A continuous simulation stormwater management model (with 33 years of historical precipitation) was used to determine how the design criteria from five different stormwater management pond ordinances changed the runoff from a 7.77 ha watershed following a hypothetical development scenario. All five evaluated ordinances required that the postdevelopment runoff rates from the site be less than or equal to the predevelopment runoff rates for each return period (a zero increase criteria). However, none of the five ordinances were effective at limiting the increase in runoff peak rates for the 1- and 2-year return periods for the annual runoff series, the 1-year return period for the annual exceedance (partial) runoff series duration, or more frequent precipitation events. To better control the lower frequency runoff events from stormwater ponds, the 1- and 2-year return periods should always be analyzed for a basin's design. Additionally, there was a radical change in the frequency of small and moderate runoff events occurring from the watershed following the hypothetical development.

Two equations commonly used for estimating and modeling infiltration from pervious land surfaces are those developed by Horton and the U.S. Soil Conservation Service (SCS). The main shortcoming of the Horton equation is the strong dependence of the infiltration rate on the starting time of the rain, which becomes particularly critical when a rainfall event starts at a low intensity. The SCS equation, which was originally developed for runoff and later converted to compute infiltration losses, suffers from the complete lack of a time relationship. The problems associated with these shortcomings are discussed in this paper. The Horton equation is modified to make the infiltration rate a function of cumulative antecedent infiltration. A linear filter, in conjunction with two of the Horton parameters, is suggested to delay the SCS infiltration increments. In addition, a concept proposed by Bauer to incorporate deep percolation into infiltration equations is adopted to provide for the recovery of infiltration capacity between consecutive storm bursts.

ABSTRACT: As an alternative to the conventional single‐peak design storms commonly used in hydrologic practice, a large number of Southeastern Pennsylvania storm events were selected from hourly U.S. National Oceanographic and Atmospheric Administration (NOAA) records, and their temporal distributions were analyzed. From these recorded events, design storms of a typical distribution were developed for storm durations between 6 and 18 hours. All of these generated design storms have two or more peaks. The conventional single peak as well as the “typical” multi‐peak storms were then applied to a simulated watershed. It was found that the multi‐peak storms consistently produced more dispersed hydrographs with lower runoff peaks than the conventional single peak storms.

In present hydrologic practice, it is generally recognized that the shallow overland sheet flow through the upper portions of a watershed is very slow, and that runoff gradually accelerates as it concentrates into gullies and, finally, streams. In this paper, the fractal concept is applied by testing whether a watershed's stream‐and‐swale system branches in a characteristic pattern that repeats itself into successively finer but similar segments. Commonly used geometric, geomorphologic, hydraulic, and hydrologic equations are combined to reduce the number of parameters. Kinematic wave equations are then developed for the runoff movement in the channels, and integrated to obtain an equation for the time of concentration.

The concept of fractals, in simple terms, says that the patterns of natural features repeat themselves as the feature gets divided into successively smaller segments. In this paper, the reproducitility of stream patterns is tested by the use of the fractal dimension. The fractal concept is then applied to the drainage pattern of a watershed, in which swales begin infinitely small at the divide and become gradually larger as their drainage areas increase. As a result, the time of concentration is integrated over the total runoff path length.

JAWRA Journal of the American Water Resources AssociationVolume 26, Issue 5 p. 837-837 REPLY TO DISCUSSION by Bernard L. Golding1 “Pond Sizing for Rational Formula Hydrographs”2 Gert Aron, Gert Aron Professor, Department of Civil Engineering, Environmental Resources Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802.Search for more papers by this author Gert Aron, Gert Aron Professor, Department of Civil Engineering, Environmental Resources Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802.Search for more papers by this author First published: October 1990 https://doi.org/10.1111/j.1752-1688.1990.tb01420.x 1 Discussion No. 90004D of the Water Resources Bulletin 26(5):835–836. 2 Paper No. 90004 of the Water Resources Bulletin 26(2):255–258. 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 No abstract is available for this article. Volume26, Issue5October 1990Pages 837-837 RelatedInformation

This paper summarizes the findings of a recent study at Penn State aimed at recommended hydrologic techniques for small developing watersheds. The specific desk-top methods investigated include: (1) Rational method; (2) SCS TR55; (3) Espey 10-minute unit hydrograph; (4) SCS curvilinear unit hydrograph; and (5) Pennsylvania regional flood frequency method known as PSU IV.

To utilize point estimates for more expansive areas, reduction factors are necessary to account for the attenuation of storm magnitude with increasing area. The spatial attenuation of major storms in Pennsylvania was investigated using rainfall data obtained from the National Climatic Data Center for the statewide network of raingages and from the Agricultural Research Service for the dense network of raingages on the Mahantango experimental watershed in east central Pennsylvania. Individual storms of 1, 2, 3, 6, 12 and 24 hour durations were analyzed using a Thiessen polygon weighting technique. The results of the individual storm analyses were then averaged to obtain relative storm magnitude versus area relationships for two levels of gage network density.

ABSTRACT: A statistical analysis of all available continuous hourly and 15‐minute duration rainfall records for Pennsylvania was performed to develop an updated procedure to estimate design storms. As a resuit of this study, Pennsylvania was divided into five homogeneous rainfall regions and a set of rainfall intensity‐duration curves developed for each region, for return periods of 1 to 100 years and durations ranging from 5 minutes to 24 hours. The PDT‐IDF curves were judged to be a better representation of Pennsylvania rainfall than the nationwide TP‐40 maps, particularly for storm events of 10‐years and lower return periods.The average time distribution of 24‐hour storms in Pennsylvania was found to be well represented by the SCS Type II distribution. The Corps of Engineers SPS 24‐hour distribution was found to differ appreciably from both the SCS Type H and the Pennsylvania 24‐hour storm distribution. For storm durations between 15 and 90 minutes the standard Yarnell intensity‐duration curves closely resemble Pennsylvania storm distributions.

The most commonly used source of rainfall estimates is the U. S. Weather Bureau Technical Paper 40. A more detailed study of Pennsylvania storms was conducted in 1970 under the sponsorship of the Pennsylvania Department of Environmental Resources. The report resulting from this study shows some very pronounced areas of large and frequent rainfall amounts. In 1985, an agreement was reached with the Pennsylvania Department of Transportation to conduct an updated rainfall frequency study, using data up to 1983, and to present the results in the form of charts from which rainfall estimates could be read conveniently for durations between 5 minutes and 24 hours, and return periods between 1 and 100 years. The development of these charts is the main topic of this paper.

Rainfall duration, amount, and intensity are among the major contributors to highway drainage and inundation problems. For the design of any hydrologic structure, ranging from the simplest rational flow rate estimates to the most sophisticated stormwater runoff simulation, design rainfall estimates of acceptance reliability are needed. A statistical analysis of all available continuous hourly and 15-minute duration rainfall records were used to develop an updated procedure for estimating design storms for Pennsylvania. Pennsylvania was divided into five homogeneous regions using the statistically-derived 1-year 1-hour, 1-year 24-hour, 100-year 1-hour, and 100-year 24-hour rainfall duration-intensity storms. A set of rainfall duration-intensity curves were developed for each of the five regions, for seven return periods between 1 and 100 years and durations ranging from 5 minutes to 24 hours. As a secondary study the areal distribution of typical storms was analyzed and the average rainfall depth was plotted as a ratio of maximum point rainfall over the range of 0 to 2500 square miles.

The karsted limestone valleys of central Pennsylvania contain two populations of sinkholes. Solution sinkholes occur in the Champlainian limestone units along the margins of the valleys. Solution sinkholes are permanent parts of the landscape and, although a nuisance to construction, do not present other problems. The second population is the suffosional or soil-piping sinkholes These occur on all carbonate rock units including the Beekmantown and Gatesburg dolomites that comprise the two principal carbonate aquifers in the valley. Suffosional sinkholes are the principal land-use hazard.

JAWRA Journal of the American Water Resources AssociationVolume 19, Issue 2 p. 305-305 DISCUSSION: by Michael A. Collins1 “Fitting a Gamma Distribution Over a Synthetic Unit Hydrograph”2 Gert Aron, Gert Aron Respectively, Professor of Civil Engineering, and Research Asociation, The Pennsylvania State University, 212 Sackett Bldg, University Park, Pennylvania 16802.Search for more papers by this authorElizabeth L. White, Elizabeth L. White Respectively, Professor of Civil Engineering, and Research Asociation, The Pennsylvania State University, 212 Sackett Bldg, University Park, Pennylvania 16802.Search for more papers by this author Gert Aron, Gert Aron Respectively, Professor of Civil Engineering, and Research Asociation, The Pennsylvania State University, 212 Sackett Bldg, University Park, Pennylvania 16802.Search for more papers by this authorElizabeth L. White, Elizabeth L. White Respectively, Professor of Civil Engineering, and Research Asociation, The Pennsylvania State University, 212 Sackett Bldg, University Park, Pennylvania 16802.Search for more papers by this author First published: April 1983 https://doi.org/10.1111/j.1752-1688.1983.tb05334.x 1 Discussion No. 82218D of the Water Resources Bulletin 19(2): 303–304. 2 Paper No. 81067 of the Water Resources Bulletin 18(1): 95–98. 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue2April 1983Pages 305-305 RelatedInformation