3/2/2015

Watersheds as a planning unit

Recommended Watershed Terminology

• Region Subregion Basin Subbasin Watershed Subwatershed Drainage Site

http://www.watershed.org/?q=node/187

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USGS Regions, Sub‐basins

USGS Regions (2 digit) USGS Sub‐regions (4 digit)

Hydrologic Unit Codes (HUC) USGS Sub‐basins (8 digit)

Basins as a Planning Unit http://www.portal.state.pa.us/portal/server.pt/community/state_water_plan/18721

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Watersheds as a Planning Unit http://www.dcnr.state.pa.us/brc/rivers/riversconservation/

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Map Scale • 1:100,000 = representative fraction or ratio

Streams ‐ Small vs. Large Scale representations in a GIS

1:100,000 1:24,000

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Watersheds

Definition: Area of land that drains water to a specific point or water body

Watershed boundary (surface water divide)

Drainage Area

Terminology: Watershed outlet (pour‐point) Catchment ‐ area of land receiving rainfall Watershed ‐ area of land draining water Sub‐watershed, Basin, Sub‐Basin, Regions…

WV Sub‐basins

USGS 8‐Digit sub‐basins in WV

1:250,000

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NRCS Watersheds

NRCS 10 and 12 watersheds in WV (5th and 6th level)

1:24,000

Watershed ‘Scale’

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Watershed as a planning unit

Watershed Attributes Other Topographic Attributes:

‐ Drainage Patterns ‐ Drainage Area ‐ Length ‐ Average Slope ‐ ‐ ‐ Shape factors

Help us understand the natural behavior of watersheds

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Understand Geomorphology

• Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical or chemical processes operating at or near Earth's surface – (from Greek: γῆ, ge, "earth"; μορφή, morfé, "form"; and λόγος, logos, "study")

• Geomorphologists seek to understand why: – landscapes look the way they do (current) – to understand landform history and dynamics (past), and – to predict (future) changes through a combination of: 1. field observations, 2. physical experiments, and 3. numerical modeling

• Geomorphology is practiced within physical geography, environmental planning, geology, geodesy, engineering geology, archaeology, and geotechnical engineering

• This broad base of interests contributes to many research styles and interests within the field

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Watershed Attributes

Drainage Patterns

http://maps.psiee.psu.edu/ImageryNavigator/

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Dendritic Drainage Pattern

Dendritic drainage systems are the most common form of drainage system

• There are many contributing which are then joined together into the of the main river

• They develop where the river channel follows the slope of the terrain

• Dendritic systems form in V‐shaped valleys

• As a result, the rock types must be impervious and non‐porous

Parallel Drainage Pattern

This system forms on uniformly sloping surfaces

• A parallel drainage system is a pattern of caused by steep slopes with some relief

• Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction

• streams tend to stretch out in a parallel‐like fashion following the slope of the surface

• A parallel pattern sometimes indicates the presence of a major fault that cuts across an area of steeply folded bedrock

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Trellis Drainage Pattern

Trellis drainage is characteristic of folded mountains, such as the Appalachian Mountains in North America

• The geometry of a trellis drainage system is similar to that of a common garden trellis used to grow vines

• As the river flows along a strike , smaller tributaries feed into it from the steep slopes on the sides of mountains

• These tributaries enter the main river at approximately 90 angles, causing a trellis‐like appearance of the drainage system

Radial Drainage Pattern

In a radial drainage system, the streams radiate outwards from a central high point

• Volcanoes usually display excellent radial drainage

• On these features the drainage may exhibit a combination of radial patterns

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Valley Fill

http://blogs.wvgazette.com/coaltattoo/2009/03/25/epa-on-mountaintop-removal-whats-it-all-mean/

WV Physiographic Provinces

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Drainage Patterns and Physiography

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Map Measurements

Area: example... ‐ 1 grid cell = 10 acres ‐ # cells x grid area = DA

http://www.pasda.psu.edu/default.asp

Measurements

Area: example... ‐ 1 grid cell = 10 acres

40 cells = 400 acres

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Watershed Shape Factor

Drainage Area (Main Channel Length)²

The size, shape and relief of the 1 basin are important controls. Water takes longer to reach the trunk 2 stream in a large, round basin than in does in a small, narrow one

Basic Hydrograph

Hydrograph (or storm graph) plots discharge in cubic meters per second (cms) over time (could be hours or days

The shape of the graph varies dependent on the number of contributing features that influence flow

Base flow = ‘normal’ and is from groundwater seeping into the channel

Rising limb = indicates rapid increase due to rain event

Peak flow = when river reaches its maximum level

The time difference between peak of the rain event and peak discharge is the lag time (basin lag)

http://www.bbc.co.uk/scotland/education/int/geog/rivers/hydrographs/index.shtml

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Influence of Steepness

Where gradients are steep, water runs off faster, reaches the river more quickly and causes a steep rising limb

Prolonged heavy rain causes more overland flow than light drizzly rain

http://www.bbc.co.uk/scotland/education/int/geog/rivers/hydrographs/index.shtml

Stream Order

• Strahler Stream Order

“3rd order watershed”

Also Shreve, Horton

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Stream Measurements

Flow length: ‐ Length of each stream reach

Avg. slope: ‐ΔElev./Flow length

Streams ‐ Small vs. Large Scale representations in a GIS

1:100,000 1:24,000

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Bifurcation Ratio

Bifurcation Ratio expresses the ratio of the number of streams of any giver order to the number in the next lower order or The slope of a line relating number of streams to stream order

#(n) order B.R.= #(n+1) order

Bifurcation Ratio • If the bifurcation ratio of a river network is low, there is a higher chance of flooding

• The water will be concentrated in one channel rather than spread out, as a higher bifurcation ratio would indicate

• The bifurcation ratio can also show which parts of a is more likely to flood, comparatively, by looking at the separate ratios

• The of a river, typically found by following the branch with the highest Strahler number

• Gleyzer et al. (2004) describe how to compute Strahler stream order values in a GIS application • This is implemented by RivEX, an ESRI ArcGIS 10.2.1 tool • The input to their algorithm is a network of the center lines of the bodies of water, represented as arcs (or edges) joined at nodes • Lake boundaries and river banks should not be used as arcs, as these will generally form a non‐ network with an incorrect topology

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Drainage Density

Drainage density is simply a length per unit of area -Usually ranging from 1 to 1,000

Stream Length Drainage Density = Drainage Area

Regional Curves

QaDA ()b a, b = fitting coefficients DA = drainage area

Sherwood, J., Huitger, C, 2005. Bankfull Characteristics of Ohio Streams and Their Relation to Peak Streamflows, Scientific Investigations Report 2005‐5153

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Hydrologic Response

• Watershed attributes influence runoff response, (along with landuse/landcover, soils…)

Response Type Characteristic (1) "Flashy" (2) "Sluggish" Area Small Large Drainage Density High Low Shape Equidimensional Elongated Slope Steep Flat Soils Thin Thick Vegetation Sparse Dense

Hydrologic Cycle

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Compartments

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