ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
ISPRS
128
MODELING LAND USE EFFECT ON URBAN STORM RUNOFF AT THE WATERSHED SCALE
Chansheng HE
Department of Geography
Western Michigan University
Kalamazoo, Ml 49008-5053, U.S.A.
KEYWORDS: AGNPS, GIS-interface, simulation, and nonpoint source pollution.
ABSTRACT
Assessment of land use impact on water quality at the watershed scale is essential to watershed management. This paper integrates
GIS and AGNPS (Agricultural Nonpoint Source Pollution Model), a computer simulation model to analyze the effect of land use change
on nonpoint source pollution in a study watershed. ArcView Nonpoint Source Pollution Modeling (AVNPSM), an interface between
ArcView GIS and AGNPS is developed in support of agricultural watershed modeling. The interface is PC-based and operates in a
Windows environment. It consists of five modules: a parameter generator, input file processor, model executor, output visualizer, and
statistical analyzer. Basic input data to the interface include: soil, digital elevation model, land use/cover, water features, and
management practices. Application of the AVNPSM to the study watershed indicates that it is user friendly, and robust, and
significantly improves the efficiency of the nonpoint source pollution modeling process.
1. INTRODUCTION
The Dowagiac River is a major tributary of the St. Joseph River
in southwestern Michigan, U.S.A. Its total drainage area is
73,435 hectares. Agriculture is the major land use in the
watershed, accounting for 61 percent of the total land. Corn,
soybeans, hay, and wheat are the major crops, representing 98
percent of the harvested crop acreage (Michigan Agricultural
Statistics Service 1994; 1995; 1996).
In recent years, local communities and the Michigan
Departments of Environmental Quality and Natural Resources
have formed a MEANDRS (Meeting Ecological and Agricultural
Needs within the Dowagiac River System) group to restore and
enhance the ecological and agricultural capacity of the
Dowagiac River Watershed. Implementation of this goal requires
assessment of land use and its impact on water quality and
identification of critical area for targeting the management
practices in the entire watershed. This paper describes the
function of ArcView Nonpoint Source Modeling (AVNPSM), a
Windows-based interface in facilitating watershed modeling and
its application in analyzing the effect of the land use change on
water quality of the Dowagiac River Watershed and identifying
areas with high potential of surface runoff, sediment, nitrogen
(N), phosphorus (P), and chemical oxygen demand (COD) yield.
2. ANALYSIS PROCEDURE
A watershed is a hydrologic system that consists of all the
tributaries and drainage areas from upstream to its mouth.
Analysis of a watershed must consider all the interacting factors
in the entire watershed. In assessing the land use impact on
nonpoint source pollution in the Dowagiac River Watershed,
these factors include precipitation, topography, land cover, soil,
hydrography, and management practices. In order to integrate
all these factors in this project, a computer simulation model,
Agricultural Nonpoint Source Pollution Model (AGNPS) (Young
et al. 1987) is used to estimate soil erosion, sediment loading,
and nutrient (N, and P) yields and to identify the critical areas in
the Dowagiac River Watershed. A unique feature of the AGNPS
is that it links the upper reaches to the downstream reaches in
simulating the hydrologic and sediment transport processes and
makes it possible to assess the effect of upstream land use
practices on the water quality of the river downstream.
2.1 Model Description
AGNPS (Version 5.0) is a single storm-event based simulation
model for evaluating sediment and nutrient transport from
agricultural watersheds (Young et al. 1987; USDA
Agricultural Research Service 1995). The model includes three
basic components: hydrology, erosion and sediment, and
nutrients (N, P, and Chemical Oxygen Demand). The hydrologic
component calculates overland runoff (in inches) and peak flow
rate (in cubic feet per second ) based on the SCS (Soil
Conservation Service) curve number equation.
Km, w • SS (1)
(Sfornt Mfall + 0.8* MnicH Factor)
Where storm rainfall represents total rainfall from a storm in
inches, and retention factor is calculated by Eq. 2:
Retention Factor 3 — - 10 (2)
Curve Number
Where the curve number is the SCS Curve Number, which is
related to soil and land use factors.
Upland erosion is computed based on the Universal Soil Loss
Equation (USLE):
Where, A is the computed average soil loss per unit area,
expressed in tons/acre; R is the rainfall and runoff factor and is
the number of rainfall erosion index (El) plus a factor for runoff
from snowmelt or applied water; K is the inherent erodibility of a
particular soil; L is the slope-length factor, S is the slope-
steepness factor; C is the cover and management factor; P is
the support practice factor; and slope shape factor represents
the effect of slope shape on soil erosion (1.0 for uniform slope
shape, 1.3 for convex slope shape, and 0.88 for concave slope
shape) (Wischmeier and Smith 1978).
In the nutrient component, AGNPS divides nutrient transport into
the soluble nutrients, which are transported in the runoff, and
the sediment nutrients, which are transported in the sediment.
The soluble nutrients (N and P) are the amount of initial soluble
N and P in the top 1 cm of soil prior to the rainfall event in
Ibs/acre (or kg/ha). Sediment attached nutrient is the amount of
nutrient (N or P) contained in the sediment.
AGNPS works on a cell basis. The amount of nutrients (N and P
and COD) is calculated for each cell. The nutrients from the
cells flowing into the current cell are added to the amount that
was generated within the current cell. The calculated amount is
decayed as it runs through the channel to get the amount
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