ch 7 water and land use

8/3/2019 Ch 7 Water and Land Use

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Water & Land Use



The Hydrologic Cycle



Rainfall Intensities,

10-year, 24-hour storm



Intensity-Duration-Frequency Curves for Seattle and Miami,both of which receive about 48 inches of rainfall per year



Precipitation rate and infiltration rate determine the runoff rate.

Infiltration rate depends on soil texture, soil moisture, and vegetative cover.



Stream Order



Watershed Characteristics

Boundary or Divide

Watershed area

Basin length: the

distance from thefirst order channelfurthest upstream tothe basin outlet

Drainage density:the length of all thechannels divided bythe basin area

Perennial streamsrun all year long

Intermittent streams

run in wet seasonEphemeral streams run during andimmediately afterstorms



Delineating

Watersheds

on topographic

maps:

8 steps



Delineating Watershed Boundaries1. Identify the outlet point on a stream or river that defines the watershed

draining to that point.

2. Find and trace drainage channels within the watershed. On color topomap, they are blue lines. “V” shape of elevation contours point upstream.

3. Find and “X” out neighboring channels outside the watershed. Thewatershed boundary will be between the channels in the basin (step 2)and these outside channels.

4. Consider yourself a drop of water and check the direction of drainage byinspecting the slope direction between the “in” and “out” channels.

5. Find and mark the high points (peaks and saddles) between the “in”

and “out” channels. These will be on the watershed boundary.

6. Connect these points with light pencil, intersecting the contour lines atroughly a right angle.

7. Consider yourself a drop of water again and check where you would goif you fell inside or outside the line. Make corrections as necessary.

8. Finalize Map.



A

B



Delineating watersheds using GIS



Stream Meanders

and the Flood Plain



Changing centerline of Matapole River, California

over a 30-year period



bankfull width

Bankfull and floodplain definitions



The Hydrograph

(cubic feetper second)



Urbanization,

Impervious

Surface, and

the WaterBalance



Change in Hydrograph due to Urbanization

Peak Flow up, Base Flow down



Quantifying change in stream flow due to

land use change

Many methods and modelsRational method and TR-55 in book

We will apply Win TR-55 in assignment and WS next week



http://www.wsi.nrcs.usda.gov/products/W2Q/H&H/tools_models/wintr55.html





Relationship of % Impervious Surface of Watershed

to Stream Quality



Schueler, Fraley-McNeal, Cappiella, 2009

Schueler’s original Impervious Cover Model put another way



Reformulated Impervious Cover Model (ICM)

Schueler, Fraley-McNeal, Cappiella, 2009



Not just peak and base water flows that

impair streams….it’s water quality, too.Clean Water Act

Pollutants and effects

Water Quality Standards

Impairment of waters

Runoff and non-point sources (NPS)

Best Management Practices (BMPs), SMP, IMPs

Low Impact Development



37 Years of the Clean Water ActGoal: ―Fishable & swimable waters‖

Elimination of pollutant discharges

There has been significant improvement in the quality of natural waters from reduction of organic and sediment

discharges

BUT…

Continued impairment of waters

Problem shift from easy clean up of conventional pollution from

discharge pipes to harder clean up of runoff pollution and toxics

Have to move from technology-based effluent permits to TMDLs



Water Pollutants, Sources, Effects



Water Quality Standards:Step 1: assign beneficial uses to each water body/segment



WQS:Step 2: Establish standards for each beneficial use



States monitor their waters and group assessed

waters into the following categories:

1. Attaining WQS

a. Good/Fully Supporting: meets WQS

b. Good/Threatened: meets WQS but may degrade in near future

2. Impaired, Not Attaining WQS

a. Fair/Partially Supporting: meets WQS most of the time but

occasionally exceed them

b. Poor/Not Supporting: does not meet WQS

3. WQS not attainable

a. Use-attainability analysis shows that one or more designated uses

is not attainable because of specific conditions.



Impairment of Streams by Watershed

Impaired waters by watershed, 1998

Q lit f N ti ’ W t 2004



Quality of Nation’s Waters, 2004



2004

Rivers & Streams

1998: 35% impaired2004: 44% impaired



Top ten causes of impairment of rivers



Top ten sources of impairment of rivers

2004 Lakes



2004 Lakes1998: 22% impaired

2004: 64% impaired



Biggest problem now Nonpoint Sources



2008



Fairfax County Impaired 2004, 2006



Fairfax County Impaired 2006, 2008



And this despite significant efforts to improveStream Protection Strategy

Stormwater regulations for new development

MS4 program, 10 TMDL plans, extended RPAs

Watershed Management Program: 25-year priorities for improvement



Municipal Separate Stormwater System

(MS4) regulationsPhase I (early 1990s): MS4 in cities > 100,000 population

subject to NPDES permits (300,000 permits)

Phase II (2003): cities >50,000 (states extend to smaller)must obtain MS4 permit and develop a stormwater

management plan (SWMP) (200,000 permits)

Hard to manage, GAO (2007) and NRC (2009) critical of EPA program: ―EPA should take a watershed approach‖

EPA in national rulemaking for revamped program

Virginia is also revamping its stormwater regulations



Total Maximum Daily Load (TMDL)

approach for impaired watersDetermining the TMDL to achieve WQS – this often

requires sophisticated monitoring data and modeling of

discharges, receiving waters, and, for NPS, watersheds.

Allocating TMDL to sources— this requires factoring in

equity and economic considerations.

Basing permits of regulated sources on TMDL allocations

Managing unregulated sources to achieve TMDLallocations



Water Quality Trading

Use within TMDL plan to achieve WQS at lower cost

Takes a watershed approach to permitting

Coordinates point and non-point source controlsProvides compensation to farmers to control

their runoff pollution





Pollutant Suitability: compares

type/form of the pollutant and the timing

and alignment of the discharge within the

watershed, the supply and demand of

pollutant reduction credits, uncertainty of

non-point source controls, and the relative

water quality equivalence of each

discharger’s pollutant reduction. Financial attractiveness based on

relative incremental cost of control and

WQ equivalence.

Market infrastructure to assure

compliance with WQS and executing andmonitoring trades.

Stakeholder readiness and

engagement.

ch 7 water and land use

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