Integrating Spatial Informationfor Community-Based Management

of a Hillside Watershed

J.C. Luijten1, E.B. Knapp2, J.W. Jones1

1 University of Florida, Gainesville, FL2 International Center for Tropical Agriculture, Cali, Colombia

Presentation at the session “Agricultural Systems Designed for Ecological and Social Benefits”, 90 th Annual Meeting, ASA/SSSA/CSSA, Baltimore, MD, Oct 18-22, 1998

The Watershed

• Hydrologic perspective:

Synonym for drainage basin or catchment area.

• Systems perspective:

A complex and dynamic ecosystem, with a hydrological basis, and in which natural processes occur, agricultural and/or industrial activities take place, and people interact with each other and with their natural environment.

Watershed Characteristics• Watersheds components (land and water resources, people, farms,

industries, organizations, etc.) exist in association with one another and interact with their environment. The human factor is important!

• Watersheds have hydrological and ecological functions, and provide communities and their members with human needs and services.

• Watersheds provide a vehicle to consider critical linkages between upstream & downstream effects and on-farm & off-farm effects.

• A watershed is a useful scale on which to address multiple stakeholders and common property/open access resource issues.

Colombia, South AmericaRio Cabuyal Watershed(3,245 ha, in Departmento del Cauca)

Equator

Spatial extent:W 76o36’20” - 76o28’30”N 2o41’16” - 2o52’08”

20 km

14.5 km

Digital Elevation Model

1200-12501250-13001300-13501350-14001400-14501450-15001500-15501550-16001600-16501650-17001700-17501750-18001800-18501850-19001900-19501950-20002000-20502050-21002100-21502150-22002200-22502250-23002300-2350

Metersabove MSL

20 km

14.5 km

Cabuyal watershed,Colombia

N

S

Watershed Management

• Decision makers and watershed managers aim at minimizing conflicts and guiding future development in directions that are desirable for local communities and the natural resource base.

• It has been recognized that environmental and natural resource problems communities face can be addressed effectively through collective action across the entire watershed.

• Accurate data on the state of resources and DSS allow decision makers to systematically analyze options for future resource use.

Generic Modeling and Simulation Approach

Decision Support System

• A suite of GIS-based tools for information supply- water routing; stream and sub-basin delineation.- statistics and indicators on watershed characteristics.

• A GIS-based Spatial Water Budget ModelA continuous, watershed scale, grid-based simulation model that estimates water supply and demand over space and and time.

(a) land unit water balance(b) water flow to streams(c) stream water flow(d) water storage in reservoirs(e) water use (agricultural, industrial, domestic)

Materials

• Software- ArcView GIS 3.1 with Spatial Analyst extension- Soil Water Balance Model is entirely written in Avenue

• Basic Spatial Data- Digital Elevation Model

- Climate, farm and industry locations, communities

- Soils, geology, land use (Landsat TM imagery)

• Domestic, industrial and agricultural water demand

Impervious Rock bed

Soil Layer 1(root zone)

PIR

RO

D

ET

LF

Soil Layer 2

Soil Layer 3

P = Precipitation

IR = Irrigation

ET = Evapotranspiration

LF = Lateral Flow

RO = Surface Runoff

D = Drainage

Land Unit Water Balance

Stream Water Flow

VRO, j

VLF, j

VUSE, j

Vj-1,j

Vj ,j+1

VST, j

V j,j+1 = daily flow volume from stream cell j to j+1, m3/dV RO,j = surface runoff into stream cell j, m3/dV LF,j = lateral flow into stream cell j, m3/dV USE,j = water extracted from stream cell j, m3/dV ST,j = water stored in stream cell j, m3/d

LandStream

Water Extraction

• Numerous water extraction points anywhere in the stream.• Different water volumes can be extracted each day.• Simulation performed on a daily basis.

• Example water uses:- irrigation- domestic use- cassava and coffee processing industries- reservoir management

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50

60

70

80

90

100

1 31 61 91 121 151 181 211 241 271 301 331 361 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rio Ovejas, measured and simulated stream flow, 1974100

90

80

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20

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0

m3s-1

Simulated streams and flow rates (minimal 5 l/s), Cabuyal

2 3 4 1

Flow at Outlet1: 50 l/s (Aug.)2: 200 l/s (Oct.)3: 500 l/s (Nov.)4: 2000 l/s (Jan.)

NW flowdirection

Distance to streams, Rio Cabuyal watershed

Mid season Dry season

0 - 100100 - 200200 - 300300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900900 - 1000

> 1000

0 - 100100 - 200200 - 300300 - 400400 - 500500 - 600600 - 700700 - 800800 - 900900 - 1000 > 1000

Wet season

Meters