show that the non-reflecting flux function performs extremely well when waves advance toward the boundary with a small incident angle (approximately less than 45° from the boundary normal direction), while very minor reflections are present when the incident angle is larger. The presence of minor reflections, when the incident angle is large, is consistent with non-reflecting conditions previously implemented in finite-difference based schemes.

Cumulative hazard: The case of nuisance flooding

The cumulative cost of frequent events (e.g., nuisance floods) over time may exceed the costs of the extreme but infrequent events for which societies typically prepare. Here we analyze the likelihood of exceedances above mean higher high water and the corresponding property value exposure for minor, major, and extreme coastal floods. Our results suggest that, in response to sea level rise, nuisance flooding (NF) could generate property value exposure comparable to, or larger than, extreme events. Determining whether (and when) low cost, nuisance incidents aggregate into high cost impacts and deciding when to invest in preventive measures are among the most difficult decisions for policymakers. It would be unfortunate if efforts to protect societies from extreme events (e.g., 0.01 annual probability) left them exposed to a cumulative hazard with enormous costs. We propose a Cumulative Hazard Index (CHI) as a tool for framing the future cumulative impact of low cost incidents relative to infrequent extreme events. CHI suggests that in New York, NY, Washington, DC, Miami, FL, San Francisco, CA, and Seattle, WA, a careful consideration of socioeconomic impacts of NF for prioritization is crucial for sustainable coastal flood risk management.

Increased nuisance flooding along the coasts of the United States due to sea level rise: Past and future

Author(s): Moftakhari, HR; AghaKouchak, A; Sanders, BF; Feldman, DL; Sweet, W; Matthew, RA; Luke, A | Abstract:

Compounding effects of sea level rise and fluvial flooding

Significance Population and assets in coastal regions are threatened by both oceanic and fluvial flooding hazards. Common flood hazard assessment practices typically focus on one flood driver at a time and ignore potential compounding impacts. Here we outline a unique bivariate flood hazard assessment framework that accounts for the interactions between a primary oceanic flooding hazard, coastal water level, and fluvial flooding hazards. Using the notion of “failure probability,” we also assess coastal flood hazard under different future sea level rise scenarios. The results show that, in a warming climate, future sea level rise not only increases the failure probability, but also exacerbates the compounding effects of flood drivers. Sea level rise (SLR), a well-documented and urgent aspect of anthropogenic global warming, threatens population and assets located in low-lying coastal regions all around the world. Common flood hazard assessment practices typically account for one driver at a time (e.g., either fluvial flooding only or ocean flooding only), whereas coastal cities vulnerable to SLR are at risk for flooding from multiple drivers (e.g., extreme coastal high tide, storm surge, and river flow). Here, we propose a bivariate flood hazard assessment approach that accounts for compound flooding from river flow and coastal water level, and we show that a univariate approach may not appropriately characterize the flood hazard if there are compounding effects. Using copulas and bivariate dependence analysis, we also quantify the increases in failure probabilities for 2030 and 2050 caused by SLR under representative concentration pathways 4.5 and 8.5. Additionally, the increase in failure probability is shown to be strongly affected by compounding effects. The proposed failure probability method offers an innovative tool for assessing compounding flood hazards in a warming climate.

An intercomparison of remote sensing river discharge estimation algorithms from measurements of river height, width, and slope

The Surface Water and Ocean Topography (SWOT) satellite mission planned for launch in 2020 will map river elevations and inundated area globally for rivers >100 m wide. In advance of this launch, we here evaluated the possibility of estimating discharge in ungauged rivers using synthetic, daily ‘‘remote sensing’’ measurements derived from hydraulic models corrupted with minimal observational errors. Five discharge algorithms were evaluated, as well as the median of the five, for 19 rivers spanning a range of hydraulic and geomorphic conditions. Reliance upon a priori information, and thus applicability to truly ungauged reaches, varied among algorithms: one algorithm employed only global limits on velocity and depth, while the other algorithms relied on globally available prior estimates of discharge. We found at least one algorithm able to estimate instantaneous discharge to within 35% relative root-mean-squared error (RRMSE) on 14/16 nonbraided rivers despite out-of-bank flows, multichannel planforms, and backwater effects. Moreover, we found RRMSE was often dominated by bias; the median standard deviation of relative residuals across the 16 nonbraided rivers was only 12.5%. SWOT discharge algorithm progress is therefore encouraging, yet future efforts should consider incorporating ancillary data or multialgorithm synergy to improve results.