System Performance Evaluation and Diagnostic Analysis of Canal Irrigation Projects
S. T. Chari, S. Jonna, P. V. Raju, C. S. Murthy and K. A. Hakeem
Water Resources Group, National Remote Sensing Agency
Dept of Space, Govt. of India
Hyderabad - 500 03
Abstract
Satellite remote sensing techniques can efectively complement and supplement ground data collection towards objective and reliable evaluation of irigation system performance and diagnosti analysis. Multidate satellite data during the rabi seasons prior to and after implementation of National Water Management Project NWMP have been analysed to provide spatial information on irrigated area and paddy productivity right up to distributary command level add through the years since 1986-87 rabi season. The Bhadra project performance is seen to have significatntly improved after NWMP in terms of increased irrigated area, improved paddy yield, decreased depth of water applied and improved water use efficiency with respect to paddy production. Diagnostic analysis has indicated problem distributaries of gap in irrigation utilisation, less nad stagnant paddy yield and poor water use efficiency. Equity in water application has also been diagnosed. Distributaries with large gap in paddy yield between head reach ad Satellite remote sensing applications are thus seen to be effective tools for irrigation water management.
Introduction
The Bhadra rrigation Project in Karnataka State is one of the subprojects of National Water Management Project NWMP of India. The NWMP objective is to increase the agricultural productivity and farms income inexisting irrigation schemes by providing predictable, reliable and equitable irrigation service. The productivity would be measured in regard to agricultural yield and area irigated. The project incorporates monitoring and evaluation at various levels to provide information on system performance evaluation and diagnostice analysis, necessary for corrective measures. Satellite remote sensing techniques have been employed to effectively complement and supplement the ground mechanism in this project.
System performance indicators are depth of water applied irrigation intensity, major crop yield and water use efficiency. Equity of irrigation service has also been evaluated. Diagnostic analysis is carried out using temporl and spatial information at distributor level, Problem distributaries have been identified in regard to irrigation gap, low crop yield, low/no yield improvement through years and low water use efficiency. While many earlier studies have demonstrated the utility of satellite data in providing crop area statistics and crop yield assessment (Groten 1993, Rasmussen 1992) Tennakoon et all 1992, Thiruvengadachari 1981, Teng 1990 ) Over large administrative units, the investigation in Bhadra Project perhaps is the first attempt to provide informaton on spatal and tempra varability of performance indcatiors at distributary comand leve (Thiruvengadachari et a 1994.)
Basic Data and Methodology
Multidate Indian Remote Sensing Satellite (IRS) LISS I data during the rabi seasons since 1986-87 have been analysed (LANDSAT MSS/TM data to a limited extent has been used to fill tbe gaps in temporation coverage/non availability of IRS data) Kharif season could not be analysea in view of continuous cloud cover preciuaing satelite vrew of the ground. Liss I sensor data was used since even at the spatial resolution of 72.5 meters this data could provide distributary level information on major crop groups and is also cost/time effective.
The satellite data has been digitally classified into paddy and non paddy crop areas. Though the latter has been further clasificed into individual crop types such as groundnut, sugarcane and garden crops, these were later lumped into one category, in view of reduced classification accuracy resulting from non contiguous smaller patchiness of such crops. Different classification schemes, ranging from single date to multidate data analysis and use of vegetation index along with raw bands, were attempted to provide the best delineation of irrigated crop area.
A base map of the command area, defining the distributary command boundaries, is prepared from survey of India topographic map in 1:50000 scale and revenue survey map in 1:7920 scale, taking the aid of topography, drainage network and other features. The base map is digitised and overlaid on the classified crop map, to enable crop statistices extraction under each distributary.
The crop condition is indicated by the normalised difference vegetation index (NDVI) which is an arithmetic combination of reflected radiation in the visible and near-infrared wavelengths of IRS/LANDSAT sensor.
The satellite data analysis is supported by field visits and ground data. The paddy yield model has been developed based on crop cutting experiments conducted during 1992-93 rabi season in the command area and NDVI of paddy.
Though irrigated crop area and yield as well as depth of water and water use efficiaency have been estimated at distrubutary level, only summary statistics are provided in subsequent sections.
System Performance Evaluation
Irrigated Crop Area
Irrigation is being provided to a significantly larger area after NWMP implementation (Table 1) . The irrigation intensity in the current rabi season is 87 percent compared to 76 percent in the pre NWMP 1986-87 rabi season. Irrigation utilisation is highest in head end Bhadravathy division followed by Malebennur and Davangere deivisions. The tail end Davangere division has registered an increase of 9 percent in irrigation intensity. Aalysis of irrigation intensity at canal subdivision and at distributary level idicates that the irrigation intensity is high in No. 3 subdivision of Bhadravathi division. The intensity is decreasing towards the tail end of Malebennur division, following similar trends before and after NWMP. The trend of decreasing irrigation intensity is seen in Dvangere division also. In general, while irrigation intensity has increased in recent rabi seasons, the spatil, while irigation intensity has increased in recent rabi seasons, the spatial variability is still following the pre NWMP trend. This non uniformity in irrigation intensity needs to be narrowed and equity established. Redistribution of water from distributaries with larger than 100 percent irrigation intensity can lead to greater equity.
The change in cropping pattern before and after NWMP is given in Table 2. The percent paddy area in the command area has increased from 56 percent in 1986-87 rabi and stabilised at 69 prcent in the recent rabi seasons. The percentage area under paddy crop is 49 percent in Bhadravathy division and around 76 percent in Malebennur division. Percent paddy area in Davangere division however is showing a significant increase in the recent two rabi seasons, perhaps indicative of improved water availability in this tail end division. Significant acroce is also feen in the tail end most No. 1 sub-division within vangere division. The spatial pattern of percent paddy area in cent rabi seasons is remarkably similar to the variability in 1986-87 rabi season, indicating alround farmer preference for paddy crop with improved irrigation service.
