Ett restaureringsarbete pågår i Vallentunasjön under ledning av Täby och Vallentuna kommuner. Syftet är att minska näringsämnena i Vallentunasjön, då sjön är övergödd. Tidigare har man provat olika metoder för att minska näringsämnena, men resultatet har varit dåligt. Den nya metoden går ut på att pumpa ut slammet från sjön kontinuerligt året om. Kemiska analyser har gjorts på sjövattnet och slammet före och efter isläggningen, för att se om metoden är hållbar.  Mätningar från Vattenkemikursen KH1400 åren 2013 till 2015 har använts som kompletterande mätningar i detta examensarbete.[10]    Sjövattnet och slammet testades med analyser för att kunna dra slutsatser gällande hur miljöfarligt det pumpade vattnet är. Torrsubstansen bestämdes i vattnet och slammet för att undersöka om det pumpade slammet kan avskiljas genom sedimentering. Fosforanalyser användes som måttstock för att uppskatta mängden pumpat slam. Genom analys av fosfor, vars koncentration kan mätas med hög precision, uppskattades slammängden med hjälp av Redfields formel. Två pumpar beskrivs i denna rapport och det är Fiskevårdsföreningens pump och EON’s pump där EON’s pump används för värmeproduktion. Denna metod fungerar då det pumpades ut ungefär 1.5 ton fosfor per år med EON’s pump, vilket är tillräckligt. Nästa frågeställning är att se om slammet kan koncentreras genom sedimentering. Det visade sig att slammet kan koncentreras, så att torrsubstansen ökade från 3 % till 30 %. Under ett år, transporteras ca 5 800 ton slam från Vallentunasjön genom EON’s pumpsystem. Det behövs ungefär 580 lastbilar för att transportera iväg slammet. Om slammet koncentreras genom sedimentation behövs 58 lastbilar. Huruvida slammet, som pumpas och transporteras, har en hög metallhalt är en fråga, som behöver analyseras och diskuteras i ett nytt projekt. Det krävs fler analyser för att se huruvida det pumpade sjövattnet innehållande slammet är miljöfarligt. Det skulle ta ca 3-5 år att pumpa bort slammet i sjön med EON´s pump. / A restoration work is being carried out in the Lake Vallentuna under the leadership of Täby and Vallentuna municipalities. The aim of this project is to reduce the nutrients in Lake Vallentuna, since the lake is eutrophicated. Previously, various methods have been tested to reduce the amount of nutrients, but the result has not been good enough. The new method is to pump out the sludge continuously throughout the year. Chemical analysis has been made on the water and the sludge from Lake Vallentuna, before and after the formation an ice cover on the lake, in order to investigate whether the method could be successful. Measurements in the water chemistry course KH1400, made in the years 2013, 2014 and 2015 have been used as a supplement in this thesis.[10] Lake water and the sludge have been analyzed. The dry matter of the lake bottom water and the sludge were determined to investigate whether the sludge can be separated by sedimentation or not. The concentration of phosphorous has been used as a yard stick to estimate the amount of pumped sludge.  The Redfield formula gives the relationship between phosphorous and total mass of sludge, assuming that the sludge consists of dead algea . Two pumps are described in this report. One is managed by Fiskevårdsföreningens (VFOF) and one is managed by EON. The latter pump is used for heat production. This method could be successful, because approximately 1.5 tons phosphorous per year of were transported, which is sufficient. The next issue was to investigate whether the sludge could be concentrated by sedimentation. It was found that the sludge could be concentrated by sedimentation and that the dry substance increased from 3 % to 30 %. It was found, that in one year, approximately 5 800 tons of sludge can be separated by pumping and sedimentation. This corresponds to 580 trucks (each loading 10 tons).  If the sludge is concentrated by sedimentation 58 trucks are required.  Whether the pumped and transported sludge has a high metal content is an issue, that needs to be investigated and considered in a special project, which requires further analyses. It would take 3-5 years to remove the excess phosphorus from Lake Vallentuna by continuous pumping.

Vegetation in rivers increases flow resistance and bank stability, reduces bed resistance and flow conveyance, improves water quality, promotes habitat diversity, and alters both mean and turbulent flow. By reducing bed resistance and altering turbulent characteristics, vegetation can change the distribution of deposition and erosion processes. To understand all above mentioned vegetation effects, more research is needed. The goal of this dissertation was to determine the impacts of vegetation on bed resistance and sediment transport and identify a best approach for quantifying vegetation induced friction resistance. To achieve this, both experimental study and numerical simulation were performed. A series of laboratory experiments were conducted in an open channel flume to investigate the impacts of vegetation density on bed resistance and bed load transport for emergent vegetation condition. The bed resistance in a mobile bed channel is equal to the summation of grain and bed form resistances. An attempt has been made to make a separation between grain and bed form resistances, which is challenging and has never been reported in literature. An alternative approach is used to calculate the grain resistance. A new iterative method was derived to calculate the bed form resistance. Empirical relations were formulated to calculate the bed form resistance and bed load transport rate using a newly defined flow parameter that incorporates the vegetation concentration. The bed elevations and bed form height were measured by the Microsoft Kinect 3D Camera. It was found that the height of bed form depends on the vegetation concentration, which determines whether ripple/dune or scour holes are dominant on the bed surface. For sparsely vegetated flows, the bed form height and resistance are decrease rapidly as the vegetation concentration was increased, and they decreased gradually when the vegetation concentration was high. To quantify the vegetation induced friction resistance, a 3D numerical simulation was conducted using the Delft3D-FLOW open source program. The study area is Davis Pond freshwater marsh area near New Orleans, Louisiana. The dominant vegetation type for the study area is Panicum hemitomon. The study area was divided into several sub-areas depending on the existence of channels, overbanks, and vegetation height. Several approaches were used to approximate the vegetation roughness; a constant Manning's n coefficient, a time-varying n or Chezy's C coefficient, and the modified momentum and k-ɛ equations for each subarea. To quantify the time varying roughness coefficients, four equations for calculating n values were incorporated in the Delft3D-FLOW program in addition to two options offered by this program to calculate C values. It is concluded that the use of the time varying roughness coefficient gives better results than other approaches. Among the selected equations to calculate the time varying vegetation roughness, the equations that account for the effect of the degree of submergence and the vegetation frontal area per unit volume, symbolized as a, gave the closet matches with the observations. The sensitivity of modeling results to the selection of vertical grid (σ–and Z-grids), a value, and grid size were analyzed. It is found that using the σ-grid yielded more accurate results with less CPU times and the best range of a value for the Panicum hemitomon vegetation type is from 8.160 to 11.220 m⁻¹. Also it was observed that the adoption of a coarse mesh gives reasonable simulation results with less CPU time compared with a fine mesh. A non-linear relation between the vegetation resistance, in terms of n value, and degree of submergence was observed.

As more sites containing contaminated sediments are remedied with sediment caps, so grows the interest among site managers and engineers in the benefits afforded by active capping. While traditional sediment caps can effectively manage strongly solid-associated contaminants in many situations, under certain conditions active caps or amendments may be needed to effectively reduce risk to an acceptable level. This research assessed the predicted and observed breakthrough of dissolved organic contaminants in two newly developed geotextiles; one designed to sorb non-aqueous–phase liquids (NAPLs), the other dissolved-phase contaminants. The performance of the geotextiles was then compared to that of another remediation technology that has been deployed in the field for two years. All active materials were then evaluated based on their sorption capacity and their predicted life under field conditions. The sorbent containing geotextiles designed for active capping applications were tested in columns to simulate field conditions, where upwelling groundwater would be contaminated by impacted sediments, thereby transporting contaminants to the water column. The contaminants of interest in these studies were three polycyclic aromatic hydrocarbons (PAHs) of varying hydrophobicity. Breakthrough curves for the materials vii of interest were constructed for the three PAHs and were fit to an advection-dispersion model to predict the mass of contaminants sorbed onto them. This mass was then compared and verified to be similar to values found in literature. The performance of the geotextiles was compared to that of organoclay deployed in Portland, OR, at the McCormick & Baxter Creosoting Company Superfund Site. In 2004, over 22 acres of sediment at the site were remedied with both passive and active caps to mitigate the effects of decades worth of contamination. In certain portions of the site, a 12 inch thick layer of organoclay was employed, while at other portions of the site, conventional sand or a thin reactive core mat with the equivalent of approximately 1 cm of organoclay were employed. The continued effectiveness of these sediment caps was evaluated using a variety of laboratory techniques, including measuring samples’ hexane extractable material, which is a proxy for NAPL contamination, as well as their PAH bulk concentrations. These analyses performed on core samples allowed for the generation of vertical profiles critical to cap evaluation. Despite possessing a significantly greater specific sorption capacity, the geotextiles could not offer the same protection for the extended period of time that the bulk organoclay could. The greater mass of organoclay deployed in bulk at the McCormick & Baxter site allowed a much greater sorption capacity to be placed. It would take over sixty stacked layers of the one of the geotextiles evaluated in these studies to achieve the same capacity for dissolved-phase contaminants as the 1 ft organoclay cap. However, no significant penetration of NAPL into the bulk organoclay has been noted, and thus even the thin layer within a geotextile might have been sufficient at the site, despite its significantly lower overall capacity. The data generated provides information as to the expected capacity of the various sorbent placement approaches and can help guide decisions at other sites. / text

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The effects of geopressuring and kerogen decomposition on mineral-fluid equilibria were calculated in order to predict the diagenetic-alteration mineralogy produced in equilibrium with kerogen-rich, geopressured sediments. These calculations indicate that several processes specific to kerogen-rich geopressured sediments contribute to the development of a characteristic alteration mineralogy. These processes are: (1) the upward flow of fluids in geopressured sediments, in contrast to the generally downward flow of fluids in normally-pressured sediments; (2) the coincidence of the depths of geopressuring (2-3 km; Fertl et al., 1976), with the geothermal temperatures necessary for CO₂ release (100°-135°C; Hunt, 1979), and CH₄ release (>90°C; Hunt, 1979); and (3) the opposing rates of sediment burial and CO₂ and CH₄ transfer into the upward-flowing fluids, which result in the geopressured pore fluids becoming enriched, and in some cases saturated, with respect to CO₂ and CH₄. Three patterns of mineral deposition during diagenesis of kerogen-rich geopressured sediments are predicted. Quartz deposition should occur at the top of the geopressured zone and decrease rapidly with increased depth as a result of the decreased flux of upward fluid flow with increased depth. Carbonate deposition should occur above the zone of CO₂ release from kerogen degradation as a result of the upward flux of CO₂ saturated fluids and subsequent decreases in fluid temperature, pressure and CO₂ solubility. Kaolinite-carbonate could deposit within and above the zone of CO₂ release from kerogen as a result of silicate dissolution by CO₂-rich acid pore fluids, followed by the potential for albite-carbonate deposition upon CO₂ depletion. In contrast, laumontite and anhydrite should not deposit during diagenesis of kerogen-rich geopressured sediments, but could deposit during diagenesis of normally-pressured or kerogen-poor geopressured sediments. An additional difference between these diagenetic environments is that quartz deposition would not be expected in normally-pressured sediments in which fluids are expected to be flowing downward. These mineralogic relationships compare favorably with observed relationships in the kerogen-rich geopressured sandstones of the Frio formation from the Texas Gulf Coast.

Data compiled from standardized procedures for width measurement at established streamflow gaging stations were used to develop a power-function relation between width in feet (W(A)_), and mean discharge in acre-feet per year (Q), for high-gradient perennial streams. Highgradient channels, which generally exhibit low variability for most factors influencing the width-discharge relation, were selected to indicate a standard exponent in the power-function equation. Flume data supported extrapolation of the high-gradient relation, Q = a w(A)¹•⁹⁸, through five orders of discharge magnitude. Further support for a standard exponent of the regression equation was provided by data from Kansas streams that had very silty beds and similar gradients, climate, and vegetation. Regression analysis of data from these streams gave an exponent of 2.01. Hence, a constant exponent of 2.0 was used for the width-discharge relation of all streams. To account for the effect of sediment on channel geometry, silt-clay percentages of the bed and bank material of 98 perennial streams of the western and midwestern United States were introduced into the standard width-discharge relation. Bed and bank cohesiveness, as indicated by silt-clay content, is considered a measure of channel competence. Narrowest streams for a specific mean discharge occur where channel competence, due to fine material and other variables including channel armoring and lush riparian vegetation, is greatest. Thus, at constant discharge, stream width varies inversely with both bed and bank silt-clay content. Multiple-regression analysis yielded the equation: Q = 2.0 w(A)²•⁰ (SC(bd))⁰•²² (SC(bk))⁰•⁵⁷ where SC(bd) and SC(bk) are percent silt-clay of bed and bank material, respectively. The average standard error of estimate for the relation is 58 percent, much of which is inferred to result from excessive width caused by bank erosion of historically recent flood events. Other causes of deviation from the relation include errors associated with the collection and analysis of data, climate and riparian vegetation, discharge variability, and armoring by coarse sediment sizes. Studies showing that stream channels are widened during periods of flooding suggest that most streams subsequently narrow toward an equilibrium width at normal discharges. Assuming that about one-sixth of the data sets, those exceeding one standard deviation, indicate streams too narrow owing to unrepresentative data or recently deficient runoff, the multiple-regression equation was modified to define channel equilibrium. For known conditions of mean discharge and sediment characteristics, an equilibrium width, W(eq) , can be calculated. Comparison with the measured width, W(A), defines the instability ratio, W(A)/W(eq) , The instability ratio identifies the degree to which channel width varies from assumed equilibrium, and ranges from 1.0 to 1.5 for most perennial streams. The ratio of suspended load to bed load appears to be a principal determinant of channel morphology, whereas sediment yield affects the rapidity with which channel healing can occur after widening by flooding. Greatest channel instabilities generally occur in sandchannel streams of arid to semiarid areas. In humid areas, lush vegetation, which encourages accretion of fine sediment sizes to bank material, induces channel stability. Low discharge variability, as shown by springs and regulated streams, generally results in low values of instability. Utility of the multiple-regression equation includes estimation of discharge from ungaged basins, and prediction of short-term changes in channel morphology resulting from altered supplies of water or sediment. Isolation of the influence of sediment on the width-discharge relation also permits consideration of the effects of other variables on channel shape.

In 1983, Laursen and Flick (1) proposed an equation to predict the depth of scour at the toe of a sloping sill. The equation was developed for use with clear-water only since their experiments did not fully investigate the effect of sediment transport. Their report also left open the question of the possible ramifications of sediment transport on the depth of a scour hole. This thesis is an exploratory investigation of the effect of the sediment transport phenomenon on the depth of a scour hole. It will discuss and compare both the clear-water and sediment transport conditions and to explore if the sediment transport rates to be expected in most streams would have a substantial effect on the scour at the toe of a sloping sill.

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