A circular shaped culvert was tested with 0, 2, 5, 7, and 10% slopes. The scour hole characteristics of depth, width, length and volume after 316 minutes of testing were correlated to the discharge intensity for each slope. The results indicated that a sloped culvert can potentially increase the maximum dimensions of scour by 10 to 40 percent over those for a horizontal culvert.
Impoundments constructed to encapsulate waste materials must resist the natural erosive processes to prevent exposure and release of the waste. One erosive process that has been difficult to predict is gully intrusion. This study was conducted to analyze the gully erosion processes and determine their effect on long-term embankment erosion and estimate the potential impacts on waste stabilization. A comprehensive procedure has been presented for estimating the magnitude and location of a potential gully intrusion into a soil covered, waste impoundment. The estimation procedure requires that the user obtain information pertaining to the regional hydrology, site soils, proposed impoundment geometry, and design life. Data from 27 field sites and seven laboratory experiments were analyzed to produce three dimensionless equations allowing the user to estimate the maximum depth of gully incision on a sloped surface or embankment as a function of: total volume of runoff, embankment geometry, and clay content of the soil comprising the embankment. It is noted that while a limited set of field data was available for synthesis into the prediction equations, the procedure presented is a first step into the determination of the magnitude and location of gullying into sloped surfaces.
ABSTRACT One component of the local scour process near a culvert outlet is the formation of an aggraded mound downstream of the scour area. This investigation presents a series of observations and empirical relationships depicting the formation, growth, and estimated maximum dimensions of a mound in a uniformly graded sand material due to clear water scour. The maximum dimensions of the mound were correlated to the discharge intensity (Qg ‐0.5 D ‐2.5 ), the maximum dimensions of the scour hole, time, and tailwater elevation. The concept of an approximate area of scour influence was developed relating the mound width, scour hole length, and mound length as a function of the culvert diameter and discharge intensity.
ABSTRACT: Recent environmental concerns in floodplain management have stimulated research of the effect vegetation and debris have on flow conveyance, and their function in a productive riparian ecosystem. Although the effect of stable, in‐channel woody debris formations on flow resistance has been noted by several authors, studies concerning entrapment of detrital debris in vegetation are lacking. Logs, limbs, branches, leaves and other debris transported during flooding often become lodged against bridges, hydraulic structures, trees and vegetation, and other obstacles, particularly in and near the overbank areas. Hydraulic measurements obtained in a channel prior to and following the removal of woody debris indicated that the average Manning's n value was 39 percent greater when woody debris was present. An examination of the drag‐velocity relation for vegetation indicated that an increase in the frontal area of debris and/or vegetation results in a nearly proportional increase in Manning's n. The influence of debris on flow resistance decreased as flow depth increased.
An investigation conducted to derive a design procedure for estimating the dimensions of scour in a variety of noncohesive materials at culvert outlets is presented. Scour hole dimensions of depth, width, length and volume are correlated to the discharge intensity, mean grain diameter and standard deviation of grain diameters. A single relationship is determined for each scour hole dimension for a variety of bed materials.
This study empirically quantified the effect of sampling time on measured transport rates and fitted rating curves based on results obtained from bed load traps deployed for 2, 10, and 60 min in a coarse‐bedded stream. As expected for a skewed distribution of transport rates, 2 min deployment underpredicted transport rates obtained from 10 and 60 min deployment by factors of 2 and 3 at moderate flows (50–70% Q bkf ). At near‐bank‐full flow the underprediction by 2 min versus 10 min sampling increased to a factor of 5, while transport rates collected during 60 min deployments were reduced because of overfilled bags. At flows near incipient gravel motion, 2 min sampling overpredicted transport rates obtained by 10 and 60 min deployment by factors of 2.7 and 3.4. The overprediction is attributed to computational effects arising mainly from the lowest measurable transport rate for each sampling time. Rating curves fitted to transport rates from 2 min sampling were significantly less steep than those for longer deployment times. However, sampling time explains only a small degree of the large difference between rating curves from bed load traps and a Helley‐Smith sampler (2 min sampling).
Thornton, Christopher I., Anthony M. Meneghetti, Kent Collins, Steven R. Abt, and S. Michael Scurlock, 2011. Stage-Discharge Relationships for U-, A-, and W-Weirs in Un-submerged Flow Conditions. Journal of the American Water Resources Association (JAWRA) 47(1):169-178. DOI: 10.1111/j.1752-1688.2010.00501.x Abstract: Instream rock weirs are routinely placed into stream systems to provide grade control, reduce streambank erosion, provide energy dissipation, and allow fish passage. However, design and performance criteria for site specific applications are often anecdotal or qualitative in nature, and based upon the experience of the design team. A study was conducted to develop generic state-discharge relationships for U-, A-, and W-weirs. A laboratory testing program was performed in which scaled, near-prototype U-, A-, and W-rock weir structures were constructed in 11 configurations. Each configuration encompassed a unique weir shape, bed material, and/or bed slope. Thirty-one tests were conducted in which each structure was subjected to a sequence of predetermined discharges that minimally included the equivalent of 1/3 bankfull, 2/3 bankfull, and bankfull conditions. All tests were performed in subcritical, un-submerged flow conditions. Stage-discharge relationships were developed using multivariant, power regression techniques for each of the U-, A-, and W-rock weirs as a function of the effective weir length, flow depth, mean weir height, rock size, and discharge coefficient. Unique coefficient expressions were developed for each weir shape, and a single discharge coefficient was proposed applicable to the weirs for determining the channel stage-discharge rating.
A 3‐in. (7.62‐cm) Parshall flume is installed in a channel and flow rates are measured with lateral flume crest slopes of 0, 3.6, 6.5, 9.0, 13.3, -3.8,-4.8,-7.2, and -11.8%. The apparent discharge is compared to the measured discharge for each slope with free outfall conditions. The results indicate that the Parshall flume accuracy is in error approximately 7% at a lateral slope of ±10%. It is determined that the flow measurement requires a 0.75% adjustment for each 1% of lateral settlement at the flume crest. A method for correcting the apparent discharge with the measured discharge is presented for variable lateral slope conditions.
