10/4/ slide sample of Presentation. Key Principles to Current Stormwater Management

Transcription

1 40 slide sample of Presentation Please contact if you would like the complete presentation Key Principles to Current Stormwater Management Distributed Control Measures Integrated Planning Multiple Objective / Function Urbanization Impacts to Surface Runoff Hydrology Increased runoff volume Increased peak flowrate Reduced time of concentration Increased flow frequency Reduced infiltration Modified flow patterns Loss of surface storage Increased temperature Reduced sediment sources Stormwater pollutants /bacteria Non-stormwater discharges 1

2 What is Hydromodification - Hydromod? Development Hydromodification Impacts Focus on changes to the downstream streams that changes in hydrology causes Urban Related Hydromodification Increase Imperviousness Changes in runoff volume and frequency Changes in sediment supply Direct channel changes Hydromodification Impacts Increase Erosion Sediment Changes Habitat Loss / Degradation Bio/ecological Impacts Urbanization Changes Watershed Hydrology Increased Imperviousness Efficient conveyance Vegetative cover Topography Landuse Flow diversions Riparian encroachment Changes in Urban Storm Runoff and Stream Flow Increased peak runoff rates Faster Response More frequent runoff events Higher flow velocities Sediment supply change Observed Stream Channel Responses to Hydrologic Changes Increased stream erosion Enlarged channels Deeper/wider Flooding problems Habitat damage Increase sedimentation / erosion Sediment size change Stormwater Pollution Impact from Urbanization EPA estimates the No. 1 source of surface water pollution is caused by stormwater runoff and caused pollution of nearly 40% of US waterbodies Non-point source pollution Initial first flush runoff washes off 85% of pollutants within first 15minutes of storm Generally first ½-inch runoff from impervious area - Small portion of storm runoff but large percentage of all pollutant loading Federal CWA - NPDES Permit Program National Pollutant Discharge Elimination System (NDPES) part of the 1972 Clean Water Act (CWA) Administered by the EPA Point source Non-point source (i.e. stormwater) Originally excluded from NPDES but environment groups sued Stormwater targets Industrial Municipal Separate Stormwater Systems (MS4) 2

3 Recent Changes in Federal NPDES / State Implementation Requirements Requirement Existing Changes Site Design None Infiltration control measures (LID) to maximum extent onsite Infiltration / Hydromodifiaction / Groundwater Recharge Water Quality Erosion Control None Volumetric Controls / Maintain Annual recharge / Duration flow control Treatment of Water Quality Control Volume Erosion Control Standard Practices Infiltration controls measures Water Quality Monitoring Numeric Standards Limits Surface Runoff Hydrology Fundamental Concepts Surface Runoff is excess rainfall not abstracted Basics of surface hydrology are simple Moving volumes (water) over time Volume = Area x Depth Rainfall depth is considered a volume Velocity = Distance / Time Rate of Flow = Q = Volume /Time Also is Q = (Area)x(Velocity) Volume delivered over time = (rate)x(time) V= Q x t Volume Volume Area Volume Volume Depth Flowrate Precipitation and Storm Events Rainfall varies in time and area where it falls Storm events characterized by total volume, intensity, and duration (inches, in/hour, minutes, or hours) Precipitation and Storm Events Rainfall events are random Analysis of long historical records will provide statistical pattern of the rainfall occurrence Probability (p) and Recurrence Interval (T) used to define storm magnitude/severity where p=1/t Example: 10-year storm P= 0.10 Storm that will be reached or exceeded on average once every 10-years Orange County (Example) 10-year 24-hour rain = 3.7 inches 10-year 1-hour rainfall = 0.78 inches 100-year 24-hour rainfall 5.6 inches 3

4 Simplified Method to Determine Runoff Potential Important method facilitates evaluating benefits of sustainable design practices quickly on stormwater runoff SCS Curve Number Method provides number from 1 to 100 that indicates the runoff potential conversion of rainfall SCS curve number function of soil type, vegetative cover, and impervious area. Procedure found in TR-55 published by SCS (NRCS) and calculator and tables Q/H&H/Tools_Models/other/TR55.html SCS (NRCS) TR-55 Method Simple Hydrology Equations Site Design General Equation Gives Runoff Depth: Knowing That I=0.2S, the Equation Becomes: P Must Be Greater Than or Equal to 0.2S Where: Q = Precipitation excess (inches) P = Cumulative Rain (inches) S= Soil - water retention potential CN = SCS Curve Number Q = Q = 2 ( P Ia ) ( P I ) + S a ( P 0.2S ) P + 0.8S 1000 S = 10 CN 2 What is a Runoff Hydrograph? Watershed Response from Storm Illustrates how flowrate varies in time Time is a key characteristics of the watershed Runoff Volume is area under hydrograph Small Site Rational Method Hydrology for Flowrate Simplified hydrology formula for determination of flowrate from small site Applicable to less than 640 acres Q = Peak flowrate (cfs) = C x I x A C = runoff coefficent 1.0 acre I = intensity (in/hr) A = acres For Parking Lot Example: Q = 1.0 x 1.0 in/hr x 1.0 ac = 1.0 cfs inlet 4

5 What is stormwater Detention? Stormwater detention is the temporary storage of runoff and released at lower rate than it entered the storage reservoir/pond Primary benefit to attenuate peak flow rate Storm Water Quality - Design Storm Capture Volumes Examples: 6 month, 24 hour (Wa) 0.5 in runoff (Fl) 1 inch of runoff (Mn) 0.5 inches from impervious area (Md) Recommended: 85th percentile runoff event, Average Annual 24-hour Water Harvesting Water Balance Analysis Mass Balance Storage = Inflow Outflow Inputs = Rainfall+Runoff+Urban Dry Flows Output=Evaporation+Irrigation Use+Infiltration Conventional Stormwater Treatment BMPs Detention Storage Dry Detention Wet Detention 5

6 Conventional Stormwater Treatment BMPs Infiltration Conventional Stormwater Treatment BMPs Vegetative Infiltration Trench Bioretention Infiltration Basin Treatment Wetland Biofilter Conventional Stormwater Treatment BMPs Mechanical/Chemical What is Low Impact Development (LID)? LID is a stormwater management technique that mimics nature (runoff) LID manages rainfall at the source by mimicking site pre-development hydrology Utilizes techniques that infiltrate, filter, store, evaporate, and detain stormwater close to the sources Stormwater is treated in small cost effective landscape features through the site instead of just at the end of pipe Hydrodynamic Separation Media Filtration Perlite/Zeolite 6

7 Measuring Sustainability Measuring Sustainability Measuring Sustainability Low performance High performance Low performance Water Quality Treatment High performance New Technologies Present New Opportunities for Artful Expression Measuring Sustainability Low performance High performance 7

8 Value Added Evolution of Stormwater Management Structural BMPs Non- structural BMP Techniques to Provide Art / Creative Form with Stormwater Create interesting pathways for destinations points of stormwater systems Stormwater Infrastructure Stormwater Treatment Landscape Techniques Art / Aesthetics Urban Drainage Detention Flood Control Structural BMPs LID Features Eco Landscaping Green Infrastructure Sustainable Design Environmental Site Design Allow public to touch and interact with water / stormwater systems Techniques to Provide Art / Creative Form with Stormwater Contrast different materials natural vs manmade and imbed artistic forms Techniques to Provide Art / Creative Form with Stormwater Create visual interest in water through unique shape and change in direction Focal points of stormwater visual interest Recreate natural water features which use natural forms and water movement and motion 8

9 Techniques to Provide Art / Creative Form with Stormwater Techniques to Provide Art / Creative Form with Stormwater Use unique conveyance (flumes/bioswales) to emphasize water path interest / curiosity Emphasize water movement with waterfalls/pools Stormwater basins/ponds have visual interest different themes / geometry Use sounds of water and different rhythms falling different height and materials Modular Resides Above Roof System, Not Integral to It, Less Likely to Impact Warranty Pre-Grown Off-Site, Easy to Install, Provides Instant Visual Impact Module Dimensions Limit Root Mass and Available Moisture Reservoir Rigid Module Doesn t Always Work with Curvelinear Design Concepts Green Walls 9

10 Below-Ground Modular Tank Frees Up Programmable Space Reliable No Evaporation Loss No Vector Breeding Secure Less Costly, Configurable to Odd Shapes, Requires More Pumping Bio-Swale Potential Landscape Amenity Habitat Potential, Filtration Function Adds to Aquifer More Costly, Less Capacity Some Evapotranspiration Loss Below-Grade Infiltration Chamber Frees Up Programmable Space No Evaporation Loss Adds to Aquifer More Costly No Habitat, but No Vector Breeding Ground Either 10