Table of Contents 1 Introduction ................................................................................................................ 1 2 Brahmani and Baitarani catchments........................................................................ 3 3 Rengali dam and reservoir characteristics.............................................................. 6 4 Flood forecasting system.......................................................................................... 8 4.1 Present forecasting method ......................................................................................... 8 4.2 Flood mitigation with Rengali dam, possibilities and history ........................................ 9 4.3 Proposed flood forecasting system ............................................................................ 15 4.4 Hydrologic-hydrodynamic modelling system.............................................................. 15 4.5 Real-time rainfall data and Quantitative Precipitation Forecasts ............................... 19 5 Telemetry system..................................................................................................... 20 5.1 Objectives .................................................................................................................. 20 5.2 Bid requirements ........................................................................................................ 21 5.3 General concept......................................................................................................... 21 5.4 Data Processing Centre ............................................................................................. 24 5.5 Data Acquisition System ............................................................................................ 24 Variable ................................................................................................................................ 25 5.6 Data Communication System..................................................................................... 27 5.7 Hardware requirements.............................................................................................. 29 5.8 Training ...................................................................................................................... 31 5.9 Maintenance............................................................................................................... 31 6 Development of forecasting system ...................................................................... 31 Annexes Report on field visit to study area ....................................................................................... 1 Development of preliminary rainfall-runoff model............................................................. 1 Float-counter-weight water level sensor with shaft encoder .............................................. 1 Vented gauge pressure sensor ........................................................................................... 1 Tipping Bucket Raingauge................................................................................................... 1 Data logger............................................................................................................................. 1 i 1 Introduction In the delta of Brahmani and Baitarani rivers in Orissa almost every year inundations take place causing considerable damage. Floodings can be reduced by temporary storage of water behind Rengali dam on Brahmani river, which controls roughly some 50% of the total catchment area draining to the delta. To use the dam for flood mitigation, floods are being forecasted based on real-time information of rainfall and discharge in the two basins. The lead-times for forecasting at present are limited as only the contributions of the basins in Orissa are covered by the forecasting system. This includes the entire Baitarani basin and Brahmani river below Panposh. Upstream of Panposh, the Koel and Sankh rivers drain, which constitute over 75% of the catchment area controlled by the Rengali dam. By expanding the flood forecasting system to the upper reaches of the Brahmani basin lead- times can be extended and knowledge about the flood volumes to be temporarily stored at Rengali can be improved considerably. The shortfalls of the present system were realised long time back. In August 1992 the Central Planning Unit, Irrigation Department, Orissa finalised a feasibility study on “Telemetry System for Rengali Dam Project”. In this study it proposes a communication system for real-time collection of hydro-meteorological data in the Brahmani basin which covers such an expansion to improve the flood forecasting. This was further taken up in World Bank’s Staff Appraisal Report (SAR) of the Hydrology Project (July, 1995). In the SAR activities related to the improvement of flood forecasting in Brahmani basin are covered under the heading: “Improvement to Real-Time Water Resources Management”, with a total budget of Rs.24.7 million. The proposed activities include: 1. Provision of additional telemetering equipment in the Brahmani basin, in two phases: • Phase I: installation of ten telemetering stations in the basin in Orissa to provide a lead time of about 24 hours for the inflow forecasts to the reservoir and the delta. • Phase II: extension of the telemetering system to include the upper catchment of Brahmani river in Bihar in order to provide a longer forecast lead time. 2. Flood Forecasting Study for the Brahmani River, including the development of a real- time flood forecasting system. Catchment modelling techniques, to be validated by using all available historical rainfall and flow data, will be applied in operating the system. The results of the study would be used to define the locations for the telemetering stations to be installed in the basin. The Consultant visited the study area late June 1998 and discussed the problems and options for flood forecasting and telemetry thoroughly with the concerned officers of Orissa State, see Annex 1. Background information was retrieved from the 1992 feasibility study. At the same time it was realised that since 1992 communication technologies have improved, whereas furthermore, the quoted report is not explicit on the proposed modelling system. Therefore, a review of the original proposal would be required. Based on the discussions a document was drafted covering Consultant’s view on the forecasting options. This document describes the flood forecasting system components and provides a fresh look at the required communication system to generate data for operation of an effective flood forecasting system for the two river basins, operated from Rengali dam site. Page 1 For full coverage of the background of the flood forecasting system and basin particulars reference is made to the above mentioned feasibility study. Some relevant aspects are repeated here in Chapter 2 (basin characteristics) and Chapter 3 (Rengali dam) to ease the reading. In brief the proposed flood forecasting system is dealt with in Chapter 4 and the requirements for the telemetry system in Chapter 5. In Chapter 6 a development strategy for the implementation of the forecasting system is outlined. Page 2 2 Brahmani and Baitarani catchments Basin characteristics The headwaters of Brahmani river are mainly formed by the Koel, Karo and Sankh rivers. The Brahmani known as South Koel in the upper reaches rises near Nagri village in the Ranchi district of Bihar. After its confluence with Sankh river at Panposh, the Koel river is called Brahmani river. Flowing in south-easterly direction, it reaches the delta at Jenapur and drains ultimately into the Bay of Bengal near Dhamara after traversing a distance of some 800 km. It drains a total catchment area of about 38,000 km2, of which nearly 22,200 km2 lies in Orissa. The Baitarani river originates from Guptaganga hills near Gonasika village in Keonjhar district of Orissa. Initially the river flows in a northern direction for about 80 km and then takes an abrupt right turn near Champua and flows in a south easterly direction and finally discharges into Bay of Bengal through the deltaic area of river Brahmani. The river travels a total distance of 360 km and drains an area of over 14,000 km2. The layout of the Brahmani and Baitarani catchments is shown in Figure 2.1. Catchment particulars are summarised in the Tables A1 and A2 of Annex 2. Rainfall distribution There are 41 raingauge stations in the catchment area of river Brahmani and 15 in the Baitarani basin for which daily rainfall data are available. A study of rainfall based on data from 1901 to 1950 (IMD, 1962) in and around the Brahmani and Baitarani basins reveals, that the area is more or less homogeneous. About 80% of the annual normal rainfall occurs during the 4 months of south-west monsoon season (June to September). The annual normal rainfall varies from 1250 mm to 1750 mm over the Brahmani basin and from 1250 mm to 1500 mm over the Baitarani basin. The coefficient of variation of annual rainfall is only about 20%, which shows that the rainfall in the region is fairly dependable. Temperature and humidity distribution The mean maximum temperature varies from 350C to 42.50C over the catchment areas of rivers Brahmani and Baitarani in the month of May. The mean minimum temperature varies from 150C to 100C over Brahmani catchment and from 150C to 12.50C over Baitarani catchment in the month of January. However, the extreme temperatures in summer (max.) and winter