An analytical approach to ascertain saturation-excess versus infiltration-excess overland flow in urban and reference landscapes

Coupling time-lapse ground penetrating radar surveys and infiltration experiments to characterize two types of non-uniform flow

Understanding linkages between heterogeneous soil structures and non-uniform flow is fundamental for interpreting infiltration processes and improving hydrological simulations. Here, we utilized ground-penetrating radar (GPR) as a non-invasive technique to investigate those linkages and to complement current traditional methods that are labor-intensive, invasive, and non-repeatable. We combined time-lapse GPR surveys with different types of infiltration experiments to create three-dimensional (3D) diagrams of the wetting dynamics. We carried out the GPR surveys and validated them with in situ observations, independent measurements and field excavations at two experimental sites. Those sites were selected to represent different mechanisms that generate non-uniform flow: (1) preferential water infiltration initiated by tree trunk and root systems; and (2) lateral subsurface flow due to soil layering. Results revealed links between different types of soil heterogeneity and non-uniform flow. The first experimental site provided evidence of root-induced preferential flow paths along coarse roots, emphasizing the important role of coarse roots in facilitating preferential water movement through the subsurface. The second experimental site showed that water infiltrated through the restrictive layer mainly following the plant root system. The presented approach offers a non-invasive, repeatable and accurate way to detect non-uniform flow.

Improved approach for evaluating saturated surface infiltration capacity of interlocking-block permeable pavements

Different infiltration tests of permeable pavements provide different measurements of the infiltration capacity. These measurements often do not represent the fundamental flow properties, and hence cannot be directly compared. This presents an undesirable obstacle to the sharing of experience and to obtaining a better understanding of the infiltration performances of different permeable pavements. This problem is especially acute in the case of interlocking-block permeable pavements (IBPPs), owing to the presence of joints and the different sizes, shapes, and laying patterns of paving blocks. To overcome this problem, the present study proposed a new approach for evaluating the infiltration capacity of an IBPP while retaining the same measuring devices in use today. This approach makes use of a finite-volume computational fluid dynamic method to develop a simulation model for an infiltration test. Once calibrated to define the hydraulic parameters of the IBPP being tested, the model can be applied to calculate the saturated infiltration capacity of the IBPP under actual rainfall conditions. The model also permits the calculation of a conventional infiltration capacity measurement, such as the average infiltration rate in mm/h as measured by a particular infiltration test, or the time required to drain the tested water depth. Thus, the proposed approach provides a meaningful common basis for comparing the infiltration capacities of different permeable pavements, including porous asphalt, pervious concrete, and IBPPs.

Estimating Surface and Groundwater Irrigation Potential under Different Conservation Agricultural Practices and Irrigation Systems in the Ethiopian Highlands

This study was conducted at the Dangishta watershed in the Ethiopian highlands to evaluate irrigation potential from surface and groundwater sources under different farming and water application systems. Daily streamflow and the groundwater table were monitored from 2015 to 2017. Shallow groundwater recharge was estimated using the water table fluctuation method. Automated baseflow separation techniques were used to determine the amount of runoff and baseflow from the total streamflow records. The potential of groundwater and runoff to sustain dry season irrigation (i.e., low flow) was evaluated considering two tillage systems (i.e., conservation agriculture, CA; and conventional tillage, CT), and water application (i.e., drip and overhead) systems for major irrigated crops (i.e., onion, garlic, cabbage, and pepper) grown in the Dangishta watershed. We found that the annual groundwater recharge varied from 320 to 358 mm during the study period, which was about 17% to 22% of the annual rainfall. The annual surface runoff depth ranged from 192 to 268 mm from 2015 to 2017. The results reveal that the maximum seasonal irrigable land from groundwater recharge was observed under CA with drip irrigation (i.e., 2251 and 2992 ha from groundwater recharge and surface runoff, respectively). By comparison, in the CT practice with overhead irrigation, the lowest seasonal irrigable land was observed (i.e., 1746 and 2121 ha from groundwater and surface runoff, respectively). From the low flow analysis, about 199 and 173 ha of one season’s irrigable land could be irrigated using the CA and CT systems, respectively, both with drip irrigation. Similarly, two-season overhead irrigation potential from low flow under CA and CT was found to be about 87 and 76 ha, respectively. The dry season irrigable land using low flow could be increased from 9% to 16% using the CA system for the various vegetables, whereas drip irrigation could increase the irrigable land potential by 56% compared to overhead irrigation. The combined use of groundwater recharge and runoff could sustain up to 94% of the dry season low flow irrigation through the combination of the CA system and drip irrigation. Decision makers must consider the introduction of feasible and affordable technologies to make use of groundwater and direct runoff, to maximize the potential of dry season production through efficient and appropriate CA and water management practices.

K in an Urban World: New Contexts for Hydraulic Conductivity

Hydraulic conductivity (K) is a key hydrologic parameter widely recognized to be difficult to estimate and constrain, with little consistent assessment in disturbed, urbanized soils. To estimate K, it is either measured, or simulated by pedotransfer functions, which relate K to easily measured soil properties. We measured K in urbanized soils by double-ring infiltrometer (K _dring), near-saturated tension infiltrometry (K _minidisk), and constant head borehole permeametry (K _borehole), along with other soil properties across the major soil orders in 12 United States cities. We compared measured K with that predicted from the pedotransfer function, ROSETTA. We found that regardless of soil texture, K _dring was consistently larger than K _minidisk; with the latter having slightly less sample variance. K _borehole was dependent upon specific subsurface conditions, and contrary to common expectations, did not always decrease with depth. Based on either soil textural class, or percent textural separates (sand, silt clay), ROSETTA did not accurately predict measured K for surface nor subsurface soils. We go on to discuss how K varies in urban landscapes, the role of measurement methods and artifacts in the perception of this metric, and implications for hydrologic modeling. Overall, we aim to inspire consistency and coherence when addressing K-related challenges in sustainable urban water management.

Iterative scenarios for social-ecological systems

Managing social-ecological systems toward desirable regimes requires learning about the system being managed while preparing for many possible futures. Adaptive management (AM) and scenario planning (SP) are two systems management approaches that separately use learning to reduce uncertainties and employ planning to manage irreducible uncertainties, respectively. However, each of these approaches have limitations that confound management of social-ecological systems. Here, we introduce iterative scenarios (IS), a systems management approach that is a hybrid of the scopes and relationships to uncertainty and controllability of AM and SP that combines the "iterativeness" of AM and futures planning of SP. Iterative scenarios is appropriate for situations with high uncertainty about whether a management action will lead to intended outcomes, the desired benefits are numerous and cross-scale, and it is difficult to account for the social implications around the natural resource management options. The value of iterative scenarios is demonstrated by applying the approach to green infrastructure futures for a neighborhood in the city of Cleveland, Ohio, U.S., that had experienced long-term, systemic disinvestment. The Cleveland green infrastructure project was particularly well suited to the IS approach given that learning about environmental factors was necessary and achievable, but what would be socially desirable and possible was unknown. However, iterative scenarios is appropriate for many social-ecological systems where uncertainty is high as IS accommodates real-world complexity faced by management.

Urbanization drives convergence in soil profile texture and carbon content

Urban development has driven extensive modification of the global landscape. This shift in land use and land cover alters ecological functioning, and thereby affects sustainable management agendas. Urbanization fundamentally reshapes the soils that underlay landscapes, and throughout the soil profile, extends impacts of urbanization far below the landscape surface. The impacts of urbanization on deeper soils that are beyond the reach of regular land management are largely unknown, and validation of general theories of convergent ecosystem properties are thwarted by a dearth of both level of measurement effort and the substantial heterogeneity in soils and urban landscapes. Here, we examined two soil properties with strong links to ecological functioning-carbon and mineral-fraction particle size-measured in urban soils, and compared them to their pre-urbanization conditions across a continental gradient encompassing global soil diversity. We hypothesized that urbanization drove convergence of soils properties from heterogeneous pre-urban conditions towards homogeneous urban conditions. Based on our observations, we confirm the hypothesis. Both soil carbon and particle size converged toward an intermediate value in the full data distribution, from pre-urban to urban conditions. These outcomes in urban soils were observed to uniformly be fine textured soils with overall lower carbon content. Although these properties are desirable for supporting urban infrastructure (e.g. buildings, pipes), they constrain the potential to render ecosystem services. Since soil profile texture and carbon content were convergent and observed across 11 cities, we suggest that these property profiles can be used as a universal urban soil profile to: 1) provide a clear prediction for how urbanization will shift soil properties from pre-urban conditions, 2) facilitate the adoption of commonly-accepted soil profiles for process models, and 3) offer a reference point to test against urban management strategies and how they impact soil resources.

Urban stormwater characterization, control, and treatment

This review summarizes over 280 studies published in 2019 related to the characterization, control, and management of urban stormwater runoff. A summary of quantity and quality concerns is provided in the first section of the review, serving as the foundation for the following sections which focus on the control and treatment of stormwater runoff. Finally, the impact of stormwater control devices at the watershed scale is discussed. Each section provides a self-contained overview of the 2019 literature, common themes, and future work. Several themes emerged from the 2019 literature including exploration of substrate amendments for improved water quality effluent from stormwater controls, the continued study of the role of vegetation in green infrastructure practices, and a call to action for the development of new models which generate reliable, computationally efficient results under the physical, chemical, biological, and social complexity of stormwater management. PRACTITIONER POINTS: Over 280 studies were published in 2019 related to the characterization, control, and treatment of urban stormwater. Studies on bioretention and general stormwater characteristics represented the two most common subtopics in 2019. Trends in 2019 included novel substrate amendments, studies on the role of vegetation, and advancements in computational models.

Preliminary Characterization of Underground Hydrological Processes under Multiple Rainfall Conditions and Rocky Desertification Degrees in Karst Regions of Southwest China

Karst regions are widely distributed in Southwest China and due to the complexity of their geologic structure, it is very challenging to collect data useful to provide a better understanding of surface, underground and fissure flows, needed to calibrate and validate numerical models. Without characterizing these features, it is very problematic to fully establish rainfall–runoff processes associated with soil loss in karst landscapes. Water infiltrated rapidly to the underground in rocky desertification areas. To fill this gap, this experimental work was completed to preliminarily determine the output characteristics of subsurface and underground fissure flows and their relationships with rainfall intensities (30 mm h−1, 60 mm h−1 and 90 mm h−1) and bedrock degrees (30%, 40% and 50%), as well as the role of underground fissure flow in the near-surface rainfall–runoff process. Results indicated that under light rainfall conditions (30 mm h−1), the hydrological processes observed were typical of Dunne overland flows; however, under moderate (60 mm h−1) and high rainfall conditions (90 mm h−1), hydrological processes were typical of Horton overland flows. Furthermore, results confirmed that the generation of underground runoff for moderate rocky desertification (MRD) and severe rocky desertification (SRD) happened 18.18% and 45.45% later than the timing recorded for the light rocky desertification (LRD) scenario. Additionally, results established that the maximum rate of underground runoff increased with the increase of bedrock degrees and the amount of cumulative underground runoff measured under different rocky desertification was SRD > MRD > LRD. In terms of flow characterization, for the LRD configuration under light rainfall intensity the underground runoff was mainly associated with soil water, which was accounting for about 85%–95%. However, under moderate and high rainfall intensities, the underground flow was mainly generated from fissure flow.