Georgia Water Resources Conference

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Georgia Water Resources Conference

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Georgia Water Resources Institute

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Regional Curves for Urban Channel Geometry in Atlanta

(Georgia Institute of Technology, 1999-03) Snyder, Soley B. ; Ferguson, Bruce K.

This paper presents regional curves for urban stream geometry in the Atlanta area. Curves relating drainage area to cross-sectional area, bankfull channel width, and bankfull depth have been constructed, and provide averages which may be used for urban stream channel rehabilitation projects.
Erosional Process and Its Potential Control at Thurmond Lake

(Georgia Institute of Technology, 1999-03) Ferguson, Bruce K.

Thurmond Lake is a Corps of Engineers reservoir that, like many other reservoirs, suffers from eroding shorelines. A study of Thurmond found that the complex shoreline configuration controls the occurrence of fetch and concentration of wave energy, and thus of erosional process. Bluff recession, which is the visible and damaging feature of shore erosion, is a consequence of downcutting of the bench. Halting bluff recession requires combating undercut at the bluffs base. Alternative structural and. bioengineering stabilization measures are described and evaluated. General guidelines for shoreline installations are given, including the most reliable months for access, the elevation required to protect from wave "runup", the requirement of wings and toes to prevent flanking and undercutting, and selection and installation of plants for bioengineering.
Mitigation of Urban Runoff Impacts on Atlanta Streams

(Georgia Institute of Technology, 1999-03) Brosnan, Thomas ; Ferguson, Bruce K. ; Iosco, Robert ; Moll, Gary ; Schueler, Thomas ; Sotir, Robbin B. ; Watson, Rick

An interdisciplinary scientific panel was convened to assess the condition of Atlanta's streams and to identify those watershed management actions with the greatest potential to improve water quality and riparian and stream habitat in the Atlanta region. Broad recommendations included a description of elements to incorporate into a watershed management program for Atlanta, and specific suggestions for demonstration projects in four small, headwater watersheds. The four chosen demonstration sub-watersheds collectively reflect the gradient of impervious cover and stream quality present in Atlanta, and individually represent conditions comm.only observed throughout the area. Therefore, the general recommendations for these demonstration areas should be broadly applicable to the rest of the region.
Development Ordinances to Protect Streams

(Georgia Institute of Technology, 1999-03) Nichols, David B. ; Ferguson, Bruce K. ; Weinberg, Scott ; Alabanza Akers, Mary Anne

Communities across the State of Georgia unknowingly contribute to nonpoint source pollution of local streams through their adopted land development ordinances. By dictating excessive quantities of impervious surfaces and the continuation of sprawling patterns of land use, these ordinances are a major factor in the degradation of local streams. This paper presents some alternatives that communities could incorporate into their own development codes to reduce the impacts of new land development
Flood and Sediment Interpretation at the Historic Scull Shoals Mill

(Georgia Institute of Technology, 1997-03) Ferguson, Bruce K.

Interpretation of the written historic record was combined with observation of alluvial land forms to construct the history of sedimentation at a historic mill site, and to inform possibilities for flood protection. The results correctly predicted additional, previously hidden remains and demonstrate the crucial role of sedimentation in the village's economic history.
Downstream Hydrographic Effects of Urban Stormwater Detention and Infiltration

(Georgia Institute of Technology, 1995-04) Ferguson, Bruce K.

Urban stormwater hydrographs with various degrees of detention and infiltration were routed through 30 hypothetical drainage networks. Only infiltration reduced flow volume. Infiltration shortened flow duration while detention lengthened it. Both detention and infiltration reduced peak rate of flow, but not to the degree for which they were designed; their effectiveness varied with drainage networks and urban hydrologic changes. These results encourage balanced consideration of infiltration and detention for solving specific problems of flooding and erosion in specific watersheds.
Establishing Dynamic Equilibrium in an Urban Stream

(Georgia Institute of Technology, 1995-04) Lucas, W. Drew ; Ferguson, Bruce K.

Channelization of urban streams has reduced infiltration and riparian habitat, increased flooding and isolated urban residents from natural processes. One possible way to restore environmental integrity of channeled streams is to re-establish dynamic equilibrium, where outflows of sediment and water are equal to those entering upstream. This paper describes a design methodology to guide reestablishment of dynamic equilibrium in channelized urban streams. In a hypothetical landscape design, dynamic equilibrium is reestablished for a prominent Atlanta channeled urban stream. Three main aspects of dynamic equilibrium were considered in the design: 1) fluvial geomorphology, 2) riparian habitat and 3) human use of the stream. This paper affirms that the principle of dynamic equilibrium can be used as a guide for establishing urban channel forms and associated riparian habitat zones. Human use and site specific exigencies can be integrated into the stream with restored form and function through landscape design.
Stream Rehabilitation in a Disturbed Industrial Watershed

(Georgia Institute of Technology, 1993-04) Ferguson, Bruce K. ; Gonnsen, P. Rexford

Since 1988, a 140 acre industrial watershed in Athens, Georgia has been treated with an unusual combination of stormwater and sediment controls. The site had a prior history of sedimentation, channelization, and altered hydrologic regime. Rehabilitation design was aimed at capturing mobile sediment, stabilizing stream channels, suppressing peak storm flows, augmenting base flows, and establishing wetlands. This multipurpose approach, and some aspects of the specific features developed to implement it, were not foreseen in the state's erosion and sediment control manual (State Soil and Water Conservation Committee, 1978). This paper reports the results of the project through the present date. As described below, the objectives have been substantially realized.
Comparison of Infiltration and Detention in the Georgia Piedmont Using Recent Hydrologic Models

(Georgia Institute of Technology, 1991) Ellington, M. Morgan ; Ferguson, Bruce K.

Infiltration is a possible alternative to detention for control of urban stormwater. Infiltration is capable of controlling peak flows as is detention, but also promises the advantages of flow volume control, base flow augmentation, and water quality improvement. However, the feasibility of infiltration in the Georgia Piedmont has been questioned because of the region's combination of high rainfall and slowly permeable soils. To test the feasibility of infiltration in this region, Patton (1986) designed infiltration systems as hypothetical replacements for existing detention systems on two urban development sites in the Atlanta area. Both the detention and infiltration systems were based on the Rational formula and equivalent design storms. When the two types of systems were compared, Patton found that infiltration, when designed to meet the same hydraulic standards as detention, was surprisingly feasible in terms of construction cost and land area occupied while offering more environmental benefits than detention. This paper summarizes a study (Ellington, 1991) to update Patton's work. In this study both detention and infiltration systems on Patton's study sites were redesigned using two relatively recent hydrologic models, the Soil Conservation Service (SCS) method of estimating storm runoff, and the long-term water balance as it applies to accumulation of standing water in closed reservoirs. Hydrologic performance was modeled, and cost indicators estimated, for four conditions: undeveloped, developed with no stormwater control, developed with detention, and developed with infiltration.
Evaluation and Control of the Long-Term Water Balance on an Urban Development Site

(Georgia Institute of Technology, 1991) Ferguson, Bruce K. ; Ellington, M. Morgan ; Gonnsen, P. Rexford

The long-term water balance is promising but previously unused technique for evaluating and controlling the hydrologic effects of urban development. The water balance is a summary of all the inflows and outflows, over a period of time, of a land area such as a hillslope, a watershed or a political unit. The long-term water balance refers specifically to the average levels and seasonal fluctuations of flows over a period of years, indicating the overall pattern of interaction of a land area with the hydrologic environment. Although the water balance has long been a prominent concept in geography, where it is used as a summary index of the moisture and energy endowments of regional environments, its application to management of specific urban development projects has not been fully explored. A more traditional approach to urban stormwater management is the design storm. Some design storms are defined by average recurrence intervals. Others are uniform storm phenomena, such as the first one or two inches of runoff from any storm. The application of this concept is appropriate for management of peak flood flows. Interest in flood control has made the design storm essentially the exclusive approach to regulation of stormwater in Georgia. However, a design storm is not a significant part of the total water resources of an area; it does not indicate overall moisture endowments of the environment. For example, in northern Georgia, where the annual precipitation averages roughly 50 inches, a 10 year design storm is only about 6 inches in.24 hours. Thus the design storm lasts only a fraction of one percent of the elapsed time during its recurrence interval, and 500 inches of rain go by while stormwater facilities wait for the 6 inches for which they were designed. A broad interest in water resources demands a more comprehensive management of the stormwater resource. The long-term water balance summarizes average seasonal patterns of hydrologic inputs, outputs and changes in storage. The long-term water balance could be used to evaluate such important specific long-term parameters as baseflow runoff, ground water recharge, and soil moisture levels. Through environmental connections between the hydrologic environment and vegetative and human communities, these parameters indicate potential levels of on-site and downstream water supplies, assimilative capacity, recreational resources, wetlands, and aquatic life. The application of the long-term water balance to a proposed urban development might suggest types of impacts and approaches to stormwater control that would not be considered by applying the design-storm idea alone. One control approach that deserves to be evaluated this way is infiltration, which uses closed basins to force runoff water to enter and be stored in subsurface soil voids (Ferguson, 1990a; Ferguson and Debo, 1990). This paper presents preliminary development of a model for simulating the long-term water balance of urban development sites, and application of the model to a specific development to illustrate potential water-balance effects of urbanization and alternative methods of stormwater control.