Instantaneous Peak Flow Research Articles

ESTIMATING THE Q100 IN BRITISH COLUMBIA: A PRACTICAL PROBLEM IN FOREST HYDROLOGY1

ABSTRACT. Estimates of peak flows, with specified return periods, are needed in practice for the design of works that affect streams in forested areas. In the province of British Columbia (B.C.), Canada, the new Forest Practices Code specifies the 100‐year instantaneous peak flow (Q100) for the design of bridges and culverts for stream crossings under forest roads; and many practitioners are engaged in making such estimates. The state of the art is still quite primitive, very similar to the state of urban hydrology 30 years ago, when popular estimating techniques were used with little consideration given to their applicability. Urban hydrology then evolved on a much more scientific basis, such that within about a 10‐year period, standard approaches to design were developed. Forest hydrology should follow the same pattern, at least as far as estimating design flows is concerned. Popular present day design procedures include the rational method and other empirical approaches based on rainfall data, as use of the standard flood frequency approach is limited by the paucity of relevant flow data. Estimating procedures based on peak streamflow measurements and statistics are likely to evolve, and these will include distinctions for rain, snowmelt, and rain on snow floods. Guidelines will also be developed for selecting and applying appropriate procedures for particular areas.

RUNOFF RESPONSE FROM TWO RECLAIMED WATERSHEDS1

ABSTRACT: Detailed studies of the surface hydrology of reclaimed surface‐mined watersheds for both rainfall and snowmelt events are non‐existent for central Alberta yet this information is crucial for design of runoff conveyance and storage structures. A study was initiated in 1992 with principal objectives of quantifying surface runoff for both summer rainfall and spring snowmelt events and identifying the dominant flow processes occurring in two reclaimed watersheds. Snowmelt accounted for 86 and 100% of annual watershed runoff in 1993 and 1994, respectively. The highest instantaneous peak flow was recorded during a summer rainfall event with a return period of greater than 50 years. Infiltration‐excess overland flow was identified as the dominant flow process occurring within the Sandy Subsoil Watershed, whereas saturation overland flow was the principal runoff process occurring within the West Watershed.

743-4 Dynamic Three-dimensional Reconstruction of Flow Acceleration Towards Regurgitant Orifices in a Pulsatile Flow Model

To investigate 3-D reconstruction imaging of dynamically accelerating flow convergence (FC) phenomena for quantitating regurgitant flow rates, we used an in vitro pulsatile flow model (Harvard piston pump, model 1423) for two types of regurgitant orifices: rectangular (RECl length = 8 x width, orifice area = 0.24 cm 2 ), and an oblique mitral valve prolapse (MVP, orifice area = 0.28 cm 2 ). Four different dynamic flows were imaged using a Interspec echo system with 3 Nyquist limits (9, 17, 35 cm/sec). These color Doppler FC images were three dimensionally reconstructed with a TomTech computer for each flow. Simulated ECG signals were obtained from an electromagnetic devise attached to the pulsatile pump to synchronize echo Doppler images and TomTech ECG gating (16 gates/beat). Instantaneous peak flow rates were measured using a transonic flow probes and meters attached to the flow models and these reference data were compared with FC data. Over peak flow rates 4.0–18 I/min, the FC method using the 3D measured hemispherical isovelocity assumption showed variable underestimation for both RECT and MVP, especially for low flow rates and higher Nyquist limits (up to 78%, r = 0.56). Hemielliptical FC data derived from three 3D reconstructed orthogonal axes demonstrated a good correlation with actual flow rates with slight underestimation for RECT (18%, r = 0.92) but for MVP showed more variable underestimation for all conditions (27%, r = 0.86). Three dimensional reconstruction of dynamic FC estimated with a hemielliptic model showed better estimation of flow rates for a flat RECT orifice compared to the simple hemispherical model but for more geometrically complicated orifices with flow changing dynamically and variable constraint effects, projection axis measurements are insufficient for the accurate flow rate estimation and surface reconstruction and direct 3D implemented surface area measurements are required.

Response of a stream in disequilibrium to timber harvest

Timber was harvested on South Fork of Thomas Creek, White Mountains of Arizona, USA, for the first time in 1978–1979. This caused significant increases in annual flow volumes and annual instantaneous peak flows. North Fork remained untouched, but both streams were in disequilibrium before harvest time. Due to wetter years during the postharvest period, North Fork also experienced some flow increases, but the difference was not significant. Flow increases cause increased erosion in disequilibrium channels. While in South Fork channel cross sections enlarged by 10% since preharvest time, those in North Fork enlarged by only 2.5%. The number of knickpoints tripled in South Fork, which was about double that in North Fork. Knickpoint development resulted in destruction of the natural control structures (log steps and transverse gravel bars) in South Fork (47%), while in North Fork they increased by 23%. Knickpoints are scarps on the channel bed that have the appearance of gully headcuts. The tripling of the number of knickpoints signifies that adjustment processes of the bed profile are intensified drastically in South Fork. The geomorphic changes signify that due to increases in discharge, the extent of disequilibrium is exacerbated in South Fork. Yet, volumes of erosion are relatively small, as will be sediment volumes leaving the watershed at a given time, because of the stepwise sediment transport occurring in this ephemeral stream.

DISCUSSION1

JAWRA Journal of the American Water Resources AssociationVolume 27, Issue 1 p. 125-127 DISCUSSION1 “Instantaneous Peak Flow Estimation Procedures for Newfoundland Streams,” by U. S. Panu and D. A. Smith2 L. M. Lye, L. M. LyeSearch for more papers by this authorE. Moore, E. Moore Respectively, Assistant Professor and Professor, Faculty of Engineering and Applied Science, Memorial University of Newfoundland, A1B 3X5, Canada.Search for more papers by this author L. M. Lye, L. M. LyeSearch for more papers by this authorE. Moore, E. Moore Respectively, Assistant Professor and Professor, Faculty of Engineering and Applied Science, Memorial University of Newfoundland, A1B 3X5, Canada.Search for more papers by this author First published: February 1991 https://doi.org/10.1111/j.1752-1688.1991.tb03120.x 1 Discussion No. 88066D of the Water Resources Bulletin. 2 Paper No. 88066 of the Water Resources Bulletin 25(6):1151–1162. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume27, Issue1February 1991Pages 125-127 RelatedInformation

PREDICTING INSTANTANEOUS PEAK DEMAND IN RURAL DOMESTIC WATER SUPPLY SYSTEMS1

ABSTRACT: Many rural areas of the United States still have no public domestic water systems. Typical land use patterns in these areas may require 1/2 mile or more of pipe per farm connection. Public systems serving these areas are economically feasible only if realistic short‐term peak demand standards are available for their design. The lack of reliable data upon which to establish such criteria has resulted in a large variation in criteria among state and federal agencies involved in financing and in approving construction of these systems. During the summer of 1975 three distribution laterals of a rural system in Utah were master metered and instantaneous peak flows were recorded for 4 months. The metered lines served 4, 12, and 22 farm houses each. The frequency distribution of peak flows has been analyzed and compared with that developed during similar research in Mississippi and with the existing design standards of the Farmers Home Administration and the State of Utah.

Hydrologic Effects of Deforesting Two Mountain Watersheds in West Virginia

The upper half of one watershed and the lower half of another were deforested and maintained barren from 1965 to 1967. Forest on the remaining halves was cut in 1968. Water yield increases from both watersheds averaged almost 6 inches during the half deforested stage and rose to over 10 inches after complete deforestation. The duration of the flows greatly increased on both watersheds. Other hydrologic effects (instantaneous peak flows, stream temperature, specific conductance, and turbidity) were greater on the lower half deforested watershed. These results show again that forest cutting causes substantial increases in streamflow, but, more important, they provide some landmark values on hydrologic effects of complete deforestation.

Diversion at Portage Mountain Project

A 15 yr flood of 270,000 cfs was ued for the design of the diversion facilities during dam construction. The design flow was determined by extending flow records through correlation with neighboring rivers. The diversion path was an open cut intake channel, 800 ft long and 280 ft wide, leading into three 48-ft diam., horseshoe-shaped, concrete-lined tunnels, designed for free flow. Savings resulted from using depressed tunnel inverts with upshots at the outlet portals, and from the 2-ft thick unreinforced lining. The depressed inverts provided supercritical flow in the tunnels and the upshots proved beneficial in deflecting flow form the river bottom at the tunnel outlets. Diversion was accomplished by blowing a rock plug at the entrance to the intake channel and completing closure of the diversion cofferdam. The tunnel successfully carried an instantaneous peak flow of 314,000 cfs.