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Cropping Area Assessment in Flood Prone Areas Using Gis

Md. Omar Faruk
Agricultural Engineer
EGIS, Hous-49, Road-27. Banani, Dhaka 1213.

Tofael Ahamed
Lecturer
Dept. of Farm Power & Machinery, Bangladesh Agricultural University, Mymensingh, Bangladesh.

Abstract/ Executive Summary:

Bangladesh is one of the largest delta of the world comprising of three major rivers: Ganges, Jamuna and Meghna. Every year a significant part of the country goes under floodwater and the land resources including agricultural crop are damaged. Different flood controlling and management techniques have been adopted to reduce such damages in different areas of the country. But there is no predictive methodology for cropping area assessment for a flooding year. This study focuses on the methodology of predicting agricultural cropped area using Geographic Information System for 1998 flooded year. The developed methodology was applied to the Compartmentalization Pilot Project at Tangail in Bangladesh. The study results were compared with the CPP agricultural field survey data and obtained 91 percent accuracy for transplanted aman and 77 percent for broadcasted aman.

Keywords: Flood Prone Areas, GIS techniques, Cropping Area

Location: Tangail district

Start Date:

End Date:

Program Area: Knowledge Management

Non-commodity: GIS

Objectives:

To develop a methodology for agricultural cropping area assessment for a particular flooded year using GIS techniques at Compartmentalization Pilot Project (CPP) area of Tangail in Bangladesh.

Methodology:

The study area is located in the floodplains of the river Jamuna. The area covers Tangail sadar (82.5%), Delduar (14%), Basail (3%) and Kalihati (0.5%) thanas of Tangail district (CPP, 1996). Total area of the project is 13,200 ha including households (3098 ha), agricultural land (9764 ha), river and beels (338 ha). The location map of the study area .

Digital Elevation Model (DEM): DEM for the study area was created from Finnish Mapping Project (FINMAP) which Was compiled from aerial photograph of 1990 with a 0.10 metres contour interval (EGIS, 2000). The settlement, water body and river coverage were also digitized from FINMAP of 1: 10,000 scale. Contour lines of ground elevation were digitized directly from FINMAP and were converted into spot elevation points. These coverages were geo-referenced to Bangladesh Transverse Mercator (BTM) coordinate system (FAP, 1993). The OEM was then generated from the spot elevation of 10 metres grid using a methodology that interpolates a spot value based on Inverse Weighted Distance (IWD) of seven points using ArcView GIS software.

Agricultural crop coverage: The agricultural practices of the study area are dominated by transplanted and broadcasted aman in the Kharif II season. The agricultural land use acreage for the year 1998 were collected from the CPP agriculture division to compare with the GIS results. The acreage of different crops were: aman 3852 ha, sugarcane4 71 ha and the rest were water bodies and settlements. The acreage of aman in 1998 season was significantly lower than that of previous year due to the catastrophic flood in the area. Sowing of broadcasted aman normally starts in April-May and planting of transplanted aman in July. It was found that if the water depth over the land is more than 30 cm, then it IS not possible to transplant aman. The transplanted am an is grown in FO-Fl lands and broadcasted aman in F2 lands in the study area. In this study, it is considered that transplanted aman is cultivated in all the agricultural lands under FO and FI and broadcasted am an in F2. The land type classification were done based on the water depth range prescribed by Master Plan Organization (MPO, 1986).

Water level data :Hydrology of the study area is characterized by controlled flooding. Due to the implementation of the project, a significant change in the water depth and duration of inundation has been observed by CPP during 1993, 1996, 1997 and 1998. The observed data at 25 water level gauge stations (June-October 1998) were collected from the CPP hydrology division and monthly highest seven day moving average water level data were used to calculate depth and extent of inundation.

GIS analysis :ArcView GIS software were used for the analysis of water level data in association with the digital elevation model (OEM) to determine the suitable area for transplanted and broadcasted aman. Water level surface was made using the monthly highest water level with seven days moving average. Water level data were considered as a "Z" value and inverse weighted distance (IWD) with seven neighbouring water level stations were considered for interpolation with spatial resolution of 10 metres. To determine the depth of inundation at any point in the study area, water level surface was subtracted from the OEM. The inundation depth of each month of the area was calculated in the same method considering the maximum value of water level with seven days moving average.

Source of Information: Journal of the Institution of Engineers, Bangladesh Agricultural Engineering Division, Vol. 29/AE, No.1, Dec. 2002

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

A predictive methodology using GIS has been developed to assess the cropping area in a flooding region for two main crops transplanted aman and broadcasted aman in the Kharif II season. The analysis was done based In the water depth over the lands. The result shows that it IS possible to apply this methodology to assess the crop coverage in flooding region of Bangladesh. GIS technique for cropping inventory in flood damage area is statistically significant and test area is acceptable In respect to compartmentalization approach.

Knowledge Management: Journal