Working with Natural Stream Systems

Transcription

1 Working with Natural Stream Systems Graydon Dutcher Delaware County Soil & Water Conservation District Stream Corridor Management Program

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7 Tropical Storm Sandy October 29,2012

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9 What is a Watershed? The area of land in which all precipitation (rain, snow, etc.) that falls on it drains to a common waterway, such as a stream, lake, estuary, wetland, aquifer, or even the ocean. 9 Adapted from EPA Website, 2009

10 Why Do Streams Look the Way They Do? Geology Slope Soils Amount of water Timing Duration Magnitude Landuse Vegetation Infrastructure

11 Streams obey certain physical laws Properly size itself to transport water and sediment Maintain its dimension, pattern and profile 11

12 Streams Move More Than Water As water moves over the land it picks up sediment, forming the stream channel Streams create and maintain their shape and size themselves, a result of: Volume of water Amount of sediment Type of sediment

13 Sediment Balance Streams are said to be in equilibrium when the volume of water is enough to transport the available sediment without building up the channel (aggrading) or cutting down the channel (degrading). Adapted from Applied River Morphology, Dave Rosgen,

14 Sediment Balance Based on their ability to transport sediment, streams adjust their: Shape Slope Size Shape Size All contents copyright? Arizona Board of Regents 14

15 Sediment Balance Shear Stress Measure of the force that makes the sediment move The deeper the water the greater the stress The steeper the stream the greater the stress Need to take these factors into account 15

16 How does the sediment stay in balance? Erosion: The wearing away of rocks, sediment and soils by the action of water, wind or a glacier. Degradation Deposition: The accumulation or laying down of matter by a natural process. Aggradation

17 Erosion Streambank

18 Erosion Mass failures

19 Erosion Mass failures

20 Erosion Lateral Migration

21 Erosion Hoof Shear

22 Erosion Bedrock Weathering

23 Deposition Center Bar

24 Deposition Transverse Bar

25 Deposition Side Bar

26 Deposition Mouth of Tributary

27 Deposition Undersized Hydraulic Structure

28 Deposition Point Bar

29 Point Bar Formation

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31 Two Main Stream Types Step - Pool Sequence - streams are usually found in the headwaters or on steep slopes Riffle - Pool Sequence - streams are usually found in the broad valleys and on flat slopes 31

32 Step-Pool Riffle-Pool

33 Stream Type: Step - Pool Adapted from Applied River Morphology, Dave Rosgen, 1996

34 Stream Type: Riffle - Pool Riffles Pools 34

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36 Floodplain Definition The floodplain is the area bordering a stream, constructed by the river and inundated during periods of high flow.

37 Floodplain Function Energy dissipation during flooding events Velocity and energy decreases Lowers flood peaks due to storage and infiltration Water released more slowly downstream Provide a place for debris and sediment to be deposited Natural process of topsoil formation

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41 Floodplain Drainage The floodplains are sloped so that the water drains back into the stream channel as water levels recede. Valley Wall Valley Wall

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43 Floodplain The floodplain is part of the river during storm conditions 43

44 Today s Floodplains are not necessarily Tomorrow s floodplain If large areas of the floodplain are filled, then there will be an increase in the land area needed to store flood waters. This means your home, farm, or business may be impacted.

45 Development on the Floodplain Buildings Bridge approaches Roads Parking lots Etc.

46 Development on the floodplain can lead to significant stream issues including erosion & infrastructure damage 46

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54 When the channel is disconnected from the floodplain Velocity and energy of Stream increases Erosion increases More damage to infrastructure from debris The flood stage is higher 54

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56 Headcut Definition Instability that progress upstream and downstream from a local disturbance. 56

57 Headcut 57

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59 Would you work here? Single channel Meanders Floodplain 59

60 Is this what you would do here? 60

61 The lack of a floodplain will cause the stream to build one to maintain its natural functions. 61

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65 This downstream adjustment created a head-cut upstream 65

66 This slope was actively migrating as the stream continued to lower its bed to adjust its profile. This increased potential risk to those downstream. 6+ feet 66

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70 Channel Straightening

71 Channel Straightening

72 Channel Straightening Shorter distance means a steeper slope 400 Straightened Channel A steeper slope increases velocity A steeper slope increases erosion on the streambank and bed 500 Meandered Channel 72

73 Channel Straightening - Repair

74 Dredging After R. Hey,

75 Berms

76 Berms Failure

77 Berms Failure

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82 DCSWCD Contact Information Delaware County SWCD 44 West Street, Suite 1 Walton, NY (607) (Stream Program) Rick Weidenbach Executive Director Graydon Dutcher Stream Program Coordinator Tom Mallory, PE Stream Program Engineer Gale Neale, Joel Fisk, Stream Program Technicians Jessica Rall, & Jeff Russell Stream Program Technicians Catherine Skalda Catskill Stream Buffer Initiative Coordinator

83 Questions? Graydon Dutcher CPESC Delaware County Soil and Water Conservation District Stream Management Program Coordinator (607)