Even when similar methods are utilized, average recession rates can vary
significantly among watersheds despite close proximity. For example, a recent study in the similar-sized Walnut Creek basin within the adjacent Rolling Loess Prairies Level IV Ecoregion (47f) in Iowa reported an average annual recession rate of 18.8 cm (Palmer et al. 2014), significantly higher than the rate observed in the Onion Creek watershed. The Walnut Creek watershed has more rolling topography and primarily loess-derived soils (Palmer et al. 2014). The reason for the difference in observed recession rates over this relatively short distance can likely be attributed to abrupt topographic and geologic changes, along with associated soil properties. Results from this study show that considerable judgment should be used in comparing measured recession rates on an inter-basin scale, as variations in topography and geology can occur over short distances, and average recession rates will reflect these changes. Our average recession rate data can most reasonably be extrapolated to similarly sized basins within the Des Moines Lobe Ecoregion (47f) with comparable landform and land use conditions. Erosion pin measurements
Stott, D.E., C.A. Cambardella, M.D. Tomer, D.L. Karlen, and R. Wolf. 2011. A soil quality assessment within the Iowa River South Fork watershed. Soil Water Manage. Conserv. 75:2271-2282.
Tufekcioglu, M., T.M. Isenhart, R.C. Schultz, D.A. Bear, J.L Kovar, and J.R. Russel. 2012. Stream bank erosion as a source of sediment and phosphorus in grazed pastures of the Rathbun Lake Watershed in southern Iowa, United States. J. Soil Water Conserv. 67(6): 545-555.
Figure 33. Phosphorus ppm from a floodplain core in the study segment.
Subtle or minor changes in bed/bar storage like scour and glide extension can release significant amounts of gravel to the active channel. Presently, bank gravel deposits in the bank are likely an important source of gravel to the study segment. Nevertheless, There are three tributaries in the study segment, two unnamed second order streams and Goff Creek a third order stream. Only one of these tributaries has a delta chert gravel bar at the confluence with the James River (Figure 31) indicating it as a probable source of gravel to the study segment that could move downstream. Conversely, the absence of delta gravel bars at the other two tributaries does not mean that the other two tributaries are not sources of gravel to the channel since both of the confluences are at outside meander bend locations, which areas with higher velocity relative to the rest of the stream ( Motta et al., 2012) . It is possible that the gravel from these tributaries is transported from the confluence during flood events and deposited downstream.
Livestock grazing of riparian zones can have a major impact on stream banks if improperly managed. The goals of this study were to determine the sediment and
phosphorus losses from stream bank soils under varying cattle stocking rates and identify other factors that impact stream bank erosion in the Southern Iowa Drift Plain. The study was conducted on thirteen cooperating beef cow-calf farms within the Rathbun Lake watershed in South CentralIowa. Stream bank erosion rates over three years were estimated by using the erosion pin method. Eroded stream bank lengths and area, soil bulk density and stream bank soil-P concentrations were measured to calculate soil and total soil-P lost via stream bank erosion. Results revealed that the length of severely eroded stream banks and compaction of the riparian area were positively related to an increase in number of livestock grazing on the pasture stream reaches. While there was no direct relationship between bank erosion and stocking rate, the erosion rates from two sites enrolled within the Conservation Reserve Program (CRP) were significantly lower than those from all grazed pasture sites especially when seasonal effect, specifically winter/spring, was considered. This result suggests that use of riparian areas as pasture has major negative impacts on water quality and channel integrity through increased sediment and phosphorus from bank erosion, and that impact could be reduced through management of livestock grazing within these riparian areas.
5 culvert shapes that range from twelve inches (30.5 cm) to twenty-seven feet (8.2 m) (Normann et al., 2005). Culverts in the United States are most often constructed of reinforced concrete (RCP), non-reinforced concrete, corrugated aluminum and corrugated steel (Normann et al., 2005). The culvert material defines the culvert roughness coefficient. “Roughness is represented by a hydraulic resistance coefficient, such as Manning’s n (Normann et al., 2005). The most common culvert materials are reinforced concrete and corrugated steel. Typical Manning’s n values for reinforced concrete pipe range from 0.010-0.015, and for corrugated metal pipe n values range from 0.011-0.28 (Normann et al., 2005). For the arch culvert the “bottomless” or natural channel culvert material classification is used, however the culvert itself is generally constructed of reinforced concrete. The material selection is based on structural strength, hydraulic roughness, durability, and resistance to corrosion (Normann et al., 2005). The variability in climatic changes is an important determinate in the type of culvert used due to the potential for abrasion and corrosion. Geomorphologic features of a specific location are another determining factor in the type of culvert that is used. Bed form changes aspects of installation, maintenance and the overall feasibility of a culvert. The constraints of physiographic region alter culvert hydraulic characteristics. In the northwestern US, culverts are significantly different from those in the coastal regions because the bed load sediment is drastically different (Bates, 2005). Culverts in North Carolina do not have extensive general constraints; however, the eco-region (Coastal Plain, Piedmont, Mountains) in which the culvert is placed in addition to the specific location and climatic data should be considered.
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The subsequent impacts of ‘diffuse’ and ‘point’ source P pressures on stream ecology were investigated for objective 3 by comparing seasonal P concentrations with concomitant ecological quality metrics that were derived from surveys taken at the catchment outlets each May and September between 2009 and 2014. Median TRP concentrations (of continuous hourly data) during summer (i.e. June, July and August) were compared with macroinvertebrate and diatom quality indices for September. Similarly, median TRP concentrations during ‘spring’ (here referring to the months February, March and April, i.e. the three months prior to the ecology survey) were compared with macroinvertebrate and diatom quality indices for May. Whilst two ecological surveys per year are not expected to fully capture the temporal community dynamics in response to sudden stressors (e.g. Feeley et al., 2012), they nevertheless provide seasonal insights which are not afforded by national statutory data-sets (one survey every three years) and which capture time-integrated diffuse and point source P pressures (over seasonal time-scales).
The major sources of P to rivers include those from human popula- tion centres (waste water ef ﬂ uent) and intensive agriculture (organic and inorganic nutrients in runoff), with the former considered to be pri- marily a point source issue and the latter a more diffuse phenomenon (Bowes et al., 2005). For agriculture, mitigation measures are generally targeted at a combination of residual (e.g. soil P stores where P is also in- cluded in the territorial regulations), incidental (e.g. recently applied fertilisers) and point (farmyards and facilities) sources of nutrients (DEFRA, 2004; Swedish Board of Agriculture, 2009; SI 31, 2014). These PoMs under the WFD are expected to contribute to the achievement of good ecological status. However, the results of the ﬁ rst round of River Basin Management Plans show that more than half of Europe's surface water-bodies are in less than good ecological status (European Environ- ment Agency, 2012). Furthermore, national environmental quality stan- dards (EQS) for riverine P concentrations (e.g. 0.035 mg L −1 un ﬁ ltered molybdate reactive P in Ireland) are still exceeded in many parts of Europe (European Environment Agency, 2010). With the second round of River Basin Management Plans under development, the lack of clear improvements may prompt the introduction of additional mitigation measures. However, the risk of increasing economic burdens on farming communities (or increasing support) will be an important consideration to ensure that existing measures and expectations of improvement (and any further measures) are based on robust supporting science.
2018a, b]. They are designed to mimic natural riffles, but are characterized by a greater regu- larity and structural stability. Artificial riffles are also rougher than the natural ones and span the entire river channel. Water flow strongly accel- erates in the riffle area [Mooney 2007, Plesiński and Radecki-Pawlik 2018a, b]. Increased rough- ness is attained via the use of broken rocks with a large diameter across the artificial riffle area – the rocks dissipate the energy of flowing water. The use of riffles is slowly replacing the use of traditional drop structures and low head dams, which is due to the new environmental regula- tions. Well-designed manmade riffles do not prevent fish from migrating upriver. In addition, they improve the oxygen conditions in the river, foster river self-cleaning processes, and are not an aesthetic eyesore [Bojarski et al. 2015, Torre
water. Further work, however, measuring benthic ﬂuxes to the surface water is required to con ﬁrm this. DOC patterns varied seasonally, and were typically higher in porewaters than surface water at all sites in summer and autumn likely re ﬂecting the increase in DOC production during this time (see above) and resulting in the streambed being a source of DOC during these seasons. In winter and spring, however, pat- terns were not consistent between sites, with porewater concentrations at sites 1 and 2 not consistently higher or lower than in the surface water. At site 3 porewater concentrations were generally similar or lower than in the surface water, indicating that the gravel-dominated sediments were a weak sink of DOC at these times.
forts to reduce P loading to streams. Given the well-de- fined baseflow and eventflow end-members that could be derived from the high resolution Cannonsville P load data, the interpretation here is that the curvilinear rela- tionship (Figures 4 and 7) reflects net P retention along the stream-watershed continuum during mixing of the eventflow and baseflow end members. The use of end member mixing approach to estimate P processing comes with some limitations. The choice of event flow end member can also influence the magnitude of the esti- mated P processes. Further study is needed to gain fuller understanding of the balance of processes that determine the eventflow end-member load at intermediate to high flow conditions, especially in watersheds dominated by nonpoint export, such as differential erosion associated with events of different magnitudes, intensities, seasons, and pre-existing conditions; re-deposition and other processing active during overland flow; and in-stream processing.
Abstract: The article presents the initial part of the research of the efficiency of erosion and flood control measures designed in the experimental basin of the Němčický stream. A long term observation of discharges, rainfalls, and some water quality indicators was introduced at 2 experimental profiles. We have elaborated a study of the erosion threat for discovered areas, where the realisation of protective measures is necessary to reduce soil loss. Besides the erosion control, the sheet grassing contributes to a better water retention by the agricultural countryside. The efficiency of the designed measures ascertained by model evaluation proved that grassing of 49 ha of arable land (from total 183 ha) and the exclusion of erosive dangerous crops growing (on 21 ha) should decrease the centenary discharge by 18% and the amount of the transported suspended matter by 29%. The observation will continue after realisation of the erosion control measures and of a polder, which was de- signed for sufficiently effective flood protection, and the measurements will be compared with the preliminary and model values.
composition of geochemical tracers (i.e. 2, 3 …21) is undertaken. The uncertainty for the relative contribution of sediment sources was determined using a Bayesian-mixing model. The results obtained indicate that, for the study area the main sources of uncertainty were associated with the number of individual source. This study illustrates the usefulness of multivariate statistical techniques for analysis and interpretation of complex data sets in sediment fingerprinting assessment, and the spatial variability of relative contributions associated with uncertainty for effective land management. Therefore, it can be concluded that this model can be used as sediment fingerprinting associated with uncertainty in Zidasht catchment and these methods can be tested in other regions. Consequently, the improvement of the exiting uncertainty model by considering the grain size and organic matter corrections should contribute to better assessment of sediment fingerprinting as well in reducing sediment mobilization and transfer using effective land management and soil erosion control methods.
Similarly to the setting with atomic messages, INT-PST ensures that no adversarial query to the receiv- ing oracle causes the message stream output by Recv to deviate from the message stream input to Send. This notion is quite simple to formulate. Formalizing the stronger INT-CST property demands more care. Intuitively, from ciphertext integrity we expect that when processing any ‘out-of-sync’ ciphertext, the al- gorithm Recv should return an error message. However, when considering a stream-based interface it may happen that Recv processes an out-of-sync ciphertext which does not yet contain ‘enough information’ to be recognized as being invalid; in this case the receiving algorithm would buffer (part of) the ciphertext and wait for further fragments until a sufficiently long ciphertext string is available to be processed and deemed as valid or invalid. In such a scenario, a naive adaptation of the INT-sfCTXT definition of [BKN04] would allow trivial attacks by declaring successful any adversary that makes the Recv buffer (part of) an out-of-sync ciphertext, without producing non-trivial output. Our notion of ciphertext-stream integrity carefully identifies the case just described and, by letting the receiving oracle wait for further ciphertext fragments, declares the adversary successful only if Recv outputs a non-empty message fragment resulting from an out-of-sync or exceeding portion of the ciphertext stream.
Logically, a synopsis belongs to a specific plan operator, storing state that may be required for future evaluation of that operator. (In our implementation, synopses are shared among operators whenever possible, as described later in Sect. 4.1.) For example, to perform a windowed join of two streams, the join operator must be able to probe all tuples in the current window on each input stream. Thus, the join operator maintains one synopsis (e.g., a hash table) for each of its inputs. On the other hand, operators such as selection and duplicate-preserving union do not require any synopses.
This result shows that the precognitive setting has a significant advantage in some cases. Nonethe- less, we show a lower bound, indicating that its worst-case performance cannot be much better than the worst-case performance of a standard stream algorithm. The proof of the lower bound shares some techniques with the proof of Theorem 6, especially the use of permutations. It additionally relies on the observation that while the stream algorithm knows in advance what elements will be available for selection and when, it is still constrained to selecting the elements in the order that they are provided by the stream. It also must keep to a certain order of selections to emulate the pool algorithm, since the pool algorithm makes decisions based on previously observed responses. Thus, in the proof of the lower bound, we construct a pool algorithm that might select two permutation elements, but the order in which they would be selected depends on the responses to selected base elements. As a result, the precognitive algorithm cannot tell in advance in which order the two elements must be selected. The probability of both orders appearing early enough in the stream is low, so that even when the whole stream is taken into account, an exponential dependence cannot be avoided, though this dependence is weaker than the one shown in Theorem 6 for standard stream algorithms.
desorption of Ca in greater proportion to Mg from the stream substrate (Fig. 4). The lowest ratio occurred at five hours, representing the start of the Ca and Mg resorption during the recovery stage. At 5 hours (Fig. 4), Mg was resorbed in greater proportion to its stream concentration than was Ca. Two hours after the acid addition stopped, Ca and Mg concentrations started slowly to increase (Fig. 2). Although the Ca/Mg ratio recovered to its original value by the end of the experiment, the concentrations had not. The rate of recovery was slower than the mobilisation of base cations during the acidification phase. The shape of the curve for sum of base cations (BC) through time (acidification and recovery) is consistent with the conceptual model of Norton et al. (1999).
versions of HEC-RAS were limited to a quasi-unsteady flow and vertical bed change. Quasi- steady flow does not conserve flow, which can lead to distorted results (Gibson et al., 2017). This version also does not retain hydrologic memory of previous time steps, because the model computes individual backwater time steps. This only allows the user to account for one flow in a given event, rather than all of the flows within the event. The most recent version of HEC-RAS eliminates these limitations by including unsteady flow capabilities and consideration for lateral cross-section change with BSTEM. Rivers adjust laterally as well as longitudinally, and therefore having a model that can reflect these geomorphic adjustments is more suitable. The unsteady flow approach conserves water volume, resulting in more practical solutions. This version utilizes the veneer method, which applies erosion and deposition evenly over a cross-section (Gibson et al., 2015).
CHAPTER 4: GEOMORPHIC RESPONSE 4.1. INTRODUCTION
Sediment pulses dramatically alter river systems, with wide-ranging geomorphic and ecological implications that warrant study. Dam removals are among main anthropogenic causes of sediment pulses and provide exciting research opportunities, allowing for careful before-after study design to better understand this phenomenon. For example, the recent dual removal on Washington’s Elwha River generated a wealth of data and important insights into river behavior under unsteady sediment supply regime. Substantial channel changes, which would normally be expected from a high-magnitude disturbance were described, including channel planform change, wood changes, widespread aggradation, and pool filling (Draut and Ritchie, 2015; East et al., 2015; Ritchie et al., 2018). Findings suggest that dams impose adverse effects on salmonid fish (Muhlfeld et al., 2012), which have been observed to mediate following removal (Brenkman et al., 2019; Quinn et al., 2017). This in conjunction with looming FERC compliance pressure for aging structures makes removal an increasingly appealing option (Bednarek, 2001), all but guaranteeing more large sediment pulses that require better understanding of the potential consequences to river ecosystem downstream.