Design of Settling Basins in Irrigation Network Using Simulation and Mathematical Programming

One of the problems in irrigation structures is sedimentation control in the inlet to the irrigation networks. Water quality for agriculture requires that the sediments be controlled at their entrance point to the networks. This is possible by constructing a settling basin (SB). The bigger the basins, the better the retardation of the sediments but the expenses are higher too. Different mathematical models are developed for SBs. Most of these models show the relationship between efficiency and effective parameters with mathematical formulas. In this research, a computer simulation model was written for calculating the efficiency of a SB. Using this model, another computer program was developed in which design parameters (length, width, depth, slope, and water velocity in the basin) were determined such that the basin has the specified characteristics and minimum construction costs. In this respect, operations research and a lexicographic enumeration algorithm was used. Validation of the computer simulation was performed by applying it to two SBs in Nekouabad diversion dam, west of Isfahan, Iran. The average actual efficiencies of right and left Nekouabad SBs were 31.2 and 36.2%, respectively, while the average calculated efficiencies for right and left SBs were 35.4 and 40.2%, respectively. Application of this program for designing an optimum SB for Nekouabad diversion dam was shown to be promising.     

Nitrogen Transformations during Soil–Aquifer Treatment of Wastewater Effluent—Oxygen Effects in Field Studies

Depth-dependent oxygen concentrations and aqueous-phase total ammonia and nitrate/nitrite ion concentrations were measured in the field during the infiltration of wastewater effluent. Measurements illustrated the dependence of nitrogen fate and transport on oxygen availability. Infiltration basins were operated by alternating wet (infiltration) and dry periods. During infiltration periods, ammonia was removed within the top few feet of sediments via adsorption. Biochemical activity rapidly eliminated residual molecular oxygen in the infiltrate, making the soil profile anoxic. During dry periods, oxygen reentered the basin profile and sorbed ammonia was converted to nitrate via nitrification. Oxygen penetrated to a depth of about 0.6?m?(2?ft) within the first few days of dry periods. At greater depths, oxygen levels increased more slowly due to a combination of slow transport kinetics and biochemical (nitrogenous) oxygen demand. During normal wet/dry basin cycles consisting of about 4 wet and 4 dry days, the local vadose zone remained anoxic at depths greater than about 1.5?m?(5?ft) below land surface. As a consequence, conditions for denitrification were satisfied in the deeper sediments. That is, the nitrate nitrogen produced in near surface sediments moved freely downward with infiltrating water where it encountered an extensive anoxic zone before reaching local monitoring or extraction wells. The relative importance of dissolved organics and sorbed ammonia as electron donors for denitrification reactions remains to be established.     

Hydraulic Model for Sedimentation in Storm-Water Detention Basins

Treatment of storm-water runoff may be necessary before discharge to surface waters. In urban areas, space constraints limit selection of conventional treatment systems, and alternative systems are needed. This research program involves design and laboratory testing of a small footprint nonproprietary detention basin which consists of pipes and box culvert sections with a specialized inlet and outlet system. This system can be placed below grade near the roadway section as part of the conventional drainage system and does not require additional right-of-way. A mathematical model, based entirely on hydraulic principles, is developed to estimate particle removal efficiency of the rectangular detention basin for the treatment of storm-water runoff by extending ideal horizontal tank theory under the condition in which water level is varied. A physical model was built in 1/5 scale to measure particle removal performance and validates the conceptual model. Experiments were performed for steady inflow conditions with different inflow rates, durations, and suspended sediment concentrations. Measured time series outflow suspended sediment concentrations and particle removal efficiency compare well with calculated results from the conceptual model. The outflow particle-size distribution can also be estimated using the conceptual model.     

Quantifying Long-Term NPS Pollutant Flux in an Urbanizing Watershed

Long-term nonpoint source (NPS) pollutant flux is described within the rapidly developing Occoquan watershed west of Washington, D.C. Data consist of up to 24 years of observed rainfall, integrated pollutant discharge, and land use/land cover from four headwater basins of the Occoquan River. Three of the four study basins, ranging in size from 67 to 400?km2, are predominantly forest and mixed agriculture. The fourth basin, the 127?km2 Cub Run watershed, has urbanized rapidly over the past 20 years. Higher annual NPS sediment and nutrient fluxes in Cub Run after 1983 are linked to increased soil disturbance from urban construction and increased storm volumes resulting from increased mean impervious percent. Over the long-term, storm fluxes of NPS particulate P, soluble P, particulate N, and soluble N make up 92, 67, 89, and 50%, respectively, of the total fluxes of those constituents, with between 88 and 98% of mean annual total suspended solids fluxes delivered by storm flow. Higher NPS pollutant fluxes in Cub Run basin after 1983, and specifically during the growing season, indicate a seasonal impact of replacing vegetated cover with impervious surface.     

Storage Volume and Overflow Risk for Infiltration Basin Design

This study presents a risk-based approach for the design of infiltration basins. The design parameters include basin storage volume, drain time, and overflow risk. At a basin site, the storm-water detention storage volume is determined by design runoff capture volume, tributary watershed area, and runoff coefficient. The basin geometry is dictated by the water volume balance between the surface storage volume in the basin and the subsurface storage capacity in soil pores. The drain time at a basin site is found to be a function of initial soil water content, soil porosity, infiltration rate, and distance to the ground-water table. After knowing the basin geometry and size, the basin's performance can be evaluated by the overflow risk analysis using the local average event rainfall depth and interevent time. In practice, a sensitivity test on overflow risk can be conducted with a range of basin storage volumes. The risk-based approach presented in this study provides an algorithm to calculate the long-term runoff capture percentage for a basin size. The diminishing return on runoff capture percentage can serve as a basis to select the proper basin storage volume at the site.     

Dynamic Characteristics of Particle Size Distribution in Highway Runoff: Implications for Settling Tank Design

To understand the characteristics of particle size distribution (PSD) in highway runoff and to facilitate designing best management practices, PSD (2–1,000?μm) was monitored in seven rainfall events in the 2002–2003 rainy season at three highway sites in west Los Angeles. Most of the particles in number were less than 30?μm in diameter and more than 90% were less than 10?μm. Particle number concentration decreased rapidly to 6?mm of accumulated rainfall and then declined more slowly throughout the storm. Particle number concentration was correlated with total suspended solids (TSS) and turbidity. Grab sample particle median diameter increased with increasing TSS. A two-compartment settling tank was evaluated using the measured PSD and was effective in removing both small and large particles. Capturing and retaining the first 20% of the runoff volume on seasonal average can remove 40% of the total particulate load based on calculated particle mass. Using literature data for metal concentrations sorbed to particles, this size holding compartment coupled with a similar size continuous flow clarifier can achieve 65–90% removal for the metals investigated.     

Sediment Removal Efficiency of Settling Basins

Experimental investigations have been carried out on the sediment removal efficiency of settling basins. Laboratory data on removal efficiency from the present and earlier studies were first used for checking the accuracy of the existing empirical and analytical methods for determination of the sediment removal efficiency of settling basins. The existing relationships were not found to yield satisfactory results over the whole range of data. Therefore, reanalysis of these data was done and a new relationship developed. The effect of continuous flushing of a sediment-water mixture from the settling basin on its removal efficiency was also studied through analysis of experimental data.     

Modeling a Retention Treatment Basin for CSO

Combined sewer overflows (CSOs) result in hazardous and unsightly contamination of receiving waters, particularly swimming areas. The removal of suspended solids and associated biological oxygen demand (BOD) can accelerate the recovery following a CSO event. This paper presents a numerical model to simulate the solids removal efficiency of a retention treatment basin (RTB) that utilizes polymers to improve the flocculation and settling rates for the suspended solids. The model includes settleable, nonsettleable, and floatable solids. The sludge is treated as a non-Newtonian fluid. Discrete, zone, and compression settling/floatation regimes are included. In-tank flocculation and a storage zone for sludge flushing are also included in the model. The model was calibrated and validated with data from a RTB pilot plant, and was applied to evaluate preliminary designs for a prototype RTB for the City of Windsor. The calibrated model showed that the optimum location of the target baffle was approximately 30% of the distance to the scum baffle. For design flows of 20?m/h and run durations of up to 2?h, it was found that the removal was insensitive to slopes from ?1 to ?3% and depths greater than 2.5?m (L/H = 10). The simulations indicate that 70 to 78% of solids removal can be achieved at surface overflow rates up to 25?m/h.     

Particle Size Distribution in Highway Runoff

Particles in highway runoff contain various sorbed pollutants, and many best management practices (BMPs) are selected for particle removal efficiency, which makes particle size distribution a crucial BMP design parameter. Particles between 2 and 1,000?μm in diameter were quantified for three rainfall events during the 2002–2003 rainy season at three highway sites in west Los Angeles. Rainfall, runoff flow rate, and a large suite of water quality parameters were also measured. An experimental protocol was developed for bottle cleaning, sample storage, and mixing that provided repeatable results. Particle aggregation occurred which required samples to be analyzed in less than 6?h; the concentration of small particles decreased with a corresponding increase in the concentration of larger particles in stored samples. The particle concentration decreased as the storm progressed and the number of large particles decreased more rapidly than the total number of particles. Particles demonstrated a strong first flush. On average, 40% of the particles were discharged in the first 20% of the runoff volume.     

Geographic Variability of Rainfall Erosivity Estimation and Impact on Construction Site Erosion Control Design

The Revised Universal Soil Loss Equation (RUSLE) is used often by erosion control planners to estimate the soil loss from urban construction sites when sizing sediment ponds and determining the soil loss under vegetative mats. This project used the existing, complete-year rainfall record for 27 sites in the state of Pennsylvania to compare the USDA isoerodent maps to the annual rainfall erosivity, R, values calculated using the USEPA equations for the National Resource Conservation Service Type II rainfall. The USDA and USEPA maps showed a general trend of increasing median annual R from west-to-east and north-to-south. A trend analysis relating the median R values calculated during this project to geographic location had similar, large-scale geographic trends as the USDA and USEPA maps. However, the R values more closely followed a combination of the annual rainfall pattern and topography (the Appalachian mountains bisect the state). Two case studies of the impacts of these calculations were developed to show the impact of using different values of R on the design of sediment ponds and predicting vegetation establishment. The results of these scenarios indicate that the source of data to predict R can affect the frequency and cost of sediment pond maintenance and may under-predict the protection level required of a vegetated erosion control mat.     

Airborne Particles in New Museum Facilities

Over the period July 1996–April 1998, airborne particle concentrations and chemical composition were measured both inside and outside the new J. Paul Getty Museum outside Los Angeles. The purpose of these experiments was to determine the relationship between the stages of construction and operation of the building and the soiling hazard to the collections. Particular attention was paid to tracking the concentrations of fine black soot particles and mineral dust particles. The time needed to “air out” the building following construction can be seen from the data collected, as well as the inherent particle removal efficiency of the filters within the building ventilation system, and the effect of entry of the general public into the building. During the period of observation when the building was under construction, weekday coarse dust particle concentrations on occasion reached very high levels (600–1,100?μg?m?3; 24 h average), falling to relatively low values averaging 26?μg?m?3 over weekend periods when construction activity subsided. In March, 1997, with construction largely completed and with the heating, ventilation, and air conditioning (HVAC) system in full operation, indoor coarse dust concentrations fell to 1.7% of those outdoors. Beginning at this time, indoor fine particle concentrations relative to those outdoors declined steadily over a period of about one to two months, reaching levels of 3.9% of those outdoors during the period June 3–December 6, 1997 when construction was completed but before entry of the general public into the building. Thus, the coarse and fine particle removal efficiencies of the building HVAC system absent major indoor sources are at least 98 and 96%, respectively. Following the opening of the museum to the public, indoor particle concentrations increased by approximately 1?μg?m?3 in each of the coarse dust and fine smoke-size particle size ranges indicating that there is a small but measurable effect due to increased air infiltration as doors are opened and closed more frequently and due to particles shed by the visitors. Indoor particle concentrations inside the new Getty Museum in the presence of the general public are only 3.2?μg?m?3 of coarse dust and 1.8?μg?m?3 of fine particles on average over the period January–April, 1998.     

Case Study of a Full-Scale Evapotranspiration Cover

The design, construction, and performance analyses of a 6.1?ha evapotranspiration (ET) landfill cover at the semiarid U.S. Army Fort Carson site, near Colorado Springs, Colo. are presented. Initial water-balance model simulations, using literature reported soil hydraulic data, aided selection of borrow-source soil type(s) that resulted in predictions of negligible annual drainage ( ? 1?mm/year). Final construction design was based on refined water-balance simulations using laboratory determined soil hydraulic values from borrow area natural soil horizons that were described with USDA soil classification methods. Cover design components included a 122?cm thick clay loam (USDA), compaction ? 80% of the standard Proctor maximum dry density (dry bulk density ～ 1.3?Mg/m3), erosion control measures, top soil amended with biosolids, and seeding with native grasses. Favorable hydrologic performance for a 5?year period was documented by lysimeter-measured and Richards’-based calculations of annual drainage that were all <0.4?mm/year. Water potential data suggest that ET removed water that infiltrated the cover and contributed to a persistent driving force for upward flow and removal of water from below the base of the cover.     

Distribution of Particulate-Bound Metals for Source Area Snow in the Lake Tahoe Watershed

The porous matrix and long residence time of snow in traffic corridors can result in the accretion of particulate matter (PM) and metals. This temporary repository contributes PM-based and dissolved metals to surrounding environs during snowmelt. This study focused on distribution and settling of PM-based metals (Al, As, Cd, Cr, Cu, Fe, Pb, and Zn) in snow. Snow was sampled from six sites during four winter seasons. PM-based metals are examined herein as a function of PM granulometry, specifically particle-size distributions (PSDs) and PM surface area. Cumulative metal mass distributions across each PSD are modeled as gamma functions. Results indicate Al (15 g/kg) and Fe (4.2 g/kg) are the highest PM-based concentrations; Cd (0.18 mg/kg) and As (4.9 mg/kg) are the lowest. The PM size (d50?m) associated with the median metal mass ranges from 179 to 542?μm. The constitutive gamma results are integrated with Hazen’s settling algorithm to model PM-bound metal separation for a sedimentation basin at a local snow storage site. Flows are modeled in the storm water management model (SWMM) from snowmelt and historical rainfall time series. Results indicate that Type I sedimentation is capable of separating the sediment fraction (>75?μm) and majority of metal mass. While the basin is effective at separation of coarser PM-based metals, additional practices such as pavement and drainage appurtenance cleaning, as well as adsorptive-filtration can further manage suspended PM and metals, as well as dissolved metals.     

Design and Management of Subsurface Horizontal Drainage to Reduce Salt Loads

Many irrigated areas have shallow water tables creating waterlogging and salinization problems. This has often been controlled by installation of subsurface horizontal pipe drainage; however, these systems export large amounts of salt off farm in the drainage effluent. Improved design and management of subsurface drainage systems to reduce drainage salt loads were tested in a replicated field experiment. Deep, widely spaced drains allowed to flow without control were compared to drains with management to reduce drain flow. These were also compared with shallow, closely spaced drains that protected the root zone only and an undrained control. The deep drains flowed continuously during the two irrigation seasons with an electrical conductivity of around 11 dS∕m resulting in a drainage salt load of 5,867 kg∕ha. The management measures reduced drainage volume and salinity resulting in a 50% reduction in salt load. The shallow drains only flowed directly after an irrigation or rainfall event with low salinity, around 2 dS∕m, resulting in a 95% reduction in salt load. This showed that by management there is great potential for reducing salt mobilization in existing drainage systems, and for new systems shallower drains will minimize salt loads.     

Feasibility Study and Conceptual Design for Using Coagulants to Treat Runoff in the Tahoe Basin

Fine particles entrained in storm-water runoff are likely to pass through storm-water treatment basins because of their slow settling velocities and the natural biotic and abiotic mixing processes common to ponds and basins. In Lake Tahoe, targeting fine particles <20?μm in diameter is critical to abating turbidity and phosphorus inputs disproportionately responsible for reducing the lake clarity and impacting regional water quality goals. Iron- and aluminum-based coagulant dosing has been commonly used in water and wastewater treatment plants for removal of fines, turbidity, and dissolved organic carbon. However, application of these coagulants for treating storm water is not common. This study used settling columns to show the feasibility of coagulant dosing to target fine particle removal from storm water in shallow treatment basins and wetlands. Coagulation reduced mean turbidity and phosphorus by 85–95% within 10 h of dosing, compared to 20 and 55% reductions in turbidity and phosphorus, respectively, for nontreated storm water over the same amount of time. To achieve equivalent treatment levels, an order of magnitude increase in time was required for the nontreated storm water. These results have important implications on approaches to treat storm water in the Tahoe Basin. First, these findings suggest that whereas most treatment basins and wetlands will not effectively remove fines and total phosphorus within a 24-h hydraulic residence time, those which utilize coagulant dosing should effectively remove fines and total phosphorus. Second, coagulant dosing relies on mechanical equipment such as pumps and flow meters. These equipments cannot accommodate normal variations in storm-water flow which can range over four orders of magnitude. Thus, to fully leverage the investment of this technology, modifications in hydrologic designs are necessary. We suggest equalization basins upstream of treatment basins to shift treatment from storm water entering a treatment complex to that leaving the equalization basin. This configuration buffers flows at the coagulant dosing location and increases the storage capacity of the storm-water treatment complex. Finally, given the paucity of available acreage in the Tahoe Basin and its high cost, coagulant dosing systems could be retrofitted to existing treatment basins and wetlands, enabling these treatment areas to be more effective in targeting phosphorus and fines, service drainage areas two or three times greater than currently, and reduce land area needed for treating storm water. We present a conceptual layout, a process and instrumentation diagram, and cost estimates to implement this technology at a larger scale. We believe that this technology should receive serious consideration for its application at a field or pilot scale where other potential issues can be further investigated and addressed.     

Effects of Stormwater Infiltration on Quality of Groundwater Beneath Retention and Detention Basins

Infiltration of storm water through detention and retention basins may increase the risk of groundwater contamination, especially in areas where the soil is sandy and the water table shallow, and contaminants may not have a chance to degrade or sorb onto soil particles before reaching the saturated zone. Groundwater from 16 monitoring wells installed in basins in southern New Jersey was compared to the quality of shallow groundwater from 30 wells in areas of new-urban land use. Basin groundwater contained much lower levels of dissolved oxygen, which affected concentrations of major ions. Patterns of volatile organic compound and pesticide occurrence in basin groundwater reflected the land use in the drainage areas served by the basins, and differed from patterns in background samples, exhibiting a greater occurrence of petroleum hydrocarbons and certain pesticides. Dilution effects and volatilization likely decrease the concentration and detection frequency of certain compounds commonly found in background groundwater. High recharge rates in storm water basins may cause loading factors to be substantial even when constituent concentrations in infiltrating storm water are relatively low.     

Optimization of Settling Tank Design to Remove Particles and Metals

Mass reduction rates of particles and metals were simulated for a two-compartment settling tank composed of a storage compartment and a continuous flow compartment. Particle-size distribution, rainfall, and flow data from 16 storm events measured at three highway sites were used. The volume ratio (i.e., ratio of surface areas for a given depth) between storage and continuous flow compartment was optimized for a given design storm size to maximize total mass reduction rates of particles and heavy metals. Measured settling velocity profiles of runoff samples were used in the simulation. Simulation results showed that in a given total design storm, larger storage compartment fractions (>0.95) enhanced the removal of smaller particles (2–104?μm) and particulate phase metals, and even a small fraction (<0.05) of continuous flow compartment effectively removed larger particles (104–1,000?μm). A volume fraction of 0.75 for the storage compartment is suggested to optimize annual reductions of particles and associated heavy metals.     

Discharge and Suspended Sediment Transport during Deconstruction of a Low-Head Dam

In March of 2003, the 43?m wide, 2.2?m high St. Johns Dam (Sandusky River, Ohio) was breached to lower the water level in the reservoir. In November of the same year, the dam was removed in an effort to restore aquatic habitat and connectivity in the river. During both the breach and the dam removal, high resolution time series of discharge and suspended sediment concentrations were monitored 200?m downstream of the dam. Discharge and suspended sediment during the breach were not discernible from background values. In contrast, the dam removal resulted in a peak suspended sediment concentration of 59?mg/L and a peak discharge of 33.5?m3/s, which returned to background levels of 19?mg/L and 1.5?m3/s, respectively, approximately 8?h after the removal. The floodwave during the removal attenuated by 50% at the City of Fremont, 53?km downstream, illustrating the diffusive nature of the channel and the limited risk of flooding downstream. Levels of suspended sediment and discharge during the removal were comparable to subsequent discharge events. Spatial distributions of turbidity in and upstream of the dam pool and archived turbidity data from the City of Tiffin, 13?km downstream of the dam, suggest that sediments stored in the impoundment did not statistically enhance turbidity up to 2 years after the removal. Generally, the removal had a minor impact on water quality and posed no risk to public safety or to downstream aquatic habitats.     

Experimental Assessment of Stormwater Infiltration Basin Evolution

Infiltration basins are frequently used for stormwater drainage. They can operate for periods over 20 years but long-term evolution is not well understood or controlled. The two main problems encountered are clogging, which compromises the hydraulic capacity of the basin, and possible contamination of underlying soil and groundwater. This paper focuses on studying long-term evolution of clogging and soil pollution of infiltration basins. Basins of different ages are compared. Also, clogging and soil pollutant concentrations are explored for four infiltration basins in Lyon, France. Ages of the sites range from 10 to 21 years old. Clogging is characterized by the hydraulic resistance. Soil samples were collected at different depths in each basin and analyzed for different pollution parameters (metals, hydrocarbons, pH, and particle size distribution). All four basins have good infiltration capacities. Their hydraulic resistance is low. Such uniformity is surprising because of the age difference between the basins. Pollutant concentrations decrease rapidly with depth whereas pH and grain size increase. Concentrations reach an acceptable value at a 30 cm depth, even after 21 years of operation. Multivariate data analysis does not show significant relation between age, hydraulic resistance, and pollution.