Manning Roughness Coefficient Research Articles

Runoff Simulation Model for Small Watersheds

ABSTRACT Adynamic hydrologic model, which simulates space and time distributed rainfall excess and runoff in a small watershed resulting from a single rainfall event, is presented. The model uses efficient algorithms and requires information on watershed topography, soil and land use characteristics and time varying rainfall records. Since the only model parameters are the SCS runoff curve number and the Manning's roughness coefficient, the model is simpler and easier to apply to watersheds where sufficient data are not available. Model validation is demonstrated on the USD A experimental watershed W-5, Mississippi and sensitivites of the model parameters are analyzed.

Routing Procedure for Ungaged Channels

A hydraulic streamflow routing method was developed using the continuity equation and the control volume form of the energy equation. The required input data consists of a geometric description of the cross‐section, Manning roughness coefficients, channel slope, reach length and inflow hydrograph. The routing procedure was compared with dynamic wave and hydrologic routing methods. For these comparisons, two prismatic channels with different cross‐sectional shapes were analyzed using varying inflow hydrographs and channel slopes. This analysis included both subcritical and supercritical flow. Further analysis of the routing technique was performed by applying the routing procedure to natural streams. The two streams modeled contained irregular cross‐sections with variations in geometrical shape, slope and discharge. Gaged data provided upstream and downstream discharge hydrographs. The developed streamflow routing technique was demonstrated to perform well. The model can be applied in most situations common to open channel flow. The model does not have convergence problems due to irregular cross sections.

RESISTANCE TO FLOW OVER RIPRAP IN STEEP CHANNELS1

ABSTRACT: A series of flume tests were conducted to determine the flow resistance of angular shaped riprap in steep channels. Flow resistance was expressed in terms of the Darcy‐Weisbach friction factor and the Manning's roughness coefficient. Prototype channels of 4 ft. (1.2 m) and 12 ft. (3.7 m) in width were constructed at slopes ranging from 0.01 to 0.20. The channel beds were comprised of angular riprap of median diameters of 1, 2, 4, 5, and 6 inches (2.59, 5.59, 10.41, 12.95, and 15.75 cms). The Darcy‐Weisbach and Manning's coefficients were determined for each test condition prior to bed failure.The resulting Darcy‐Weisbach coefficients were related to the channel energy gradient and the bed relative submergence for highly turbulent flow. Also, Manning's roughness coefficients were related to the product of the median stone diameter and energy gradient. Because of the angular shape of the riprap and the wedging and/or packing of the bed materials, the resistance to flow was found to exceed the flow resistance values predicted by previous studies. Expressions were presented for estimating the resistance to flow for angular riprap in steep channels.

Subsidence of flood waves in overbank flow areas

Those semi-empirical exponential equations which can describe subsidence of flood peak discharges in channels during overbank flow periods are developed by using dimensional analysis to analyze the numerical results computed from various flood routing techniques based on unsteady free surface flow equations. The subsidence is expressed as a function of eight dimensionless parameters related to the geometry and Manning roughness coefficients of main channel and overbank sections, bed slopes, duration of flood wave, rising time and recession time of overbank flow hydrograph. Two different shapes of inflow flood hydrographs are considered. The derived equations are tested by applying them to calculate the subsidence of flood peak discharges in the Nam Pong and Chao Phraya Rivers in Thailand. The results are found to be very good. Sensitivity analysis shows that the method is not sensitive to error of + 20% in input data. Backwater effects may be included with some modifications.

Incorporating fluvial change in hydrologic simulations: a case study in coastal North Carolina

A case study of hydrologic simulations of flow from artificially drained lowlands of North Carolina shows that failure to account for change in the fluvial system can significantly influence model results. Neglecting consideration of deterioration (loss of water-carrying capacity) in artificial channels can dramatically influence estimates of discharge into sensitive estuarine waters. Major land use and resource management decisions in the region are now being debated, based on hydrologic simulations. Knowledge of artificial channel deterioration (or lack thereof) could be critical for important policy decisions. Such decisions cannot be held in abeyance until data on rates and processes of channel deterioration are available. Therefore a preliminary model of channel deterioration is presented. It is shown that a negative exponential model can describe changes in the Manning roughness coefficient after an artificial channel is excavated. Where fluvial system change could influence simulation results and the time scales of change are less than or equal to the period covered by simulation, efforts should be made to incorporate such change in modelling.

Hydraulic effects of aquatic weeds in U.K. rivers

AbstractThe effects of large aquatic plants (aquatic macrophytes) have been given limited attention in literature dealing with open channel flow. This is despite a large number of river channels in the U.K. being affected by profuse growths of these plants. This paper contributes to three major areas in relation to aquatic macrophytes and river channels.First, a literature review examines four areas of vegetated channel research. Early work on vegetated channels concentrated upon grass‐lined farm drainage channels in the U.S.A. This was complemented by flume studies of predominantly artificial vegetative roughness elements. The review discusses research into large aquatic plants in stream channels, and the discussion draws together a number of disparate areas of research into vegetated channels including theoretical considerations.Secondly, the paper discusses results obtained from laboratory flume experiments, using real plants, and field monitoring on the River Ebble, Wiltshire, U.K. The relationship between discharge and Manning's roughness coefficient (n) is examined. Field monitoring results are presented as generalizations in the relationship between Manning's n when the monitoring sites were vegetated and unvegetated. The relationship between plant cover in the channel and Manning's n is also examined. Two measurements of plant cover are employed: the percentage cross‐sectional area of channel vegetated, and biomass per unit area. The field data for Manning's n and discharge are then discussed in detail in a case study of one site on the River Ebble.Finally, the results obtained from field monitoring are compared to previous research. In the light of these comparisons and detailed examination of the field and flume data, a conceptual model of the effects of aquatic plant growth on channel roughness, mean flow depth, and flow stage is represented. Using this model, an estimate can be made of the likely effect of changing plant cover and discharge on flow stage in an open channel.

Comparative analysis of some explicit-implicit streamflow models

The numerical performance and cost analysis of four streamflow models are presented. These models are constructed from the well-known equations of Saint-Venant. The Galerkin finite element method and the Newton-Raphson iterative method were utilized for the models' solution of depth and velocity of flow. Because of the large computer storage associated with complete solutions of Saint Venant equations, particularly for floods of long durations, the approximate models (kinematic- and diffusion-waves) were introduced to investigate the savings which could be made by using each of these models. Model predictions were contrasted with previously found solutions of a flood-wave in an idealized geometry. The effects of large time step ( Δt) and the time-weighting factor, (θ) for implicit models on cost and the numerical distortion of the hydrographs were examined. Results indicate that the computer cost is a direct function of the level of model approximation. For field application of the implicit models, regression equations relating: 1. (1) Manning's roughness coefficient and discharge; 2. (2) area and depth of flow; and (3) top-width and depth of flow were utilized. Relative to idealized channel the degree of nonlinearity for the natural channel not only affected model performance but increased the amount of computations and thus the cost. Convergence and unconditional stability were observed for implicit models for θ in the range of 0.55 and 1.00. For the explicit model, instability restricted the choice of Δt.

Estimation of Manning's Roughness Coefficient from Data of Flood Flow

Estimation of Manning's Roughness Coefficient from Data of Flood Flow

Hydraulics of High‐Gradient Streams

Onsite surveys and 75 measurements of discharge were made on 21 high‐gradient streams (slopes greater than 0.002) for the purpose of computing the Manning roughness coefficient, n, and to provide data on the hydraulics of these streams. These data show that: (1) n varies inversely with depth; (2) n varies directly with slope; and (3) streams thought to be in the supercritical flow range were actually in the subcritical range. A simple and objective method was employed to develop an equation for predicting the n of high‐gradient streams by using multiple‐regression techniques and measurements of the slope and hydraulic radius. The average standard error of estimate of this prediction equation was 28% when tested with Colorado data. The equation was verified using other data available for high‐gradient streams. Regimeflow equations for velocity and discharge also were developed.

A teacher/student commentary on a field test of Manning's roughness coefficient

Abstract This paper describes and appraises a two‐day field project designed by a member of staff to be carried out by a group of students in a series of stream sections. The main aims of the project were (1) to help students develop a better understanding of stream processes, but more importantly (2) to help students develop an awareness of how ideas evolve, (3) how to test their ideas using a sound procedural methodology and (4) how to assess the implications of their results. The paper outlines how the project developed in collaboration with six students, examines the varying contributions made by staff and students at each stage and discusses the problems that arose during its execution. The project itself involved determining the most accurate method of predicting mean flow velocity in a stream using three different methods of estimating Manning's roughness coefficient.

Analysis of breakup and ice jams on the Athabasca River at Fort McMurray, Alberta

During breakup, severe ice jams form at Fort McMurray, Alberta because of the dramatic change in the character of the Athabasca River at that location. Such jams, which produce water levels in the order of 10 m above the normal open water stage, were documented in 1977, 1978, and 1979. Additional channel surveys and improved estimates of discharge made since the initial analysis have redefined the ice jam characteristics. The Manning roughness coefficient of the underside of the ice jams was found to be 0.072. The new discharge estimates, which were up to twice those previously reported, result in a calculated coefficient of internal friction of 0.8–2.7. This is 30–100% greater than previous estimates, but still similar to values determined for ice jams at other locations.Even with the variation in the coefficient of internal friction, the river stage due to an ice jam at Fort McMurray could be computed with reasonable accuracy for a range of given discharges. If jams form downstream of the mouth of the Clearwater River at discharges greater than 800 m3/s (considerably less than the 1-in-2-year open water flood), flooding will occur within lower Fort McMurray. Unfortunately, the frequency of such an event is unknown because the probabilities of both the discharge being exceeded and the jam occurrence cannot be defined. Key words: ice, breakup, ice jam, ice roughness, flooding, hydraulics.

Mathematical modelling for formation and propagation of floods in a data-deficient basin

Abstract Applicability of some rational concepts and techniques to real-world river basin problems with the usual limitations with regard to the data available was investigated. Two distinct but interrelated hydrologic processes, one of flood formation in a basin and the other of flood propagation down a river channel, related to the Jhelum River basin in the Kashmir Valley in India were considered for appropriate modelling. For the former, the concept of instantaneous unit hydrograph (IUH) representing the basin response in transforming the incident rainfall into flood runoff and the Nash model for deriving the IUH were applied. In such an application, the effects of the lumping of the varying intensities of rainfall occurrences into daily rainfall amounts on the derivation of the two Nash model parameters and on the reproducibility of the peaks of flood runoff through convolution of the IUH with the observed rainfall have been indicated. Further investigation into the analysis of all aspects of these effects is needed to arrive at definitive conclusions. For the other process, a modified Muskingum method based on a finitedifference approximation of the diffusive transport equation is proposed. As a concomitant requirement in this study an expression for variation of Manning's roughness coefficient with stage and a mathematical formulation for river rating for all stages of flow including flood flows have been obtained and tested for their validity for a particular section of the Jhelum River.

Seasonal Variations of Manning's Roughness Coefficient in a Subtropical Marsh

ABSTRACT Manning's roughness coefficient, N, ranged from 0.16 to 0.55 in a subtropical marsh over the flow depth varying between 65 to 40 cm. The N value increas-ed with a decrease in flow depth. The roughness coeffi-cient tripled over a six month period from June to November. The N value in a nonsprayed area was twice of that determined in a chemically defoliated area. The N value and vegetation density were parabolically related. The increase in N value was directly proportional to the 1/2 power of vegetation density and 2A power of flow depth in all types of vegetation.

Palaeohydraulics of a tabular, cross-stratified sand in the Brampton Esker, Ontario

Several hydraulic techniques were used to estimate the flow depth (0.3 m) associated with the deposition of a tabular set (micro-delta) of cross-stratified sand in the Brampton esker. The competency of the flow, deduced from both the grain size and structural characteristics of the set, gave a value of approximately 0.65 m/sec for the palaeo-velocity of the flow. Estimates of palaeo-depth and velocity facilitated calculation of the Froude and Reynolds numbers, about 0.38 and 1.24 · 10 5, respectively. Extrapolation of other parameters included bed shear stress τ 0 (4.50 N/m 2), shear velocity U * (0.067 m/sec), dimensionless Chezy coefficient C/√ g (9.7), slope of the energy gradient S(0.00153), Darcy-Weisbach friction factor f(0.085), Manning roughness coefficient n(0.027) and discharge of bed-material load (19 metric tons/day/m). The figures cited are reasonable estimates only. The occurrence of regressive ripples in the bottomset of the micro-delta aided in the hydraulic interpretation. These flow characteristics are only representative of the final stages of deposition at one location on the flank of the esker. The core of the esker was probably deposited under different hydraulic conditions.

Prediction of the advancing wetting front in border strip irrigation

Four methods of predicting the advance of the water front in border irrigation are compared for nine sets of experimental data reported in the literature. The water balance method (Bishop et al., 1967), the method of Katopodes and Strelkoff (1977) based on zero inertia hydraulics and the method of Michael (1978) enable the distances that the wetting front advances to be calculated for various advance times. A new method presented in this paper, although less accurate than that of Katopodes and Strelkoff, and particularly for nearly flat border strips, enables the coefficients of exponential advance equations to be simply calculated. The dependence of all four methods on reliable infiltration characteristics and on the accurate prediction of the Manning roughness coefficient is emphasized.

Numerical techniques for estimating best‐distributed Manning's Roughness Coefficients for open estuarial river systems

A finite difference version of the Levenberg‐Marquardt method for nonlinear least squares problems has been extended to include inverse problems in distributed estuarial hydraulic systems. The objective in solving the inverse problems was to establish a numerical simulation procedure for estimating best‐distributed Manning's roughness coefficients from sets of observed tide heights. As an illustration, spatially varying Manning's roughness coefficients for the Upper Delaware River Estuary system were determined for several representative sets of tide height data for the period October 1973 to June 1974. The roughness coefficients were modeled as polynomial functions of distance. Manning's n was thus found generally to vary inversely with distance from the head of tide at Trenton to Wilmington. The spatially distributed tidal‐averaged Reynolds number Re was used to correlate Manning's n and Darcy‐Weisbach's f. The resultant n‐Re relationships displayed three distinct hydrodynamic flow regimes characterized as having turbulence. Both n and f were found to be independent of Re for Re > 1.52 × 106 but inversely related to Re for Re < 1.2 × 106. Among the numerical techniques used to simulate tidal hydraulic transients it was found that a ‘hopscotch’ finite difference method yielded the best compromise between computational economy and overall accuracy.

Evaluating models for the estimation of furrow irrigation infiltration and roughness

Several methods have been proposed for estimating infiltration and roughness parameters in surface irrigation using mathematical models. The EVALUE, SIPAR_ID, and INFILT models were used in this work. The EVALUE modeluses a direct solution procedure, whereas the other two models are based on the inverse solution approach. The objective of this study is to evaluate the capacity of these models to estimate the Kostiakov infiltration parameters and the Manning roughness coefficient in furrow irrigation. Twelve data sets corresponding to blocked-end and free drainingfurrows were used in this work. Using the estimated parameters and the SIRMOD irrigation simulation software, the total infiltrated volume and recession time were predicted to evaluate the accuracy of the mathematical models. TheEVALUE and SIPAR_ID models provided the best performance, with EVALUE performing better than SIPAR_ID for estimating the Manning roughness coefficient. The INFILT model provided lower accuracy in cut-back irrigation than in standard irrigation. The performance of SIPAR_ID and INFILT in blocked-end and free draining furrows was similar.

Direction of research

The Thames Estuary, Greater London represents a particularly challenging application for broad-scale strategic analysis of flood risk. It needs a robust flood model and comprehensive risk analysis framework to support the design of London's long-term flood risk management strategy. Traditionally, flood inundation modelling and risk analysis have to be performed by dividing the entire region into smaller disconnected flood plains due to the restriction of model capability and limitation of computational power. This approach essentially neglects the interaction of flood waves between different sub-floodplains and overlooks the broad-scale effects on flood risk. This work aims to test the High-Performance Integrated hydrodynamic Modelling System (HiPIMS) developed at Newcastle University for high-resolution flood simulations over a very large domain, covering 1250 km2 of the flood-prone zones in the Thames Estuary, London, UK. This unified modelling strategy directly takes into account the broad-scale effects caused by localised interventions and disturbances, and hence support more comprehensive flood risk analysis and management. As part of the integrated simulation work, model calibration has been done to choose an appropriate value of Manning's roughness coefficient (n) through systematic numerical experiments at resolutions from 40m to 5m. Results are compared with the observed tidal water levels at eight gauging stations along the estuary. In the ongoing work, the calibrated model is being used to conduct further simulations to investigate the flood risk in the estuary as a result of climate change and sea level rise.