Jason R. Vogel, Ph.D., P.E. Biosystems and Agricultural Engineering Oklahoma State University

Transcription

1 Stormwater 101 OKLAHOMA STATE UNIVERSITY Biosystems and Agricultural Engineering Department Jason R. Vogel, Ph.D., P.E. Biosystems and Agricultural Engineering Oklahoma State University

2 Stormwater is excess rainfall that flows over land or through storm drains (not taken up by soil and plants) to streams and creeks Stormwater can pick up pollution and carry it to streams and lakes Rules and regulations try to prevent contamination of stormwater with pollutants

3 Stormwater causes: Flooding Transport of pollutants (sediment, nitrogen, phosphorus, lead and other toxics) to streams Erosion of stream channels 47 percent of oceans and estuary impairments 22 percent of lake impairments 14 percent of stream impairments

4 Point source pollution from a pipe or building From a person dumping oil or paint down a storm drain Concentrated sources, easily traced

5 Diffuse sources, not easily traced

6 The 1972 Clean Water Act (PL ) defined Point Sources and Nonpoint Sources. Point source: pollution that issues from a pipe or manmade channel. Nonpoint source: everything else. Storm Water is a blend of the two.

7 Industrial or Municipal Storm Water is considered a point source. Industrial or Municipal Storm Water is regulated by the state permit system. The Oklahoma Pollution Discharge Elimination System (OPDES).

8 Runoff from feedlots (CAFOs) Runoff from industrial storage areas Runoff from rooftops and parking lots in urban areas Runoff from construction sites Urban runoff from residential areas with fertilizer, pesticides, and pet wastes Does not include agricultural runoff

9 Storm Water causes: Flooding Carries pollutants (sediment, nitrogen, phosphorus, lead and other toxics) Causes erosion of stream channels Degrades aquatic habitat The 2002 EPA report says storm water causes: 47 percent of oceans and estuary impairments 22 percent of lake impairments 14 percent of stream impairments

10 Phase I (1992) cities over 100,000 population construction sites 5 acres and larger. Phase II (March 10, 2003) urbanizing communities population over 10,000 and density 1,000 per sq mile. (45 entities in Oklahoma) construction sites 1 acre and larger.

11 The state designates MS4s, municipalities and other entities that control separate storm water sewer systems in urbanizing areas. Some MS4s are designated because they discharge to sensitive waters. All MS4s must meet Phase II requirements

12 Construction site runoff control is required everywhere in Oklahoma because sediment is the number one pollutant in Oklahoma.

13 Sediment is the number one pollutant because It smothers fish spawning areas. It fills lakes and ponds. It carries other pollutants. It degrades habitat.

14 Land Use Change

15 Stormwater runoff Sediment production Chemicals in runoff Land productivity Channel properties and geomorphology Riparian zones Water quality Habitat

16 This diagram shows how development and its corresponding increase in impervious cover disrupts the natural water balance. In the post-development setting, the amount of water running off the site is dramatically increased.

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18 Runoff Coefficient (Rv) Relationship Between Watershed Imperviousness (I) and the Storm Runoff Coefficient (Rv) (Source: Schueler, 1987) Watershed Imperviousness (%) This graph shows that as the percentage of watershed imperviousness increases, the volumetric runoff coefficient increases as well.

19 This graph illustrates the effects of urbanization on hydrograph peak discharge. In predeveloped conditions, flow gradually increases to a relatively flat peak and gradually descends to a low flow condition. In the urbanized condition, flow rapidly increases to a peak and just as sharply descends, often to a lower flow condition than pre-development.

20 This stream has a surrounding area of approximately 30% impervious cover. The large amount of impervious cover has increased the size of the stream by a factor of five to ten. The manhole in the middle of the diagram was originally in the floodplain and is an indicator of the degree to which channel erosion has occurred. Photo Copyright 1999, Center for Watershed Protection

21 The stream pictured here has downcut several feet in elevation because of the increased stormwater flow. In this case, the forested wetland in the floodplain is now hydraulically disconnected from the stream that sustained it. Photo Copyright 1999, Center for Watershed Protection

22 Photo Copyright 1999, Center for Watershed Protection Embeddedness is another impact of urbanization and is characterized by the packing of pebbles or cobbles with fine grained silts and clays. This slide illustrates a relatively clean substrate with an isolated area of fouling.

23 In extreme examples of embeddedness, habitat, water and dissolved oxygen exchange become greatly reduced. Photo Copyright 1999, Center for Watershed Protection

24 This graph of a stream in the coastal plain of Delaware depicts the typical relationship between sensitive aquatic species as a function of impervious surface.

25 Studies by Devivo, et al. and Couch have shown that as human population densities increase, the Index of Biological Integrity, which measures the quality of the fish community, also decreases.

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27 Peak Discharte (cfs) Runoff Volume (ac-ft) Peak Discharge Runoff Vol Undisturbed Tilled Residental High Rise Land Use

28 Sediment Yield (tons) Peak Sed Conc (mg/l) Sediment Yield Peak Concentration Undisturbed Good Pasture Crop Land Construct Land Use

29 Ratio Undisturbed Forest Pasture Tilled Construction Land Use

30 Scour or deposition Widen or become more narrow Get deeper or shallower

31 Relative Value Width Depth 0 Undisturbed Good Pasture Crop Land Construct Land Use

32 Most Common Technology in Use Today

33 Stormwater basins come in a variety of shapes and sizes Basins under streets and - - with simple outlets parking lots Small basins Looking down into the basin inlet Looking down into the basin weir outlet

34 STORMWATER BASINS FOR CONTROLLING URBAN RUNOFF CONTINUED Large dry basins Large wet basins With permanent pools and weir outlets

35 Example: 1. A = 100 ac 2. Predisturbed = forest 3. Post disturbed = 60% imp 4. Predisturbed peak discharge = 42.3 cfs 5. Post disturbed peak discharge = cfs 6. Area required to match predisturbed= 4 ac 7. Percent of development required for basin = 4%

36 Example: 1. A = 100 ac 2. Predisturbed = forest 3. Post disturbed = 60% imp 4. Predisturbed runoff volume = 4.52 ac-ft 5. Post disturbed runoff volume = 24.4 ac-ft 6. Area required to match predisturbed using infiltration basin (sandy clay soil) = 66 ac 7. Percent of development required = 66%