1. Basic Hydrology & Hydraulics: DES 601
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Solids Transport and Stormwater Management Concepts

2. What is sediment? Matter that settles to the bottom of a liquid
Matter transported by water or wind
May be particles that are derived from rocks, biological materials, or chemical precipitates
Highway sediments may be a mix of materials, including pavement dust, natural soils, vehicle rust particles, tire dust particles.
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3. Soil erosion (scour)
Caused by impact and dislodgment of individual soil particles by rain drop impact.
Caused by flow of water over soil surfaces.
Caused by movement of water in channel systems.
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4. Erosion and transport mechanisms
Rill and sheet erosion
Gully erosion
Bed and bank erosion
Suspended material transport
Bed material transport
Wash load transport
Australian Dept. of Environment
Rill erosion progressing to gullies
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5. Suspended material transport
Channels accumulate sediment from sheet/rill and gully erosion
Lighter sediment carried as suspended material
Heavier materials settle to bottom, added to material eroded from banks and bed
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6. Bed material transport
Stream bed load is part of total sediment load that moves along bottom of channel
Sediment particles roll, bounce, or slide along bottom
When stream has ability to re-suspend, some of particles will move
When it loses ability to carry particles in suspension, they will drop out again
Depends on local stream velocity and settling velocity of individual particles
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7. Wash material transport
Material that tends to flow through a reach without significant interaction with the bed
Material is usually coarse sand, smaller in size
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8. Solids transport – bed & suspended load
El Paso District
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9. Solids transport – bed & suspended load
Terrell County
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10. Solids transport – debris
Also have bouyant solids (debris) in the flow
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11. Storm Water Defined in Construction General Permit as Rainfall runoff;
Snow melt runoff;
Surface runoff and drainage.
Defined in the HDM 13-2 as
Overland flow
Flow in ditches
Flow in storm drain
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12. Storm Water Management
Structural (ditches, ponds, etc.) and non-structural measures to
Control quantity (how much)
Arrival time (when)
Quality (how dirty)
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13. Best Management Practices
Practices to mitigate quantity and quality issues
Processes
Street cleaning
Scheduling
Devices
Detention ponds
Rock filter dams
Vegetative buffer
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14. Best Management Practices
Water quality issues tend to dominate design practice.
Practices need not be “devices”
Construction activities
Erosion control
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15. Storm Drain Systems
EPA NPDES municipal separate storm sewer systems influence BMP selection
Edwards Aquifer Recharge Zone (TNRCC) also influences BMP selection
Division of Environmental Affairs
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16. Erosion Control
Turbidity (cloudiness) and Total Suspended Solids are used as regulated parameters for Storm Water Management – Erosion control greatly influences these parameters
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17. Erosion Control Flat side slopes in channels, swales, etc.
Protection at culvert outlets
Berms and similar protective devices
Rock filter dams are temporary sediment controls that can be left in place and eventually become a berm that self-seeds and provided hydraulic detention as well as vegetative buffering
Ground cover selection
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18. Erosion Control Select route where erosion is unlikely
Design slopes flatter than required by soil considerations
Reduce area of unprotected soil exposure
Reduce duration of unprotected soil exposure
Protect bare soil with vegetative cover, mulch, erosion resistant materials
Retard (delay) runoff with engineered devices (ponds)
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19. Channels and Chutes
Surface channels to carry storm water with minimal erosion – velocities are important
Chutes (steep channels) carry water at high velocity – energy dissipation is vital
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20. Quantity (How Much) Management
Storage
Delays arrival at a location
Infiltration
Increases rate of water flow into soil
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21. Hydraulics as pre–requisite
Generally the hydraulics of storm water management is accomplished by various approaches discussed earlier in the course
There is some added effort in velocity management (to control erosion) and sizing storage facilities
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