Converging RCC Stepped Spillways

Approximately half of the over 11,000 small watershed dams designed and constructed under the supervision of the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) will reach the end of their planned service life within the next 10 years. Many of these dams have inadequate spillway capacity due to changes in hazard classification and revised dam safety laws. Urbanization of surrounding areas limits the rehabilitation options of these dams. Roller compacted concrete (RCC) stepped spillways provide an effective solution to this problem. Recent years have seen a growth in the research and application of RCC, but there are no readily available generalized guidelines. Research has been performed on converging spillway chutes with vertical training walls. Public safety, aesthetics, and construction efficiency suggest sloped training walls are often a more desirable option.

In recent years, hazard classifications for many existing embankment dams have changed because hydrologic conditions have been altered. Consequently, many of these dams no longer provide adequate spillway capacity according to state and federal dam safety regulations. Stepped spillways are a popular choice for providing increased spillway capacities to existing embankment dams. Stepped spillways in these applications are typically placed over the existing embankment or auxiliary spillway; thereby, the chute slope is the same as the downstream embankment face or auxiliary spillway slope. Design guidelines and literature in general for these stepped spillways are very limited, so further research on these stepped spillways is warranted. A two-dimensional, physical model was constructed to evaluate the inception point, velocities, and energy dissipation in a 4(H):1(V) spillway chute having 38 mm (1.5 in.) high steps. Model unit discharges ranging from 0.11 m3 s-1 m-1 (1.2 cfs ft-1) to 0.82 m3 s-1 m-1 (8.8 cfs ft-1) were tested. Water surfaces, bed surfaces, and velocities were collected during the tests. An inception point relationship provided by H. Chanson may be used to determine the inception point for slopes as flat as 4(H):1(V) when F* ranges between 10 and 100. The velocity profiles transition from uniform at the crest to approaching a one-sixth power law distribution at the inception point for all tested flows. Energy losses increase in a linear fashion from near zero at the crest to approximately 30% near the inception point for all tested flows. This research will assist engineers with the design of stepped spillways applied on relatively flat embankment dams.

Roller Compacted Concrete (RCC) is becoming an increasingly popular method of building and protecting dam embankments. Numerous RCC spillways have been built worldwide and Murum Dam is one of the RCC spillways that have been built in Sarawak, Malaysia. This paper will discuss on analysis of different flow regime that occur at stepped spillways in Murum Dam using numerical simulation. This study consists of creating the three-dimensional model of the spillway and run a simulation by inserting different velocity for different type of flow. Flow regime in stepped are divided into three type which is nappe, transitional and skimming flow. The simulation shows that nappe, transitional and skimming flow occur in both laminar and turbulent flow even different input in velocity. The results show turbulence model have the highest velocity of 361.38 m/s and highest pressure 6.5 × 107 Pa.

Following the passage of the Farm Security and Rural Investment Act of 2002, also known as the "2002 Farm Bill", which significantly increased funding for conservation programs, the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS), the USDA Agricultural Research Service (ARS) and other USDA agencies created the Conservation Effects Assessment Project (CEAP) in 2003. The goal of CEAP is to measure the effects of agricultural conservation practices and develop the science-base for managing agricultural landscapes for environmental quality. The CEAP Watershed Assessment Studies, a partnership between NRCS, ARS, and numerous other federal and university partners, quantify the effects of conservation practices on water quality, water availability, and soil health within small watersheds. Field and watershed studies also help build understanding of the processes that are influenced by or drive conservation practice effects. This brochure describes the currently active 23 watershed studies at 18 locations and the research findings to date. These findings, the improved simulation models, and the newly developed conservation practices and assessment tools contribute towards more effective conservation strategies to address goals and document outcomes for the USDA Mississippi River Basin Healthy Watersheds Initiative, the Great Lakes Restoration Initiative, the Chesapeake Bay Watershed Initiative, the Lake Champlain Basin Initiative, and local source water protection efforts

In recent years, hazard classifications for many existing embankment dams have changed because hydrologic conditions have been altered. Consequently, many of these dams require increase spillway capacity in order to meet state and federal dam safety regulations. Stepped spillways have become a popular choice for providing increased spillway capacities to existing embankment dams. Stepped spillways in these applications are typically placed over the existing embankment. Consequently, the chute slope has the same slope as the downstream embankment face or in some cases have the same slope as the existing auxiliary spillway. Typical slopes for existing embankments range from 2(H):1(V) and flatter. Design guidelines and literature in general for these stepped spillways are very limited, so further research on these stepped spillways is warranted.

This paper covers a technical comparison of results from two physical scale models and a computational fluid dynamics (CFD) model that was undertaken for a masonry stepped spillway at Grassholme reservoir. The spillway is known to be deficient in terms of the depth of the collection channel and the size of the stepped spillway. Using the performance of the spillway during a flood in 1991 as a benchmark, the two modelling methods are compared. It is found that the physical scale models cannot match the full scale behaviour of spillway. The CFD model was undertaken in a way so as to account for air entrainment and flow bulking, and this formed a better estimate of the chute behaviour witnessed during 1991.

In the last decades numerous stepped spillways were built, mostly on the downstream face of roller compacted concrete (RCC) dams. Stilling basins are often used as an energy dissipater. Although the hydraulics of stepped chutes was extensively investigated in the last decades, only fragmentary information is available on the hydraulic characteristics of stilling basins preceded by stepped chutes. Therefore, an experimental campaign was performed on a large-scale physical model of a stepped chute with adjustable slope terminating in a plain stilling basin, to study the effect of stepped chute approach flows on the hydraulic features in the basin. Experiments were conducted for two chute slopes and various discharges. Results on the basin flow features as tailwater depths, dynamic bottom pressures as well as roller and jump length characteristics are presented and discussed, focusing on the effect of stepped chute slope on the basin bottom pressure characteristics. The results show that increasing the chute slope from 30o to 50o pronounces the bottom mean, fluctuating and extreme pressures up to approximately one tailwater depth downstream of the jump toe. For 50° sloping stepped chutes, the extreme pressure coefficients reached up to about 3 times the values reported in literature for smooth chutes.

Stepped chutes are commonly used for overtopping protection for embankment dams. Aerated flow is commonly associated with stepped chutes if the chute has sufficient length. The aeration and turbulence of the flow can create a significant amount of splash over the training wall if not appropriately accounted for in the design of the structure. According to the United States Department of Agriculture (USDA)-Natural Resources Conservation Service (NRCS) Technical Release 60 Earth Dams and Reservoirs, a structural spillway should be designed to pass the freeboard hydrograph such that it does not cause serious damage to the embankment or the structure itself. For stepped spillways, researchers have suggested the training wall height equal a design factor ranging from 1.4 to 1.5 multiplied by the bulked flow depth, y90. Yet, literature suggests that the design factor is a recommendation with little to no research provided to actually quantify what the design factor should be. Researchers at the USDAAgricultural Research Service (ARS) Hydraulic Engineering Research Unit (HERU) in Stillwater, OK conducted a series of tests in a near prototype scale stepped chute facility to determine the design factor for training walls necessary to minimize the erosive splash that could result from the aerated flow. Tests were conducted in a stepped chute with a slope of 18.4 degrees for a wide range of skimming flow conditions. Data indicates for a step height, h, to critical flow depth, dc, ratio of less than 0.4, the design factor for the training wall is 1.4; thus, the training wall height is equal to 1.4y90. For h/dc ≥ 0.4, the design factor increases from 1.4 at h/dc = 0.4 up to 2.0 for h/dc = 1.0. These design factors are recommended for use on chute slopes ranging from 10 to 30 degrees. This research is intended to assist design engineers with appropriately designing stepped chute training walls to minimize the erosive splash that can occur as a result of aerated, turbulent flow.

In 1991, the U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) established its Soil Moisture–Soil Temperature (SM–ST) Pilot Network consisting of 21 stations in 19 states in the contiguous United States. At each station, soil temperatures were measured at up to six different depths from 5.08 to 203.20 cm (or 2–80 in.) below the surface. Before 1997, the observations were made every 6 h, and they increased to hourly beginning in 1997. The goal of this network is to provide near–real time soil temperature and soil moisture observations in different regions across the United States for agricultural and water use management as well as for climate research. To improve the usefulness and increase the value of both the data and this network, a quality-control method for the soil temperature data was developed. The method used a soil heat diffusion model and its solution at individual sites to screen and distinguish erroneous soil temperature data and to provide their estimates. Evaluation of the quality-control method showed its accuracy and reliability, particularly when it was applied to hourly data. Application of this method to the data has yielded a high-quality, high-resolution soil temperature database from 1994 to 1999 for the network, which is accessible at the USDA National Water and Climate Center's Web site.

The existing Scoggins Dam and reservoir are in Washington County, Oregon, and the title is held by the U.S. Bureau of Reclamation (Reclamation). Reclamation has previously identified dam safety concerns related to the existing embankment dam. Regional project sponsors, including Clean Water Services, have identified the need for expanded storage capacity in the reservoir to meet growing water demands and address water quality issues in the Tualatin River downstream of the dam. As part of efforts to resolve dam safety issues and increase the water storage in the reservoir, a comprehensive feasibility level design of a new 185-foot-high Roller Compacted Concrete (RCC) dam. Extraordinary seismic hazards have been identified in the region associated with the Cascadia Subduction Zone (CSZ). Further, any dam alternative carried forward for funding, final design, and construction will have to meet the Public Protection Guidelines (PPG) of Reclamation that require a formal quantitative risk analysis. A risk-informed design approach was adopted to configure the layout and cross-section properties of the dam. A multi-phase site characterization program and preliminary RCC mix design program were performed to support the design. In addition, models were developed, and an extensive suite of both (two-dimensional) 2D and (three-dimensional) 3D structural analyses were performed for seismic loadings with total durations of over 200 s, strong shaking of over 140 s, and peak ground accelerations of over 2 gravitational accelerations (g) (up to 50,000-year return period event). This paper describes the feasibility design configuration of the dam, including the seismic hazard characterization, structural analysis models, and seismic response modeling results. The expected performance of the dam relative to the risk-informed design criteria and Reclamation PPGs will be generally described.

Over the past 150 years, land-use changes from native ecosystems to row crop corn and soybeans have negatively impacted a variety of ecosystem services in the United States (US) Corn Belt, including nutrient attenuation, water storage, landscape heterogeneity and habitat. In landscapes dominated by agricultural land use, restoring floodplains through United States Department of Agriculture (USDA) Natural Resource Conservation Service (NRCS) programs (e.g., Emergency Watershed Protection program) could offer disproportionate opportunities to positively enhance ecosystem service benefits - yet, identifying and prioritizing opportunities for conservation practices, including floodplain easements, to maximize environmental outcomes and financial resources remains challenging. This research sought to identify, prioritize, and evaluate costs associated with potential floodplain easements across the state of Iowa. Leveraging key geospatial data layers and criteria, including proportion of field within the 2-, 5-, and 10-year floodplain, field boundaries, and land use characteristics, we identified 2,767 high priority easement locations based on the frequency of inundation of the fields, representing a total area of 57,500 ha (0.4% of the state area). Approximately 138,500 additional suitable floodplain easements were also identified for potential consideration. To estimate acquisition, direct, and total costs associated with potential easements, we used a variety of data, including soils data and a crop productivity index, land value data, and partial enterprise budgets. Estimated costs to restore only high priority easement opportunities total approximately $995,000,000. This analysis aims to assist natural resource practitioners and conservation planners in identifying, prioritizing, and estimating costs for potential floodplain easement locations and can be applied across the state of Iowa and in other regions where data exist.

Soils represent a fundamental abiotic parameter in defining the characteristics of an ecosystem.The United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS)produces the most detailed digital spatial data sets that are publicly available. The Soil Survey Geographic(SSURGO) Database contains basic attributes for the continuous coverage of soils across the United States. Inits standard format, the SSURGO data set is incompatible for use within the ArcView Soil and WaterAssessment Tool (SWAT). A modified version of the State Soil and Geographic (STATSGO) Database is thetemplate soils data set used by ArcView SWAT. This paper presents the methodology and development of aSSURGO 2.0 dataset pre-processor extension for the ArcView SWAT model. A case study for the Leon Creekwatershed near San Antonio, Texas is given. Results indicate that water yield differences occur when using theSTATSGO and SSURGO data sets in the ArcView SWAT model under identical modeling conditions.

The Wind Erosion Prediction System (WEPS) is a process-based, daily time-step, computer model thatpredicts soil erosion via simulation of the physical processes controlling wind erosion. WEPS is intendedprimarily for soil conservation and environmental planning. WEPS 1.0 is the first implementation of WEPSintended for use by the United States Department of Agriculture, Natural Resources Conservation Service(USDA-NRCS). It includes a graphical user interface to allow the user to easily select climate stations, specifyfield site dimensions, pick a predominant soil type, and describe any field wind barriers and managementpractices applied to an agricultural field. This interface allows the user to quickly assess a sites susceptibility towind erosion and evaluate the impacts that alternate practices and conditions might have on reducing thatsusceptibility. Features and capabilities of WEPS 1.0 user interface include 1) the ability to define wind barriercharacteristics and their location on the boundaries of the simulation region, 2) selection of soils obtained fromthe NRCS National Soil Information System (NASIS) soil database, and 3) detailed specification of actualmanagement practices employed by land managers. Display of output information regarding soil loss bytransport mode, direction, and size (saltation/creep, suspension, PM10) is also available.

Evidence of paleoprocesses in some poorly developed soils on consolidated material in the Sierra de Carrascoy (SE Spain)

PurposeThis paper aims to quantify the impact of environmental contamination on farmland valuation. It applies data fusion and hedonic pricing approaches to quantify the contribution of nitrogen and phosphorus loading on farmland sales transactions. It further suggests approaches to improve internalization of environmental cost in valuation approaches using shadow pricing. The work informs the field of environmental, social and governance (ESG) investing by fusing environmental data with financial transactions.Design/methodology/approachThis paper is an empirical study implementing hedonic pricing of farmland in the Lake Huron major drainage area. Data sources and fusion were derived from AcreValue, the United States Department of Agriculture's Gridded Soil Survey Geographic database (gSSURGO) and the United States Geological Survey's Spatially Referenced Regression on Watershed Attributes database (SPARROW).FindingsThe results suggest that environmental contamination has statistically significant positive determination power on farmland prices such that prices increase with contamination. Conventional metrics such as percentage of cultivated land in the parcel, root zone depth, whether the parcel is designated by the Natural Resource Conservation Service as prime farmland, and the size of the farmland parcel contribution to farmland value as well. The results indicate that environmental impacts are not accurately accounted for in farmland transactions.Research limitations/implicationsThis paper points to inaccurate valuation of environmental contamination in farmland value. While geocoding allowed for positioning of farmland sales transactions relative to modeled areas of contaminant loading in the Lake Huron drainage area, the interpretation indicates that value is driven by cultivation. Hence, generalization to other areas needs a cautious approach. Empirical testing across locations and drainage areas with diverse farmland features will serve to verify the modeled data used in this study.Practical implicationsThe lack of integration of externalities in land valuation has implications on lending and disclosure practices, as financial service providers increasingly seek to account for ESG risk on their loan books and broader investment portfolios. The impact of farmland accounting practices for contamination such as shadow pricing may impact land valuation based on future cash flows, and may serve to inform sustainability-linked lending practices to farm operations.Originality/valueThis is the first paper to fuse data from AcreValue, gSSURGO and SPARROW to discover the explanatory power of nutrient contamination in farmland value in the Lake Huron major drainage area.