Study guide
12.3 In-Water & Dewatering Controls: Temporary Stream Crossings, Turbidity Curtains, and Sediment Bags
Free CESSWI Certified Erosion, Sediment and Stormwater Inspector Study Guide 2026 Exam
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1 Chapter 1: CESSWI Program Overview, Scope of Practice & Professional Ethics
1.1 CESSWI Scope of Practice, Eligibility, and Exam Structure 1.2 Certification Renewal, PDH Requirements, and Audit Policies 1.3 EnviroCert Code of Ethics and Professional Conduct
2 Chapter 2: Federal, State, and Local Stormwater Regulations
2.1 Federal Water-Pollution History and Stormwater Phases 2.2 CWA Sections, Water Quality, and Related Federal Programs 2.3 EPA Construction Permit Coverage and Operational Clocks 2.4 Industrial MSGP and Municipal MS4 Programs 2.5 Regulatory Compliance, Enforcement Mechanisms, and Penalties
3 Chapter 3: Soil Mechanics, Erosion Processes, and Climatic Factors
3.1 Soil Formation, Horizons, and Geomorphology 3.2 Soil Texture, Mechanics, and Revegetation 3.3 Splash, Sheet, Rill, Gully, Channel Erosion, and Slope Movement 3.4 Wind Erosion, Sediment Transport, Climatic Erosivity, and Resource Impacts
4 Chapter 4: Hydrology, Runoff Characteristics, and Drainage Principles
4.1 The Hydrologic Cycle, Watershed Drainage Planning, and Precipitation 4.2 Hydrologic Soil Groups, Disturbed Profiles, and Time Parameters 4.3 Hydrograph Characteristics, Curve Numbers, and Runoff Estimation Equations
5 Chapter 5: Inspection Fundamentals, Duties, and Field Procedures
5.1 Inspector Roles, Scope of Authority, and Core Professional Skills 5.2 Pre-Inspection Document Review and Inspector Support Equipment 5.3 Systematic Field Inspection Sequence, Post-Inspection Meetings, and Follow-Through
6 Chapter 6: Inspection Elements for Active Construction Sites
6.1 Pre-Construction Meetings, Entrance Posting, and On-Site Document Inspections 6.2 Inspecting Active Construction Controls and Diagnosing BMP Failure Modes 6.3 Final Stabilization Verification, Final Inspections, and Notice of Termination
7 Chapter 7: Stormwater Monitoring, Field Sampling, and Chain of Custody
7.1 Permit Monitoring Triggers and Water-Quality Indicators 7.2 Sampling Preparation and Analytical Parameters 7.3 Sampling Locations, Collection Methods, and Field Meter Calibration 7.4 Sample Preservation, Data Recording, Shipping, and Chain of Custody
8 Chapter 8: Inspection Documentation, Reporting, and Map Management
8.1 Inspection Notes and Evidence Procedures 8.2 Objective Findings and Photographic Evidence 8.3 Proper Reporting Techniques and Corrective Action Log Management 8.4 Site Drawing (Map) Management, Compliance Resolution, and Enforcement Records
9 Chapter 9: Professional Communication and Site Safety for Inspectors
9.1 Communication Protocols in Pre-Construction, Post-Inspection, and O&M Meetings 9.2 Dealing with Difficult People, Problematic Sites, and Unpleasant Findings 9.3 Site Hazard Recognition: Physical, Biological, Trenching, and Confined Spaces 9.4 Hazardous Substances, Safety Data Sheets (SDS), Spill Response, and PPE
10 Chapter 10: Stormwater Plan Reading, Map Interpretation, and Site Calculations
10.1 Stormwater Plan Types, Credentials, and Authority 10.2 SWPPP Components and Permit Notifications 10.3 Civil Plan Sets, Legends, Phased Sequencing, and Living Site Maps 10.4 Topography, Contour Lines, Slope Calculations, and Plan Amendments
11 Chapter 11: BMP Framework, Site Planning, and Erosion Control Practices
11.1 Six Functional BMP Categories, Preservation of Vegetation, Phasing, and Tree Protection 11.2 Seeding and Sod Establishment 11.3 Hydroseeding and Hydromulching Inspection 11.4 Mulch and Rolled Erosion-Control Products 11.5 Tackifiers, Soil Binders, Roughening, and Temporary Cover
12 Chapter 12: Perimeter, Linear, and In-Water Sediment Control Practices
12.1 Perimeter & Sheet-Flow Sediment Barriers: Silt Fence, Fiber Rolls, Straw Bales, and Filter Dikes 12.2 Access & Roadside Sediment/Runoff Controls: Stabilized Entrances, Cut-Back Curbs, and Ditch Checks 12.3 In-Water & Dewatering Controls: Temporary Stream Crossings, Turbidity Curtains, and Sediment Bags
13 Chapter 13: Sediment Basins, Traps, and Runoff Conveyance Controls
13.1 Sediment Basins and Traps 13.2 Porous Baffles and Surface Skimmers 13.3 Runoff Conveyances: Diversions, Swales, Pipe Slope Drains, and Rock Check Dams 13.4 Riprap and Gabion Inspection 13.5 Retaining Walls, Outlet Protection, and Wet Ponds
14 Chapter 14: Storm Drain Inlet Protection and Good Housekeeping BMPs
14.1 Storm Drain Inlet Protection: At-Grade, Curb, Block & Gravel, Excavated, Fabric Drop, Gravel Bag, Stone Collar, and Pre-Manufactured 14.2 Good Housekeeping Part 1: Concrete Washout, Equipment Maintenance, Materials Management, and Secondary Containment 14.3 Good Housekeeping Part 2: Stockpiles, Dust Control, Wind Fence, Street Cleaning, Sanitary Waste, and Trash
15 Chapter 15: Post-Construction Stormwater Management BMPs
15.1 Vegetative & Structural Dispersion BMPs: Final Ground Cover, Headwalls, Level Spreaders, Filter Strips, and Riparian Buffers 15.2 Permeable Surfaces and Construction Protection 15.3 Infiltration, Bioretention, and Media Filters 15.4 Detention, Retention & Proprietary BMPs: Dry/Wet Basins, Wetlands, Inline Storage, Catch Basin Inserts, Vaults, and Manufactured Devices
12.3 In-Water & Dewatering Controls: Temporary Stream Crossings, Turbidity Curtains, and Sediment Bags
Key Takeaways Explain This Topic AI
Temporary stream crossings require prior Clean Water Act Section 404/401 permits and rank from least to greatest impact as: (1) span bridge (preferred, zero fill below OHWM), (2) culvert crossing backfilled solely with clean coarse stone, and (3) low-water ford (ephemeral channels only)
A turbidity curtain is NOT a dam or bulk water filter; it creates a calm containment zone in lakes, rivers, or estuaries so suspended sediment settles downward within the curtain footprint
Turbidity curtains are classified into Type I (calm water), Type II (currents up to 1.5–2 knots / 2.5–3.5 ft/s), and Type III (tidal/severe currents up to 3 knots / 5 ft/s), must hang 1 to 2 feet above the bottom mud, and must never be deployed perpendicular across a flowing river
Dewatering sediment bags must rest on a flat vegetated buffer, gravel pad, or straw-bale platform with secondary perimeter containment, must be replaced when 1/2 full, and must meet the 2022 EPA CGP 50 NTU weekly average turbidity benchmark where applicable
Last updated: October 2026
Note
Using dimensions in this section: Construction dimensions, material sizes, slopes, cleanout fractions, and drawdown ranges below describe example practice details. Verify the approved design, manufacturer instructions, and applicable permit before using a number as an inspection acceptance criterion. Regulatory thresholds identified explicitly as EPA/OSHA requirements remain distinct.
Temporary Stream Crossings the approved practice detail
Allowing earthmoving scrapers, dump trucks, or excavators to drive directly through an unprotected stream channel crushes aquatic habitat, breaks down streambanks, and sends massive plumes of suspended sediment downstream. Whenever construction equipment must cross a stream, creek, or wetland corridor, an engineered temporary stream crossing is mandatory.
Regulatory Permitting Prerequisites
Because constructing a crossing in Waters of the United States (WOTUS) or state waters involves work below the Ordinary High-Water Mark (OHWM), the owner/operator must obtain prior regulatory authorization before any in-stream work begins:
Clean Water Act Section 404 Permit from the U.S. Army Corps of Engineers (USACE) (often under Nationwide Permit 14 for Linear Transportation Projects or NWP 33 for Temporary Construction, Access, and Dewatering);
Clean Water Act Section 401 Water Quality Certification from the state environmental agency; and
State Stream-Alteration / Fish and Game Streambed Permits (which frequently restrict in-water construction to dry-season work windows and prohibit blocking fish migration).
Three Structural Crossing Types (Ranked Least to Greatest Impact)
Crossing Type Structural Configuration Hydraulic & Ecological Impact Permitted Stream Conditions
1. Temporary Bridge (Span Bridge) Prefabricated modular steel bridge, timber crane mats on abutment sills, or flatcar spanning bank-to-bank above the OHWM Lowest Impact (Preferred): Zero fill in channel; zero obstruction to flood flows or fish passage Perennial streams, cold-water fisheries, high-velocity channels, and sensitive wetlands
2. Temporary Culvert Crossing Corrugated metal (CMP) or HDPE pipes laid on non-woven geotextile and backfilled exclusively with clean, washed coarse stone/riprap Moderate Impact: Temporary rock fill in channel; sized for 2-year to 10-year peak storm with armored overflow dip Small to medium perennial or intermittent streams where spanning is structurally infeasible
3. Temporary Ford (Low-Water Crossing) Non-woven geotextile pad topped with coarse riprap, gabion mattresses, or articulated concrete blocks flush with streambed Highest Crossing Disturbance: Tires pass through shallow water over armored bed Strictly limited to shallow intermittent or ephemeral channels with very low flow and infrequent crossings
Critical Siting, Approach Drainage, and Restoration Rules
Perpendicular Orientation at a Straight Reach: Position the crossing at a 90 ∘ 90^\circ 9 0 ∘ perpendicular angle across a narrow, straight stream reach with stable banks—never on an eroding meander bend.
No Earthen Fill in Culvert Crossings: Temporary culvert crossings must be backfilled from the geotextile bed to the driving surface exclusively with clean, washed coarse aggregate and riprap (topped with smaller crushed stone for traction). Never use native earthen soil as culvert backfill , as overtopping storm flows will wash the entire dirt fill embankment downstream.
Approach Road Cutoff Drainage: Dirty haul-road runoff must never run down the approach ramps into the creek. Install water bars or diversion swales on both approach roads 25 to 50 feet 25\text{ to }50\text{ feet} 25 to 50 feet back from the streambanks to divert road runoff into a vegetated filter strip or sediment trap before it reaches the crossing.
Complete Removal and Bank Stabilization: Immediately upon completion of construction access, remove all bridge mats, pipes, riprap fill, and geotextile during low-flow conditions, restore the original streambed contours, and stabilize disturbed banks with erosion control blankets and native riparian plantings.
Turbidity Curtains / Barriers the approved practice detail
A turbidity curtain (floating silt barrier) is a flexible, vertical underwater barrier suspended from floating surface buoys and weighted at the bottom by a ballast chain. It is deployed in lakes, reservoirs, ponds, rivers, or tidal estuaries to enclose shoreline or in-water soil-disturbing activities such as bridge pier cofferdam construction, dredging, bank riprap placement, or storm outfall installation.
Important
Crucial Exam Concept — A Turbidity Curtain Is NOT a Dam: A floating turbidity curtain is never designed to hold back or filter bulk water flow across a river channel . Approximately 95 % + 95\%+ 95% + of the curtain skirt is typically made of impermeable PVC- or vinyl-coated polyester geomembrane (only specialized panels use permeable geotextile windows). Its sole hydraulic function is to deflect ambient currents around the work zone and create a quiescent (calm) containment zone inside the curtain so suspended silt particles settle vertically onto the bed within the enclosed footprint before escaping into the open water body.
Structural Anatomy and Type I, II, and III Classifications
Every manufactured turbidity curtain includes four core structural assemblies:
Top Flotation Elements: Sealed expanded polystyrene or urethane foam logs wrapped in bright high-visibility yellow/orange PVC fabric, sized to provide at least 200 % 200\% 200% buoyancy (capable of supporting twice the submerged weight of the skirt and ballast).
Top Load-Bearing Tension Cable: In moving water (Types II and III), a galvanized steel wire rope ( 5 / 16 in. 5/16\text{ in.} 5/16 in. or larger) is sewn into a reinforced webbing pocket just below the floats so anchor forces pull on the steel cable rather than tearing the vinyl skirt.
Vertical Skirt: Impermeable PVC/vinyl geomembrane or heavy woven geotextile fabric joined in 50 - to 100 -foot 50\text{- to }100\text{-foot} 50 - to 100 -foot sections using reinforced grommeted, laced, or bolted seams.
Bottom Ballast Chain and Anchors: A continuous galvanized steel chain pocket at the bottom hem keeps the skirt hanging vertically against current lift, supplemented by Danforth/fluke bottom anchors and visible mooring buoys every 25 to 100 feet 25\text{ to }100\text{ feet} 25 to 100 feet .
Curtain Classification Hydrodynamic Environment Maximum Current Velocity Typical Wave Height & Structural Requirements
Type I Protected / Calm Water (ponds, small lakes, sheltered coves, canals) Zero to minimal current ( < 0.5 knot < 0.5\text{ knot} < 0.5 knot / < 1 ft/s < 1\text{ ft/s} < 1 ft/s ) Waves < 1 ft < 1\text{ ft} < 1 ft ; lightweight skirt, standard foam float ( 6 – 8 in. 6\text{–}8\text{ in.} 6 – 8 in. ), light ballast chain, no heavy tension cable required
Type II Moving Water / Moderate Conditions (rivers, streams, large lakes) Up to 1.5 to 2 knots 1.5\text{ to }2\text{ knots} 1.5 to 2 knots ( 2.5 to 3.5 ft/s 2.5\text{ to }3.5\text{ ft/s} 2.5 to 3.5 ft/s ) Waves up to 2 – 3 ft 2\text{–}3\text{ ft} 2 – 3 ft ; requires top load-bearing steel tension cable, 8 – 12 in. 8\text{–}12\text{ in.} 8 – 12 in. floats, heavy ballast chain, and intermediate anchors
Type III Severe / Tidal or Fast-Current Waterways (estuaries, coastal harbors, large rivers) Up to 3 knots 3\text{ knots} 3 knots ( 5 ft/s 5\text{ ft/s} 5 ft/s ) Waves > 3 ft > 3\text{ ft} > 3 ft and reversing tidal currents; heavy-duty steel tension cables, 12 – 18 in. 12\text{–}18\text{ in.} 12 – 18 in. floats, dual-anchor arrays (both sides for tides)
Mandatory Installation, Inspection, and Removal Rules
Maintain a 1 - to 2 -Foot 1\text{- to }2\text{-Foot} 1 - to 2 -Foot Clearance Above the Bottom Bed: The vertical skirt depth must be sized so the bottom ballast chain hangs 1 to 2 feet 1\text{ to }2\text{ feet} 1 to 2 feet ABOVE the streambed or lake bottom during normal low water. If the skirt is too long and rests in the bottom mud , wind waves and currents cause the heavy ballast chain to drag back and forth like a broom across the benthic sediment, resuspending more turbidity than the curtain prevents (and burying the skirt in silt so it cannot be retrieved without tearing).
Never Install Perpendicular Across a Flowing River: Installing a curtain at 90 ∘ 90^\circ 9 0 ∘ across a moving river forces the entire river discharge against the impermeable skirt; hydrodynamic drag will immediately drag the anchors, submerge the floats ("planing/diving"), or snap the tension cable. Always deploy the curtain parallel to the main river current or angled gently outward from the shoreline to deflect flow smoothly around the work cell.
Tidal Dual-Anchoring: In tidal estuaries where flow reverses direction twice daily, anchor the curtain on both the inside and outside so the skirt does not flip into the work zone at slack tide.
Removal Protocol: Never unshackle or drag a turbidity curtain out of the water immediately after dredging or bank grading stops! The curtain must remain stationary in place until all suspended turbidity inside the enclosure has settled back to ambient background levels ; then carefully unpin and fold the curtain onto the bank or work barge without agitating settled bottom sediment.
Sediment Bags / Dewatering Filter Bags the approved practice detail
Excavating utility trenches, bridge footings, or foundations below the water table—or drawing down a flooded excavation after a storm—requires pumping sediment-laden water. Pumping muddy trench or basin water directly into a storm drain inlet, roadside ditch, or stream is strictly illegal.
A sediment bag (dewatering filter bag) is a large, factory-sewn rectangular sack (typically 10 ft × 15 ft 10\text{ ft} \times 15\text{ ft} 10 ft × 15 ft or 15 ft × 15 ft 15\text{ ft} \times 15\text{ ft} 15 ft × 15 ft ) manufactured from heavy-duty, non-woven, needle-punched polypropylene geotextile. The pump discharge hose ( 2 - to 6 -inch 2\text{- to }6\text{-inch} 2 - to 6 -inch diameter) is inserted into a sewn spout sleeve and clamped tightly with a steel band clamp or heavy web strap so pumped water is forced through the three-dimensional geotextile pores under pressure.
Siting, Secondary Containment, and Regulatory Compliance
Siting on a Permeable, Non-Erodible Pad: Place the sediment bag on a flat or gently sloping well-vegetated buffer strip, a 6 -inch 6\text{-inch} 6 -inch bed of clean crushed aggregate, or an elevated platform of straw bales / timber pallets . Increasing under-bag drainage area prevents the bottom panel from blinding against mud and increases flow capacity.
Prohibited Siting: NEVER place a dewatering sediment bag on a steep or bare earthen slope! Water weeping rapidly out of all four sides of the bag will immediately coalesce and scour severe erosion gullies down the bare slope.
Secondary Perimeter Containment: Surround the downgradient side of the sediment bag pad with a secondary linear barrier (such as a silt fence J-hook or a compost filter sock) so filtered effluent spreads into shallow sheet flow across vegetation before reaching any conveyance.
2022 EPA CGP Part 3.3 Dewatering Inspection & 50 NTU Turbidity Benchmark:
Inspect dewatering operations at least once every day on which dewatering water is discharged.
Where the 2022 EPA Construction General Permit requires turbidity benchmark monitoring (for dewatering discharges to sediment-impaired or high-quality Tier 2/2.5/3 waters), collect daily grab samples of the effluent after the sediment bag and compare against the 50 NTU 50\text{ NTU} 50 NTU weekly average benchmark .
If the excavation contains visible oil sheen, floating grease, or petroleum contamination , a standard geotextile bag is insufficient—insert an oil-absorbent hydrophobic boom/pad inside or around the bag, or route water through an oil-water separator / granular activated carbon treatment system.
If clays and fine silts remain above 50 NTU 50\text{ NTU} 50 NTU , route the pump through a portable weir tank (frac tank) or approved anionic polymer flocculant dosing system prior to filtration.
Replacement at 1 / 2 1/2 1/2 Capacity: Shut off the pump immediately if the hose neck leaks, if seams split, or when the bag becomes 1 / 2 full 1/2\text{ full} 1/2 full of trapped sediment (or when pore blinding causes excessive ballooning/backpressure). Fold the spent bag closed, excavate or lift it with equipment straps, and dispose of or stabilize the dewatered spoil upland.
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