Stormwater Management Why and What Is Stormwater Management?

Stormwater Management Why and What is Stormwater Management?

• Implementaon of structural and non-structural measures to manage problems and prevent new problems • Protecng life and lessening public health and safety risks • Reducing monetary damage to private and public property • Protecng quality of surface and ground water • Minimizing disrupon of community aﬀairs Stormwater Management Relaonship to Sustainability • Water is limited resource – Arid environment – Reduced water supplies • Water quality impacts to downstream water bodies (beaches, streams, lakes) • Groundwater recharge from rainfall – Quality and quanty • Wildlife and riparian corridors • Impacts to stability of natural creeks / rivers with increased erosion Convenonal Approaches to Stormwater Management

Floodplain Management Stormwater Management

Conveyance Oriented Storage Oriented Legal Aspects of Drainage Design Drainage Law - General • Legal aspects of drainage design are just as important principles as the engineering and must be aware of the general doctrines

• Engineer must be must be aware of lawsuits for “negligence in design” or failure to perform in accordance with “industry standards” Drainage Law - General

• Drainage law based varies widely between states and based on case law • Generally based on three doctrines: 1. Common Enemy Doctrine 2. Civil Law Rule or Natural Flow Rule 3. Rule of Reasonable • Disnguishes between “surface waters” and “water course” California Drainage Law

An upper landowner is entled to discharge surface water from his land as the water naturally flows. If he modifies the natural flow, he is liable for any damage done to a lower landowner unless the lower landowner had acted “unreasonably” in altering the natural drainage over his land. The determinaon of reasonable or unreasonable is a queson of fact to be determined by the court in each case Keys v. Romley (1966) Inns v. San Juan School Dist. (1963) Drainage Law Design Applicaons

• Perpetuate natural drainage as praccal • Return flow to its natural velocity and depth at the outlet to the downstream property • Do not divert addional surface waters or drainage area to lower property owner • Do not increase floodwaters on adjacent property owners through floodplain modificaons General Storm Drain Design Process General Steps for Storm Drain Design

1. Baseline data collecon 2. Watershed boundary and surface flow paerns 3. Develop conceptual alternaves layouts 4. Planning level hydrology and feasibility analysis Oponal 5. Preliminary conduit alignment 6. Detailed watershed subarea delineaon 7. Hydrology analysis and preliminary storm drain sizing 8. Street hydraulics 9. Catch basin hydrology 9. Storm drain preliminary profile and connector pipes 10. Storm drain hydraulic analysis and refined alignment/sizing 11. Street inlet design 12. Overflow analysis – Major Storm/Extreme Event 13. Specialty structure hydraulics Efficient Design Must Balance Limitaons STEP 1 – Baseline Data Inventory/ Mapping/Criteria

Regulatory Constraints Physical Constraints • Topographic mapping/Property boundaries – Field survey/verify connecon points upstream and downstream • Ulity Locaons – Underground and surface/aerial STEP 1 – Baseline Data Inventory/ Mapping/Criteria STEP 2 – Watershed Boundary and Surface Flow Paerns STEP 3 – Conceptual Planning Alternave Layouts STEP 4 – Planning Level Hydrology and Alternave Feasibility Analysis STEP 4 – Planning Level Hydrology and Alternave Feasibility Analysis

ALTERNATIVE Weighting A B C D E F G OBJECTIVE Factor

Costs 3 5 1 3 3 5 4 2

Constructability 1.5 3 4 2 2 5 4 3

Utility Conflicts 1 5 2 3 4 2 3 5

R/W Acquisition 2 3 5 4 4 3 1 3

Traffic Control 1 1 4 5 1 4 5 5

Public Disruption 1 2 5 4 2 3 5 4

Construction Unknowns 1 4 5 3 4 4 1 1

Permitting 1.2 5 5 2 1 5 5 3

Maintenance 1 4 5 4 3 4 5 5

Hydraulics 1.5 2 3 5 5 5 1 3

Local Drainage 1 4 3 3 2 3 5 4

TOTAL SCORE 54.5 53.5 51.9 44.7 62 51.5 48.6

STEP 5 – Preliminary Conduit Alignment STEP 6 – Detailed Watershed Subarea Delineaon STEP 7 – Hydrology and Preliminary Storm Drain Sizing

• Raonal Method hydrology should perform inial pipe sizing for minimum travel me • Storm drain designed for “full ﬂow” use maximum ﬂow area of pipe unlike sewers – Limitaons of maximum HGL but should always be below street surface / no pressure manholes – HGL should be a minimum of 0.5 below the street guer at the catch basin inlet – Should be a minimum of 3 below the street surface at the end of pipe where future extension may occur STEP 7 – Hydrology and Preliminary Storm Drain Sizing

Kings Handbook Pipe Sizing Method •Simple and fast method without computers

•For full ﬂow – depth/diameter = D/d = 1.0 and K’=0.463

•Assume S f = (0.9)So accounts for minor losses STEP 8 – Catch Basin Hydrology and Street Hydraulics

• “Catch basin” hydrology diﬀerent than “mainline” storm drain hydrology • Determine street hydraulic capacies • Locate upstream catch basins by maximizing use of street hydraulic capacity as long as possible STEP 9 – Storm Drain Proﬁle

• Preliminary vercal alignment – Hydraulic requirements – Physical underground constraints STEP 10 – Storm Drain Hydraulics and Reﬁned Alignment / Sizing STEP 11 – Street Inlet Design

• Inlet type and size • Number of inlets • Flow intercepted/Bypass • Local depression layout • “Connector Pipe” ﬂow STEP 12 – Overﬂow Analysis – Major Storm Event • Extreme storm event greater than design storm • 100-year event for local 10-year storm drain systems STEP 13 – Specialty Structure Hydraulic Design / Layout Comprehensive Design Approach Ensure Opmum Design Street and Inlet Hydraulics Street Hydraulics – Flooded Width Limitaons/Protecon Level Criteria

• Medians and le hand pocket area not travel lanes • Flooded width not exceed 2- from median in super- elevated Street Hydraulics – Flooded Width Limitaons/Protecon Level Criteria 1.12 0.5 0.67 0.67 V = 1.12So S x T V =n S 0.5 S 0.67T 0.67 n o x Street Hydraulic Analysis

Simpliﬁed Hydraulic Equaons for Triangular Guer FHWA Street Hydraulics Design Tools County of Orange Hydraulics Tools – Street Flow Depth Below Vercal Curve Street Hydraulics – Flooded Width Hydroplaning Hazard

• Funcon of water depth, road geometry, speed, tread depth, re pressure, pavement surface • Hydroplaning at 55 mph with only a water depth of 0.08 inches

Reducing Hydroplaning Potenal 1. Design the street geometries to reduce the drainage path lengths of the water flowing over the pavement. 2. Increase the pavement surface texture depth by such methods as grooving. Increases the drainage capacity at the re pavement interface. 3. The use of drainage structures along the roadway to capture the flow of water over the pavement will reduce the thickness water Street Inlet Types / Classificaons

Classiﬁcaons • Connuous Grade • Low-point • Sump Street Inlet Locaons • Corners of arterial highway intersecons • Low points – localized and sumps • Flow exceed street capacity limits, either dry-lane requirements or top of curb • Upstream of sump condions to reduce ﬂooding

• Begin and end of super-elevated street secon (Sx = 0.0) • Street intersecons and upstream of bridge where 100% intercepon required • At reducons in street grade to prevent sedimentaon and increase safety • Freeway ramp “gore” points Street Inlet Locaons

• Before curves on steep streets where water has potenal to escape guer • Locaons to intercept irrigaon runoff / flood runoff/ sediment prior to entering the travel lane • Prior to major intersecons with cross guer if possible to intercept paral flow such that deep flow within cross guers will not cause traffic hazards Undesirable Inlet Locaons

• Inlet at medians requiring local depressions • Grate inlets should not be used at medians (future pavement overlay create a drop) • In a curb return • Driveway • Handicap ramps • Locaons where debris and sediment will clog the inlet Locang Street Inlets - Examples General Hydraulic Characteriscs of Connuous Grade Street Inlets • Connuous grade inlet capacity involves three elements: – Approach flow (Q) – Incepted flow (Qi) – By-pass flow ((Qb)

• Capacity of an inlet is not the maximum ﬂow quanty that an inlet can take, but is the amount intercepted for a given set of condions • Eﬃciency of an inlet is E = Qi / Q • Depth of water in the guer and the approach velocity are the major factors in the capacity

• Greater cross slope (Sx )then greater capacity • Steeper longitudinal slope (So ) then less capacity • Allowing a small ﬂow to by-pass inlet greatly increases capacity

General Hydraulic Characteriscs of Connuous Grade Street Inlets • Local depression improves capacity • Capacity increases with local depression depth, width and length

• All inlets clog so appropriate clogging factors, curb opening less than grates • Curb opening inlets loose capacity as grade increases , ineffecve above 5% then should use grate Standard County Side Opening Inlet – Hydraulic Opening Heights • Connuous grade inlets must have depth of flow less than opening (weir flow not pressure flow) • Flow depth plus local depression (y + a) should be less than “hydraulic opening” Curb Height Curved Plate Square Plate 4-inch 5.7” 4” 6-inch 7.5” 6” 8-inch 9.3” 7.9”

Curved Face Plate Square Face Plate Connuous Grade Side Opening – Hydraulic Analysis

Orange County Charts 1.Calculate depth of ﬂow from street hydraulics 2.Verify ﬂow depth (y) plus L.D. (a) is less than inlet face hydraulic opening

3.Determine length for total intercept (L t) 4.Select the actual length (either 3.5,7, 14,21 )

5.Determine actual ﬂow intercepted Q i vs. Q and the amount of “by-pass”. Maximum of 15% by-pass is allowed •If addional basins needed to intercept ﬂow, the minimum separaon between basins in series is 12-feet County of Orange Design Tools – Connuous Grade Inlets County of Orange Design Tools – Connuous Grade Side Opening Inlets Sump Condion – Side Opening Inlet

• Low ﬂow depths inlet operates as a weir or less than the height of opening: 3/ 2 Qi = CwLd

• Ld = L +1.8W (for depressed inlets) • Depths exceeding the opening d>1.4h then the inlet submerged - operates as an oriﬁce

• Weir coefficient is Cw = 2.3 and the orifice coefficient is Co = 0.67 • Between depths of “h” and “1.4h” the inlet operates in a transion zone which is capacity is not defined FHWA Hydraulic Tools – Sump Side Opening County of Orange Hydraulic Tools – Sump Side Opening Grate Inlet Characteriscs

• Use of grate inlets for a sump in a street is not permied • Grates will plug from collecng debris, plus it always rains on trash day • Grates designed to be “bicycle safe” so res don’t get stuck. Generally 50% of the grate area is actually “clear opening” • Minimum clear space between longitudinal bars is 1” and cross bars acceptable minimum spacing at 9”. • Grate width typically designed to ﬁt within guer width of 2.0 feet. Connuous Grade Side Opening – Hydraulic Analysis

FHWA HEC-15 or HEC-22 Design Charts

1.Determine length for total intercept (L t) 2.Select the actual length (either 3.5,7, 14,21)

3.Determine actual ﬂow intercepted Q i vs. Q and the amount of “by-pass”. Maximum of 15% by-pass is allowed Connuous Grade Side Opening – Hydraulic Analysis

FHWA HEC-15 or HEC-22 Design Charts (cont.) 4. Select the actual length (either 3.5,7, 14,21 ) 5. Determine actual flow intercepted or the efficiency of the inlet (E) 1/8 E = 1 – (1 – L/LT) 6. Calculate amount of by-pass flow

7. If local depression then adjust Sx = Sequivalent FHWA Design Tools – Connuous Grade Inlet Hydraulics Connuous Grade – Grate Inlets

• Grate inlets will intercept all guer flow passing over grate if it is long enough and guer velocity is low • As approach velocity increases more splash-over occurs • Total flow intercepted by the grate is the frontal flow (Qf)plus the side flow (Qs )intercepted (very small poron) 0.15V 1.8 R = 1/(1+ )1.8 s S0L.152.3V Rs = 1/(1+ x 2.3 ) S 1L.8 0.15Vx R 1/(1 Connuous Grade Grate Inlet – Hydraulic )1.8 s = + 0.152.3V R = 1/(1+S x L ) s S L2.3 x analysis

FHWA Hydraulic Equaons

Side Flow Eﬃciency:

Frontal Flow Eﬃciency: Rf = 1 – 0.09 (V – Vo)

Total Eﬃciency: E = Rf Eo + Rs (1-Eo)

FHWA Hydraulic Tools – Grates Connuous Grade Grate Sump Inlet - Characteriscs

• Grates in sumps can be used in parking lots or street alleys or landscaped area, but not in streets • Hydraulics are based on a “clean grate” then reducon factors for clogging • Low depths up to 0.4 feet grates act as weir • Grates funcon as orifice for depths greater than 1.4 feet • Depths between 0.4 and 1.4 feet the operaon is not defined since vorces occurs at the impinging flows from each side of the grate submerge • Proposing a grate in a sump should consider 100% clogging and define an emergency overflow path FHWA Hydraulic Tools – Grate Sump Inlet Combinaon Inlet Combinaon Inlet Hydraulics

• Combinaon inlets are on connuous grade where curb opening and grate are side-by-side use the grate capacity alone for design • Combinaon inlets where the grate is located downstream of part of the curb opening then the capacity is the sum of the capacity of the curb opening (length with no grate) plus the grate – Frontal flow coming to the grate is reduced by the curb opening upstream of the grate. Sloed Drain Hydraulics Storm Drain Hydraulic Analysis Storm Drain Hydraulic Design Operaon Requirements • Storm Drain generally designed for pressure flow condions or pipe operang full • Calculated Hydraulic Grade Line (HGL) should be less than the street surface and Tailwater (TW) in the catch basin should be less than street inlet flowline with 0.5 freeboard or 3.0 below road surface for future extension of storm drain Water Surface Profile Analysis – Pressure Flow

• Starts at downstream hydraulic control and proceeds upstream from EGL • Add energy losses (fricon and minor) to calculate upstream EGL

HGL = EGL – Hv EGL2 = EGL1 + ∑hL Water Surface Proﬁle – Open Channel

Standard Step Method •Procedures used by most programs like WSPG •Iterave process with upstream depth assumed then Speciﬁc Energy for upstream calculated by two methods and depth adjusted unl answer converges

Direct Step Method

∆X = (E2 - E1 )/(SO - Sfavg ) 25 / 2 QA = Ck'Ac dd A = C d 2 A Water Surface Proﬁle Analysis – Primary Energy Losses

Fricon Loss

Hf = SfL Kings Handbook Equaons for Pipes

Normal depth

Area paral full Pipe

Crical depth Kings Handbook – Pipe Hydraulics Tables – Manning’s P = pressure = cd 3 Addional Hydraulic Tools for Pipe Hydraulic Analysis • LACFCD tables for momentum and pressure values in “parally full” pipes useful for speciﬁc force analysis of Hydraulic Jumps

(P + M)1 = (P + M)2 • Otherwise would be diﬃcult to analyze in part full pipes LACFCD Pipe Hydraulic Tools 2 (V1 −V2 ) H = ex 2g Water Surface Proﬁle – Minor Losses

• Manhole Hm = Km Hv

• Sudden Contracon Hc = Kc · Hv2

• Sudden Expansion

• Bend /Curve Hb = 0.25 · Kb · H v

1.22 • Transion Ht = 3.5 · (Tan(0.00872665 · delta))

• Catch Basin Hcb -= Kcb · H v Juncon Loss – Pressure Flow

• Juncon analysis is performed using the momentum balance or speciﬁc force • Includes fricon loss through structure • Adjust for change in velocity heads upstream and downstream Juncon Loss – Pressure Hydraulics

Change in HGL = ∆HGL =

**Important to see how HGL can be changed Juncon Energy Loss = Hj

Hj =HGL + Hv1 – Hv2 + Hf Structure Fricon Loss

180(14.32) −135(14.03) −15(8.49)cos(45) − 30(7.55)cos(30) (0.018 + 0.0157 Δy = +12 ⎛ 9.62 +12.57 ⎞ 2 32.2⎜ ⎟ 2 Example – Pressure Pipe Juncon ⎝ ⎠ Q V − Q V − Q V cosθ − Q V cosθ (SF + S f ) Δy = 2 2 1 1 3 3 3 4 4 4 + L 1 2 (A + A ) struc 2 g 1 2 Example – Pressure Pipe Juncon 2 Example – Pressure Pipe HGL Analysis

Downstream water surface or HGL1

HGL1 = EGL1 – Hv = 204 – 3.52 = 200.48 or D1 = 200.48 – 193.45 = 7.03 * pipe is under pressure 1/ 2 1/ 2 ⎛ Δ ⎞ ⎛ 60 ⎞ hbend = kb (H v ) = 0.25⎜ ⎟ (H v ) = 0.25⎜ ⎟ (3.52) = 0.74 ft ⎝ 90 ⎠ ⎝ 90 ⎠ Pressure Pipe HGL Example (cont.)

Upstream EGL2 and HGL2

hmh = Kmh (Hv) = 0.10 (Hv) = 0.10 (3.22) = 0.35ft

EGL2 = EGL1 + ∑hL = 204.0 + 9.16 + 0.74 + 0.35 = 214.25

Example – Pressure Manhole Pipe Expansion – No Flow Change Example – Connector Pipe Hydraulics

EGL3 = Inside catch basin = EGL2 + hen = 215.96 + 0.2 (1.42) = 216.24 - where entrance loss into catch basin = hen = ken (hv) where ken = 0.2 - check pipe inlet control using FHWA “Inlet Control Nomograph for Concrete Pipe” with groove end head wall 0r H.W. = 8.9(1.25) = 11.12 ft Example – Pressure Pipe with Hydraulic Jump Upstream Part Full

PP – PF = MF - MP

3 2 2 2 cd – (0.784) d (D1 – d/2) = kF (Q/d) – kp (Q/d) D − dia. x = 1 S S o − f Example – Locaon of Pressure Pipe Unseal – Subcrical Flow

• if x > Length (L) of pipe reach, then reach flows under pressure • if X < L, then pipe reach unseals 1 2 Pipe Juncon Analysis – Open Channel (A A ) 1 + 2 (Ζ + D1 − D2 ) =

Supercrical check: Hydromodificaon Local Hydrologic Cycle – Urban Development Modificaon Urbanizaon Impacts to Watersheds • Impervious surface area increase • Runoff conveyance system (pipes) – More efficient hydraulics • Landuse is changed (formerly natural vegetaon) • Topography is modified • Development encroaches on stream corridor • Stream may be engineered including channelizaon and hardening Urbanizaon Impacts to Runoff Hydrology • Increased runoff volume • Increased peak flowrate • Reduced me of concentraon • Increased flow frequency • Reduced infiltraon (groundwater recharge) • Modified flow paerns • Loss of surface storage • Increased temperature (thermal impacts) • Reduced sediment sources • Stormwater pollutants /bacteria • Non-stormwater discharges Urbanizaon Impacts/Changes in Runoff Hydrograph Response What is Hydromodificaon “Hydromod”? • Focus on changes to the downstream streams that changes in hydrology causes • Urban Related Hydromodificaon – Increase Imperviousness – Changes in runoff volume and frequency – Changes in sediment supply – Direct channel changes • Hydromodificaon Impacts – Increase Erosion – Sediment Changes – Habitat Loss / Degradaon – Bio/ecological Impacts Convenon Development Hydromodificaon Impacts

Urbanizaon Changes in Urban Observed Stream Changes Storm Runoﬀ and Channel Responses Watershed Stream Flow to Hydrologic Hydrology Changes

• Increased • Increased peak • Increased stream Imperviousness runoff rates erosion • Efficient conveyance • Faster Response • Enlarged channels • Vegetave cover • More frequent • Deeper/wider • Topography runoff events • Flooding problems • Landuse • Higher flow • Habitat damage • Flow diversions velocies • Increase • Riparian • Sediment supply sedimentaon / encroachment change erosion • Sediment size change LID Hydromodificaon Migaon What is “Low Impact Development” (LID)? • LID is site development strategy that emphasizes integraon of site planning and best management pracces that mimic natural hydrologic funcons of the site 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 – Ulizes techniques that infiltrate, filter, store, evaporate, and detain stormwater close to the sources – Stormwater is treated in small cost effecve landscape features through the site instead of just at the “end of pipe” What are the Problems with Tradional Stormwater Management Tradional stormwater pracces are designed to control peak flow of runoff and protect downstream properes from flooding •Don ’t provide for groundwater recharge •Don ’t promote base flow condions •Aren ’t designed to reduce bank-full condions in natural streams (i.e. stream stability) •Just beginning to address water quality treatment LID Residenal Site Design Common Types of LID Pracces • Disconnecvity (DCIA) • Bioretenon area / rain gardens • Porous pavement • Green roofs • Cluster development • Water harvesng / rain barrels • Integrated manmade lake systems • Infiltraon trench • Soil Amendment • Inlet Retorfits • Green space / vegetated buffers • Constructed wetlands • Dry wells • Enhanced open swales Example - Bioretenon Facilies

• Soil and plant-based ﬁltraon device • Removal Mechanism – physical – biological – chemical

Bioretenon along Streets Flow Through Planters Bioretenon Examples Commercial Installaon Bioretenon Facilies

• Soil and plant-based retenon or ﬁltraon device • Removal Mechanism – physical – biological – chemical – Straining • Have two types of designs that have emerged: – Classic retenon design – Flow through ﬁlter

How much space do I need?

WQV A = hf • A = Bioretenon cell area, 2 • WQV = Water quality volume, 3

• hf = Average design ponding depth, (tradionally a maximum 1 of ponding, 0.5 preferred) Design Guidelines

• Design storage area to accommodate the WQV with a maximum of 1 of ponding • Offline design is preferred (flow by-pass aer unit is ‘full’) • Soil Matrix: 50% sand (ASTM C-33), 20% compost, 30% site soil (max 5% clay content, porosity 0.25, 1.5 to 3% organic maer) • Depth to GW: 2’ with underdrain, 10’ without • Depth of soil matrix: 2.5 to 4 feet – based on root depth of planngs and volume needed for storage Design Guidelines (Con’t) • Storage area below the underdrain is required for nitrate removal (1 foot deep min). • Can add dead storage below the underdrain to accommodate hydromodificaon or other migaon requirements • Underdrain – 4” PVC perforated pipe (Sch 40), two should be used that join at a 6” dia pipe – slope 0.5% or greater. • Use a graded gravel filter bed: perforated pipe surrounded by a pea gravel diaphragm (1/4” to ½” dia, 6” thick) surrounded by stone ½” to 1.5” in diameter. Hydrologic Analysis of LID Part of Design Decision Making Process • Objecve of the LID design is to maintain exisng runoff volumes and peak runoff rates • Ulizes basic hydrology principles discussed • Focus on hydrologic characteriscs of site • Runoff volume correlates directly to Runoff CN • Time concentraon influences peak flow rate • Evaluate exisng condions and development condions without LID to determine impacts How does LID influence Site Hydrology LID Techniques to Reduce Development CN LID Techniques to reduce Development Time of Concentraon Example Calculaon –Runoff CN LID Analysis Example: 1 acre residenal lot 20% impervious and 80% open space

Step 1: Exisng condion soil group B with “Woods” in fair condion cover • SCS Curve Number = 55 Orange County – 85th Percenle Rainfall Mapping Example Calculaon –Runoﬀ CN LID Analysis

Step 2: Convenonal CN without LID

Example Calculaon –Runoﬀ CN LID Analysis Step 3: Low Impact Development CN

Example – Amount of Site Stormwater Volume Retenon

Example: Same 1.0 acre site calculate retenon volume requirements to apply with LID features to migate CN=63 to CN = 55. Assume design storm is 3.0 inches. •Runoﬀ Volume Increase = Post Development Volume – Pre-development Volume

Example – Amount of Site Stormwater Volume Retenon Example – Amount of Site Stormwater Volume Retenon