BEST MANAGEMENT PRACTICES FOR STORM WATER AND INFILTRATION CONTROL1

ABSTRACT: Water quality controls of storm water runoff and infiltration should be a major part of a nonpoint source control program. Although surface runoff and ground water controls are often approached separately, coordination between the two is essential. For practical reasons, a rather simplified technology-based approach appears to be desirable. Areas affected vary greatly as to their sensitivity to pollution; and the various classes of pollutant source vary greatly as to their potential harmfulness. In effect, a matrix approach appears best, in which both vulnerability of the area and harmfulness of the pollutant source would have weight in determining which level of best management practices (BMP) would be appropriate, whether standard, special, or complete prohibition of the type facility under given circumstances.     

THE EFFECT OF MAINTENANCE ON STORM WATER DETENTION BASIN EFFICIENCY1

ABSTRACT: Storm water detention is an effective and popular method for controlling the effects of increased urbanization and development. Detention basins are used to control both increases in flow rates and sedimentation. While numerous storm water management policies have been proposed, they most often fail to give adequate consideration to maintenance of the basin. Sediment accumulation with time and the growth of grass and weeds in the emergency spillway are two maintenance problems. A model that was calibrated with data from a storm water detention basin in Montgomery County, Maryland, is used to evaluate the effect of maintenance on the efficiency of the detention basin. Sediment accumulation in the basin caused the peak reduction factor to decrease while it increased as vegetation growth in the emergency spillway increased. Thus, the detention basin will not function as intended in the design when the basin is not properly maintained. Thus, maintenance of detention basins should be one component of a comprehensive storm water management policy.     

HYDROLOGIC BUDGET FOR A FRESHWATER MARSH IN FLORIDA1

ABSTRACT: Accurate water balance calculations are essential for water resource and environmental management decisions, but many of the terms used in the equation are difficult to measure. In this study, a method for measuring rates of evapotranspiration and net seepage from a freshwater marsh in southwest Florida is described. The results are compared to evaporation pan estimates as well as to calculations that balanced all the terms in the hydrologic budget. The measured rates of evapotranspiration showed a. distinct seasonal trend ranging from an average high of 0.24 in/d during July 1992 to a low of 0.06 in/d in January 1993. Evapotranspiration rates were higher than Class A evaporation pan measurements during July and August, indicating transpiration by plants exceeded evaporation by pans. Net ground water seepage flowed out of the marsh except during periods of high water table conditions. When all terms in the hydrologic budget were evaluated, the equation balanced on a yearly basis with an error of 2 percent, on a seasonal basis with errors less than 7 percent, but on a monthly basis errors were as great as 30 percent. Total annual rainfall on the marsh was 45 percent of the total marsh hydrologic input and was approximately equal to the loss by evapotranspiration of 41 percent.     

A MODELING APPROACH FOR STORM WATER QUANTITY AND QUALITY CONTROL VIA DETENTION BASINS1

ABSTRACT: Storm water detention basins have historically been employed for quantity (i.e., flooding) control only. However, recently it has been suggested that these basins may also provide a practical means of storm water quality control. This paper presents the formulation of a mathematical modeling approach which may be used by professionals to simultaneously design detention basins for the dual purpose of storm water quantity and quality control. Model simulations demonstrate that for a given basin, pollutant removal increases as storm frequency increases. The importance of particle size distribution and settling velocity for net pollutant removal is illustrated, The design procedure is demonstrated, and pollutant loading diagrams for estimating pollutant removal as a function of storm size are developed.     

MODIS Biophysical States and NEXRAD Precipitation in a Statistical Evaluation of Antecedent Moisture Condition and Streamflow1

Abstract: The potential of remotely sensed time series of biophysical states of landscape to characterize soil moisture condition antecedent to radar estimates of precipitation is assessed in a statistical prediction model of streamflow in a 1,420 km² watershed in south‐central Texas, Moderate Resolution Imaging Spectroradiometer (MODIS) time series biophysical products offer significant opportunities to characterize and quantify hydrologic state variables such as land surface temperature (LST) and vegetation state and status. Together with Next Generation Weather Radar (NEXRAD) precipitation estimates for the period 2002 through 2005, 16 raw and deseasoned time series of LST (day and night), vegetation indices, infrared reflectances, and water stress indices were linearly regressed against observed watershed streamflow on an eight‐day aggregated time period. Time offsets of 0 (synchronous with streamflow event), 8, and 16 days (leading streamflow event) were assessed for each of the 16 parameters to evaluate antecedent effects. The model results indicated a reasonable correlation (r² = 0.67) when precipitation, daytime LST advanced 16 days, and a deseasoned moisture stress index were regressed against log‐transformed streamflow. The estimation model was applied to a validation period from January 2006 through March 2007, a period of 12 months of regional drought and base‐flow conditions followed by three months of above normal rainfall and a flood event. The model resulted in a Nash‐Sutcliffe estimation efficiency (E) of 0.45 for flow series (in log‐space) for the full 15‐month period, ?0.03 for the 2006 drought condition period, and 0.87 for the 2007 wet condition period. The overall model had a relative volume error of ?32%. The contribution of parameter uncertainties to model discrepancy was evaluated.     

A PLANNING METHOD FOR EVALUATING DOWNSTREAM EFFECTS OF DETENTION BASINS1

While storm water detention basins are widely used for controlling increases in peak discharges that result from urbanization, recent research has indicated that under certain circumstances detention storage can actually cause increases in peak discharge rates. Because of the potential for detrimental downstream effects, storm water management policies often require downstream effects to be evaluated. Such evaluation requires the design engineer to collect additional topographic and land use data and make costly hydrologic analyses. Thus, a method, which is easy to apply and which would indicate whether or not a detailed hydrologic analysis of downstream impacts is necessary, should decrease the average cost of storm water management designs. A planning method that does not require either a large data base or a computer is presented. The time co-ordinates of runoff hydrographs are estimated using the time-of-concentration and the SCS runoff curve number; the discharge coordinates are estimated using a simple peak discharge equation. While the planning method does not require a detailed design of the detention basin, it does provide a reasonably accurate procedure for evaluating whether or not the installation of a detention basin will cause adverse downstream flooding.