Assessment of Instream Flow Requirement of Dudhkumar River

ASSESSMENT OF INSTREAM FLOW REQUIREMENT OF DUDHKUMAR RIVER

MD. JAKIR HOSSAIN

DEPARTMENT OF WATER RESOURCES ENGINEERING BUET, DHAKA

ASSESSMENT OF INSTREAM FLOW REQUIREMENT OF DUDHKUMAR RIVER

A project by

MD. JAKIR HOSSAIN

In partial fulfillment of the requirement for the degree of Master of Engineering (Water Resources).

Department of Water Resources Engineering Bangladesh University of Engineering and Technology Dhaka

March, 2010

CERTIFICATE

This is to certify that this project work has been done by me and neither this project nor any part thereof had been submitted elsewhere for the award of any degree or diploma.

Countersigned Signature

Professor Dr. M. Monowar Hossain Md. Jakir Hossain (Supervisor)

Bangladesh University of Engineering and Technology

Department of Water Resources Engineering

We hereby recommend that the project work prepared by Md. Jakir Hossain

entitled ‘Assessment of Instream Flow Requirement of Dudhkumar River’ be accepted as fulfilling this part of the requirement for the degree of Master of Engineering (Water resources).

Chairman of the Committee Professor Dr. M. Monowar Hossain (Supervisor)

Member Professor Dr. M. Mirjahan

Member Associate Professor Dr. Md. Ataur Rahman

March, 2010

ABSTRACT

This study deals with the assessment of Instream Flow Requirement (IFR) of Dudhkumar river using three methods of hydrological approach. Methods used are (i) Mean Annual Flow (MAF) method, (ii) Flow Duration Curve (FDC) method and (iii) Constant Yield (CY) method. Dudhkumar river is located in the north-east corner of north-west region of Bangladesh. It is an international river shared by Bhutan, India and Bangladesh. The present study is a preliminary level desk-top analysis using historical river flow data.

Instream flows are defined as those flows which are needed to be maintained in the river for sustaining the various functions of a river, e.g. carrier function, production function, regulation function etc. Instream flows are essential within a stream to maintain its natural resources at desired level. Knowledge of instream flow requirement assists in planning of new development projects, in evaluating existing projects as well as for proper understanding of the issues relating to the natural environment of the stream.

According to the MAF method, IFR has been computed for eight habitat quality classes, the choice of which depends on the management objectives. The computed IFR varies from 48 m3/s (which represents the ‘poor’ habitat quality) to 950 m3/s (which represents the ‘flushing’ habitat quality). For the sake of the present study, out of eight habitat quality, two habitat quality namely ‘good’ and ‘outstanding’ have been considered for dry (low flow) season. For the monsoon (high flow) season only ‘flushing’ habitat quality has been considered. The corresponding IFR for ‘good’ and ‘outstanding’ habitat quality is found to be 95 m3/s and 190 m3/s respectively for the low flow season. IFR for the ‘flushing’ habitat quality is found to be 950 m3/s for both low and high flow season.

According to the FDC method, computed IFR during the low flow season varies from 72 m3/s (in March) to 190 m3/s (in November) having an average of 113 m3/s. In the high flow season it varies from 580 m3/s (in June) to 1190 m3/s (in July) having an average of 937 m3/s. According to the CY method, the computed IFR during the low flow season varies from 90 m3/s (in March) to 234 m3/s (in November) having an

average of 147 m3/s. In the high flow season it varies from 435 m3/s (in October) to 1032 m3/s (in July) having an average of 744 m3/s.

Possible water demand that could be met from Dudhkumar river has been assessed considering irrigation demand for Kurigram Irrigation Project, North Unit and domestic water demand in the area. It is to be mentioned here that there is no classified waterway in Dudhkumar river. Peak diversion requirement at Pateswari is found to be 35.55 m3/s occurring in the month of January. The 2nd peak diversion requirement occurs in the month of March. This diversion requirement includes the irrigation and domestic water demand in the project area. For comparing demand availability scenario, IFR determined by the MAF method for two options have been considered. Option-I consists of ‘good’ and ‘flushing’ habitat quality for the low and high flow season while Option-II consists of ‘outstanding’ and ‘flushing’ habitat quality for low and high flow season respectively.

Flow availability at Pateswari has been assessed for 75% and 90% dependability. It is found that 75% dependable flow in low flow season varies from 80 m3/s (March) to 220 m3/s (November). On the other hand 90% dependable flow in low flow season is found to vary from 72 m3/s to 190 m3/s. In the high flow season 75% dependable flow varies from 360 m3/s to 950 m3/s, while the 90% dependable flow vary from 250 m3/s to 780 m3/s.

From a comparison of water availability and various demands, it is found that during the months of April, June, July, August, September, October, January, February and March there is shortage of water to meet the total requirement if 90% dependable flow, IFR under Option-I and other demands are considered. If 75% dependable flow availability is considered, the duration of deficit period shortens and April, June, July, September, October, January, February and March remain as the deficit period. If IFR under Option-II is considered, the shortage of water to meet the demands increases. Given the nature and details of environmental issues that influence the instream flow requirement and the limitations of the present study, further investigation may be carried out encompassing wider aspect of the environment.

ACKNOWLEDGEMENT

I would like to express my deepest gratitude and profound respect to my thesis supervisor Dr. M. Monowar Hossain, Professor, Department of Water Resources Engineering, BUET, for his valuable suggestion, guidance and encouragement that he provided during the course of the thesis. In particular I would like to acknowledge his continuous encouragement for timely completion of the thesis without which it would have been difficult to complete it in time.

I am grateful to Dr. M. Mirjahan, Professor, Department of Water Resources Engineering, BUET; and Dr. Md. Ataur Rahman, Associate Professor, Department of Water Resources Engineering, BUET for their peer review and suggestion in successfully completing the thesis.

I also like to express my heart full gratitude and thanks to Ms. Sarwat Jahan, Senior Specialist, Institute of Water Modelling and Mr. Hazrat Ali, Associate Specialist, Institute of Water Modelling for their assistance by providing data and information required for the study.

Lastly, I express my gratitude to my family members for their patience and encouragement while carrying out the study.

iii

TABLE OF CONTENTS

Abstract …………………………………………………………………………………. i Acknowledgement ...... iii List of Tables ………………………………………………...... …………………..…... vi List of Figures …………………………………………………………………….….. vii Abbreviations and Notations ………………………………………………….….… viii

Chapter 1: Introduction ...... 1 1.1 Insteram Flow ...... 1 1.2 Selection of the River ...... 1 1.3 Description of Dudhkumar River ...... 2 1.4 Objectives of the study ...... 7 Chapter 2: Review of Literature ...... 9 2.1 Instream Flow Assessment ...... 9 2.2 State of Instream Flow Management in various Countries ...... 9 2.2.1 Instream Flow Management across the Globe ...... 9 2.2.2 Instream Flow Management in U.S.A...... 10 2.2.3 Instream Flow Management in India ...... 11 2.2.4 Instream Flow Management in Bangladesh ...... 13 2.3 Instream Flow Methodologies ...... 16 2.3.1 Hydrological Methodologies ...... 18 2.3.1.1 Types of Hydrological Methodology ...... 19 2.3.2 Hydraulic Rating Methodologies ...... 22 2.3.3 Habitat Rating Methodologies ...... 23 2.3.4 Holistic Methodologies ...... 23 2.3.5 A Comparative Statement of the Methodologies ...... 25 Chapter 3: Methodology ...... 29 3.1 Data Collection ...... 29 3.1.1 Water Level ...... 29 3.1.2 Discharge ...... 32 3.2 Instream Flow Assessment ...... 33 3.2.1 Mean Annual Flow Method ...... 33 3.2.2 Flow Duration Curve Method ...... 33 3.2.3 Constant Yield Method ...... 35

Chapter 4: Results and Discussion ...... 37 4.1 Assessment of Instream Flow Requirement ...... 37 4.1.1 Mean Annual Flow (MAF) Method...... 37 4.1.2 Flow Duration Curve (FDC) Method ...... 41 4.1.3 Constant Yield (CY) Method ...... 41 4.1.4 Summary of Instream Flow Requirement by various Methods ...... 42 4.2 Other Sectoral Water Demand ...... 44 4.2.1 Agricultural Demand ...... 44 4.2.2 Domestic and Industrial Demand ...... 45 4.3 Flow Availability ...... 46 4.4 Comparison of Water Demand and Availability ...... 47 Chapter 5: Conclusion and Recommendation ...... 49 5.1 Conclusion ...... 49 5.2 Recommendation ...... 50

References ……………… …………….…………… ……………………………52

Appendix-A: Tables …… …………….…………… …………………….…….A-1

Appendix-B: Figures …... …………….…………… …………………………...B-1

LIST OF TABLES

Table-2.1: Name of Various Methods and the Number of States using them for assessing IFR in the U.S.A...... 11 Table-2-2: The Opposite ends of the Methodologies ...... 17 Table-2-3: Percentage of MAF for various Habitat Quality ...... 20 Table-2-4: A Comparison of Different Methodologies ...... 28 Table-3-1: Summary of Collected Data ...... 29 Table-3-2: Status of Daily Water Level Data Collected ...... 30 Table-3-3: Status of Daily Discharge Data Collected (before filling missing data) ...... 32 Table-3-4: Yearly Maximum, Average and Minimum Discharge (m3/s) at Pateswari .. 34 Table-3-5: Median Monthly Flow (m3/s) of Dudhkumar River at Pateswari ...... 36 Table-4-1: Monthly Average Discharge (m3/s) of Dudhkumar River at Pateswari ...... 38 Table-4-2: Instream Flow Requirement (m3/s) according to MAF Method ...... 40 Table-4-3: Instream Flow Requirement (m3/s) according to FDC Method ...... 41 Table-4-4: Instream Flow Requirement (m3/s) according to CY Method...... 42 Table-4-5: Summary of IFR computed by the three Methods ...... 43 Table-4-6: Monthly Diversion Requirement from Dudhkumar River at Pateswari ...... 46 Table-4-7: Flow Availability of Dudhkumar river at Pateswari ...... 47 Table-4-8: Comparison of Various Water Demand and Availability at Pateswari ...... 47 Table-A.1: Daily Water Level (mPWD) of Dudhkumar River at Pateswari …… ... A-01 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari …... A-21 Table-A.3: Flow Duration Curve for the month of January …………………….… A-41 Table-A.4: Flow Duration Curve for the month of February ……………………... A-42 Table-A.5: Flow Duration Curve for the month of March ……………………….. A-43 Table-A.6: Flow Duration Curve for the month of April ……………………….... A-44 Table-A.7: Flow Duration Curve for the month of May ………………………….. A-45 Table-A.8: Flow Duration Curve for the month of June ………………………….. A-46 Table-A.9: Flow Duration Curve for the month of July …………………………... A-47 Table-A.10: Flow Duration Curve for the month of August ……………………… A-48 Table-A.11: Flow Duration Curve for the month of September ………………….. A-49 Table-A.12: Flow Duration Curve for the month of October …………………….. A-50 Table-A.13: Flow Duration Curve for the month of November …………………...A-51 Table-A.14: Flow Duration Curve for the month of December ………………….. A-52

LIST OF FIGURES

Figure-1.1: Location Map of Dudhkumar River ...... 3 Figure-1.2: Catchment map of Dharla and Dudhkumar river...... 5 Figure-1.3: Water Level Hydrograph of Dudhkumar river at Pateswari ...... 6 Figure-1.4: Discharge Hydrograph of Dudhkumar river at Pateswari ...... 6 Figure-1.5: Typical Cross section of Dudhkumar, upstream of Pateswari R.B...... 7 Figure-1.6: Typical Cross section of Dudhkumar, downstream of Pateswari R.B...... 7 Figure-3.1: Water Level Hydrograph at Pateswari ...... 31 Figure-4.1: Variation of Max. Mean and Min. of Monthly Mean Flow at Pateswari .... 38 Figure-4.2: Variation of IFR computed by the three Methods ...... 43 Figure-4.3: Water Demand – Availability Scenario ...... 48 Figure-B.1: Kurigram Irrigation Project (North Unit) and River System …………. B-01 Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari ...... B-02 Figure-B.3: Navigational Route of BIWTA ……………………………………… B-11

vii

Abbreviations and Notations

BBS Bangladesh Bureau of Statistics BIWTA Bangladesh Inland Water Transport Authority BUET Bangladesh University of Engineering & Technology BWDB Bangladesh Water Development Board CY Constant Yield, a method for assessing Instream Flow Requirement DRIFT Downstream Response to Imposed Flow Transformations EFA Environmental Flow Assessment EFR Environmental Flow Requirement FCDI Flood Control, Drainage and Irrigation FDC Flow Duration Curve Ghagot A local variety fish. GW Ground Water IFA Instream Flow Assessment IFIM Instream Flow Incremental Methodology IFR Instream Flow Requirement JICA Japan International Co-operation Agency KIPNU Kurigram Irrigation Project, North Unit LFS Low Flow Season M Meter Mm milli meter MAF Mean Annual Flow MoWR Ministry of Water Resources NCIWRDP National Commission for Integrated Water Resource Development Plan NWMP Nation Water Management Plan PHABSIM Physical Habitat Simulation Model PWD Public Works Datum Q Discharge R.B. Railway Bridge SW Surface Water WL Water Level

viii

Chapter 1: Introduction

1.1 Insteram Flow

An Instream Flow Assessment (IFA) for a river may be defined simply as an assessment of how much of the original flow regime of a river should continue to flow down it in order to maintain specified, valued features of the ecosystem (King et. al., 1999). An instream flow assessment produces one or more descriptions of possible modified hydrological regimes for the river, each linked to a predetermined objective in terms of the ecosystem’s future condition. For instance, these objectives may be directed at the maintenance or enhancement of the entire riverine ecosystem, including its various aquatic and riparian biota and components from source to sea; at maximizing the production of commercial fish species, at conserving particular endangered species or protecting features of scientific, cultural or recreational value.

An instream flow assessment is often regarded synonymous with Environmental Flow Assessment (EFA). It assumes that only the flow of water in the river channel contributes to the maintenance of a river environment (ecosystem), whereas out-of- stream flow does not. Within the river corridor, ecosystems can be defined, such as isolated oxbows, the floodplain and fringing wetlands, that are influenced by the river flow, e.g. via groundwater flows, flood flows, creeks and natural channels. As long as these connections are part of the natural river environment, river water requirements of these ecosystems can be considered as part of the instream flow requirement. An instream flow can also be defined for navigation requirements or for hydro-power, as these functions are also dependent on (part of) the river ecosystem (Marchand, 2003).

1.2 Selection of the River

The economy of Bangladesh is agrarian. Agriculture contributes about 22% to the national GDP and employs about 48.10% of the labour force (BBS, 2006). Like many other parts of Bangladesh, agriculture is the main economic activity in the catchment area of Dudhkumar inside Bangladesh. Irrigation, which is an essential input for High Yielding Variety rice production during the dry season, is mostly dependent on groundwater, which is expensive and deleterious to soil fertility. The surface water potential of Dudhkumar river has remained unutilized. Recently, Government of

Bangladesh has decided to implement the irrigation network and allied infrastructure of the Kurigram Flood Control, Drainage and Irrigation Project, North Unit (KIPNU) by withdrawing water from Dudhkumar river. The project area is located on the right side of Dudhkumar river. If irrigation component of the project is implemented, a substantial part of the dry season flow of Dudhkumar river would be diverted for irrigation which may significantly reduce the dry season flow availability and subsequently may have influence on the riverine ecosystem. Furthermore, the flora and fauna including fish habitat may be affected.

Realizing the importance of Dudhkumar as an international river, its importance in sustaining the environmental integrity in the region and the Government’s recent decision to implement the Kurigram Irrigation Project, North Unit, this river has been selected for determining the Instream Flow Requirement.

1.3 Description of Dudhkumar River

There are about 310 rivers in Bangladesh out of which 57 are transboundary rivers (BWDB, 2005). The Dudhkumar river is one of them. The river is located in the north- east corner of the North-West region of Bangladesh, as may be seen in Figure-1.1. It is an international river, shared by Bhutan, India and Bangladesh. The river originates in the Himalayan foothills in Bhutan and flows south south-easterly direction from the foot hills through India to its outfall into the Brahmaputra river in Bangladesh. The river enters in Bangladesh near Shilkhuri of Bhurungamari Upazila in Kurigram district (Haque, 2008). Total catchment area of the river is about 5,800 km2 out of which about 240 km2 is in Bangladesh. About 96% of the catchment area lies outside Bangladesh (JICA, 1990; Pakistan Techno Consult, 1969). Total length of Dudhkumar river is about 220 km. In Bangladesh it travels a distance of about 51.00 km in the south south- easterly direction to meet with the Brahmaputra river at Noonkhawa. A catchment map of Dudhkumar and Dharla river is shown in Figure-1.2.

In the upper reach of Dudhkumar river important tributaries are Torsha, Kaljani, Raidak etc. (Techno Consult Eastern Limited, 1975). Within Bangladesh, there are several small rivers that drain into the Dudhkumar river, notable are Satkura dara, Phulkumar river, Girai khal, Dikdari dara, Santashi khal etc. as can be seen in Figure-B.1, Appendix-B. The above mentioned khals and rivers work as drainage channel of

KIPNU and adjacent area to the Dudhkumar river. However, depending on the water level in Dudhkumar river, backflow into the Kurigram FCDI (North Unit) project area occurs during the monsoon season.

INDIA

Dudhkumar river Dharla river Brahmaputra river Teesta river

Bay of Bengal

Figure-1.1: Location Map of Dudhkumar River

Hydrology of the catchment area of Dudhkumar river is mainly governed by rainfall runoff and cross boundary flows through Dudhkumar river. The mean annual rainfall gradually decreases from 3000 mm in the north to 1800 mm in the south, with an

average annual rainfall of 2700 mm (DPM et al., 2005). From available record and data it is found that flows in the Dudhkumar river at Pateswari during the dry season (November to May) comes down to an average of 159 m3/s and during the monsoon season (June to October) the average flow is about 897 m3/s. Based on the data available from BWDB, the maximum and minimum discharge is found to be 9250 m3/s and 52.30 m3/s that occurred on 6th October, 1968 and 18th April, 1992 respectively. A water level hydrograph and a discharge hydrograph of Dudhkumar river at Pateswari for the period of 1968 to 2007 is shown in Figure-1.3 and Figure-1.4 respectively. A more enlarged, five year block wise, hydrograph of water level and discharge may be seen in Figure-B.2, Appendix-B. From the figures it can be seen that there are sudden rise of water level and discharge in Dudhkumar river, which imply the flashy character of the river.

Topography within the KIPNU area varies from 20.00 mPWD to 33.42 mPWD (IWM, 2009) and the land slope is from the northwest to the southeast direction. Although the area is generally flat, but there are some localized low lying areas that are locally known as beel or Jola.

The steep slope and hilly catchment area across the border contributes to its flashy characteristics and flash flood causes widespread damages frequently. Dudhkumar is a semi braided river and morphologically highly dynamic. Being a semi braided river, it is associated with the development of loops. Sometimes channels move quite fast and consequent abandonment of meander loop through cut off. Such natural cut off can occur frequently within 1-2 years (HCL et. al. 2009). The sediment size, d50, at Pateswari and Tangonmari is found to be 0.21 mm and 0.16 mm respectively (HCL et al. 2009). The average slope of the river is about 10 cm/km. Average cross sectional area of the river is about 1506 m2. Average width of the river at high and low water level is about 284.24m and 225.34m respectively (BWDB). Typical cross section of the river at immediate upstream and downstream of Pateswari railway bridge is shown in Figure-1.5 and Figure-1.6 respectively.

KIPNU

Source: JICA (1990) Figure-1.2: Catchment map of Dharla and Dudhkumar river.

Daily Water Level Station: Pateswari; River: Dudhkumar

32.00

31.00

30.00

29.00

28.00 Water Level (m PWD) (m Level Water

27.00

26.00

25.00 01-Jan-65 01-Jan-66 01-Jan-67 01-Jan-68 01-Jan-69 01-Jan-70 01-Jan-71 01-Jan-72 01-Jan-73 01-Jan-74 01-Jan-75 01-Jan-76 01-Jan-77 01-Jan-78 01-Jan-79 01-Jan-80 01-Jan-81 01-Jan-82 01-Jan-83 01-Jan-84 01-Jan-85 01-Jan-86 01-Jan-87 01-Jan-88 01-Jan-89 01-Jan-90 01-Jan-91 01-Jan-92 01-Jan-93 01-Jan-94 01-Jan-95 01-Jan-96 01-Jan-97 01-Jan-98 01-Jan-99 01-Jan-00 01-Jan-01 01-Jan-02 01-Jan-03 01-Jan-04 01-Jan-05 01-Jan-06 01-Jan-07 01-Jan-08 01-Jan-09

Date

Figure-1.3: Water Level Hydrograph of Dudhkumar river at Pateswari

Mean Daily Discharge Station: Pateswari; River: Dudhkumar

10000

9000

8000

7000

/s) 6000 3

5000

Discharge (m 4000

3000

2000

1000

0 1-Apr-68 1-Apr-69 1-Apr-70 1-Apr-71 1-Apr-72 1-Apr-73 1-Apr-74 1-Apr-75 1-Apr-76 1-Apr-77 1-Apr-78 1-Apr-79 1-Apr-80 1-Apr-81 1-Apr-82 1-Apr-83 1-Apr-84 1-Apr-85 1-Apr-86 1-Apr-87 1-Apr-88 1-Apr-89 1-Apr-90 1-Apr-91 1-Apr-92 1-Apr-93 1-Apr-94 1-Apr-95 1-Apr-96 1-Apr-97 1-Apr-98 1-Apr-99 1-Apr-00 1-Apr-01 1-Apr-02 1-Apr-03 1-Apr-04 1-Apr-05 1-Apr-06 1-Apr-07

Date

Figure-1.4: Discharge Hydrograph of Dudhkumar river at Pateswari

32 32 30 30

28 28

26 26

24 24 Bed level (m PWD) Bed level (m PWD) 22 22 0 500 1000 0 200 400 600 800 1000 Distance from left bank (m) Distance from left bank (m)

Figure-1.5: Typical Cross section of Dudhkumar, upstream of Pateswari R.B.

32 30 28 26

Bed level (m PWD) 22 0 200 400 600 Distance from left bank (m)

Figure-1.6: Typical Cross section of Dudhkumar, downstream of Pateswari R.B.

From the Figures of cross section it may be seen that at the upstream of the bridge the river width is much larger compared to that at the downstream side. Furthermore, at the upstream side, thawleg lies towards the right bank while at the downstream side it is towards the left bank of Dudhkumar river.

1.4 Objectives of the study

Dudhkumar is one of the main perennial rivers of the north-western region of Bangladesh. Life and livelihood of local people and environmental setting of the area is largely dependent on the hydrological characteristics of Dudhkumar river. Existence of the river in a form conducive to the environment is pre-requisite for overall economic development and environmental sustainability of the area. Furthermore, the Dudhkumar is an international river shared by Bhutan, India and Bangladesh. As such, it is imperative that an assessment of the instream flow requirement is made before any intervention is made on the river, particularly for diversion of its flows. With these

aims, the main objective of the study is to determine the instream flow requirement of Dudhkumar river based on hydrologic approach. The specific objectives of the study are set as below: • To assess the instream flow requirement of Dudhkumar river at Pateswari using hydrological approaches. • To assess the likely consumptive water demand for agricultural and domestic & industrial need that are likely to be met from the Dudhkumar river. • To compare the instream flow requirement with available dry season flow.

Chapter 2: Review of Literature

2.1 Instream Flow Assessment

Tharme (1996) traced the evolution of environmental flow methodologies worldwide. He noted that historically, the United States of America was at the forefront of research in this field with the first ad-hoc methods appearing in the late 1940s and a series of more formally documented techniques emerging in the late 1970s. In most other parts of the world, Environmental Flow Assessment (EFA) processes became established far later, with approaches to determine environmental water allocations only beginning to appear in literature in the 1980s. Early on and still today in some countries, the focus of environmental flow assessment is the maintenance of economically important freshwater fisheries, especially salmonid fisheries, in regulated rivers. The main objective is to define a minimum acceptable flow based almost entirely on predictions of instream habitat availability matched against the habitat preferences of one or a few species of fish. It is assumed that the flows recommended to protect target fish populations, habitats and food resources would ensure maintenance of the river ecosystem. From these early attempts to quantify appropriate stream flows for fish, many new methods and innovations have evolved and recently, a much more comprehensive approach to EFAs has been adopted in both theory and practice (Arthington, et al, 2004).

2.2 State of Instream Flow Management in various Countries

2.2.1 Instream Flow Management across the Globe

On a global scale, existing and projected future increase in water demand have resulted in an intensifying and complex conflict between the development of rivers, on one side, as source for water and energy; and on the other side, the conservation of the biologically diverse and integrated ecosystem dependent on the rivers. It has led to the establishment of the science of environmental flow assessment whereby the quantity and quality of water required for ecosystem conservation and resource protection are determined. A global review of the present status of environmental flow assessment methodologies revealed the existence of some 207 individual methodologies, recorded for 44 countries (Tharme, 2002). Actual implementation of methodologies was

apparent in most of the countries. However, interest in a range of specified methodologies was demonstrated in countries like Cambodia, Tanzania and Mozambique, where research and activities on environmental flow assessment methodologies is in its infancy.

2.2.2 Instream Flow Management in U.S.A.

Pioneering work on Instream flow was done in the USA and since 1960s and 1970s an assortment of methods has been developed predominantly by biologists and hydrologists working for agencies having regulatory responsibilities related to water development and management. Although historically, the United States has been at the forefront in the development and application of methodologies for prescribing environmental flows, using about 37% of the global pool of techniques, parallel initiatives in other parts of the world have increasingly provided the impetus for significant advances in the field (Tharme, 2002). Such efforts over the last 40 years have provided the momentum for detailed ecological studies leading to a significant growth in the understanding to the relation between river flow and aquatic environment.

In the period since 1960s, within the USA the importance for instream flow assessment has become regarded as essential to maintain and restore values and use of water for fish, wildlife, ecological processes and other environmental, recreational and esthetic purposes (Jahn, 1990; cited in Bullock et. al. 1991). By the mid 1980s, at least 20 states provided legislative recognition to instream flow for fish aquatic resources. Data from Lamb and Doersken (1987), as shown in Table-2.1 below, illustrate that Instream Flow Incremental Methodology (IFIM) became the most widely used method for determining instream flow requirement for major resource schemes in the United States, followed by other simpler method such as the Tennant method which are suitable for minor schemes and basin wide planning.

Table-2.1: Name of Various Methods and the Number of States using them for assessing IFR in the U.S.A.

Method Number of States using the method Instream Flow Incremental Methodology 38 Tennant Method 16 Wetted Perimeter 6 Aquatic Base Flow 5 7-day, 10-year Low Flow (7Q10) 5 Professional Judgment 4 Single Cross-section (R-2 CROSS) 3 USGS Toe-width 2 Flow records/duration 2 Water Quality 2 Average Depth Predictor (AVDEPTH) 1 Habitat Quality Index 1 Oregon fish-flow 1 US Army Corps of Engineers 1 Hydraulic Modelling (HEC-2) 1 Source: Lamb and Doersken, 1987

2.2.3 Instream Flow Management in India

Like many countries of the world, in Indian water resources planning and management culture, water flowing to the sea was, and predominantly still is, regarded as waste. The water development approach was to harness river water through dams, barrages or other structures to the extent technically feasible. Even the new National Water Policy of India (MoWR, 2002) still ranks ‘ecology’ as the fourth item in the list of priorities for water allocation. As the degradation of water related environment started to manifest itself, the environmental concerns have started to gain strength. Perhaps, this is the juncture, from where and when the term ‘minimum flow’ originated. Minimum flow was understood as a flow, which is needed, to be released downstream of the dams for environmental maintenance. As the term implies, such releases were the minimal. In fact, there is no documented evidence suggesting that such releases were actually made.

The status of environmental flow assessment research in India may be considered to be in its infancy. The National Commission for Integrated Water Resource Development Plan (NCIWRDP, 1999) effectively concluded that given the limited knowledge base of

the present day to make approximate calculation of the environmental flow requirement, it is not possible to estimate the amount of water needed for environmental purposes. A provisional projection of the environmental water needs has been given as 5 km3, 10 km3 and 20 km3 for the years 2010, 2025 and 2050 respectively. The values given were not referenced to rivers and wetlands, and were just bulk volumes for the entire country without any geographical specification. The NCIWRDP estimates were not based on any scientific reasoning.

The issue of minimum flow was highlighted in a judgment of the Supreme Court of India in 1999, which directed the government to ensure a minimum flow of 10 m3/s in the Yamuna River, which flows through Delhi, for improving its water quality.

In 2001, the Government of India constituted the Water Quality Assessment Authority which in turn constituted a Working Group to advise the Authority on “minimum flows in rivers to conserve the ecosystem”. The Working Group reviewed the existing practice of environmental flow assessment and suggested that due to a variety of reasons, including the high hydrological variability, difficult tradeoffs between environment and agriculture, expensive waste treatment, disputes for water between States, etc., the practices adopted in other countries for assessment of environmental water demand are unlikely to be applicable in India. The Working Group also suggested that only a simple method (like Tennant method) may be adopted for estimating ‘minimum flows’ to be maintained in the rivers in India. These flows would primarily serve the purpose of maintaining prescribed Water Quality standards.

Perhaps the first scientific attempt to assess environmental water demand for the entire India has been recently done in Amarasinghe et al. (2005). This estimate is based on the global study conducted by Smakhtin et al. (2004a; 2004b) and was made separately for major river basins/drainage regions of India. The estimate turned out to be about 476 km3 which constitutes approximately 25% of the total renewable water resources in the country. However, in fact, this was not an estimate of environmental flows per se, but rather an estimate of the total volume of environmental flows.

The Institute of Hydrology (Roorkey) has initiated a project aiming at environmental flow assessment in the Brahmani-Baitarani River system. A hydrology based, Range of

Variability Approach, has been used for EFA. This work focuses more on the incorporation of aquatic life (fish) considerations into assessment and analysis of runoff-sediment relationships to quantify flow requirements for channel maintenance (Smakhtin et al., 2006).

2.2.4 Instream Flow Management in Bangladesh

In Bangladesh, flood control and irrigation development have been the main focus of water resources management without due attention to the low flow and instream flow management. Historically water has been managed from supply perspective with an emphasis on maximizing the economic return from its use. With increased awareness during the 1990s, particularly coined during the Flood Action Plan studies, the focus has now shifted towards round the year water management taking into consideration the environmental perspective of water resources management. Environmental implication of water resources development has been explicitly recognized in the National Water Policy (NWPo) and the National Water Management Plan (NWMP).

In Bangladesh no systematic study and research has been done for defining the environmental flow requirement. The instream requirement set forth in different Plan and project related studies, until now, has been on an ad-hoc and empirical basis. From a river management point of view, scientifically justified methods and guidelines are needed for determining flow requirement to safeguard the aquatic environment, livelihood of subsistence users and requirement of downstream users. In this regard water management in Bangladesh lags behind in the development of appropriate management tools for recommending the flow regimes considering environmental and ecological aspects (Bari, et al. 2006). Although few studies have been carried out at the academic and research level focusing few rivers mainly to gain experience in this field, but none of the recommendations have been applied in the real life management of the water resources of these rivers.

Rahman (1998) conducted an investigation to determine the instream flow requirement of the Ganges river, one of the mighty rivers of Bangladesh. In this study the author applied three methods of the hydrological approach. The computed instream flow requirement based on analysis of Flow Duration Curve method ranges from 1,580 m3/s in dry season to 40,000 m3/s in the wet season. The corresponding values for the

Constant Yield method ranges from 1,990 m3/s to 40,200 m3/s and those for the Mean Annual Flow method varies from 1,150 m3/s to 23,080 m3/s. A comparison of these values with minimum discharge revealed that in the pre-Farakka period, the minimum observed discharge met the flow requirement for instream protection whereas that for the post-Farakka period falls much below the required flow. The study concluded that since the minimum flow is less than the recommended flow for instream protection, the Ganges has suffered substantial morphological and environmental degradation. The study recommended to undertake studies to apply methods involving correlation of various parameters to habitat condition, since the method used in the study can provide only preliminary estimates of instream flow requirement; before undertaking any detailed, expensive and time-consuming analysis and study.

Zobeyer (2004) undertook a study to determine instream flow requirement for Surma river, located in the north-east region of Bangladesh, from flow-habitat relations developed for dominant fish species. In his study PHABSIM model has been applied only for adult life stage of Ghagot, Baghair and Bacha fish species. Considering the Weighted Usable Area versus discharge curves and seasonal availability of these three fish species, instream flow requirement becomes 150 m3/s for November to May, 500 m3/s for June to September and 300 m3/s for October. But considering the available median monthly flows for the months from November to April, a discharge of 150 m3/s may not be set as instream flow for these months, because in these months 50% of the time flow is well below 150 m3/s. So, median monthly flow of each of these months may be considered as instream flow for that month. In this study it has been concluded that no one method would provide for all needs and minimum flow assessment can be re-evaluated with changing demands.

Bari et al. (2006) conducted a research with the principal aim to understand the issue of instream flow requirements in selected rivers of Bangladesh in terms of their functions and problems, gain experience in the use of various techniques for instream flow need assessment and to suggest a suitable methodology for assessing Instream flow requirement. The research was jointly conducted by BUET and Delft Cluster institutions (Delft Hydraulics and Delft University of Technology) in collaboration with related organizations in Bangladesh. Considering the functions and problems of rivers, national interest in river management and characteristics variability of hydrological

regions, four rivers were selected for this study from three different hydrological and climatic regions of Bangladesh. The rivers are (i) Surma-Kushiyara, (ii) Teesta and (iii) Gorai. Three methods that have been applied in the study, namely (i) hydrologic method, (ii) Instream Flow Incremental Methodology (IFIM) using the Physical Habitat Simulation (PHABSIM) model and (iii) the Ecotope method. The study observed that no one method can provide for all needs and minimum flow assessment should be re- evaluated with changing demands and management strategies. A range of approaches requiring different levels of expertise and amount of data should be appropriate. The study also observed that habitat suitability criteria such as depth, velocity and substrate preference have more influence on flow assessment than any other aspects of the analysis.

Saha (2007) conducted a study on Gorai river for assessment of instream flow requirement based on salinity intrusion and fish habitat consideration. For salinity consideration, the target was to assess the flow requirement for irrigation water quality, sources of drinking water and household use, and to support Sundari tree in the mangrove. For fish habitat consideration, two target species were selected, Ayeer and Bacha. The study concluded that (i) flow requirement for the selected fish species also suffices salinity intrusion prevention, (ii) of the two selected fish species, flow requirement for Ayeer fish is about the same as the requirement for salinity prevention which is about 250 m3/s and (iii) flow required for Bacha fishes is almost double the amount required for Ayeer fishes.

Sudip et al. (2009) conducted a study to assess the environmental flow requirement for the Karnaphuli river. The study attempted to assess flow requirement for different species of fishes. Fishes were categorized into three categories. In group-I, Chital, Foli, Rita, Catla, Ilish and Kalbaush fishes were considered. The preferred water level and velocity for those fishes are 0.60 m and 1.01 m/s to 1.25 m/s respectively. In group-II, Magor, Singhi, Koi, Tagra, Pabda, Gazar and Shoal fishes were considered; the preferred water level and velocity for those fishes are 0.50 m to 0.60 m and 0.14 m/s to 1.25 m/s respectively. In group-III, Mala, Puti and Small Shrimp fishes were considered; preferred water level and velocity for these fishes are 0.15 m and 0.18 m/s to 0.47 m/s respectively. Required flow for these categories of fishes were computed considering the preferred habitat of these fishes and the required flow was compared

with the presently available flow in Karnaphuli river. The computed minimum discharge required for group I, II and III categories of fishes are 179.48 m3/s, 24.88 m3/s and 31.99 m3/s respectively. The study concluded that based on the water level requirement for fish habitat, the study reach of the river exhibits environmental flow for all three categories of fishes. But according to discharge requirement, environmental flow is satisfied for the last two categories of fishes while it does not satisfy for the first category which comprise of big fishes.

2.3 Instream Flow Methodologies

Considering the objectives of the decision making process, Stalnaker et al. (1995) classified environmental flow methodologies into two broad categories, namely (i) standard-setting and (ii) incremental. According to the standard setting methodologies, the analyst is required to determine and recommend an instream flow requirement to guide general and usually low-intensity decision making process to set a limit below which water cannot be diverted. This process may be called preliminary level planning. On the other hand, incremental methodologies refer to high-intensity, high-risk negotiation over a specific development project. The term incremental implies the need to answer the following question: what happens to the variable of interest (e.g. aquatic habitat, recreation value etc.) when the flow changes. Instead of making a clear distinction between the two methodologies, it is appropriate to view these two types of methodologies on a continuum ranging from the setting of non-controversial standards for overall planning to conflict over establishing incremental differences in flow levels. Whether a problem falls under the category of standard-setting or incremental is not distinguished from scientific credibility point of view (Bari et al. 2006).

Many methods have been developed during the last several decades, primarily in the United States and then in Europe, Australia and South Africa to establish environmental flow requirement. Some techniques were developed for protection of specific species, while others were developed for broader ecosystem. Since many different types of environmental flow assessment methods are available and used in different parts of the world, these methods can be classified in one or other way. According to the classification scheme suggested by Jowett (1997), Gordon et al. (1992) and King et al. (2000), different methods used worldwide for determining environmental flow requirement can be grouped into the four main categories;

(1) Standard-setting Methods (i) Hydrological Methodologies (ii) Hydraulic Rating Methodologies (2) Incremental Methods. (i) Habitat Rating Methodologies (ii) Holistic Approaches

Recently another approach of environmental flow assessment has been developed, known as the Ecotope method, which enables integration of river and floodplain ecosystem and other functions. The ecotope approach is based on the premise that the environmental functions of a river are determined by the entire river dynamics in time and heterogeneity in space (Bari et al. 2006). Various characteristics of the two broad categories of instream flow assessment techniques have been summarized by Stalnaker et al. (1995). Table-2.2 below shows various problem solving spectrum based on standard setting and incremental methodologies.

Table-2-2: The Opposite ends of the Methodologies

Standard Setting Incremental Low controversy project High controversy project Reconnaissance level planning Project specific Few decision variables Many decision variables Inexpensive Expensive Fast Lengthy Rule of thumb In depth knowledge required Less scientifically accepted More scientifically accepted Not well suited for bargaining Design for bargaining Based on historical flow Based on fish habitat Source: Bari et al. (2006)

From Table-2.2 it can be seen that standard setting methodologies are suitable for reconnaissance level analysis involving few decision making variable and less expensive whereas incremental methodologies are suitable for complex cases where decision making variables are many and comparatively more expensive. It is to be

mentioned that expert judgment is required in both standard-setting and incremental methodologies. This judgment is required in reaching a conclusion based on the technology that is chosen as well as in choosing the method. A brief description of the major four categories of methods for estimating instream flow requirement is presented in the following sections.

2.3.1 Hydrological Methodologies

As the name implies, hydrological methodologies (sometimes referred to as historic flow methods) rely solely on the recorded or estimated flow regime of the river. They represent the simplest set of techniques where, at a desktop level, hydrological data, as naturalized, historical monthly or average daily flow records, are analyzed to derive standard flow indices which then become the recommended environmental flows. Commonly, the Environmental Flow Requirement (EFR) is represented as a proportion of the flow (often termed as the ‘minimum flow’, e.g. Q95 – the flow equaled or exceeded 95 percent of the time) intended to maintain river health, fisheries or other highlighted ecological features at some acceptable level, usually on an annual, seasonal or monthly basis. In a few instances, secondary criteria in the form of catchment variables, hydraulic, biological or geo-morphological parameters are also incorporated. As a result of the rapid and non-resource intensive provision of low-resolution flow estimates, hydrological methodologies are generally used mainly at the planning stage of water resource developments or in situations where preliminary flow targets and exploratory water allocation trade-offs are required (Arthington et al. 1998; Tharme, 1996; Tharme, 2003).

The ecological goal of most historic flow methods is to sustain existing life forms by recommending a minimum flow that is within the historic flow range. Factors like food, habitat, water quality and temperature are not considered explicitly, but are assumed to be satisfactory because the aquatic species have survived such conditions in the past.

The most widely used common techniques for assessing instream flow requirement under this category are (Bari et al. 2006); (a) Mean Annual Flow Method (also known as Tennant method or Montana method), (b) Flow Duration Curve Method,

(c) Constant Yield Method, and (d) Range of Variability Approach. Out of the above four, first three methods have been used for determination of instream flow requirement in the present study and are briefly discussed in the following sections.

2.3.1.1 Types of Hydrological Methodology

Mean Annual Flow (MAF) Method: This method is widely known as Tennant method. It is also known as the Montana method although it is not used in that State (Reiser et al. 1989). It is perhaps the most widely known and used method of similar categories. It is the second most popular method in the USA and is used or recognized by 16 states (Reiser et al.1989). The Tennant method assumes that some percentage of the mean annual flow is needed to maintain a healthy stream environment. The method is based on the assumption that the flow of a stream is a composite outcome of several characteristics such as size of the drainage area, geomorphology, climate, vegetation and land use (Bari et al. 2006). Tennant examined cross-section data from 11 streams in Montana, Nebraska and Wyoming. He found that stream width, water velocity and depth all increased rapidly from zero flow to 10% of the mean flow, and that the rate of increase declined at flows higher than 10%. At less than 10% of the mean annual flow, he considered that water velocity and depth were degraded and would provide for ‘short-term’ survival of aquatic life. He considered that 30% of the average flow would provide satisfactory stream width, depth and velocity for a ‘baseflow regime’. At 10% of average flow, average depth and velocity was 0.30m and 0.25 m/s respectively, and Tennant considered these to be lower limits for aquatic life. He showed that 30% of average flow or higher provided average depths of 0.45m–0.60m and velocities of 0.45 m/s – 0.60 m/s and considered these to be in the good to optimum range for aquatic organisms. His studies conducted over a period of ten years using this method have shown that aquatic habitat conditions are similar in most streams carrying same proportion of flows. Analysis in 21 different states in the USA has substantiated these correlations (Bari et al. 2006). Eight classes of flow classifications have been suggested by Tennant after analyzing a series of field measurement and observations to correlate habitat quality and various percentage of mean annual flow.

Table-2.3 shows Tennant’s recommendation for instream flow to support varying qualities of fish habitat. In this Table ‘habitat quality’ represents the quality of the habitat that the authority desires to achieve and ‘percentage of mean annual flow’ represent the percent of MAF that is needed to achieve that habitat quality. Seven of these classifications (from ‘optimum’ to ‘severe degradation’) characterize habitat quality for fish and aquatic wild life and the eighth (‘flushing or maximum’) provides a flushing flow. According to the MAF method, the required percentages of MAF for habitat quality range from <10% (severe degradation) to 60-100% (optimum range), the flushing flow requirement being 200% of MAF. The Tennant method requires that MAF can be calculated from an historic and or synthetic flow.

Table-2-3: Percentage of MAF for various Habitat Quality

Percent of Mean Annual Flow (MAF) Habitat Quality Low Flow Season High Flow Season Flushing or maximum 200 200 Optimum 60-100 60-100 Outstanding 40 60 Excellent 30 50 Good 20 40 Fair 10 30 Poor 10 10 Severe degradation <10 <10

Source: Bari et al (2006)

The Tennant method differs from other methods of that category in that it is based on the assumption that a proportion of the average flow would maintain suitable depths and water velocities for trout and this assumption obviously applies only to rivers similar in size and gradient to Tennant’s study rivers. Whether the goal of sustaining existing aquatic life is achieved or not will depend upon the percentage of flow retained or exceedance levels selected. However, even within this group of methods there can be conflicting ecological goals. Tennant (1976) claimed that one virtue of his method was that it never produced a zero flow recommendation. Some Australian ecologists believe

that ‘an aquatic ecosystem is tightly coupled with its catchment’ (Cullen, 1992) and therefore suggest that the natural flow regime of a river is a guide to instream flow requirements, including practically all aspects of the flow regime, such as seasonal patterns of flow, low flow, periods of no flow and flood flow (Karim et al., 1995). Mean annual flow method is a ‘low risk’ approach to an instream flow policy aimed at maintaining an ecosystem in its existing state and precludes the possibility that a riverine ecosystem can be enhanced by other than a natural flow regime.

Flow Duration Curve (FDC) Method: In the Flow Duration Curve (FDC) method historic flow record is utilized to construct flow-duration curve for each month and to provide cumulative probabilities of exceedance for various flows. Using daily flow records of at least 20 years, flow duration curve is constructed and flow recommendation is made for each months. According to this method, the recommended flow for instream protection may be set at the 90th percentile (flow equaled or exceeded 90% of the time) for normal months and the 50th percentile during high flow months. Since the level of protection is implicit in the magnitude of percentage, different exceedance probabilities have been used in various countries to specify the required flow. For example, in New Zealand, 96% exceedance probability has been used to set the minimum flow. In Denmark, a proportion of the median of the annual minima has been recommended as minimum flow. Loar and Sale (1981) reported that in the Iowa state the minimum flow is set at the 84th percentile (Bari et. al, 2006). In Bangladesh, the 50th percentile (for high flow season and intermediate flow season) and 90th percentile (for low flow season) have been used to set the minimum flow requirement (Bari et. al., 2006; Rahman, 1998). The same percentile has been used under the present study also.

The flow-duration curve method does of course retain the basic simplicity of using hydrological flow data only, but it is more accurate than other techniques in this category only because of a better representation of flow variability (Rahman, 1998). However, as reported by Richardson (1986), a complete representation of a given water shed could still be lacking.

Constant Yield (CY) Method: This method has been developed in the U.S.A. It uses a combination of median monthly flow and constant yield statistic to represent the

watershed hydrology. This method is suitable for unregulated streams having catchment area greater than 130 km2 and historic flow records of more than 25 years. In this method, the median monthly flow serves as the datum for evaluating the instream flow requirement and 100% of the median monthly flow is set as the instream flow requirement. In Bangladesh, this procedure has been used for assessment of instream flow requirement for Surma, Kushiyara, Teesta and Gorai river (Bari et. al., 2006) and for the Ganges river (Rahman, 1998). Under the present study the same procedure has been used.

2.3.2 Hydraulic Rating Methodologies

Hydraulic rating methodologies use changes in simple hydraulic variables, such as wetted perimeter or maximum depth, usually measured across single, flow-limited river cross-sections (commonly riffles), as a surrogate for habitat factors known or assumed to be limiting to the target biota.

Hydraulic methods consider river width or wetted perimeter because the stream bed supports primary and secondary stream production/functions (periphyton and benthic invertebrates) and is considered to be the food-producing area of a stream (White, 1976). The aim is to keep the main river channel ‘full’ to maximize food production. Water velocity is not usually considered in hydraulic methods, possibly because it shows less clearly defined inflection points (Mosley, 1992). Like the Tennant method, hydraulic methods never result in a zero flow recommendation.

Environmental flows are determined from a plot of the hydraulic variable(s) against discharge, commonly by identifying curve breakpoints where significant percentage reductions in habitat quality occur with decrease in discharge. It is assumed that ensuring some threshold value of the selected hydraulic parameter at a particular level of altered flow will maintain aquatic biota and thus, ecosystem integrity. This relatively low-resolution hydraulic techniques have been superseded by more advanced habitat modelling tools or assimilated into holistic methodologies (Tharme 1996; Jowett 1997; Arthington and Zalucki 1998; Tharme 2003). Few examples of hydraulic rating methodologies are (Rahman, 1998); (a) Habitat-Discharge Method, (b) Simplified Staff-Gauge Method,

2.3.3 Habitat Rating Methodologies

Habitat simulation methodologies also make use of hydraulic-habitat and discharge relationships, but provide more detailed, modelled analyses of both the quantity and suitability of the physical river habitat for the target biota. Thus, environmental flow recommendations are based on the integration of hydrological, hydraulic and biological response data. Flow-related changes in physical microhabitat are modelled in various hydraulic programs, typically using data on depth, velocity, substratum composition and cover; and more recently, complex hydraulic indices (e.g. benthic shear stress), collected at multiple cross-sections within each representative river reach. Simulated information on available habitat is linked with seasonal information on the range of habitat conditions used by target fish or invertebrate species, commonly using habitat suitability index curves (Groshens and Orth 1994). The resultant outputs, in the form of habitat-discharge curves for specific biota, are used to derive optimum environmental flows. The habitat simulation-modelling package, PHABSIM, (Bovee 1982, Milhous et al. 1989), housed within the Instream Flow Incremental Methodology (IFIM), is the pre-eminent modeling platform of this type. Few examples of hydraulic rating methodologies are (Rahman, 1998; Arthington et al. 2004); (a) Usable Width Method, (b) Weighted Usable Width Method, (c) Preferred Area Method, (d) Instrean Flow Incremental Methodology (IFIM) (e) PHABSIM

2.3.4 Holistic Methodologies

Over the last few decades, river ecologists have increasingly struggled for a broader approach to the definition of environmental flows to sustain and conserve river ecosystems, rather than focusing on just a few target fish species (Arthington and Pusey 1993; King and Tharme 1994; Sparks 1992; Richter et al. 1996). From the conceptual foundations of a holistic ecosystem approach (proposed by Arthington et al. 1992), a wide range of holistic methodologies has been developed and applied, initially in

Australia and South Africa and more recently in the United Kingdom. This type of approach argues that if certain features of the natural hydrological regime can be identified and adequately incorporated into a modified flow regime, then, all other things being equal, the extant biota and functional integrity of the ecosystem should be maintained (Arthington et al. 1992; King and Tharme 1994). Sparks (1992) suggested that rather than optimizing water regimes for one or a few species, a better approach is to try to approximate the natural flow regime that maintained the “entire panoply of species”.

Importantly, holistic methodologies aim to address the water requirements of the entire “riverine ecosystem” (Arthington et al. 1992) rather than the needs of only a few species (usually fish or invertebrates). These methodologies are underpinned by the concept of the “natural flows paradigm” (Poff et al. 1997) and basic principles of guiding river corridor restoration (Ward et al. 2001). They share a common objective - to maintain or restore the flow related biophysical components and ecological processes of in-stream and groundwater systems, floodplains and downstream receiving waters courses.

Ecosystem components that are commonly considered in holistic approaches include geomorphology, hydraulic habitat, water quality, riparian and aquatic vegetation, macro-invertebrates, fish and other vertebrates with some dependency upon the river/riparian ecosystem (i.e. amphibians, reptiles, birds, mammals). Each of these components can be evaluated using a range of field and desktop techniques (Tharme 1996; Tharme 2003; Arthington and Zalucki 1998) and their flow requirements are then incorporated into EFA recommendations, using various systematic approaches.

Holistic approaches for environmental flow assessments may include evaluation of a range of other mitigation measures, for example, how to restore longitudinal and lateral connectivity, say, by providing fish passes or altering the configuration of levee banks on a floodplain. Management of storage water levels may also be examined and recommendations made on the benefits of more, or less, stable water levels. Some holistic methodologies also take into consideration the influence of threatening processes and disturbances unrelated (or less directly related) to flow regulation and

advise on possible mitigation measures such as riparian and habitat restoration, management of invasive vegetation, fish etc. Few examples of holistic methodologies are (Arthington et al., 2004; Bari et al. 2006); a) Building Block Method, b) DRIFT, c) Ecotope method.

2.3.5 A Comparative Statement of the Methodologies

Each of the above categories of flow assessment methodologies differ in their data requirements, methods of assessing flow requirement, ecological assumptions and effect on river hydraulics. A comparative statement of the various characteristic features of the methodologies is presented in Table-2.4.

From Table-2.4 it may be seen that historic flow methods are easy to apply and produce a single flow assessment. Levels of protection are specified as percentages or exceedance values of flow, but the relationships between flow and state of the ecosystem are poorly established in most cases. Tennant (1976) established relationships between the proportion of the flow and level of ecological protection for the rivers he studied. However, in most cases the basic ecological justification for most historic-flow methods is that a proportion of the flow will retain a proportion of the natural ecosystem. Percentage or exceedance levels are not usually varied with stream size or type. If the risk of environmental degradation is higher in small streams than in large, as habitat considerations suggest, an adjustment of percentage or exceedance for stream size would result in more consistent levels of environmental protection.

Hydraulic methods focus on maintaining water in the river channel, thereby maintains the appearance of a river. Field data requirements are similar to those of habitat methods. Levels of protection are determined by either a point of inflection or percentage retention. The ecological aim is to retain the wetted perimeter and thus productive area of a stream. However, velocity and depth are also important ecological requirements and a flow assessed only on the basis of wetted perimeter may result in adverse depths and velocities depending on river type and channel shape. For this reason, levels of protection in hydraulic methods are unlikely to be closely related to the state of the ecosystem.

Habitat methods provide the most flexible approach to flow assessments, but can be difficult to apply and interpret. Habitat methods provide information on how habitat changes with flow for instream uses, either biological or recreational. Because of this, the outcome depends critically on how the method is applied, what species or uses are considered and what suitability curves are used. Levels of protection can be specified as inflection points, optima or as minimum amounts of habitat. Since levels of protection are in terms of habitat, they are closely related to intended instream uses. On a conceptual level, habitat-based methods differ from both hydrological and hydraulic methods in that they make no ‘a priori’ assumptions about the state of the natural ecosystem. Historic flow and hydraulic methods assume that lower than natural flows would degrade the stream ecosystem, whereas habitat methods accept the possibility that a natural ecosystem, or at least some particularly valued aspects, can be enhanced by other means than naturally occurring flows.

Habitat methods are most suited to situations where there are clear management goals and defined levels of protection. In fact, application of such methods often causes water managers to realize that there is no simple answer to the problem of instream flow assessment and that flow requirements can vary depending on goals and levels of protection. Historic flow methods are easier to use because they incorporate their own levels of protection. Hydraulic methods are similar to flow methods in that they produce a single answer and incorporate their own levels of protection.

Unfortunately, an understanding of the biological systems is not yet complete. Many factors influence stream ecosystems (Orth, 1987) and, practically, flow assessments can only consider the most important and influential factors. Methods are often criticized for failing to consider some aspect of the stream environment. None of the methods consider temperature, water quality or biotic interactions explicitly and any change to the stream environment could potentially cause unexpected results. Flow assessments can only make use of the best available knowledge, and if necessary be conservative.

One answer is inevitable - there would be no aquatic ecosystem or instream uses without water in a river. However, because of the degree of diversity in a river and flexibility of most aquatic organisms, there is probably no sharp cut-off or single ‘minimum flow’. Environmental response to flow is a gradient along which a decision

must be made. It is unlikely that the state of knowledge of biological systems will ever reach a degree where the effect of flow changes on stream populations can be predicted with certainty. Experience, case studies, environmental risk and out-of-stream benefits all play a part in the decision-making process (Jowett, 1997).

Table-2-4: A Comparison of Different Methodologies

Features Methods Historic flow 1 Hydraulic rating 1 Habitat rating 1 Holistic 2 Data requirement Flow record, mean daily Cross-section, slope, roughness, Cross-section, hydraulic Large array of data for various river components. discharge preferably for 20 discharge data and velocity. parameters e.g. velocity, depth yrs. etc. Substrate preference data for Even sometimes geomorphology, soil, vegetation, dominant species (habitat elevation, flooding pattern etc. through remote suitability criteria) sensing and field survey for ecotope method. Applicability Good for initial assessment. Limited. Can be used for fish species. Highly relevant as it addresses all aspects. Ecotope method is relevant for flood-plain functions. Method of assessing % of average annual or % habitat retention. % habitat retention. flow requirement monthly flow. % exceedance. Inflection point. Inflection point. Optimum/ Minimum habitat. (exceedance or percentage). Stream hydraulics Effect on width, depth and Effect on depth and velocity dependent Prescribed depth and velocity. velocity dependent on on morphology. morphology. Maintains ‘character’. Maintains ‘character’ only in terms of Potential loss of ‘character’. variable considered (e.g. wetted perimeter). Ecological Close relationship between Biological productivity related to Close relationship between assumption natural flows and existing wetted area. habitat and ecology. ecology. Models consider ecological requirements, where known. Time and cost Not significant. Not significant, sometimes data not Significant. High. required readily available. Advantages and ‘Cook-book’ flow assessment. Not necessarily a ‘cook- book’ flow Not a ‘cook-book’ approach, Application and interpretation critical disadvantages assessment, some interpretation application and interpretation required. critical. Trade-off considerations not Trade-off considerations not possible. Allows trade-offs. Allows trade-offs. possible. Flow always less than, but Flow dependent on channel shape. Flow assessment independent related to natural. of natural flow. Precludes enhancement. Levels of protection difficult to relate Enhancement potential Enhancement potential recognized. to ecological goals. recognized. Source: 1 Jowett, I.G. (1997), 2 Bari et al (2006)

Chapter 3: Methodology

3.1 Data Collection

Necessary data required for the present study, such as daily water level and daily discharge data of Dudhkumar river at Pateswari station have been collected from Processing and Flood Forecasting Directorate of Bangladesh Water Development Board (BWDB). BWDB maintains a good hydrological measurement station at Pateswari. Daily water level data for the period 1963 to 2008 and daily discharge data for the period 1968 to 2006 is available with BWDB. For the present study, daily water level data for the period January 1965 to August 2008 and discharge data for the period April 1968 to December 2006 have been collected. A summary of the status of water level and discharge data collected for the present study is presented in Table-3.1.

Table-3-1: Summary of Collected Data Station ID and Type of Data Period of Data Period of Data used Name Collected after quality checking River: Dudhkumar Daily Water Level January 1965 to April 1968 - March Station: Pateswari August 2008 2007 Station ID: SW81 Daily Discharge April 1968 to April 1968 - March December 2006 2007

From the above Table it can be seen that availability of discharge data is less compared to that of water level data. Discharge data is available upto December 2006 whereas water level data is available upto August 2008. In order to have a complete set of discharge data for the last hydrological year, 2006-2007, discharge data has been filled for the period January-March 2007. After this discharge data filling, considering a common period of data availability, water level and discharge data for the period April 1968 to March 2007 has been used in the present study.

3.1.1 Water Level

A summary status, on a monthly basis, of the daily water level data collected for the period January 1965 to August 2008 is presented in Table-3.2, and the collected WL data is presented, after necessary filling of missing data, in Table-A.1 in Appendix-A. From Table-3.2 it can be seen that only in few months water level data is missing for few days. During the period January 1965 to August 2008, water level data is available

for 15503 days. Missing data has been filled, where found necessary, to complete a hydrological year. Table-3-2: Status of Daily Water Level Data Collected

Month Year Total Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1965 31 28 31 30 31 30 31 31 30 31 30 31 365 1966 31 28 31 30 31 30 31 31 29 31 30 31 364 1967 31 28 31 30 31 30 31 31 30 31 30 31 365 1968 31 29 31 30 31 30 31 31 30 31 30 31 366 1969 31 28 31 30 31 30 31 31 30 31 30 31 365 1970 31 28 31 30 31 30 31 31 30 31 30 31 365 1971 31 13 44 1972 30 31 30 31 31 30 31 30 31 275 1973 31 28 31 30 31 30 31 31 30 31 30 31 365 1974 31 28 31 30 31 30 31 31 30 31 30 31 365 1975 31 28 31 30 31 30 31 31 30 31 30 31 365 1976 31 29 31 30 31 30 31 31 30 31 30 31 366 1977 31 28 31 30 31 30 31 31 30 29 30 31 363 1978 31 28 31 30 31 30 31 31 30 31 30 31 365 1979 31 28 31 30 31 30 31 31 30 31 30 31 365 1980 31 29 31 30 31 30 31 31 30 31 30 31 366 1981 31 28 31 30 31 30 31 31 30 31 30 31 365 1982 31 28 31 30 31 30 31 31 30 31 30 31 365 1983 31 28 31 30 31 30 31 31 30 31 30 31 365 1984 31 29 31 30 31 30 31 31 30 31 30 31 366 1985 31 28 31 30 31 30 31 31 30 31 30 31 365 1986 31 28 31 30 31 30 31 31 30 31 30 31 365 1987 31 28 31 30 31 30 31 31 30 31 30 31 365 1988 31 29 31 30 31 30 31 31 30 31 30 31 366 1989 31 28 31 30 31 30 31 31 30 31 30 31 365 1990 31 28 31 30 31 30 31 31 30 31 30 31 365 1991 31 28 31 30 31 30 31 31 30 31 30 31 365 1992 31 29 31 30 31 30 31 31 30 31 30 31 366 1993 31 28 31 30 31 30 31 31 30 31 30 31 365 1994 31 28 31 30 31 30 31 31 30 31 30 31 365 1995 31 28 31 30 31 30 31 31 30 31 30 31 365 1996 31 29 31 30 31 30 31 31 30 31 30 31 366 1997 31 28 31 30 31 30 31 31 30 31 30 31 365 1998 31 28 31 30 31 30 31 31 30 31 30 31 365 1999 31 28 31 30 31 30 31 31 30 31 30 31 365 2000 31 29 31 30 31 30 31 31 30 31 30 31 366 2001 31 28 31 30 31 30 31 31 30 31 30 31 365 2002 31 28 31 30 31 30 31 31 30 31 30 31 365 2003 31 28 31 30 31 30 31 30 31 30 31 334 2004 31 29 31 30 31 30 31 31 30 31 30 31 366 2005 31 28 31 30 31 30 31 31 30 31 30 31 365 2006 31 28 31 30 31 30 31 31 30 31 30 31 365 2007 31 28 31 30 31 30 31 31 30 31 30 31 365 2008 31 29 31 30 31 30 31 31 244 Total no. 1333 1199 1302 1290 1333 1290 1333 1332 1229 1300 1260 1302 15503 of days Total no. 43 43 42 43 43 43 43 43 41 42 42 42 510 of months Note: The numbers in each month indicate the number of WL data availability in that month.

For filling the missing WL data of February and March 1971, the water level data of February and March 1969 has been used. Since February and March are dry months, it is thought justified to use the data of 1969 to fill the data gap of 1971. To fill the missing water level data of September 2003, average of the water level of September 2002 and 2004 has been used. In some cases, WL data was found to be missing for few days, e.g. (i) 29th September 1966, (ii) 7th and 8th October 1977; (iii) 31st August 2003

etc. In these cases, missing data has been filled by linear interpolation by observing the trend of data just preceding and following the missing period. In some cases data punching error was detected, e.g. (i) on 25th August 1979 recorded WL is found to be 27.66 mPWD, whereas on 24th and 26th August 1979 recorded WL is found to be 28.74 mPWD and 28.56 mPWD respectively. In this case WL data of 25th August has been replaced by 28.66 mPWD. Similar adjustments have been made in few other cases. A hydrograph of the daily water level data is shown in Figure-3.1. A more enlarged, five year block wise, hydrograph of water level and discharge is presented in Figure-B.2, Appendix-B.

32.00

31.00

30.00

29.00

28.00 Water Level (m PWD)

27.00

26.00

Date

Figure-3.1: Water Level Hydrograph at Pateswari

From the above Figure it can be seen that there is a general rising trend of water level at Pateswari. This trend is noticeable in the post-liberation period both in the dry as well as in the monsoon season. Although the exact reason of such rising trend is not known, it may be attributed to a rise in gauze zero value or siltation in the vicinity of the WL gauge station at Pateswari.

Quality of the water level data has been checked by visual inspection of the yearly WL hydrograph. Since there is no other WL measurement station on the Dudhkumar river upstream and downstream of Pateswari, it was not possible to assess the consistency of

WL data of Pateswai by comparing with neighboring station. Although Nonkhowa is situated on the Dudhkumar river, it is subject to backwater effect from the Brahmaputra river. As such Nonkhawa WL has not been used for assessing the data quality of Pateswari.

3.1.2 Discharge

Like water level data, a summary status, on a monthly basis, of the daily discharge data collected for the period April 1968 to December 2006 is presented in Table-3.3, and the collected discharge data is presented, after necessary filling of missing data, in Table- A.2, Appendix-A.

Table-3-3: Status of Daily Discharge Data Collected (before filling missing data)

Month Year Total Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1968 30 31 30 31 31 30 31 30 31 275 1969 31 28 31 30 31 30 31 31 30 31 30 31 365 1970 31 28 31 30 31 30 31 31 30 31 30 31 365 1971 31 13 44 1972 30 31 30 31 31 30 31 30 31 275 1973 31 28 31 30 31 30 31 31 30 31 30 31 365 1974 31 28 31 30 31 30 31 31 30 31 30 31 365 1975 31 28 31 30 31 30 31 31 30 31 30 31 365 1976 31 28 31 30 31 30 31 31 30 31 30 31 365 1977 31 28 31 30 31 30 31 31 30 31 30 31 365 1978 31 28 31 30 31 28 14 31 224 1979 31 28 31 30 31 30 31 31 30 31 30 31 365 1980 31 28 31 30 31 30 9 3 30 31 254 1981 31 28 31 30 31 25 7 31 30 31 275 1982 8 22 12 9 30 31 30 31 173 1983 31 28 31 20 31 6 21 30 31 229 1984 31 28 31 90 1985 1986 30 31 12 6 31 30 31 171 1987 31 28 31 30 31 30 31 31 30 31 30 31 365 1988 31 28 31 30 31 30 31 31 30 31 30 31 365 1989 31 28 31 30 31 30 31 31 30 31 30 22 356 1990 28 30 30 31 30 31 31 30 31 30 31 333 1991 31 28 31 30 31 30 31 31 30 31 30 31 365 1992 31 28 31 30 31 30 31 31 30 31 30 31 365 1993 31 28 31 30 31 5 16 31 30 31 30 31 325 1994 31 28 31 30 31 30 31 31 30 31 30 31 365 1995 31 28 31 30 31 30 31 31 30 31 30 31 365 1996 31 28 31 90 1997 1998 19 30 31 30 31 141 1999 31 28 31 30 31 30 31 31 30 31 30 30 364 2000 31 29 31 30 31 30 31 31 30 31 30 30 365 2001 31 28 31 30 31 30 31 31 30 31 30 30 364 2002 31 28 31 30 31 30 31 31 30 31 30 334 2003 29 28 31 9 31 30 31 31 30 31 30 24 335 2004 19 30 31 31 30 31 172 2005 2006 27 28 31 30 31 30 31 31 30 31 30 27 357 Total no. 901 826 898 869 971 868 800 834 853 954 944 938 10656 of days

Total no. 30 30 29 30 32 32 27 28 30 32 32 31 363 of month Note: The numbers in each month indicate the number of data availability in that month.

From Table-3.3, it is seen that the amount of missing discharge data is more compared to that of water level data. Daily discharge data is available, although with gaps, for the period April 1968 to December 2006. During this period, discharge data is available for 10656 days. Where it is found necessary to fill missing discharge data to complete a month, missing data has been filled by using rating curve. After filling, discharge data became available for 11689 days. The discharge data is presented in Table-A.2, Appendix-A and discharge hydrograph is shown in Figure-B.2 in Appendix-B.

3.2 Instream Flow Assessment

As mentioned earlier, instream flow requirement for Dudhkumar river at Pateswari has been assessed using three methods of the hydrological approach. The methods are (i) Mean Annual Flow method, (ii) Flow Duration Curve method and (iii) Constant Yield method. All the methods belong to hydrological approach and use historical flow data.

3.2.1 Mean Annual Flow Method

According to the MAF method, IFR is set at different percentage of the mean annual flow. The percentages vary from 10% to 200% of the mean annual flow. The percentage is set considering the desired habitat quality. For determination of IFR using the MAF method, mean annual flow of Dudhkumar river at Pateswari has been computed. The computed mean annual flow for each year as well as for the whole period of data availability is presented in Table-3.4. From Table-3.4 it may be seen that mean annual flow of Dudhkumar river at Pateswari varies from 246 m3/s to 808 m3/s with an average of 475 m3/s. This average flow (475 m3/s) has been used to assess the IFR using the MAF method.

3.2.2 Flow Duration Curve Method

According to the Flow Duration Curve method, IFR has been set at the 50th (for high flow season) and 90th (for low flow season) percentile flow of the monthly flow duration curve. For this purpose, flow duration curve for each month of the year has been constructed. The flow duration curve shows the percentage of time during which a specified flow is equaled or exceeded. To construct flow duration curve, the daily discharge of each month, for the full period of data availability, is arranged in descending order and grouped into suitable number of classes. Then the number of days having flow in each class is counted and the percent of time the given flow is equaled

or exceeded is computed. The detail computation of flow duration curve for each month is shown in Table-A.3 to Table-A.14 in Appendix-A, and the corresponding graphical plot of the flow duration curve is shown in the accompanying Figures.

Table-3-4: Yearly Maximum, Average and Minimum Discharge (m3/s) at Pateswari Sl. No Hydrological Year Maximum Mean Minimum 1 1968-69 9250 758 79 2 1969-70 2360 442 72 3 1970-71 4670 694 79 4 1971-72 5 1972-73 4240 798 62 6 1973-74 993 246 80 7 1974-75 1640 404 85 8 1975-76 1160 305 71 9 1976-77 7190 808 63 10 1977-78 809 322 91 11 1978-79 1690 375 80 12 1979-80 1120 280 77 13 1980-81 1940 367 56 14 1981-82 15 1982-83 16 1983-84 2683 476 42 17 1984-85 18 1985-86 19 1986-87 1721 404 70 20 1987-88 5210 563 65 21 1988-89 4460 647 60 22 1989-90 3430 628 62 23 1990-91 2190 435 76 24 1991-92 3080 562 62 25 1992-93 1570 297 52 26 1993-94 5730 500 74 27 1994-95 1220 271 85 28 1995-96 4010 612 94 29 1996-97 30 1997-98 31 1998-99 32 1999-2000 2090 426 66 33 2000-01 2807 509 62 34 2001-02 1447 440 67 35 2002-03 1278 352 77 36 2003-04 2174 499 123 37 2004-05 38 2005-06 39 2006-07 1473 362 70 Range 809-9250 246-808 42-123 Average 2884 475 72

Note: Blank spaces mean that discharge data for the full hydrological year is not available, although data for few months of that particular year is available. As such, no maximum, mean and minimum is calculated for those hydrological years.

3.2.3 Constant Yield Method

According to the Constant Yield method, instream flow requirement for the Dudhkumar river has been set at 100% of the median monthly flows for each month. For this purpose, median monthly flow for each month has been computed in two different ways.

According to the 1st method, the median flow of each month has been computed considering the full data availability period and the median flow thus computed is shown at the bottom of Table-A.2 in Appendix-A.

In the 2nd method, median monthly flow for each month of each year has been computed separately. Thus, several median values are obtained for each month, and then the median of these values has been taken as the median for the given month over the entire period of record. The computed median monthly flow for each month of each year and for the entire period is shown in Table-3.5.

Since Dudhkumar river is an unregulated river and the drainage area exceeds 130 km2 and the availability of flow record is more than 25 years, median monthly flows can serve as the datum for assessment of instream flow requirement. Thus the instream flow requirement for each month has been taken as 100% of the average of the median monthly flows computed according to the two different methods.

Table-3-5: Median Monthly Flow (m3/s) of Dudhkumar River at Pateswari

Month Hydrological Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1968-69 120 261 516 2090 1150 825 814 297 239 160 113 99 1969-70 122 212 621 1130 960 845 383 256 181 148 112 93 1970-71 103 252 849 1700 1530 906 640 320 217 177 114 99 1971-72 1972-73 158 560 1380 1540 1660 1520 541 234 184 136 96 69 1973-74 88 131 575 303 526 300 280 188 137 102 123 112 1974-75 133 391 672 657 603 656 518 179 170 150 144 133 1975-76 116 184 483 552 495 599 450 181 130 100 93 80 1976-77 70 228 1340 2310 2020 825 371 205 152 128 107 91 1977-78 184 294 463 555 668 463 382 285 190 135 124 96 1978-79 94 201 404 1065 897 596 366 219 185 178 95 90 1979-80 90 146 172 412 545 802 411 211 165 121 94 88 1980-81 115 192 418 811 1131 590 297 239 173 127 76 62 1981-82 79 79 126 854 887 805 172 102 83 1982-83 651 391 254 169 141 117 101 1983-84 98 312 422 1148 665 1332 554 338 217 168 134 102 1984-85 1985-86 1986-87 81 165 374 911 813 1011 701 222 151 99 78 83 1987-88 91 156 208 1110 2120 1215 484 245 147 93 78 68 1988-89 73 150 225 1430 2310 2125 422 181 104 70 75 64 1989-90 80 99 534 1580 1200 1660 883 293 166 144 108 93 1990-91 120 219 812 1250 728 697 472 216 148 100 85 80 1991-92 107 241 1480 1020 1580 1055 316 192 142 110 92 67 1992-93 61 171 258 850 631 541 314 179 123 109 92 79 1993-94 108 372 624 1300 991 628 650 291 167 118 95 86 1994-95 108 164 472 343 696 487 293 176 133 100 91 95 1995-96 108 209 1335 1410 938 763 495 286 215 158 130 111 1996-97 1997-98 1998-99 1090 531 345 220 154 107 87 71 1999-2000 83 164 478 1064 710 784 611 304 198 128 112 91 2000-01 140 295 1172 701 1338 1003 344 249 165 120 95 72 2001-02 128 207 633 549 934 1163 680 299 201 135 100 81 2002-03 156 205 512 1038 763 506 324 192 146 103 89 94 2003-04 271 255 530 1437 995 802 567 265 167 171 140 136 2004-05 218 430 585 1693 659 838 555 296 208 2005-06 143 111 85 2006-07 99 159 657 768 414 831 433 215 170 146 133 117 Overall Median 108 207 530 1064 916 802 433 234 167 128 98 91

Note: Median monthly flow of each year constitute the data series for computing the monthly median flow over the period 1968-2007 for each month.

Chapter 4: Results and Discussion

4.1 Assessment of Instream Flow Requirement

Instream flow requirement for Dudhkumar river has been assessed applying three methods of hydrological approach, using historical daily discharge data of the river at Pateswari. After due consistency checking of the collected data, instream flow requirement has been assessed using (i) Mean Annual Flow (MAF) method, (ii) Flow Duration Curve (FDC) method and (iii) Constant Yield (CY) method. The methods used are reiterated here in brief and the results obtained from analysis are presented in the following sections.

4.1.1 Mean Annual Flow (MAF) Method.

As stated earlier, according to this method, instream flow requirement varies from 10% of the Mean Annual Flow (which represents the severely degraded condition and barely sufficient for short term survival) to 200% of the MAF (which represents the flushing flow requirement), with several other habitat quality objective in between the two extremities. Different percentage of the MAF, as mentioned in Table-2.3, is set as the required instream flow for different habitat quality.

For identification of the low flow and high flow season, mean monthly flow for the period of 1968-69 to 2006-07 has been determined using the daily discharge data. The computed monthly maximum, mean and minimum flow is shown in Table-4.1 and the variation of monthly maximum, mean and minimum flow is shown in Figure-4.1 From a review of the variation of the monthly average flow, as shown in Table-4.1 and the accompanying Figure-4.1, it is seen that November, December, January, February, March, April and May may be considered as the low flow season and June to October may be considered as the high flow season. It is worth mentioning that similar approach has been adopted in NWMP for classifying dry season and monsoon season. Within the low flow season, December to April may be considered as the critical low flow season.

Table-4-1: Monthly Average Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1968-69 117 308 960 2431 1204 1312 1782 308 234 157 113 103 2431 752 103 1969-70 131 275 559 1190 1020 920 401 252 187 144 110 92 1190 440 92 1970-71 162 343 1010 1901 1786 1277 838 323 225 177 131 103 1901 690 103 1971-72 1972-73 156 604 1556 2068 2102 1694 606 248 187 132 95 76 2102 794 76 1973-74 89 131 507 347 541 337 327 188 135 106 124 111 541 245 89 1974-75 165 396 713 703 805 741 503 215 165 153 144 132 805 403 132 1975-76 118 190 496 612 526 637 485 184 129 101 93 78 637 304 78 1976-77 86 222 1588 2826 2642 1165 407 209 153 127 106 90 2826 802 86 1977-78 177 303 457 567 651 461 393 279 194 141 123 98 651 320 98 1978-79 110 231 493 1002 870 590 373 245 200 167 100 89 1002 372 89 1979-80 90 161 175 459 625 730 424 213 167 123 96 88 730 279 88 1980-81 117 192 393 824 1205 622 332 243 176 123 79 64 1205 364 64 1981-82 77 80 225 845 988 755 173 102 83 988 370 77 1982-83 698 404 257 176 138 116 104 698 270 104 1983-84 85 320 466 1121 752 1391 602 349 209 172 133 101 1391 475 85 1984-85 1985-86 1986-87 90 163 457 946 911 1010 610 227 149 99 78 81 1010 402 78 1987-88 90 152 291 1352 2327 1315 551 256 145 93 78 69 2327 560 69 1988-89 76 160 326 1503 2406 2237 514 179 105 71 74 65 2406 643 65 1989-90 80 211 599 1626 1297 1831 1002 338 166 144 108 94 1831 625 80 1990-91 114 234 848 1327 779 769 497 216 148 102 83 80 1327 433 80 1991-92 108 237 1270 1307 1616 1245 351 185 142 108 90 67 1616 561 67 1992-93 65 171 314 906 619 560 332 171 124 109 95 79 906 295 65 1993-94 113 374 590 1604 1109 671 710 294 177 119 97 92 1604 496 92 1994-95 112 179 453 381 744 492 279 178 134 101 91 98 744 270 91 1995-96 117 420 1753 1521 1087 938 570 305 218 160 131 114 1753 611 114 1996-97 1997-98 1998-99 1207 698 357 225 155 108 87 71 1207 364 71 1999-00 96 181 566 1072 887 839 610 317 200 131 109 90 1072 425 90 2000-01 159 317 1211 834 1477 1006 384 239 168 121 95 71 1477 507 71 2001-02 115 257 675 610 954 1158 671 307 197 135 103 85 1158 439 85 2002-03 171 204 463 1000 791 570 369 196 145 104 89 100 1000 350 89 2003-04 275 275 604 1471 1012 813 596 290 173 176 143 141 1471 497 141 2004-05 208 370 746 1677 697 964 601 302 210 1677 642 208 2005-06 148 111 86 148 115 86 2006-07 97 194 713 806 471 775 468 228 172 148 132 123 806 361 97 Max 275 604 1753 2826 2642 2237 1782 349 234 177 144 141 2826 802 208 Mean 121 253 693 1188 1128 946 531 245 168 129 105 92 1313 455 91 Min 65 80 175 347 471 337 173 102 83 71 74 64 148 115 64 Median 113 231 566 1072 971 813 485 243 168 129 102 90 1197 429 87 St. Dev 45 106 406 589 571 419 280 57 34 27 20 19 619 166 27 No. on rec. 31 31 31 31 32 33 33 33 33 32 32 32 34 34 34

Variation of Maximum, Mean and Minimum Flow of Monthly Average Flow Max imum Mean Minimum 3000 2500

/s) 2000 3 1500 1000 Flow (m 500 0 Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Month

Figure-4.1: Variation of Max. Mean and Min. of Monthly Mean Flow at Pateswari

For determination of IFR using the MAF method, the computed mean annual flow, 475 m3/s, as shown in Table-3.4, has been multiplied by different percentages depending on the flow season and the habitat quality. The various percentages used for different flow season and habitat quality, and the computed IFR for different flow season and habitat quality is presented in Table-4.2 below.

From Table-4.2 it may be seen that instream flow requirement for different months of the year varies from as low as 48 m3/s to as high as 950 m3/s under different management objectives (desired habitat quality) for two different flow seasons. A flow of 48 m3/s is required to maintain the habitat in a poor to fair condition whereas a flow of 950 m3/s is the maximum IFR needed for flushing of the habitat.

This wide variation of IFR is quite obvious, since the assessment of IFR depends on the methodology used, season of the river flow and the desired habitat quality which the management wishes to achieve and/or maintain. For the sake of the present study, i.e. to assess the demand – availability scenario, the low flow season has been evaluated for two different habitat quality, namely (i) ‘good’ and (ii) ‘outstanding’. For the ‘good’ habitat quality 20% of the MAF is required and for the ‘outstanding’ habitat quality 40% of the MAF is required. It is worth mentioning that National Water Plan Project Ph-II has advocated the use of 40% flow as the instream flow requirement (MPO, 1991). On the other hand, for the high flow season ‘flushing’ habitat quality is considered as the desired goal for which 200% of the MAF is required. Under these conditions the IFR according to the MAF method comes out to be 95 m3/s, 190 m3/s and 950 m3/s for the ‘good’, ‘outstanding’ and ‘flushing’ habitat quality respectively.

Table-4-2: Instream Flow Requirement (m3/s) according to MAF Method

Mean Annual Low Flow Season High Flow Season Mean Annual Low Flow Season High Flow Season Habitat Quality Month 3 Habitat Quality Month 3 Flow (m /s) % of MAF IFR (m3/s) % of MAF IFR (m3/s) Flow (m /s) % of MAF IFR (m3/s) % of MAF IFR (m3/s) Jan 950 950 Jan 95 190 Feb 950 950 Feb 95 190 Mar 950 950 Mar 95 190 Apr 950 950 Apr 95 190 May 950 950 May 95 190 Jun 950 950 Jun 95 190 475 200 200 477 20 40 Jul 950 950 Jul 95 190 Aug 950 950 5. Good Aug 95 190 Sep 950 950 Sep 95 190 Oct 950 950 Oct 95 190 1. Flushing or Maximum Nov 950 950 Nov 95 190 Dec 950 950 Dec 95 190 Jan 285-475 285-475 Jan 48 143 Feb 285-475 285-475 Feb 48 143 Mar 285-475 285-475 Mar 48 143 Apr 285-475 285-475 Apr 48 143 May 285-475 285-475 May 48 143 Jun 285-475 285-475 Jun 48 143 475 60-100 60-100 475 10 30 Jul 285-475 285-475 Jul 48 143 6. Fair

2. Optimum Aug 285-475 285-475 Aug 48 143 Sep 285-475 285-475 Sep 48 143 Oct 285-475 285-475 Oct 48 143 Nov 285-475 285-475 Nov 48 143 Dec 285-475 285-475 Dec 48 143 Jan 190 285 Jan 48 48 Feb 190 285 Feb 48 48 Mar 190 285 Mar 48 48 Apr 190 285 Apr 48 48 May 190 285 May 48 48 Jun 190 285 Jun 48 48 475 40 60 475 10 10 Jul 190 285 Jul 48 48 Aug 190 285 7. Poor Aug 48 48 3. Outstanding Sep 190 285 Sep 48 48 Oct 190 285 Oct 48 48 Nov 190 285 Nov 48 48 Dec 190 285 Dec 48 48 Jan 143 238 Jan < 48 < 48 Feb 143 238 Feb < 48 < 48 Mar 143 238 Mar < 48 < 48 Apr 143 238 Apr < 48 < 48 May 143 238 May < 48 < 48 Jun 143 238 Jun < 48 < 48 475 30 50 475 < 10 < 10 Jul 143 238 Jul < 48 < 48 Aug 143 238 Aug < 48 < 48 4. Excellent Sep 143 238 Sep < 48 < 48 Oct 143 238 8. Severe degradation Oct < 48 < 48 Nov 143 238 Nov < 48 < 48 Dec 143 238 Dec < 48 < 48

4.1.2 Flow Duration Curve (FDC) Method

For assessment of the instream flow requirement using the Flow Duration Curve method, the 90th and 50th percentile flow of the flow duration curve has been taken as the IFR for the low flow and high flow season respectively. The flow duration curve method has been applied to assess instream flow requirement for Surma, Kushiyara, Teesta and Gorai river (Bari et al., 2006) and for the Ganges river (Rahman, 1998). In all the cases, the recommended flow for instream protection was set at 90th percentile for low flow season and at 50th percentile for high and intermediate flow season. In the present study, the same procedure has been adopted for setting the instream flow requirement. Considering November to May as the low flow month and June to October as the high flow month, the instream flow requirement for Dudhkumar river at Pateswari is determined by taking the 90th and 50th percentile from the flow duration curve, as shown in Table-A.3 to Table-A.14 in Appendix-A. The computed instream flow requirement, according to the FDC method, for different months of the year is shown in Table-4.3. Since November to May has been considered as the low flow month, 90th percentile flow has been taken as the IFR for the low flow period. Similarly, 50th percentile flow has been taken as the IFR for the high flow season.

Table-4-3: Instream Flow Requirement (m3/s) according to FDC Method

Monthly Instream Flow Requirement (m3/s) Flow Percentile Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Flow at 50th 115 235 580 1190 1180 1060 675 260 172 135 106 93 percentile Flow at 90th 82 140 250 675 780 605 300 190 125 100 82 72 percentile Flow Season LFS High flow season Low flow season (LFS) Suggested IFR 82 140 580 1190 1180 1060 675 190 125 100 82 72

From Table-4.3 it may be seen that IFR during the dry season, November to May, varies from 72 m3/s to 190 m3/s with an average of 113 m3/s; while in the monsoon season, June to October, the IFR varies from 580 m3/s to 1190 m3/s with an average of 937 m3/s.

4.1.3 Constant Yield (CY) Method

As stated earlier in Section-3.2.3, according to this method, instream flow requirement for the Dudhkumar river has been set at 100% of the median monthly flows for each month. For this purpose, median monthly flow for each month has been computed in

two different ways as mentioned in Section-3.2.3. A summary of the median monthly flows computed by the two methods in presented in Table-4.4. The suggested IFR for each month has been taken to be the average of the median monthly flows determined according to the two different methods.

Table-4-4: Instream Flow Requirement (m3/s) according to CY Method

Monthly median flow (m3/s) Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1st method 104 206 542 1000 921 796 436 235 167 129 102 89 2nd method 108 207 530 1064 916 802 433 234 167 128 98 91 Suggested IFR (average of the 106 207 536 1032 918 799 435 234 167 128 100 90 two methods) Flow season LFS High flow season Low flow season (LFS)

A critical review of Table-4.4 reveals that according to the Constant Yield method IFR during the dry season varies from 90 m3/s to 234 m3/s with an average of 147 m3/s while during the monsoon season it varies from 435 m3/s to 1032 m3/s with an average of 744 m3/s.

4.1.4 Summary of Instream Flow Requirement by various Methods

A summary of the instream flow requirement for the Dudhkumar river at Pateswari computed by the Mean Annual Flow method, Flow Duration Curve method and Constant Yield method is presented in Table-4.5 as well as in Figure-4.2. For the MAF method two different scenarios have been considered. Option-I comprises of ‘good’ habitat quality for the low flow season and ‘flushing’ habitat quality for the high flow season. In Option-II ‘outstanding’ habitat quality has been considered for the low flow season keeping the habitat quality for the high flow season same as that of Option-I.

From a review of Table-4.5 and Figure-4.2, it may be seen that, according to the MAF method, under Option-I, IFR varies from 95 m3/s in the low flow season to 950 m3/s in the high flow season whereas under Option-II of the MAF method, it varies from 190 m3/s in the low flow season to 950 m3/s in the high flow season. According to the FDC method IFR varies from 72 m3/s in the low flow season to 1190 m3/s in the high flow season and according to the CY method it varies from 90 m3/s in the low flow season to 1032 m3/s in the high flow season. For comparing the demand-availability scenario,

IFR computed by the MAF method only has been considered since this method is the 2nd widely used method for assessing IFR, as may be seen in Table-2.1.

Table-4-5: Summary of IFR computed by the three Methods

Instream Flow Requirement (m3/s) Months Season Mean Annual Flow Method Flow Duration Curve Method Constant Yield Method Option-I Option-II April Low 95 190 82 106 May Flow 95 190 140 207 June 950 950 580 536 July 950 950 1190 1032 High August 950 950 1180 918 Flow September 950 950 1060 799 October 950 950 675 435 November 95 190 190 234 December 95 190 125 167 Low January 95 190 100 128 Flow February 95 190 82 98 March 95 190 72 89

Note: Option-I: ‘Good’ and ‘Flushing’ habitat quality is assumed for low and high flow season respectively. Option-II: ‘Outstanding’ and ‘Flushing’ habitat quality is assumed for low and high flow season respectively.

1400 MAF method (Option-I) MAF method (Option-II) FDC method 1200 CY method

1000

800

IFR (m3/s) 600

400

200

0 Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Months

Figure-4.2: Variation of IFR computed by the three Methods

4.2 Other Sectoral Water Demand

The likely sectoral water demand that could be met from Dudhkumar river are (i) agricultural demand, (ii) domestic and industrial demand, and (iii) navigational demand. Present irrigation requirement in the Dudhkumar dependent area in Bangladesh is mainly met from ground water, except some localized use of surface water (SW) where SW of internal khals and water bodies are used for agricultural purpose. Presently no water is withdrawn from Dudhkumar river for agricultural purpose. However, BWDB has a plan to divert the waters of Dudhkumar for irrigation development in the locality, details of which is presented in Section-4.2.1.

Domestic and industrial water demand in the vicinity of Dudhkumar river in Bangladesh is presently met from ground water and this is likely to continue in near future given the present advantages of GW over SW for domestic and industrial use. However, considering the potential threat of arsenic and other contamination in GW in various parts of Bangladesh, under the present study it is assumed that domestic and industrial water demand within the KIPNU area would be met from Dudhkumar river, and as such this domestic and industrial water demand is considered to be abstracted from Dudhkumar river. As far as navigational demand is concerned, there is no designated navigational route of BIWTA in Dudhkumar river. Only country boats ply in Dudhkumar river. The present navigational route of BIWTA is shown in Figure-B.3, Appendix-B. Considering the likely sectoral water requirement that could be met from Dudhkumar river, as discussed above, agricultural water demand and domestic and industrial water demand is considered under the present study.

4.2.1 Agricultural Demand

Within the catchment area of Dudhkumar river in Bangladesh, Kurigram Flood Control, Drainage and Irrigation Project (North Unit), sometimes referred to as KIPNU, is the potential irrigation project for which water could be diverted from Dudhkumar river. Location of the project and the proposed pump stations for diverting water from Dudhkumar river is shown in Figure-B.1, Appendix-B. The project is located on the right bank of Dudhkumar river. The left side of Dudhkumar river, which is an active flood plain of the Brahmaputra river and mainly Char land, is not protected from flood. As such there is very little or no potential for development of any significant surface

water based irrigation project for utilization of water of Dudhkumar river. Presently KIPNU is under active consideration of BWDB for implementation.

In a recent study, IWM has prepared a detail irrigation development plan for the project area (IWM, 2009). According to the Plan, irrigation water would be distributed in the project area by gravity through a network of irrigation canal. Required irrigation water would be diverted from Dudhkumar river by two pump stations, one located at Pateswari and the other located at Tangonmari, about 32 km downstream of Pateswari. Peak diversion requirement at Pateswari and Tangonmari pump station has been assessed to be 35.20 m3/s and 4.16 m3/s respectively, assuming a duty of 650 ha/m3/s. Crops considered in determining the irrigation diversion requirement are (i) HYV Boro, (ii) HYV Aman, (iii) HYV Aus, (iv) Wheat, (v) Potato and (vi) Vegetable. Net irrigable area under Pateswari and Tangonmari pump station is estimated to be 22,588 ha and 2,803 ha respectively (IWM, 2009). In the IWM study, only the ‘peak diversion’ requirement (Boro season requirement) from Dudhkumar has been assessed, no ‘monthly diversion’ requirement assessment has been done. However, irrigation requirement at the field level on a monthly basis has been made in the IWM’s study and the peak field irrigation requirement for the full project area (25,392 ha cultivable area) is found to be 20.74 m3/s, occurring in the month of January. Peak diversion requirement has been estimated considering this peak field irrigation requirement, various losses such as conveyance loss, field application loss, absorption loss; pump operation hour and practical experience from similar other projects in Bangladesh.

Assessment of monthly diversion requirement under the present study has been made on a proportionate basis considering the peak field irrigation requirement (20.74 m3/s) and peak diversion requirement (39.36 m3/s). Pump station wise monthly diversion requirement has been estimated considering net cultivable area under each system and is shown in Table-4.6.

4.2.2 Domestic and Industrial Demand

In the study of IWM (2009), domestic and industrial water demand for the KIPNU area has been assessed for the year 2025 using the projected population and per capita water demand. The estimated domestic and industrial water demand for the year 2025 comes out to be about 10.42 Mm3/year, which represents a flow of about 0.35 m3/s (about

1.00% of the peak diversion requirement). As such, 1.00% of the peak diversion requirement, a flow of about 0.35 m3/s, has been considered as the domestic and industrial water demand and is shown in Table-4.6.

Table-4-6: Monthly Diversion Requirement from Dudhkumar River at Pateswari

Months Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 3 Total Field Irri. Req. (m /s) 20.74 16.62 20.16 17.23 3.55 0.67 0.00 0.00 0.00 1.62 4.42 6.23 Total Irri. Diversion Req. 39.36 31.54 38.26 32.70 6.74 1.27 0.00 0.00 0.00 3.07 8.39 11.82 (m3/s) Irri. Diversion req. 35.20 28.21 34.22 29.24 6.03 1.14 0.00 0.00 0.00 2.75 7.50 10.57 (Pateswari system, m3/s) Total Diversion req. 35.55 28.56 34.57 29.59 6.38 1.49 0.35 0.35 0.35 3.10 7.85 10.92 (Pateswari system, m3/s) 1 Diversion req. (Tangonmari 4.16 3.33 4.04 3.46 0.71 0.13 0.00 0.00 0.00 0.32 0.89 1.25 system, m3/s)

Note-1: Considering about 1.00% of peak irrigation requirement (0.35 m3/s) as the domestic and industrial demand.

It is to be mentioned here that the proposed Tangonmari pump house is located about 32.00 km downstream of Pateswari and water availability in the present study has been assessed based on discharge data at Pateswari. As such requirement for the Pateswari system only would be considered for a comparison of water demand and availability scenario.

4.3 Flow Availability

Monthly flow availability for 75% and 90% dependability at Pateswari on Dudhkumar river has been assessed using Flow Duration Curve method. Daily discharge data for the period April 1968 to March 2007, collected from BWDB has been used for this purpose. Daily discharge data of each month has been arranged in descending order and grouped into several classes with suitable class interval. Upper and lower boundary of each class, class interval, number of days having flow in each class interval and other pertinent computation as well as flow duration curve of each month is presented in Table-A.3 to Table-A.14, Appendix-A. Available flow for 75% and 90% dependability for each month, computed from the flow duration curves, is presented in Table-4.7. From the Table it may be seen that flow availability becomes lowest in the month of March and highest in the month of August. The lowest available flow is 72 m3/s and 80

m3/s for 90% and 75% dependability respectively, occurring in the month of March; while the highest available flow for 90% and 75% dependability is 780 m3/s and 950 m3/s respectively, occurring in August.

Table-4-7: Flow Availability of Dudhkumar river at Pateswari

Monthly flow availability (m3/s) Percentage of Dry Monsoon season Dry season dependability season Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 75% 95 190 360 900 950 865 460 220 147 110 92 80 90% 82 140 250 675 780 605 300 190 125 100 82 72

4.4 Comparison of Water Demand and Availability

For an understanding of water demand and availability scenario of Dudhkumar river at Pateswari, a comparison of likely water needs that are to be met from the river and water availability at Pateswari is presented in Table-4.8 and Figure-4.3. The sectoral water demand that have been considered are IFR, agricultural demand and domestic and industrial demand. It is worth mentioning that IFR greatly depends on the management goal of the river as well as the method chosen to assess IFR. For the sake of evaluating the demand – availability scenario under the present study, IFR obtained for ‘good’, ‘outstanding’ and ‘flushing’ habitat quality estimated using the MAF method have been considered.

Table-4-8: Comparison of Various Water Demand and Availability at Pateswari

Note: In Option-I, ‘Good’ and ‘Flushing’ habitat quality is assumed for low and high flow season respectively. In Option-II, ‘Outstanding’ and ‘Flushing’ habitat quality is assumed for low and high flow season respectively

1200.00 Req. (Option-I) Req. (Option-II) 75% availability 1000.00 90% availability

800.00 Instream Flow Requirement (m3/s) Total Diversion Total Requrement Water Availability (m3/s)

/s) 3

Months3 Season MAF Method req. at Pateswari (m /s) 90% 75% 3 600.00 Option-I Option-II (m /s) Option-I Option-II dependability dependability April Low 95 190 29.59 125 220 82 95 MayFlow (m Flow 95 190 6.38 101 196 140 190 June 400.00 950 950 1.49 951 951 250 360 July 950 950 0.35 950 950 675 900 High Aug 950 950 0.35 950 950 780 950 200.00Flow Sep 950 950 0.35 950 950 605 865 Oct 950 950 3.10 953 953 300 460 47 Nov 0.00 95 190 7.85 103 198 190 220 Dec 95 190 10.92 106 201 125 145 Low Apr il May June July Aug Sep Oct Nov Dec Jan Feb Mar Jan 95 190 35.55 131 226 100 110 Flow Feb 95 190 28.56 Months 124 219 82 92 Mar 95 190 34.57 130 225 72 80

Figure-4.3: Water Demand – Availability Scenario

Considering flow availability at 90% dependability and water demand under Option-I, from Table-4.8 it may be seen that during the low flow season, except the month of May, November and December; total requirement exceeds the flow availability at Pateswari. The deficit becomes significant during the months of January, February, March and April. During the high flow season, a deficit is seen in all the months.

When 75% dependable flow availability and demand under Option-I is considered, the situation during the monsoon season slightly improves, but no noticeable improvement is seen during the critical dry months i.e. January, February, March and April.

When demand under Option-II and 90% dependable flow availability is considered, deficit is seen in all the months. However, if 75% dependable flow availability is considered, it is seen that only in August and November, available flow satisfies the demand.

Chapter 5: Conclusion and Recommendation

5.1 Conclusion

Instream flow requirement of Dudhkumar river at Pateswari has been assessed using Mean Annual Flow method, Flow Duration Curve method and Constant Yield method which belong to hydrological approach for assessing IFR. These methods are suitable for reconnaissance-level desk-top analysis using only historical flow data. Necessary water level and discharge data for the period of 1965-2007 were collected form BWDB. From the foregoing analysis, the following conclusions may be drawn;

1. According to the MAF method, IFR for Dudhkumar river at Pateswari for different months varies from 48 m3/s to as high as 950 m3/s. This wide variation of IFR is due to mainly the variation of habitat quality and flow seasonality. A ‘flushing’ habitat quality requires the largest amount of flow whereas a ‘fair’ habitat quality requires the minimum amount of flow. For the sake of the present study, two different options have been considered. In Option-I, ‘good’ and ‘flushing’ habitat quality has been considered for low flow and high flow season respectively. The corresponding IFR is found to be 95 m3/s and 950 m3/s for the low flow months and high flow months respectively. In Option-II, ‘outstanding’ and ‘flushing’ habitat quality has been considered for low flow and high flow season respectively. The corresponding IFR is found to be 190 m3/s and 950 m3/s for the low flow months and high flow months respectively. However, if the choice of habitat quality is changed, IFR would also be changed. 2. According to the FDC method the IFR varies from 72 m3/s in the month of March (low flow season) to 1190 m3/s in July (high flow season), with an annual average IFR of 456 m3/s. Similarly, according to the CY method, the minimum and maximum IFR occurs in the month of March and July, and the requirement is 90 m3/s and 1032 m3/s respectively, and the annual average requirement is 396 m3/s. 3. The maximum diversion requirement at Pateswari is found to be 35.55 m3/s occurring in the month of January. 4. From a comparison of the total requirement under Option-I and flow availability for 75% dependability at Pateswari, as shown in Table-4.8, it is seen that during the months of January, February, March and April there is not enough water in

Dudhkumar river at Pateswari to meet the IFR if the planned diversion for irrigation is made. During these months total requirement is in the range of 124 m3/s to 131 m3/s whereas availability is in the range of 80 m3/s to 110 m3/s, if 75% dependable flow is considered. The flow availability further decreases if 90% dependable flow is considered A substantial part of this total requirement is the irrigation requirement which reaches its peak during these months whereas the flow availability during this period reaches the lowest. As such the crisis develops during the low flow season. On the other hand, if the irrigation requirement is not considered, the available flow may be considered to be ‘marginally sufficient’ to satisfy the IFR. If Option-II is considered, the deficit substantially increases during the low flow months since this option requires more instream flow for the low flow months. 5. If other methods are used to assess IFR the demand supply scenario may substantially change.

5.2 Recommendation

The following are the recommendations for further study and analysis:

Validation of the methods In the present study, assessment of instream flow requirement for Dudhkumar river has been done by using MAF, FDC and CY method. These methods have been developed in Europe, Australia and USA where the riverine ecosystem and aquatic flora and fauna are quite different from those of Bangladesh. The different criteria (e.g. percentages of mean annual flow as used in MAF method, percentage of dependability as used in FDC method and the percentage of median monthly flow as used in CY method) used for determining the instream flow requirement by the above methods might be suitable for those condition where they have been developed. The criteria (various percentages) used for setting IFR may not be exactly same for Bangladesh condition, rather some adjustment might be necessary. As such it would be prudent to conduct several in depth study, at least in five rivers in each of the hydrological regions of Bangladesh, focusing on the suitability of the methods and the various percentages used in determining IFR. It would help to deepen the understanding of IFR methodologies as well as the riverine ecosystem.

Data collection In the present study, the assessment of instream flow requirement at Pateswari has been done using hydrological approach which utilizes historic flow data. As such availability of good quality historic flow data is of prime importance. From the available data it is seen that in many cases daily discharge data was not available. In those cases discharge data was filled using rating curve. Availability of sufficient/more field/measured data enhances the confidence level of any investigation. As such it is suggested to develop and follow a systematic data collection program. Data collection program has to be framed keeping in mind the method and technique that would be used for IFR assessment. It is of prime importance for Bangladesh since in Bangladesh the issue of IFR/EFA is still in infancy.

Need for further investigation As mentioned earlier, the present study is a reconnaissance level desk-top analysis using three hydrological methods relying on secondary level river flow data. The demand-supply scenario, considering the planned irrigation abstraction for Kurigram Irrigation Project, North Unit; indicates that there is substantial shortage of water at Pateswary to meet the IFR during the dry season. Acknowledging that the present study is an indicative one, further investigation may be undertaken using other methods, particularly holistic approaches which encompass wider aspects of riverine environment. Furthermore, flow augmentation and mitigation measures may be explored, if needed.

References

Arthington, A. H., King, J. M., O’Keeffe, J. H., Bunn, S. E., Day, J. A., Pusey, B. J., Bluhdorn, B. R., and Tharme, R. (1992). ‘Development of an holistic approach for assessing environmental flow requirements of riverine ecosystems’, in Pilgram, J. J. and Hooper, B. P. (Eds), Water Allocation for the Environment. The Centre for Water Policy Research, University of New England, Armidale. pp. 69– 76.

Arthington A.H. & Pusey B.J. (1993). In-stream flow management in Australia: Methods, deficiencies & future directions. Australian Biologist, 6: 52-60.

Arthington A.H., Brizga S.O. and Kennard M.J. (1998). Comparative Evaluation of Environmental Flow Assessment Techniques: Best Practice Framework. LWRRDC Occasional paper 25/98. Canberra, Land and Water Resources Research and Development Corporation.

Arthington A.H. and Zalucki J.M. eds. (1998). Comparative evaluation of environmental flow assessment techniques: Review of methods. LWRRDC Occasional Paper Series 27/98. Canberra, Land and Water Resources Research and Development Corporation. 141 pp.

Arthington, A.H., R. Tharme, S.O. Brizga,, B.J. Pusey and M.J. Kennard (2004). Environmental Flow Assessment with Emphasis on Holistic Methodologies. In: Proceedings of the Second International Symposium on the Management of Large Rivers for Fisheries, Volume II. Welcomme, R. and T. Petr, Eds, FAO Regional Office for Asia and the Pacific, Bangkok, Thailand. RAP Publication 2004/17, pp. 37-65.

Amarasinghe, U. A., Sharma, B. R., Aloysius, N., Scott, C., Smakhtin, V. U., De Fraiture, C., Sinha, A. K. and Shukla, A. K. (2005). Spatial variation in Water Supply and Demand across the river basins of India. IWMI Research Report-83. Colombo, Sri Lanka.

Bari, M.F. and Marchand, M., (2006). Introducing Environmental Flow Assessment in Bangladesh: Multidisciplinary Collaborative Approach. BUET-DUT Linkage Project, Ph-III. Final Technical Report, May.

BBS, (2006). Statistical Year Book of Bangladesh, p-xx.

Bovee, K.D. (1982). A Guide to stream habitat analysis using the instream flow incremental methodology. Instream Flow Information Paper 12. Fort Collins, US Department of Fisheries and Wildlife Service.

Bullock, A., Gustard, A. and Grainger, E.S. (1991). Instream Flow Requirement of Aquatic Ecology in two British Rivers. Report No. 115.

BWDB, (2005). Rivers of Bangladesh, Bangladesh Water Development Board, June.

BWDB, Border/Common Rivers of Bangladesh, Bangladesh Water Development Board.

Cullen, P. (1992). ‘Australian aquatic ecosystems - biophysical requirements and relationships’, in Pilgram, J. J. and Hooper, B. P. (Eds), WaterAllocation for the Environment. The Centre for Water Policy Research, University of New England, Armidale.

DPM Ltd., KRANTI and BETS Ltd, (2005). Updating/Upgrading Feasibility Study of Kurigram Irrigation Project (North Unit), Final Report, July.

Fraser, J. C. (1978). Suggestions for developing flow recommendations for in-stream uses of New Zealand streams. Water and Soil Miscellaneous Publication 6. Ministry of Works and Development, Wellington.

Gordon, N.D., McMahon, T.A. and Finlayson, B.L. (1992). Stream Hydrology. An Introduction for Ecologists, John Wiley & Sons Ltd. Chichester.

Groshens T.P. and Orth D.J. (1994). Transferability of habitat suitability criteria for smallmouth bass, Micropterus dolomieu. Rivers, 4: 194-212.

Haque, M.I., (2008). Water Resources Management in Bangladesh, April.

HCL, IWM, DDC Ltd., BETS Ltd., (2009). Drainage and Morphological Study using Mathematical Modelling Technique for Drainage Improvement and Finalization of the Location of Pump Houses and Intake Channels. Kurigram Irrigation Project, North Unit, Final Report, September.

IWM, (2009). Topographic Survey and Detail Irrigation Planning using Mathematical Modelling Technique, Kurigram Irrigation Project, North Unit, Final Report, Vol- I & II; May.

Jahn, L.R., (1990). Managing riverine values and uses. Rivers-Studies in the science, Environmental Policy and Law of Instream Flow.

JICA, (1989). Feasibility Study on the Kurigram Irrigation and Flood Control Project, North Unit, Interim Report. December.

JICA, (1990). Feasibility Study on the Kurigram Irrigation and Flood Control Project, North Unit, Vol-II, Appendices, October.

Jowett, I.G. (1997). Instream Flow Methods: A Comparison of Approaches. Regulated Rivers: Research & Management, Vol. 13, 115-127 (1997), NIWA, Box 11-115, Hamilton, New Zealand.

Karim, K., Gubbels, M. E., and Goulter, I. C. (1995). ‘Review of determination of instream flow requirements with special application to Australia’, Wat. Resour. Bull., 31, 1063–1077.

King J.M. and Tharme R.E. (1994). Assessment of the Instream Flow Incremental Methodology (IFIM) and initial development of alternative instream flow methodologies for South Africa. Water Research Commission, Report No. 295/1/94. Pretoria, SA.

King, J.M., Tharme, R.E. and Brown C.A., (1999). Definition and Implementation of Instream Flows. Thematic Report for the World Commission on Dams. Southern Waters Ecological Research and Consulting: Cape Town, South Africa.

King, J.M., Tharme, R.E. and de Villiers, D.E. (2000). Environmental Flow Assessment for Rivers: Manual for the Building Block Methodology, Freshwater Research Unit, University of Cape Town, WRE Report No. TT 131/00.

Lamb, B.L. and Doersken, H.R. (1987). Instream water use in the United States – water laws and methods for determining flow requirements. National Water Summary 1987 – Water Supply and Use: Instream Water Use.

Loar, J.M. and Sale, M.J., (1981). Analysis of Environmental Issues Related to Small- scale Hydroelectric Development. Instream Flow Needs for Fisheries Resources, Publication No. 1829. Oak Ridge National Laboratory, Oak Ridge, Tennessee.

Marchand, M., (2003). Environmental Flow Assessment for Rivers. An Integrated Approach for River and Coastal Zone Management. Final Project Report, Delft Hydraulics, June.

Milhous R.T., Updike M.A. & Schneider D.M. (1989). Physical habitat simulation system reference manual, Version 2. Instream Flow Information Paper 26. U.S.D.I. Fish Wildlife Service Biological Report 8916.

Mosley, M. P. (1992). ‘River morphology’, in Mosley M. P. (Ed), Waters of New Zealand, New Zealand Hydrological Society, Wellington. pp. 285–304.

MPO, (1991). National Water Plan Project Ph-II, National Water Plan, Vol-I, Ministry of Irrigation, Water Development and Flood Control, GoB, June.

MoWR. (2002). National Water Policy. Government of India. Ministry of Water Resources, New Delhi. April.

NCIWRDP, (1999). Integrated Water Resource Development: A Plan for Action. Ministry of Water Resources, New Delhi.

Orth, D. J. (1987). ‘Ecological considerations in the development and application of instream flow-habitat models, Regul. Riv., 1, 171–181.

Pakistan Techno-Consult Consulting Engineers, (1969). Kurigram Flood Control and Irrigation Project. Feasibility Study and Report. Vol-I. December.

Poff N.L., Allan J.D., Bain M.B., Karr J.R., Prestegaard K.L., Richter B.D., Sparks R.E. & Stromberg J.C. (1997). The natural flow regime, a paradigm for river conservation and restoration. BioScience, 47: 769-784.

Rahman, M.A. (1998). A Hydrological Determination of Instream Flow Requirement of the Ganges River. M. Engg. Thesis. Department of Water Resources Engineering, BUET, August.

Reiser, D. W., Wesche, T. A. and Estes, C. (1989). ‘Status of instream flow legislation and practices in North America’, Fisheries, 14, 22–29.

Richadson, B.A. (1986). Evaluation of Instream Flow Methodologies for fresh water fish in New South Wales. Instream Protection. The Management of Rivers for Instream Use. Ian C. Camphell (Editor), Water Studies Centre, Chisholm Institute of Technology, East Caufield.

Richter B.D., Baumgartner J.V., Powell J. & Braun D.P. (1996). A method for assessing hydrologic alteration within ecosystems. Conservation Biology, 10: 1- 12.

Saha, P.P., (2007). An Assessment of Instream Flow Requirement of Gorai river Considering Salinity Intrusion and Fish Habitat. M. Engineering Thesis, Department of Water Resources Engineering, BUET, April.

Smakhtin, V.U., Revenga, C., Doll, P. (2004a) Taking into account environmental water requirements in global-scale water resources assessments. Research Report of the CGIAR Comprehensive Assessment Programme of Water Use in Agriculture. N 2, International Water Management Institute , Colombo, Sri Lanka.

Smakhtin V., C. Revenga and Doll, P. (2004b) A pilot global assessment of environmental water requirements and scarcity. Water International 29: 307-317.

Smakhtin, V. and Anputhas, M., (2006). An Assessment of Environmental Flow Requirements of Indian River Basins. International Water Management Institute. Research Report -107.

Sparks R.E. (1992). Risks of altering the hydrologic regime of large rivers. In J. Cairns, B.R. Niederlehner & D.R. Orvos eds. Predicting Ecosystem Risk. Vol XX. Princeton, NJ, Princeton Scientific Publishing Co.

Stalnaker, C., Lamb, B.L., Henriksen, J., Bovee, K. and Bartholow, J. (1995). The Instream Flow Incremental Methodology. A Primer for IFIM , Biological Report 29, National Biological Service, U.S. Department of Interior, Washington, D.C. March.

Subramanya, K., (1988). Engineering Hydrology, Second Reprint, Tata McGraw-Hill Publishing Company Limited, New Delhi.

Sudip Kumar Pal, Asiful Hoque, Iffat Tarannum; (2009). Approach to Assess Environmental Flow for the Karnaphuli River of Bangladesh. 2nd International Conference on Water and Flood Management, Vol-I, Dhaka, Bangladesh. March.

Techno Consult Eastern Limited, Consulting Engineers. (1975). Feasibility Study Report (Revised and updated), Kurigram FCDI Project, Dacca, Bangladesh, p-II- 5, January.

Tennant, D. L. (1976). ‘Instream flow regimens for fish, wildlife, recreation and related environmental resources’, in Orsborn, J. F. and Allman, C. H. (Eds), Proceedings of the Symposium and Speciality Conference on Instream Flow Needs II. American Fisheries Society, Bethesda, Maryland.

Tharme R.E., (1996). Review of international methodologies for the quantification of the instream flow requirements of rivers. Water law review final report for policy development for the Department of Water Affairs and Forestry. Pretoria, SA, Freshwater Research Unit, University of Cape Town.

Tharme, R.E., (2002). A Global Perspective on Environmental Flow Assessment: Emerging Trends in the Development and Application of Environmental Flow Methodologies for Rivers. Published online in Wiley InterScience. October.

Tharme R.E. (2003). A global perspective on environmental flow assessment: Emerging trends in the development and application of environmental flow methodologies for rivers. River Research and Applications, 19: 397-442.

Ward J.V., Tockner U., Uehlinger U. and Malard F. (2001). Understanding natural patterns and processes in river corridors as the basis for effective river restoration. Regulated River: Research and Management, 117: 311-323.

White, R. G. (1976). A methodology for recommending stream resource maintenance flows for large rivers’, in Orsborn, J. F. and Allman, C. H. (Eds), Proceedings of the Symposium and Speciality Conference on Instream Flow Needs II. American Fisheries Society, Bethesda, Maryland. pp. 376–386.

Zobeyer, A.T.M.H. (2004). Application of Physical Habitat Simulation Approach for Instream Flow Requirement in the Surma River. M.Sc Thesis. Department of Water Resources Engineering, BUET, July.

Appendices

Appendix-A: Tables

A-2 Table-A.3: Flow Duration Curve for the month of January Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 220 210 215 3 3 0.30 210 200 205 8 11 1.11 200 190 195 16 27 2.72 190 180 185 27 54 5.44 180 170 175 41 95 9.57 170 160 165 61 156 15.71 160 150 155 71 227 22.86 150 140 145 125 352 35.45 140 130 135 136 488 49.14 130 120 125 104 592 59.62 120 110 115 108 700 70.49 110 100 105 123 823 82.88 100 90 95 124 947 95.37 90 80 85 16 963 96.98 80 70 75 14 977 98.39 70 60 65 15 992 99.90

N = 992

Flow Duration curve of January Station: Pateswari 250

) 200 /s 3

150

100 Mean Daily Flow (m 50

0 0 10 20 30 40 50 60 70 80 90 100

Percent of time the indicated flow is equalled or exceeded

A-41 Table-A.4: Flow Duration Curve for the month of February Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 170 160 165 3 3 0.33 160 150 155 35 38 4.20 150 140 145 29 67 7.40 140 130 135 61 128 14.14 130 120 125 85 213 23.54 120 110 115 139 352 38.90 110 100 105 113 465 51.38 100 90 95 180 645 71.27 90 80 85 139 784 86.63 80 70 75 87 871 96.24 70 60 65 18 889 98.23 60 50 55 0 889 98.23 50 40 45 0 889 98.23 40 30 35 9 898 99.23 30 20 25 6 904 99.89

N = 904

Flow Duration curve of February Station: Pateswari 180

160

/s) 140 3

120

100

Mean Daily Flow (m 60

0 0 10 20 30 40 50 60 70 80 90 100

Percent of time the indicated flow is equalled or exceeded

A-42 Table-A.5: Flow Duration Curve for the month of March Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 180 170 175 4 4 0.42 170 160 165 2 6 0.62 160 150 155 3 9 0.94 150 140 145 9 18 1.87 140 130 135 41 59 6.13 130 120 125 44 103 10.71 120 110 115 79 182 18.92 110 100 105 89 271 28.17 100 90 95 179 450 46.78 90 80 85 194 644 66.94 80 70 75 173 817 84.93 70 60 65 132 949 98.65 60 50 55 12 961 99.90

N = 961

Flow Duration curve of March Station: Pateswari 200 180 160 /s) 3 140 120 100 80 Mean Daily Flow (m 60 40 20 0

0 10 20 30 40 50 60 70 80 90 100

Percent of time the indicated flow is equalled or exceeded

A-43 Table-A.6: Flow Duration Curve for the month of April Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 675 650 662.50 1 1 0.11 650 625 637.50 0 1 0.11 625 600 612.50 1 2 0.21 600 575 587.50 0 2 0.21 575 550 562.50 0 2 0.21 550 525 537.50 0 2 0.21 525 500 512.50 0 2 0.21 500 475 487.50 0 2 0.21 475 450 462.50 0 2 0.21 450 425 437.50 0 2 0.21 425 400 412.50 1 3 0.32 400 375 387.50 3 6 0.64 375 350 362.50 3 9 0.97 350 325 337.50 2 11 1.18 325 300 312.50 5 16 1.72 300 275 287.50 7 23 2.47 275 250 262.50 12 35 3.76 250 225 237.50 30 65 6.97 225 200 212.50 19 84 9.01 200 175 187.50 34 118 12.66 175 150 162.50 75 193 20.71 150 125 137.50 127 320 34.33 125 100 112.50 175 495 53.11 100 75 87.50 309 804 86.27 75 50 62.50 117 921 98.82 50 25 37.50 10 931 99.89

N = 931

Flow Duration curve of April Station: Pateswari 700

600

/s) 3 500

400

300

Mean Daily Flow (m 200

100

0 0 10 20 30 40 50 60 70 80 90 100 Percent of time the indicated flow is equalled or exceeded

A-44 Table-A.7: Flow Duration Curve for the month of May Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 1550 1500 1525 2 2 0.21 1500 1450 1475 0 2 0.21 1450 1400 1425 0 2 0.21 1400 1350 1375 0 2 0.21 1350 1300 1325 0 2 0.21 1300 1250 1275 1 3 0.31 1250 1200 1225 1 4 0.42 1200 1150 1175 0 4 0.42 1150 1100 1125 0 4 0.42 1100 1050 1075 0 4 0.42 1050 1000 1025 1 5 0.52 1000 950 975 1 6 0.62 950 900 925 3 9 0.94 900 850 875 2 11 1.14 850 800 825 4 15 1.56 800 750 775 2 17 1.77 750 700 725 9 26 2.70 700 650 675 3 29 3.01 650 600 625 9 38 3.95 600 550 575 19 57 5.93 550 500 525 19 76 7.90 500 450 475 22 98 10.19 450 400 425 27 125 12.99 400 350 375 48 173 17.98 350 300 325 57 230 23.91 300 250 275 93 323 33.58 250 200 225 186 509 52.91 200 150 175 265 774 80.46 150 100 125 121 895 93.04 100 50 75 66 961 99.90

N = 961

Flow Duration curve of May Station: Pateswari 1800

1600

/s) 1400 3

1200

1000

800

Mean Daily Flow (m 600

400

200

0 0 10 20 30 40 50 60 70 80 90 100 Percent of time the indicated flow is equalled or exceeded

A-45 Table-A.8: Flow Duration Curve for the month of June Dudhkumar river at Pateswari. Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 4100 4000 4050 1 1 0.11 4000 3900 3950 1 2 0.21 3900 3800 3850 1 3 0.32 3800 3700 3750 0 3 0.32 3700 3600 3650 1 4 0.43 3600 3500 3550 0 4 0.43 3500 3400 3450 0 4 0.43 3400 3300 3350 0 4 0.43 3300 3200 3250 3 7 0.75 3200 3100 3150 0 7 0.75 3100 3000 3050 0 7 0.75 3000 2900 2950 3 10 1.07 2900 2800 2850 0 10 1.07 2800 2700 2750 2 12 1.29 2700 2600 2650 1 13 1.40 2600 2500 2550 4 17 1.83 2500 2400 2450 6 23 2.47 2400 2300 2350 5 28 3.01 2300 2200 2250 7 35 3.76 2200 2100 2150 6 41 4.40 2100 2000 2050 6 47 5.05 2000 1900 1950 3 50 5.37 1900 1800 1850 1 51 5.48 1800 1700 1750 6 57 6.12 1700 1600 1650 5 62 6.66 1600 1500 1550 7 69 7.41 1500 1400 1450 11 80 8.59 1400 1300 1350 24 104 11.17 1300 1200 1250 15 119 12.78 1200 1100 1150 24 143 15.36 1100 1000 1050 25 168 18.05 1000 900 950 43 211 22.66 900 800 850 37 248 26.64 800 700 750 59 307 32.98 700 600 650 99 406 43.61 600 500 550 107 513 55.10 500 400 450 115 628 67.45 400 300 350 87 715 76.80 300 200 250 129 844 90.66 200 100 150 86 930 99.89 N = 930

Flow Duration curve of June Station: Pateswari 4500

4000

/s) 3500 3

3000

2500

2000

Mean Daily Flow (m 1500

1000

500

0 0 10 20 30 40 50 60 70 80 90 100

Percent of time the indicated flow is equalled or exceeded

A-46 Table-A.9: Flow Duration Curve for the month of July Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 7300 6900 7100 1 1 0.10 6900 6500 6700 1 2 0.21 6500 6100 6300 0 2 0.21 6100 5700 5900 1 3 0.31 5700 5300 5500 2 5 0.52 5300 4900 5100 4 9 0.94 4900 4500 4700 1 10 1.04 4500 4100 4300 4 14 1.46 4100 3700 3900 5 19 1.98 3700 3300 3500 11 30 3.12 3300 2900 3100 16 46 4.78 2900 2500 2700 20 66 6.86 2500 2100 2300 34 100 10.40 2100 1700 1900 56 156 16.22 1700 1300 1500 134 290 30.15 1300 900 1100 251 541 56.24 900 500 700 300 841 87.42 500 100 300 120 961 99.90

N = 961

Flow Duration curve of July Station: Pateswari 8000

7000 /s) 3 6000

5000

4000

3000 Mean Daily Flow (m 2000

1000 0 0 10 20 30 40 50 60 70 80 90 100 Percent of time the indicated flow is equalled or exceeded

A-47 Table-A.10: Flow Duration Curve for the month of August Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 7000 6500 6750 1 1 0.10 6500 6000 6250 0 1 0.10 6000 5500 5750 3 4 0.40 5500 5000 5250 2 6 0.60 5000 4500 4750 1 7 0.70 4500 4000 4250 9 16 1.61 4000 3500 3750 5 21 2.11 3500 3000 3250 9 30 3.02 3000 2500 2750 23 53 5.34 2500 2000 2250 44 97 9.77 2000 1500 1750 91 188 18.93 1500 1000 1250 245 433 43.61 1000 500 750 457 890 89.63 500 0 250 102 992 99.90

N = 992

Flow Duration curve of August Station: Pateswari 8000

7000 /s) 3 6000

5000

4000

3000

Mean Daily Flow (m 2000 1000

0 0 10 20 30 40 50 60 70 80 90 100

Percent of time the indicated flow is equalled or exceeded

A-48 Table-A.11: Flow Duration Curve for the month of September Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 5000 4500 4750 1 1 0.10 4500 4000 4250 3 4 0.40 4000 3500 3750 4 8 0.81 3500 3000 3250 4 12 1.21 3000 2500 2750 20 32 3.23 2500 2000 2250 27 59 5.95 2000 1500 1750 53 112 11.30 1500 1000 1250 196 308 31.08 1000 500 750 528 836 84.36 500 0 250 154 990 99.90

N = 990

Flow Duration curve of September Station: Pateswari 5000

4500

4000 /s) 3 3500 3000 2500 2000 Mean Daily Flow (m 1500 1000

500

0 0 10 20 30 40 50 60 70 80 90 100 Percent of time the indicated flow is equalled or exceeded

A-49 Table-A.12: Flow Duration Curve for the month of October Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 9500 9000 9250 1 1 0.10 9000 8500 8750 0 1 0.10 8500 8000 8250 0 1 0.10 8000 7500 7750 0 1 0.10 7500 7000 7250 1 2 0.20 7000 6500 6750 0 2 0.20 6500 6000 6250 1 3 0.29 6000 5500 5750 0 3 0.29 5500 5000 5250 0 3 0.29 5000 4500 4750 1 4 0.39 4500 4000 4250 0 4 0.39 4000 3500 3750 0 4 0.39 3500 3000 3250 2 6 0.59 3000 2500 2750 0 6 0.59 2500 2000 2250 4 10 0.98 2000 1500 1750 6 16 1.56 1500 1000 1250 38 54 5.27 1000 500 750 341 395 38.57 500 0 250 628 1023 99.90

N = 1023

Flow Duration curve of October Station: Pateswari 10000

9000 /s) 3 8000 7000 6000

5000 4000

Mean Daily Flow (m 3000 2000 1000

0 0 10 20 30 40 50 60 70 80 90 100 Percent of time the indicated flow is equalled or exceeded

A-50 Table-A.13: Flow Duration Curve for the month of November Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 650 600 625 1 1 0.10 600 550 575 0 1 0.10 550 500 525 8 9 0.91 500 450 475 11 20 2.02 450 400 425 17 37 3.73 400 350 375 42 79 7.97 350 300 325 102 181 18.26 300 250 275 224 405 40.87 250 200 225 309 714 72.05 200 150 175 234 948 95.66 150 100 125 28 976 98.49 100 50 75 14 990 99.90

N = 990

Flow Duration curve of November Station: Pateswari 700

600

/s) 3 500

400

300

Mean Daily Flow (m 200

100

0 0 10 20 30 40 50 60 70 80 90 100 Percent of time the indicated flow is equalled or exceeded

A-51 Table-A.14: Flow Duration Curve for the month of December Dudhkumar river at Pateswari.

Daily Mean Flow (Q), m3/s No. of days having No. of days (m) having Pp=[{m/(N+1)}*100], Upper Limit Lower Limit Mid Point flow in class interval flow equal or greater % of time 260 250 255 7 7 0.68 250 240 245 32 39 3.81 240 230 235 28 67 6.54 230 220 225 43 110 10.74 220 210 215 57 167 16.31 210 200 205 62 229 22.36 200 190 195 60 289 28.22 190 180 185 92 381 37.21 180 170 175 107 488 47.66 170 160 165 88 576 56.25 160 150 155 99 675 65.92 150 140 145 108 783 76.46 140 130 135 92 875 85.45 130 120 125 53 928 90.63 120 110 115 37 965 94.24 110 100 105 15 980 95.70 100 90 95 8 988 96.48 90 80 85 27 1015 99.12 80 70 75 8 1023 99.90

N = 1023

Flow Duration curve of December Station: Pateswari 300

250 /s) 3

200

150

Mean Daily Flow (m 100

0 0 10 20 30 40 50 60 70 80 90 100

Percent of time the indicated flow is equalled or exceeded

A-52

Appendix-B: Figures

Proposed Pateswari Pump station & existing R.B

Proposed Tangonmari Pump station

Source: IWM 2009.

Figure-B.1: Kurigram Irrigation Project (North Unit) and River System

B-1

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 1965-1970)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar 10000 35.00 Discharge Water Level 34.00 9000 33.00

8000 32.00

31.00 7000 30.00

6000 29.00 /s) 3 28.00 5000 27.00 WL (mPWD) WL

Discharge (m 4000 26.00

25.00 3000 24.00

2000 23.00

22.00 1000 21.00

0 20.00 1-Jul-65 1-Jul-66 1-Jul-67 1-Jul-68 1-Jul-69 1-Apr-65 1-Oct-65 1-Apr-66 1-Oct-66 1-Apr-67 1-Oct-67 1-Apr-68 1-Oct-68 1-Apr-69 1-Oct-69 1-Apr-70 1-Jan-65 1-Jan-66 1-Jan-67 1-Jan-68 1-Jan-69 1-Jan-70

Date

B-2

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 1970-1975)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar

5000 35.00 Discharge Water Level 34.00 4500 33.00

4000 32.00

31.00 3500 30.00

3000 29.00

28.00 2500 27.00 WL (mPWD)

Discharge (m3/s) 2000 26.00

25.00 1500 24.00

1000 23.00

22.00 500 21.00

0 20.00 1-Jul-70 1-Jul-71 1-Jul-72 1-Jul-73 1-Jul-74 1-Apr-70 1-Oct-70 1-Apr-71 1-Oct-71 1-Apr-72 1-Oct-72 1-Apr-73 1-Oct-73 1-Apr-74 1-Oct-74 1-Apr-75 1-Jan-71 1-Jan-72 1-Jan-73 1-Jan-74 1-Jan-75

Date

B-3

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 1975-1980)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar

8000 35.00 Discharge Water Level 34.00

7000 33.00

32.00 6000 31.00

30.00 5000 29.00 /s) 3 28.00 4000 27.00 WL (mPWD)

Discharge (m 26.00 3000 25.00

24.00 2000 23.00

1000 22.00

21.00

0 20.00 1-Jul-75 1-Jul-76 1-Jul-77 1-Jul-78 1-Jul-79 1-Apr-75 1-Oct-75 1-Apr-76 1-Oct-76 1-Apr-77 1-Oct-77 1-Apr-78 1-Oct-78 1-Apr-79 1-Oct-79 1-Apr-80 1-Jan-76 1-Jan-77 1-Jan-78 1-Jan-79 1-Jan-80

Date

B-4

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 1980-1985)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar

3000 35.00 Discharge Water Level 34.00

33.00 2500 32.00

31.00

2000 30.00

29.00 /s) 3 28.00 1500 27.00 WL (mPWD)

Discharge (m 26.00

1000 25.00

24.00

23.00 500 22.00

21.00

0 20.00 1-Jul-80 1-Jul-81 1-Jul-82 1-Jul-83 1-Jul-84 1-Apr-80 1-Oct-80 1-Apr-81 1-Oct-81 1-Apr-82 1-Oct-82 1-Apr-83 1-Oct-83 1-Apr-84 1-Oct-84 1-Apr-85 1-Jan-81 1-Jan-82 1-Jan-83 1-Jan-84 1-Jan-85

Date

B-5

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 1985-1990)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar

6000 35.00 Discharge Water Level 34.00

33.00 5000 32.00

31.00

4000 30.00

29.00 /s) 3 28.00 3000 27.00 WL (mPWD)

Discharge (m 26.00

2000 25.00

24.00

23.00 1000 22.00

21.00

0 20.00 1-Jul-85 1-Jul-86 1-Jul-87 1-Jul-88 1-Jul-89 1-Apr-85 1-Oct-85 1-Apr-86 1-Oct-86 1-Apr-87 1-Oct-87 1-Apr-88 1-Oct-88 1-Apr-89 1-Oct-89 1-Apr-90 1-Jan-86 1-Jan-87 1-Jan-88 1-Jan-89 1-Jan-90

Date

B-6

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 1990-1995)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar

7000 35.00 Discharge Water Level 34.00

6000 33.00

32.00

31.00 5000 30.00

29.00 /s) 3 4000 28.00

27.00 WL (mPWD) 3000

Discharge (m 26.00

25.00 2000 24.00

23.00

1000 22.00

21.00

0 20.00 1-Jul-90 1-Jul-91 1-Jul-92 1-Jul-93 1-Jul-94 1-Apr-90 1-Oct-90 1-Apr-91 1-Oct-91 1-Apr-92 1-Oct-92 1-Apr-93 1-Oct-93 1-Apr-94 1-Oct-94 1-Apr-95 1-Jan-91 1-Jan-92 1-Jan-93 1-Jan-94 1-Jan-95

Date

B-7

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 1995-2000)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar

4500 35.00 Discharge Water Level 34.00 4000 33.00

32.00 3500 31.00

3000 30.00

29.00 /s) 3 2500 28.00

27.00 2000 WL (mPWD)

Discharge (m 26.00

1500 25.00

24.00 1000 23.00

22.00 500 21.00

0 20.00 1-Jul-95 1-Jul-96 1-Jul-97 1-Jul-98 1-Jul-99 1-Apr-95 1-Oct-95 1-Apr-96 1-Oct-96 1-Apr-97 1-Oct-97 1-Apr-98 1-Oct-98 1-Apr-99 1-Oct-99 1-Apr-00 1-Jan-96 1-Jan-97 1-Jan-98 1-Jan-99 1-Jan-00

Date

B-8

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 2000-2005)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar

3500 35.00 Discharge Water Level 34.00

3000 33.00

32.00

31.00 2500 30.00

29.00 /s) 3 2000 28.00

27.00 WL (mPWD) 1500

Discharge (m 26.00

25.00 1000 24.00

23.00

500 22.00

21.00

0 20.00 1-Jul-00 1-Jul-01 1-Jul-02 1-Jul-03 1-Jul-04 1-Apr-00 1-Oct-00 1-Apr-01 1-Oct-01 1-Apr-02 1-Oct-02 1-Apr-03 1-Oct-03 1-Apr-04 1-Oct-04 1-Apr-05 1-Jan-01 1-Jan-02 1-Jan-03 1-Jan-04 1-Jan-05

Date

B-9

Figure-B.2: Hydrograph of Daily Water Level and Discharge at Pateswari, Dudhkumar River (Period: 2005-March 2007)

WL and Q Hydrograph Station: Pateswari, River: Dudhkumar

1600 35.00 Discharge Water Level 34.00

1400 33.00

32.00 1200 31.00

30.00 1000 29.00 /s) 3 28.00 800 27.00 WL (mPWD)

Discharge (m 26.00 600 25.00

24.00 400 23.00

200 22.00

21.00

0 20.00 1-Jul-05 1-Jul-06 1-Apr-05 1-Oct-05 1-Apr-06 1-Oct-06 1-Apr-07 1-Jan-06 1-Jan-07 Date

B-10

Figure-B.3: Navigational Route of BIWTA

B-11 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 79 144 394 4130 1210 798 1490 432 244 205 113 102 2 82 174 321 2710 1110 800 1280 419 243 199 115 101 3 81 222 325 2090 960 797 1400 400 241 198 116 100 4 83 233 295 1800 895 762 3050 383 244 192 114 99 5 83 235 304 1430 984 906 6120 379 237 191 116 94 6 82 273 331 1210 906 850 9250 378 240 185 113 93 7 86 291 288 1240 938 796 7210 354 243 183 115 92 8 89 263 294 1370 1410 694 4780 344 245 176 113 91 9 95 237 320 1160 1770 643 3120 338 242 175 114 90 10 104 225 373 1050 1750 621 2240 332 244 173 116 89 11 123 211 476 980 1670 561 1730 325 245 167 114 88 12 138 201 437 1170 1340 534 1420 315 242 166 115 87 13 167 189 370 1450 1070 483 1210 310 239 160 115 86 14 157 199 387 2030 1000 525 1040 304 241 162 114 86 15 144 261 485 2580 888 685 917 299 243 161 112 82 16 149 221 547 3070 810 668 814 294 239 160 113 80 9250 758 79 17 160 209 666 3300 774 762 767 288 241 158 114 82 18 149 216 718 3040 1180 1210 672 283 238 153 112 85

1968-69 19 144 245 833 2620 1180 1490 608 278 240 151 113 98 20 135 265 758 2900 1300 1810 590 272 237 150 111 104 21 128 280 2470 3640 1700 2740 573 267 235 144 112 118 22 120 345 2920 4420 1960 2000 569 262 230 139 113 144 23 114 606 2210 5010 1310 1630 553 257 228 136 111 147 24 121 732 995 5030 1150 2210 528 252 227 132 112 138 25 123 555 1330 3770 988 1920 512 247 221 131 113 120 26 120 449 1320 3090 1030 2380 505 244 220 126 109 113 27 108 418 1860 2340 1320 3020 471 242 215 125 107 113 28 120 402 2110 2050 1430 2890 460 245 213 120 103 116 29 111 400 2030 1800 1320 2310 448 243 211 118 117 30 113 398 2630 1560 1080 1850 455 246 207 117 111 31 463 1330 898 450 206 112 114 Max 167 732 2920 5030 1960 3020 9250 432 245 205 116 147 Mean 117 308 960 2431 1204 1312 1782 308 234 157 113 103 Median 120 261 516 2090 1150 825 814 297 239 160 113 99 Min 79 144 288 980 774 483 448 242 206 112 103 80 1 118 126 268 877 905 1320 544 292 213 156 131 103 2 118 134 231 988 933 1250 532 284 213 156 131 93 3 111 150 134 845 960 1570 501 284 213 156 121 93 4 111 134 141 748 845 1290 480 276 205 156 121 93 5 111 126 231 675 813 1150 480 276 205 156 121 93 6 111 118 378 781 813 1100 480 268 205 156 121 93 7 103 126 350 877 845 1190 469 268 205 156 112 93 8 103 118 408 1220 845 1450 469 268 197 148 112 112 9 103 118 368 1190 845 1070 469 260 197 148 112 112 10 96 111 467 1100 845 988 448 260 197 148 112 112 11 96 111 489 1070 845 905 490 268 189 148 103 112 12 96 118 478 1150 797 861 448 268 189 148 103 103 13 103 111 546 1250 764 877 427 260 189 148 103 93 14 111 167 621 1350 732 1190 401 260 189 140 103 93 15 118 184 621 1390 764 960 392 260 189 140 103 93 16 134 212 607 1660 829 829 383 252 181 140 103 93 2360 442 72 17 158 240 648 2300 1070 748 375 252 181 140 103 93 18 167 379 659 2360 1450 748 366 244 181 140 93 93

1969-70 19 193 398 662 1660 1490 797 357 244 181 131 93 82 20 175 398 662 1390 1190 732 357 237 181 131 93 82 21 175 304 621 1220 1070 689 357 237 181 131 103 82 22 175 359 621 1130 1070 648 348 237 181 140 112 82 23 167 378 702 1070 1190 607 340 237 181 148 112 82 24 167 359 845 1190 1190 580 332 229 173 148 112 72 25 150 594 877 1040 1290 558 324 229 173 148 112 72 26 142 594 988 1150 1150 702 324 221 173 148 112 72 27 134 569 861 1130 1350 702 316 221 165 140 112 72 28 126 569 797 1130 1390 797 308 221 165 131 103 82 29 126 478 732 1040 1220 702 308 221 165 131 82 30 126 417 764 961 988 594 300 221 165 131 93 31 314 933 1130 292 165 131 121 Max 193 594 988 2360 1490 1570 544 292 213 156 131 121 Mean 131 275 559 1190 1020 920 401 252 187 144 110 92 Median 122 212 621 1130 960 845 383 256 181 148 112 93 Min 96 111 134 675 732 558 292 221 165 131 93 72

21 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 111 569 297 758 2040 877 2350 402 260 201 163 102 2 100 524 340 719 1980 821 2200 402 260 192 156 101 3 94 490 424 702 2120 801 1750 388 252 192 156 100 4 89 478 2940 801 1980 736 1470 374 252 192 156 99 5 84 538 2750 758 1920 702 1270 374 252 192 156 94 6 84 567 1980 1150 2670 702 1100 362 242 192 156 93 7 84 402 1470 1420 2830 679 1020 362 242 192 156 92 8 79 252 1080 1320 2590 640 1080 354 242 184 150 91 9 79 201 962 1320 2590 623 1020 354 233 184 150 90 10 84 184 1080 1150 2280 606 906 340 233 184 150 89 11 84 192 962 962 2940 702 821 340 233 177 150 88 12 79 184 801 1020 3060 679 778 328 233 177 150 87 13 79 184 801 1320 2750 679 736 328 226 177 150 86 14 79 209 778 1750 2510 934 702 328 226 177 114 86 15 84 233 623 2280 1870 934 679 320 226 177 112 82 16 94 252 719 2940 1530 1320 640 320 217 177 113 80 4670 694 79 17 106 297 934 3400 1320 1230 606 306 217 177 114 82 18 150 821 1270 1870 1320 1080 589 306 217 170 112 85

1970-71 19 177 623 990 1640 1420 906 569 306 217 170 113 98 20 163 524 849 1580 1230 1050 552 297 217 170 111 104 21 156 439 758 1700 1190 1020 524 297 209 170 112 118 22 163 328 679 1980 1050 906 507 297 209 170 113 144 23 163 242 736 2350 1020 849 490 291 209 170 111 147 24 163 233 906 2590 1100 906 490 291 209 170 112 138 25 163 226 849 3480 1420 1270 457 277 209 170 113 120 26 177 226 849 3590 1230 1980 453 277 209 163 109 113 27 233 233 962 3590 1150 3790 478 269 209 163 107 113 28 402 242 801 3170 1050 4670 453 269 201 163 103 116 29 606 233 906 2830 1100 3880 439 269 201 163 117 30 659 242 792 2590 1100 2350 424 260 201 163 111 31 260 2200 1020 410 201 163 114 Max 659 821 2940 3590 3060 4670 2350 402 260 201 163 147 Mean 162 343 1010 1901 1786 1277 838 323 225 177 131 103 Median 103 252 849 1700 1530 906 640 320 217 177 114 99 Min 79 184 297 702 1020 606 410 260 201 163 103 80 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1971-72 19 20 21 22 23 24 25 26 27 28 29 30 31 Max Mean Median Min

22 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 116 226 1130 1230 4240 1270 1270 345 226 147 116 96 2 125 283 1200 1270 3790 2040 1170 328 226 147 116 96 3 125 269 1230 1200 3420 2830 1060 311 212 147 116 96 4 116 269 1230 1540 3340 2600 934 311 212 147 116 96 5 105 241 1300 1580 2910 2550 764 297 212 147 116 86 6 96 241 1380 1300 2720 3080 764 283 212 147 105 87 7 105 226 1380 1270 2490 2660 849 283 212 147 105 78 8 125 226 1420 1170 2430 2210 736 269 212 147 105 78 9 125 241 1340 1130 2600 1920 708 269 198 147 96 78 10 147 269 1300 1060 2490 1750 679 269 198 147 96 78 11 158 328 1300 1060 2580 1620 640 255 198 136 96 78 12 158 362 1340 1200 2430 1660 659 241 198 136 96 78 13 184 413 1420 1200 2210 1500 600 241 198 136 96 78 14 170 580 1460 1170 1980 1340 541 241 184 136 96 78 15 170 708 1500 962 1810 1270 541 241 184 136 96 69 16 184 764 1380 1500 1660 1130 541 226 184 136 86 69 4240 798 62 17 158 849 996 1200 1660 1540 541 226 184 125 86 69 18 147 934 1030 1620 1620 1420 560 226 184 125 86 69

1972-73 19 158 1030 1060 1810 1540 1230 501 226 170 125 86 69 20 158 906 1920 2490 1500 1170 481 226 170 125 86 69 21 158 877 2150 3000 1300 1170 464 212 170 125 86 69 22 170 736 2490 3170 1300 821 413 226 170 125 86 69 23 158 620 2490 3340 1500 906 396 212 170 125 78 69 24 158 560 2550 3250 1540 877 379 212 170 125 78 62 25 158 521 2490 3170 1420 1270 379 212 170 116 78 62 26 158 521 2430 3590 1540 1620 379 212 170 116 78 62 27 184 736 1660 3510 1580 2720 379 212 170 116 78 69 28 226 1200 1460 2580 1500 1810 362 212 170 116 86 69 29 226 1500 1380 3790 1380 1460 362 212 158 116 69 30 240 1270 1270 4240 1340 1380 362 212 158 116 69 31 821 3510 1340 362 158 116 78 Max 240 1500 2550 4240 4240 3080 1270 345 226 147 116 96 Mean 156 604 1556 2068 2102 1694 606 248 187 132 95 76 Median 158 560 1380 1540 1660 1520 541 234 184 136 96 69 Min 96 226 996 962 1300 821 362 212 158 116 78 62 1 80 106 160 730 614 286 272 218 155 105 132 115 2 87 106 150 648 620 291 275 216 151 105 132 114 3 90 106 170 512 543 289 289 218 149 103 132 114 4 90 99 200 450 640 280 300 215 148 103 132 113 5 87 95 229 422 843 280 334 213 146 102 130 113 6 87 93 239 379 891 276 280 209 145 102 130 114 7 86 95 226 348 826 269 280 205 143 102 129 115 8 84 93 219 342 826 266 282 199 142 101 127 115 9 83 102 191 303 770 271 308 197 145 100 126 112 10 82 126 191 258 798 266 280 195 143 99 126 112 11 82 160 192 263 865 262 272 193 142 99 125 112 12 82 160 219 279 761 260 269 191 140 97 125 110 13 82 153 314 265 787 331 543 189 138 99 123 110 14 83 152 444 279 688 416 917 187 140 97 125 109 15 83 151 617 259 549 399 670 185 138 102 123 109 16 87 149 532 251 526 572 464 183 137 105 123 108 993 246 80 17 93 149 727 243 512 521 396 181 137 105 122 108 18 99 164 974 233 507 501 371 179 135 102 122 106

1973-74 19 90 160 925 216 447 484 323 201 134 100 121 106 20 86 155 730 208 436 402 303 193 134 99 121 106 21 90 144 679 211 371 368 291 184 132 97 119 105 22 88 137 659 219 354 342 272 178 132 96 119 105 23 91 129 688 256 320 334 258 174 132 95 116 103 24 99 134 691 291 308 306 246 175 132 95 115 107 25 98 127 674 405 286 323 249 169 127 95 115 109 26 95 125 656 340 273 342 246 166 123 115 117 108 27 90 123 750 345 289 323 241 165 119 135 117 114 28 94 128 874 337 286 294 234 158 113 135 115 113 29 94 131 993 408 262 280 224 154 110 135 114 30 106 148 883 518 289 280 230 155 108 134 119 31 162 549 291 224 106 134 113 Max 106 164 993 730 891 572 917 218 155 135 132 119 Mean 89 131 507 347 541 337 327 188 135 106 124 111 Median 88 131 575 303 526 300 280 188 137 102 123 112 Min 80 93 150 208 262 260 224 154 106 95 115 103

23 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 125 281 311 702 1460 1300 685 337 153 167 150 136 2 118 357 365 662 1360 1390 713 325 153 164 153 136 3 115 357 456 651 1520 1280 708 311 151 164 153 136 4 113 320 552 620 1620 1060 552 308 147 164 153 136 5 125 311 614 631 1640 911 668 303 147 161 153 136 6 127 391 552 657 1580 792 529 291 147 161 153 136 7 133 419 614 634 1420 781 597 286 144 161 153 136 8 133 498 541 577 1120 696 611 281 142 158 153 136 9 85 504 495 552 954 727 583 278 139 158 147 133 10 115 478 586 534 753 767 566 278 139 156 147 133 11 113 444 617 473 705 640 541 241 161 156 147 133 12 113 444 631 467 640 620 524 198 184 156 147 130 13 111 484 662 470 603 761 529 192 181 153 144 130 14 111 518 713 444 560 824 507 189 181 153 144 130 15 106 515 747 487 515 671 498 181 181 153 144 130 16 120 484 645 597 484 620 521 177 178 150 142 127 1640 404 85 17 136 490 991 637 467 640 529 177 178 150 142 127 18 153 518 1020 727 461 574 518 173 175 150 139 127

1974-75 19 233 458 1140 682 490 552 515 168 175 147 139 125 20 216 425 1130 662 464 580 436 167 175 147 139 125 21 246 399 996 620 458 634 444 167 173 147 139 125 22 223 385 954 671 450 682 433 165 173 144 136 123 23 230 391 877 659 419 628 410 164 173 147 136 125 24 223 351 826 696 470 614 430 161 170 147 136 127 25 230 325 795 773 492 685 391 161 170 147 136 130 26 240 303 722 787 509 603 379 158 170 147 136 133 27 240 289 682 812 438 543 379 158 170 147 136 133 28 237 281 659 1030 611 538 371 154 170 147 136 136 29 233 278 727 1060 574 507 357 153 170 147 136 30 244 281 758 1350 722 614 331 153 170 150 139 31 289 1470 1000 331 167 150 139 Max 246 518 1140 1470 1640 1390 713 337 184 167 153 139 Mean 165 396 713 703 805 741 503 215 165 153 144 132 Median 133 391 672 657 603 656 518 179 170 150 144 133 Min 85 278 311 444 419 507 331 153 139 144 136 123 1 96 158 371 501 911 464 758 241 142 113 89 82 2 96 161 399 552 860 543 894 230 142 110 89 80 3 98 158 374 558 727 591 903 224 142 108 91 80 4 98 153 331 719 676 631 821 215 139 108 93 80 5 98 147 272 617 665 591 891 212 139 108 96 82 6 102 147 224 628 640 628 778 207 136 108 98 82 7 102 147 241 648 614 671 591 201 136 108 102 85 8 102 150 263 611 577 696 577 201 136 106 102 87 9 108 167 273 546 563 552 541 201 136 106 104 87 10 117 184 282 470 540 552 552 195 136 106 102 85 11 121 205 294 461 526 501 535 191 136 104 102 85 12 123 237 286 461 512 490 521 188 133 104 100 83 13 117 224 297 487 495 515 518 181 136 102 98 83 14 115 92 345 436 484 580 490 181 133 102 98 82 15 113 179 441 444 464 623 461 181 130 100 98 82 16 110 173 532 399 450 857 450 181 130 100 96 80 1160 305 71 17 113 165 608 535 439 764 439 175 127 100 96 76 18 115 195 552 634 422 770 374 175 127 100 93 76

1975-76 19 115 223 543 524 399 988 376 175 125 100 93 76 20 117 248 566 475 413 852 357 172 125 98 91 76 21 117 255 597 425 444 795 342 170 123 98 89 75 22 119 226 659 450 473 727 328 167 123 98 87 75 23 122 209 784 524 541 648 320 164 123 96 85 75 24 127 198 962 634 574 606 311 161 123 96 85 75 25 134 188 1090 860 507 577 306 158 121 96 85 73 26 142 184 835 1160 444 569 297 158 121 93 83 73 27 147 173 674 1070 413 541 286 156 121 93 83 71 28 150 253 634 903 390 566 263 153 119 93 82 71 29 153 207 634 781 376 546 255 147 119 91 82 71 30 156 228 524 688 382 668 252 147 117 91 71 31 267 781 379 243 115 91 71 Max 156 267 1090 1160 911 988 903 241 142 113 104 87 Mean 118 190 496 612 526 637 485 184 129 101 93 78 Median 116 184 483 552 495 599 450 181 130 100 93 80 Min 96 92 224 399 376 464 243 147 115 91 82 71

24 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 70 186 263 4980 1090 2000 708 260 181 134 115 96 2 70 207 328 6540 748 1950 688 255 177 131 115 96 3 70 242 365 7190 835 1900 637 251 177 131 112 93 4 67 270 439 5630 928 1860 614 246 174 128 112 93 5 67 263 631 3910 1330 1790 623 241 170 128 112 93 6 65 256 569 3420 2360 1860 637 241 170 134 112 93 7 65 228 594 3280 2020 2410 521 232 166 134 112 91 8 63 200 843 3030 1970 2310 453 227 163 134 112 91 9 63 246 1220 2310 1670 1530 430 223 163 134 112 91 10 65 291 1250 2200 1540 1060 419 218 159 134 110 88 11 65 297 1610 1720 1400 835 410 214 159 134 110 88 12 67 294 1350 2150 1290 1270 402 214 159 134 107 86 13 67 228 2390 3060 1390 815 391 211 155 131 107 86 14 70 194 2230 5520 1400 1530 385 211 155 131 107 96 15 70 173 2310 5150 1370 1530 379 207 155 131 107 91 16 72 173 2310 4330 1490 928 371 203 152 128 107 91 7190 808 63 17 72 194 3200 4050 1930 716 362 203 152 128 107 91 18 70 194 3840 2650 3000 693 314 203 148 128 102 91

1976-77 19 70 184 2200 2360 5630 637 306 198 148 128 102 91 20 73 249 1540 1930 5690 597 300 192 144 126 102 93 21 74 256 1520 1280 6990 645 291 188 144 126 102 93 22 77 218 1110 1120 5910 637 287 188 142 123 99 91 23 80 186 968 1140 4780 693 283 188 142 123 99 86 24 85 186 991 1130 4330 764 308 185 142 123 99 86 25 97 180 1330 1410 4100 708 345 185 139 120 96 86 26 123 164 968 1470 4050 665 314 177 139 120 96 85 27 140 156 1680 1100 3370 631 306 177 139 120 96 88 28 152 228 2360 948 2630 665 297 177 139 120 93 88 29 186 263 3250 821 2520 651 289 177 136 118 86 30 200 242 3990 835 2070 679 277 181 134 118 86 31 239 957 2070 260 134 118 99 Max 200 297 3990 7190 6990 2410 708 260 181 134 115 99 Mean 86 222 1588 2826 2642 1165 407 209 153 127 106 90 Median 70 228 1340 2310 2020 825 371 205 152 128 107 91 Min 63 156 263 821 748 597 260 177 134 118 93 85 1 116 359 453 419 541 543 368 314 231 167 127 111 2 122 342 453 427 546 504 388 309 227 167 128 110 3 120 337 430 478 558 538 447 306 228 164 125 110 4 125 348 427 515 569 481 453 311 219 159 123 107 5 138 331 433 515 541 450 470 317 215 156 124 107 6 149 323 473 546 524 425 541 323 215 156 125 106 7 139 311 490 524 521 408 500 323 211 151 125 103 8 133 300 543 552 515 405 450 311 212 148 126 103 9 132 289 504 546 515 399 439 300 207 144 123 100 10 157 279 464 521 524 385 422 294 204 143 125 99 11 164 264 450 541 543 359 396 286 204 143 125 99 12 174 248 464 541 637 374 376 283 201 139 123 99 13 178 240 461 546 747 379 388 286 196 139 123 96 14 185 243 453 555 753 396 405 289 197 139 124 95 15 151 250 481 580 775 461 416 300 193 135 125 95 16 185 261 487 566 767 507 436 286 190 135 123 99 809 322 91 17 182 258 478 589 750 535 393 277 190 134 122 97 18 186 314 501 628 809 475 382 271 188 134 123 96

1977-78 19 186 292 509 645 758 566 371 262 184 134 122 93 20 185 266 492 634 699 583 382 280 184 135 125 93 21 185 253 475 699 688 541 354 271 185 132 125 94 22 188 258 447 659 682 518 351 262 181 133 124 94 23 188 274 478 620 668 504 348 252 174 130 123 92 24 188 306 473 611 645 481 345 248 180 131 120 93 25 188 306 427 671 657 470 345 243 177 132 117 93 26 191 300 410 628 736 464 345 239 173 132 114 93 27 227 294 391 594 739 447 345 235 172 130 114 91 28 273 292 399 569 725 433 340 235 173 131 112 91 29 279 357 368 560 767 410 331 235 172 132 91 30 283 408 391 555 671 388 323 230 168 129 91 31 490 543 606 320 168 130 94 Max 283 490 543 699 809 583 541 323 231 167 128 111 Mean 177 303 457 567 651 461 393 279 194 141 123 98 Median 184 294 463 555 668 463 382 285 190 135 124 96 Min 116 240 368 419 515 359 320 230 168 129 112 91

25 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 89 158 265 639 1110 403 586 221 249 183 125 92 2 89 163 237 586 1133 400 578 217 246 184 122 93 3 86 162 245 535 1114 395 542 217 244 182 118 93 4 86 162 243 656 1138 406 474 213 238 184 115 94 5 83 167 232 1076 1156 418 501 210 235 182 111 92 6 81 176 213 1054 1232 490 481 206 233 183 109 92 7 81 175 218 927 1252 461 449 206 227 184 107 93 8 80 171 224 700 1204 449 449 202 221 182 102 93 9 81 169 226 664 1240 461 442 198 215 183 102 94 10 81 164 242 608 1264 474 442 198 206 181 100 94 11 82 169 290 528 1264 494 436 195 200 182 98 92 12 84 175 379 507 1215 524 461 191 198 181 96 92 13 85 180 416 528 1126 639 436 188 192 179 95 92 14 89 182 415 552 1000 734 400 184 190 180 95 92 15 92 188 351 887 958 667 377 181 185 181 96 90 16 96 201 360 1379 897 616 366 174 183 178 94 90 1690 375 80 17 100 213 393 1630 824 596 356 331 184 175 95 88 18 115 212 423 1690 783 542 321 318 182 172 95 88

1978-79 19 114 212 484 1630 766 571 314 319 183 166 94 88 20 137 210 522 1557 713 843 304 321 181 164 94 89 21 118 324 624 1354 556 739 295 322 183 161 92 89 22 133 330 685 1179 514 639 286 310 184 158 93 89 23 151 398 955 1099 528 659 281 303 185 153 93 89 24 148 393 989 1065 538 624 277 296 186 150 94 87 25 150 338 919 1065 556 596 267 293 184 147 94 87 26 144 297 927 1197 542 783 258 282 185 145 93 85 27 152 262 1020 1154 521 891 250 275 183 142 93 85 28 154 276 1010 1168 490 820 241 269 182 137 94 83 29 153 302 659 1156 461 718 233 262 183 134 83 30 153 357 616 1156 436 647 225 255 184 130 82 31 285 1133 424 225 182 127 81 Max 154 398 1020 1690 1264 891 586 331 249 184 125 94 Mean 110 231 493 1002 870 590 373 245 200 167 100 89 Median 94 201 404 1065 897 596 366 219 185 178 95 90 Min 80 158 213 507 424 395 225 174 181 127 92 81 1 82 102 140 221 596 883 418 251 194 140 105 93 2 84 108 137 222 589 809 445 250 192 142 105 94 3 85 106 135 437 551 918 499 243 213 139 103 99 4 87 116 130 508 546 1040 524 240 208 137 103 102 5 89 122 129 360 506 1120 595 236 195 135 103 98 6 90 126 124 304 465 1000 797 232 190 133 101 93 7 92 128 132 276 456 963 669 228 185 133 101 89 8 92 127 129 246 456 926 616 224 181 133 101 86 9 89 129 132 228 449 884 580 221 178 130 99 88 10 89 221 129 210 458 867 566 214 179 130 98 88 11 89 114 131 222 466 1020 580 216 176 128 96 86 12 88 127 139 256 443 1010 595 215 174 128 94 87 13 90 131 147 269 451 830 557 212 172 126 94 84 14 91 128 180 293 456 919 494 213 170 124 94 82 15 92 136 190 338 461 841 460 214 168 122 93 80 16 90 258 213 368 507 795 411 209 165 120 91 78 1120 280 77 17 90 224 219 405 493 740 385 208 163 120 91 77 18 91 229 249 412 507 668 352 207 161 121 93 77

1979-80 19 91 278 254 414 512 636 334 207 159 119 94 81 20 86 243 257 429 545 606 316 204 156 119 96 86 21 86 216 263 421 781 561 299 202 154 117 92 86 22 95 194 215 650 1070 533 273 200 152 117 90 85 23 94 180 183 689 981 485 282 197 149 115 88 82 24 94 171 179 721 843 462 278 195 147 115 89 82 25 94 164 172 872 803 437 273 192 147 113 92 95 26 93 158 172 875 759 413 269 190 144 113 94 93 27 92 155 169 722 797 394 262 188 144 111 97 93 28 91 150 178 741 807 386 258 188 142 111 91 90 29 91 147 193 735 819 371 254 191 140 109 92 88 30 96 146 223 726 862 388 252 189 138 107 92 31 143 665 949 252 135 107 91 Max 96 278 263 875 1070 1120 797 251 213 142 105 102 Mean 90 161 175 459 625 730 424 213 167 123 96 88 Median 90 146 172 412 545 802 411 211 165 121 94 88 Min 82 102 124 210 443 371 252 188 135 107 88 77

26 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 91 171 236 399 1301 922 532 285 218 140 99 62 2 92 173 227 482 1378 802 500 285 216 141 98 62 3 92 163 235 497 1131 704 449 279 216 142 97 59 4 89 158 225 462 979 704 411 273 208 137 96 59 5 88 163 225 434 912 720 383 264 206 138 91 59 6 100 154 222 425 915 720 366 261 203 128 86 59 7 100 150 220 447 1193 695 366 256 201 129 85 59 8 94 159 234 478 1228 647 356 253 199 130 84 57 9 92 172 269 471 1146 586 421 250 200 126 80 57 10 94 191 394 579 1108 548 392 248 194 127 79 57 11 96 177 407 601 1075 562 366 248 195 127 89 57 12 95 192 367 579 1108 594 345 245 189 128 84 57 13 106 195 344 594 1439 820 312 242 183 129 81 62 14 106 192 322 811 1543 695 294 240 177 135 77 65 15 112 180 321 775 1511 652 294 240 178 136 74 84 16 123 171 431 1083 1839 586 294 237 173 137 74 82 1940 367 56 17 123 176 594 1131 1940 586 285 238 167 130 74 77 18 121 225 515 1301 1902 541 270 235 162 124 74 80

1980-81 19 122 189 570 1273 1623 572 280 232 157 123 74 82 20 118 207 659 1475 1448 532 276 230 158 121 71 71 21 117 217 575 1399 1264 500 285 230 159 111 71 64 22 123 210 538 1185 1193 466 290 227 154 110 68 58 23 138 205 516 1086 969 461 276 225 155 109 68 56 24 145 207 492 1032 959 527 280 225 162 107 68 62 25 166 224 463 986 906 594 294 223 157 106 68 64 26 166 226 451 925 979 594 285 226 152 114 65 66 27 149 224 432 820 986 555 254 226 147 113 65 65 28 143 213 432 793 877 603 242 223 142 112 65 64 29 153 230 429 839 886 586 303 223 143 106 64 30 167 219 433 1011 817 572 303 218 144 105 63 31 216 1169 784 297 139 104 62 Max 167 230 659 1475 1940 922 532 285 218 142 99 84 Mean 117 192 393 824 1205 622 332 243 176 123 79 64 Median 115 192 418 811 1131 590 297 239 173 127 76 62 Min 88 150 220 399 784 461 242 218 139 104 65 56 1 75 65 107 937 1110 1187 226 123 89 2 76 75 106 923 1516 798 217 120 89 3 78 77 107 858 1639 793 220 117 88 4 80 74 107 937 1366 947 215 114 87 5 82 70 115 897 1240 907 209 111 87 6 81 65 125 868 858 849 204 110 87 7 83 63 133 807 793 849 200 107 86 8 85 67 141 854 793 887 196 107 85 9 83 70 133 775 757 1065 191 106 85 10 81 68 126 748 757 1133 187 105 85 11 80 70 123 731 793 1121 186 103 87 12 80 76 117 672 845 1032 182 102 87 13 80 80 111 656 811 1175 180 102 86 14 79 79 123 672 811 1392 179 102 85 15 78 74 128 685 802 989 176 102 84 16 77 77 132 748 836 759 172 101 83 1639 371 60 17 87 86 126 798 829 858 167 99 82 18 93 86 139 839 858 811 163 98 82

1981-82 19 95 86 133 958 1168 739 159 97 81 20 94 82 127 1017 1260 705 158 96 80 21 68 79 121 907 1011 688 157 95 80 22 63 80 117 798 987 629 154 94 80 23 60 89 112 766 985 578 152 94 80 24 64 87 108 713 1032 283 149 93 79 25 67 86 139 807 1061 264 146 92 79 26 66 85 474 878 1076 252 143 93 78 27 69 85 494 917 1011 243 138 92 77 28 69 89 783 1105 887 233 136 91 77 29 66 96 923 1199 829 237 133 90 76 30 63 102 1021 858 802 239 129 89 76 31 105 878 1121 125 76 Max 95 105 1021 1199 1639 1392 226 123 89 Mean 77 80 225 845 988 755 173 102 83 Median 79 79 126 854 887 805 172 102 83 Min 60 63 106 656 757 233 125 89 76

27 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 609 527 318 216 139 121 117 2 541 513 308 214 139 120 115 3 524 497 306 212 141 119 111 4 520 483 299 213 142 120 110 5 572 462 293 211 142 119 108 6 567 455 286 209 144 120 107 7 578 442 281 207 143 119 104 8 548 435 277 205 141 118 102 9 520 427 274 222 141 119 100 10 564 419 271 201 142 118 99 11 577 415 269 194 144 119 98 12 612 405 268 190 143 102 97 13 712 398 265 186 145 119 98 14 979 390 258 179 145 117 98 15 900 384 255 174 144 117 97 16 894 378 252 169 144 117 95 979 270 91 17 922 374 248 166 145 116 95 18 829 365 247 160 145 114 93

1982-83 19 764 359 240 155 144 114 91 20 834 356 237 152 141 114 91 21 836 351 235 150 141 114 111 22 932 352 232 150 138 112 124 23 881 355 230 148 135 112 118 24 815 391 228 148 133 112 116 25 744 456 228 148 132 111 109 26 703 391 226 146 131 111 108 27 665 368 224 146 129 114 100 28 637 358 224 145 125 116 100 29 605 345 222 143 120 100 30 543 335 220 141 118 101 31 327 141 120 101 Max 979 527 318 222 145 121 124 Mean 698 404 257 176 138 116 104 Median 651 391 254 169 141 117 101 Min 520 327 220 141 118 102 91 1 43 226 265 825 1237 1328 727 489 222 191 161 113 2 42 222 262 870 1055 1167 726 488 221 186 156 104 3 42 220 271 1223 863 942 603 483 216 179 155 104 4 43 212 268 1184 833 841 554 484 215 171 156 103 5 45 256 317 1437 732 857 522 479 219 165 154 105 6 45 280 705 1758 665 814 503 485 218 162 155 106 7 46 302 522 1886 612 784 472 488 217 156 153 106 8 43 329 461 917 584 772 461 472 215 155 154 107 9 43 348 408 1366 584 942 449 452 220 157 152 109 10 43 297 415 1043 555 1340 440 428 225 154 151 109 11 111 290 398 789 517 1376 867 409 224 156 153 107 12 94 250 343 695 579 1766 830 390 225 155 150 107 13 98 288 251 656 601 2260 806 376 224 154 145 107 14 101 405 236 619 549 2683 795 362 225 153 139 105 15 100 448 244 691 521 2648 760 344 225 155 134 104 16 102 359 348 726 536 2474 747 331 221 159 132 102 2683 476 42 17 99 374 311 1056 650 1623 714 314 219 168 127 102 18 98 353 394 779 536 1491 675 298 218 175 124 100

1983-84 19 100 346 429 1129 518 1439 645 282 220 182 122 100 20 97 401 494 1077 527 1335 626 270 211 192 119 98 21 99 386 644 1252 618 1583 585 258 206 175 117 100 22 96 401 769 1148 704 1647 569 243 200 177 116 100 23 95 401 820 1106 665 1555 531 241 197 171 114 95 24 99 407 668 1235 909 1288 511 238 192 169 107 94 25 103 349 623 1602 1083 1212 528 238 186 168 103 93 26 116 338 619 1386 1325 1195 506 230 184 165 103 90 27 108 312 526 1206 1066 1343 514 229 192 164 104 91 28 112 302 509 1332 975 1184 507 231 192 162 104 91 29 128 278 637 1208 866 953 497 226 186 220 109 90 30 166 271 813 1193 883 874 491 224 178 215 91 31 271 1360 975 488 175 211 86 Max 166 448 820 1886 1325 2683 867 489 225 220 161 113 Mean 85 320 466 1121 752 1391 602 349 209 172 133 101 Median 98 312 422 1148 665 1332 554 338 217 168 134 102 Min 42 212 236 619 517 772 440 224 175 153 103 86

28 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1984-85 19 20 21 22 23 24 25 26 27 28 29 30 31 Max Mean Median Min 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1985-86 19 20 21 22 23 24 25 26 27 28 29 30 31 Max Mean Median Min

29 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 76 173 138 1052 1369 883 777 313 176 121 85 76 2 76 171 147 866 1502 826 796 301 173 119 83 80 3 81 171 158 818 1721 845 791 296 170 116 82 77 4 76 166 164 752 1437 1269 740 287 168 113 82 76 5 76 173 172 714 1184 1405 714 256 163 111 83 74 6 75 198 190 927 1056 1168 704 253 162 110 81 72 7 73 194 198 914 1025 992 762 250 158 104 82 72 8 71 184 231 869 866 882 850 245 155 105 81 70 9 70 171 243 807 791 840 875 240 156 103 80 70 10 77 165 241 911 724 829 817 235 154 103 80 73 11 75 160 248 850 700 1124 772 237 151 101 79 81 12 75 156 296 802 664 1411 735 242 152 101 78 87 13 75 167 397 743 624 1301 701 232 149 101 78 91 14 76 166 344 755 607 1204 684 229 150 99 77 87 15 78 162 334 762 606 1112 702 224 153 99 77 86 16 82 157 350 812 592 1026 779 220 152 99 78 86 1721 404 70 17 91 165 400 1046 629 1016 723 216 151 97 78 83 18 94 181 675 1220 658 1002 650 217 151 97 77 81

1986-87 19 92 181 998 1147 653 1052 585 213 150 95 77 83 20 90 161 762 1018 661 1019 529 208 149 95 77 87 21 81 165 658 915 727 1005 484 202 152 93 76 88 22 99 164 609 835 741 1075 444 200 151 93 76 85 23 92 156 553 814 918 1152 408 198 149 93 75 86 24 102 150 507 830 1084 1165 372 194 139 91 75 85 25 101 152 487 1186 994 795 371 191 136 91 74 83 26 117 152 484 1471 946 766 368 189 125 89 74 81 27 127 146 577 1320 1164 757 364 189 123 89 73 81 28 132 140 900 1120 1075 770 359 184 123 87 76 84 29 140 138 1109 981 911 781 361 181 123 86 86 30 142 138 1130 925 813 818 360 177 123 85 88 31 138 1147 807 340 123 85 85 Max 142 198 1130 1471 1721 1411 875 313 176 121 85 91 Mean 90 163 457 946 911 1010 610 227 149 99 78 81 Median 81 165 374 911 813 1011 701 222 151 99 78 83 Min 70 138 138 714 592 757 340 177 123 85 73 70 1 88 103 185 1090 2120 1870 965 356 190 102 84 77 2 85 114 184 1290 2220 1790 888 355 187 101 83 74 3 93 118 169 1450 2400 2360 956 344 183 101 83 72 4 100 126 160 1290 2650 1730 979 332 180 100 82 71 5 100 125 160 947 2380 1450 811 328 177 100 82 69 6 97 152 154 831 2110 1300 702 302 175 99 82 68 7 93 149 190 830 1790 1300 629 295 172 99 80 67 8 89 143 222 795 1740 1290 582 286 169 98 80 66 9 88 136 235 830 2450 1270 540 279 166 97 78 66 10 91 141 240 987 3480 1090 508 271 163 97 79 67 11 95 156 222 987 5210 1020 484 269 159 96 79 67 12 98 167 198 875 5210 1290 464 262 156 95 77 69 13 110 185 192 917 4290 1560 447 256 152 93 77 68 14 98 167 200 912 3830 1220 417 253 152 96 75 68 15 88 154 290 863 2870 1140 399 247 148 95 75 70 16 81 148 384 1140 2460 1080 385 243 147 93 74 68 5210 563 65 17 76 146 257 1210 2360 1060 373 238 144 94 74 68 18 72 147 215 1110 2250 989 365 236 141 93 74 66

1987-88 19 73 159 146 953 2140 1640 374 233 138 93 72 66 20 71 168 112 881 2080 1770 504 227 134 92 72 67 21 68 161 103 905 2050 1450 805 224 131 91 71 70 22 67 168 133 1130 2000 1210 657 219 128 91 69 73 23 67 175 177 2130 1830 1040 572 216 121 90 69 74 24 72 178 353 2280 1570 1130 500 210 114 90 80 72 25 91 168 410 2160 1530 1130 461 207 111 87 87 72 26 98 161 496 1930 1410 1000 435 205 110 84 84 70 27 100 153 726 2210 1210 1020 406 202 110 82 79 68 28 132 163 759 2380 1110 1100 386 199 109 83 77 66 29 123 165 713 2420 1110 1130 371 196 109 87 77 67 30 104 166 752 2150 1160 1010 362 196 105 85 68 31 162 2040 1110 350 104 86 65 Max 132 185 759 2420 5210 2360 979 356 190 102 87 77 Mean 90 152 291 1352 2327 1315 551 256 145 93 78 69 Median 91 156 208 1110 2120 1215 484 245 147 93 78 68 Min 67 103 103 795 1110 989 350 196 104 82 69 65

30 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 65 84 296 224 1280 2810 1010 216 140 83 65 67 2 65 80 242 491 1090 2740 949 213 134 81 66 67 3 63 79 214 435 991 2630 867 208 127 79 67 66 4 63 84 200 828 920 2450 802 205 122 77 67 64 5 62 80 197 995 847 2300 1080 200 119 76 70 63 6 61 83 172 1430 1110 2950 928 197 115 76 71 63 7 62 94 162 2030 1430 4260 946 194 113 74 71 62 8 63 92 151 2330 1890 3790 870 193 112 74 72 62 9 64 89 160 2550 1600 4270 623 189 111 73 73 61 10 68 95 159 1900 1570 4460 568 186 109 72 74 61 11 71 135 174 1750 1560 3580 560 186 108 74 75 61 12 72 192 175 1590 2330 2980 520 183 110 75 75 60 13 69 169 173 1340 2880 3010 482 183 108 75 76 60 14 70 205 183 1210 2480 2680 455 182 107 73 77 60 15 72 215 217 1070 2310 2090 438 182 106 72 78 63 16 74 199 225 945 2670 1750 421 179 104 70 79 61 4460 647 60 17 74 182 250 838 2360 1630 422 179 103 69 78 63 18 82 152 695 790 2190 1350 392 177 102 67 76 63

1988-89 19 86 145 944 925 1870 1240 368 177 102 67 76 64 20 83 141 723 941 1890 1160 353 173 99 68 78 65 21 80 139 809 901 1900 1080 344 167 98 67 78 65 22 81 145 651 1260 2620 1030 314 164 98 67 83 73 23 80 150 512 1960 3310 1020 285 161 97 66 78 75 24 93 152 429 2940 4240 920 267 163 95 67 78 71 25 106 159 363 3280 4350 888 258 161 94 66 76 66 26 102 166 317 2440 4050 852 255 159 91 66 72 66 27 91 217 296 2350 3850 1530 243 158 90 66 71 70 28 88 232 262 2040 3530 2120 238 153 88 66 69 72 29 90 246 225 1740 4180 2130 233 150 87 65 71 30 90 374 203 1560 3950 1420 227 145 85 66 71 31 373 1520 3330 221 84 65 69 Max 106 374 944 3280 4350 4460 1080 216 140 83 83 75 Mean 76 160 326 1503 2406 2237 514 179 105 71 74 65 Median 73 150 225 1430 2310 2125 422 181 104 70 75 64 Min 61 79 151 224 847 852 221 145 84 65 65 60 1 65 92 454 1030 1180 978 2230 541 160 158 122 106 2 63 89 412 1310 1130 990 1930 536 161 155 121 102 3 62 91 448 1880 1080 1200 1800 533 163 158 118 100 4 68 96 555 1580 991 1450 1640 534 161 156 117 97 5 84 102 458 1450 947 1730 1490 530 160 154 114 95 6 73 111 478 1470 941 1960 1360 526 162 152 113 94 7 70 115 429 1600 961 1540 1250 522 163 152 110 92 8 67 121 433 1650 1020 1410 1160 514 162 152 109 91 9 67 115 485 1700 1320 1320 1130 482 164 150 107 91 10 70 112 512 1730 1200 1140 1120 453 164 150 117 89 11 74 99 372 1510 1150 1170 1140 420 174 148 104 93 12 82 90 458 1610 1120 1280 1090 390 173 148 102 94 13 89 111 380 1430 1110 1320 1030 362 173 146 100 100 14 77 108 350 1490 1160 1300 980 330 170 146 102 102 15 69 101 442 1620 1250 1590 921 304 170 144 108 101 16 67 94 1080 2040 1710 1580 883 281 169 144 111 97 3430 628 62 17 68 83 1140 2330 2120 1370 799 270 172 144 111 92 18 75 72 798 2710 1570 1770 755 261 171 142 109 89

1989-90 19 84 69 729 2810 1540 2560 780 251 171 142 104 88 20 95 68 633 2090 1640 3430 733 236 168 140 100 87 21 93 75 588 1700 1670 2980 713 224 167 140 98 85 22 93 90 560 1690 1780 2470 692 213 163 140 99 86 23 90 90 521 1440 1610 2470 666 203 166 138 97 89 24 83 80 547 1350 1320 2480 670 193 169 138 102 88 25 85 83 759 1210 1370 2150 620 185 166 136 109 94 26 92 99 1030 1230 1220 2070 608 177 164 136 102 92 27 92 226 782 1240 1120 1980 593 170 164 136 102 89 28 98 746 764 1740 1130 2070 595 167 166 134 103 102 29 101 1540 684 1350 1580 2590 585 163 166 134 98 30 92 937 681 1220 1260 2580 560 157 164 133 95 31 628 1190 1020 546 160 133 90 Max 101 1540 1140 2810 2120 3430 2230 541 174 158 122 106 Mean 80 211 599 1626 1297 1831 1002 338 166 144 108 94 Median 80 99 534 1580 1200 1660 883 293 166 144 108 93 Min 62 68 350 1030 941 978 546 157 160 133 97 85

31 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 84 192 279 889 844 558 858 250 182 108 90 82 2 80 195 343 832 728 467 743 249 180 109 89 83 3 79 221 395 719 598 434 692 246 179 121 89 84 4 81 222 686 686 546 403 657 243 179 120 87 79 5 80 183 806 722 580 368 759 240 176 119 88 81 6 83 171 967 1080 494 430 661 239 173 115 87 80 7 80 158 1220 1260 633 468 590 238 171 114 87 77 8 83 145 1020 1790 551 450 555 237 170 113 87 76 9 91 169 1030 1730 496 597 788 234 168 110 87 76 10 83 190 961 1670 531 1020 925 231 165 106 87 77 11 94 194 964 1610 945 1060 783 228 161 105 85 77 12 124 195 931 1540 1260 812 645 221 159 103 85 78 13 113 204 813 1490 1300 607 552 220 156 102 84 78 14 114 282 708 1460 1320 715 502 218 154 101 85 79 15 115 576 661 1270 997 695 472 217 150 100 86 81 16 126 376 583 1190 877 667 495 214 148 100 86 82 2190 435 76 17 112 290 548 1110 745 888 465 213 146 100 83 84 18 124 256 586 1920 750 966 418 210 143 99 82 84

1990-91 19 139 229 798 2190 660 864 388 207 141 99 81 80 20 128 219 828 2170 586 698 362 204 140 98 81 79 21 130 202 745 1800 520 602 340 201 138 96 79 78 22 136 246 1350 1590 474 553 317 201 135 94 78 81 23 151 301 1630 1230 427 566 303 198 132 95 78 82 24 150 230 1340 1040 406 720 292 197 129 95 77 81 25 135 205 1070 1010 743 1510 272 194 126 94 77 82 26 135 206 896 1120 1150 1290 268 192 123 94 76 96 27 135 215 788 1250 1500 1090 265 189 120 93 76 85 28 151 266 745 1330 1090 1060 261 188 118 92 79 80 29 137 250 811 1220 958 1410 258 186 115 92 79 30 140 235 933 1190 796 1090 255 185 112 92 78 31 236 1020 655 253 112 90 79 Max 151 576 1630 2190 1500 1510 925 250 182 121 90 96 Mean 114 234 848 1327 779 769 497 216 148 102 83 80 Median 120 219 812 1250 728 697 472 216 148 100 85 80 Min 79 145 279 686 406 368 253 185 112 90 76 76 1 90 114 251 2400 1470 541 619 203 162 120 102 66 2 98 108 272 1710 1980 595 562 197 161 116 102 64 3 98 146 239 1440 2040 802 551 191 160 115 105 66 4 122 184 282 1580 3080 1170 494 186 159 115 104 66 5 112 168 230 1550 2900 1000 467 187 158 114 102 65 6 111 178 228 1330 2350 844 458 192 157 114 101 66 7 109 202 235 1020 2090 800 514 199 157 113 100 74 8 107 190 306 1020 2360 728 427 201 154 112 99 74 9 106 200 318 1670 2720 2280 400 207 152 112 100 74 10 119 295 355 2050 2470 2410 386 205 151 111 100 75 11 133 391 512 2460 2630 2510 384 204 149 110 99 72 12 128 357 606 2840 2220 2260 368 202 148 112 98 71 13 121 324 778 2540 1900 1880 350 201 146 113 97 69 14 112 302 1420 1850 1430 1610 321 199 145 112 95 69 15 107 273 2030 1380 1320 1500 316 195 144 112 92 68 16 104 257 2500 1180 1580 1370 312 193 142 111 91 68 3080 562 62 17 100 246 2240 978 1920 1580 334 192 141 109 89 68 18 99 242 2290 775 1890 1370 302 193 139 107 88 68

1991-92 19 98 254 2210 753 1690 1030 293 187 138 106 88 66 20 99 273 2190 773 1300 1340 287 180 135 106 87 66 21 96 241 2200 745 1160 1250 282 172 133 106 84 67 22 95 214 2080 694 1050 1060 279 170 130 105 79 67 23 92 208 2150 679 925 1030 277 167 130 103 75 66 24 98 214 2150 715 765 1070 266 166 127 101 74 66 25 99 312 2010 784 710 977 254 165 128 101 74 66 26 97 259 1750 885 716 954 247 164 128 100 71 67 27 115 232 1730 994 912 1050 240 163 127 102 69 67 28 126 218 1590 817 932 914 233 162 127 100 69 65 29 133 206 1450 808 593 740 225 161 126 99 67 64 30 115 246 1510 1010 519 674 216 160 123 97 62 31 286 1090 485 209 123 98 62 Max 133 391 2500 2840 3080 2510 619 207 162 120 105 75 Mean 108 237 1270 1307 1616 1245 351 185 142 108 90 67 Median 107 241 1480 1020 1580 1055 316 192 142 110 92 67 Min 90 108 228 679 485 541 209 160 123 97 67 62

32 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 62 91 244 597 644 586 485 214 138 110 94 90 2 62 89 227 520 616 568 448 205 136 109 95 87 3 61 93 228 502 715 526 426 196 136 108 94 87 4 59 105 232 563 730 496 398 190 136 110 93 83 5 59 117 226 708 678 454 375 182 137 110 91 82 6 57 140 253 703 835 436 357 184 136 109 90 80 7 54 159 299 675 878 444 338 183 135 108 90 81 8 59 148 416 850 810 428 314 185 132 117 90 81 9 62 166 361 1020 734 410 298 187 131 124 91 80 10 64 168 309 872 706 439 267 187 130 121 89 80 11 62 163 268 953 631 436 278 189 129 119 89 79 12 62 164 259 1060 566 425 302 189 128 119 89 79 13 61 163 257 1420 536 457 303 190 127 119 91 79 14 61 160 243 1210 496 759 317 184 126 119 91 78 15 60 156 240 1490 464 806 303 181 125 117 90 75 16 57 176 234 1570 461 727 547 177 122 115 102 75 1570 297 52 17 54 175 229 1320 446 726 453 172 123 113 104 77 18 52 171 225 1240 448 753 398 168 122 111 103 77

1992-93 19 54 218 243 1130 468 769 370 159 120 109 103 75 20 57 219 244 968 430 696 343 151 119 108 102 74 21 61 229 240 898 402 637 326 151 118 108 101 74 22 68 213 284 843 406 596 315 149 117 106 101 72 23 64 206 273 846 463 561 301 148 116 104 99 72 24 66 211 282 747 574 526 291 147 117 103 99 74 25 84 203 361 716 734 483 279 146 116 101 93 74 26 81 194 410 734 864 457 270 144 115 100 92 75 27 79 191 414 733 760 475 259 143 114 99 92 81 28 94 191 573 957 733 562 248 142 113 97 91 82 29 91 191 691 882 714 595 238 141 113 96 77 30 91 209 644 740 641 555 233 140 112 96 82 31 212 634 591 221 111 93 89 Max 94 229 691 1570 878 806 547 214 138 124 104 90 Mean 65 171 314 906 619 560 332 171 124 109 95 79 Median 61 171 258 850 631 541 314 179 123 109 92 79 Min 52 89 225 502 402 410 221 140 111 93 89 72 1 87 186 262 984 2140 1150 1620 358 235 135 115 78 2 83 190 240 1498 1530 967 1180 350 230 134 117 79 3 81 178 312 1300 1190 877 1150 349 227 133 115 78 4 79 205 391 1173 1220 818 1210 343 225 131 115 78 5 77 268 451 1788 1730 798 954 335 223 130 113 78 6 76 526 618 1802 1590 865 778 335 221 129 113 76 7 75 548 666 1658 1770 827 667 332 221 128 110 75 8 75 454 668 1369 1740 769 650 329 218 126 103 76 9 75 376 636 1121 2250 735 640 327 209 125 96 75 10 79 361 624 969 1790 734 596 322 198 124 96 74 11 80 354 782 889 1480 699 650 311 189 124 99 75 12 85 372 741 819 1380 611 843 308 181 122 110 77 13 93 577 687 717 1130 566 782 298 179 118 104 78 14 100 492 575 664 991 544 816 294 177 113 98 80 15 107 475 507 632 727 551 992 293 174 111 95 81 16 109 460 455 453 663 591 970 288 167 113 93 86 5730 500 74 17 108 441 430 466 673 572 891 284 164 127 91 89 18 116 437 417 841 602 488 711 281 161 127 89 98

1993-94 19 129 523 461 1320 556 645 687 278 159 124 87 102 20 134 474 575 3020 541 531 562 273 156 117 85 106 21 155 447 711 4530 530 486 529 270 154 115 83 110 22 153 404 979 5730 530 453 496 265 146 112 81 109 23 145 392 842 3710 608 471 457 261 149 109 84 112 24 134 362 723 2520 612 480 434 257 150 107 87 122 25 139 353 658 1810 745 492 418 254 149 105 87 116 26 161 321 625 1530 778 467 408 251 144 103 83 113 27 155 276 614 1380 679 513 401 248 141 103 82 108 28 162 264 750 1270 736 721 388 245 139 101 81 113 29 156 300 667 1080 890 946 380 240 137 106 110 30 182 296 628 1030 1380 767 370 237 136 116 102 31 268 1660 1210 365 135 115 98 Max 182 577 979 5730 2250 1150 1620 358 235 135 117 122 Mean 113 374 590 1604 1109 671 710 294 177 119 97 92 Median 108 372 624 1300 991 628 650 291 167 118 95 86 Min 75 178 240 453 530 453 365 237 135 101 81 74

33 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 99 124 461 405 619 531 315 213 154 113 92 94 2 99 124 483 386 557 674 304 209 153 112 92 100 3 146 121 478 360 543 608 304 206 151 112 93 102 4 156 114 435 351 540 537 304 204 151 111 91 101 5 136 127 542 312 566 492 315 200 148 109 92 100 6 124 172 644 361 586 461 347 198 145 108 92 101 7 112 164 568 369 703 430 330 197 143 106 91 96 8 107 157 497 343 661 428 326 191 140 105 91 95 9 108 154 500 317 616 416 308 189 138 104 91 95 10 107 167 449 299 696 521 300 185 138 102 89 98 11 108 167 508 282 723 516 293 183 136 102 89 98 12 107 170 545 272 801 491 315 182 137 101 87 96 13 98 168 527 261 907 455 310 180 137 100 87 94 14 96 156 532 249 1210 475 310 178 135 100 85 94 15 91 154 543 244 1220 515 299 176 135 100 85 93 16 91 164 533 239 1160 512 295 175 133 100 90 91 1220 271 85 17 90 167 473 239 997 482 285 173 133 100 90 90 18 92 172 444 238 868 451 281 172 133 99 89 89

1994-95 19 91 169 470 244 782 508 274 172 131 96 104 89 20 93 156 523 285 712 658 269 168 131 96 100 88 21 95 141 463 284 663 702 259 164 131 96 98 88 22 98 137 398 318 666 600 252 161 129 95 94 86 23 108 152 367 351 736 510 244 157 129 95 91 89 24 115 149 333 391 874 473 239 160 129 98 91 89 25 137 158 391 409 838 445 234 158 127 98 90 92 26 143 229 339 642 752 411 229 157 122 97 91 94 27 142 209 295 820 679 390 224 156 121 97 91 107 28 129 256 263 598 641 373 222 155 119 94 90 114 29 121 299 259 587 610 350 223 153 118 94 123 30 126 382 326 690 583 331 225 154 118 93 128 31 362 674 566 218 115 93 128 Max 156 382 644 820 1220 702 347 213 154 113 104 128 Mean 112 179 453 381 744 492 279 178 134 101 91 98 Median 108 164 472 343 696 487 293 176 133 100 91 95 Min 90 114 259 238 540 331 218 153 115 93 85 86 1 129 189 1000 1460 1040 764 1430 319 254 180 145 129 2 125 193 1140 1540 938 747 1200 323 250 181 143 126 3 112 209 1270 1720 926 703 1030 310 246 179 142 123 4 108 190 1320 1720 901 708 882 303 244 177 140 116 5 105 184 1330 1640 849 699 807 297 246 173 139 113 6 102 181 1190 1830 808 680 767 291 245 171 137 111 7 98 201 1030 2330 772 709 730 281 244 169 138 110 8 95 195 1040 2550 762 799 644 272 245 167 136 109 9 94 179 984 2680 744 761 591 263 247 166 135 107 10 94 170 979 2630 740 735 549 269 248 166 133 107 11 96 163 936 2260 821 756 520 300 243 162 134 105 12 95 178 942 1990 1300 833 495 628 237 160 132 104 13 105 181 1220 1840 1650 788 543 432 232 158 131 104 14 108 177 1340 1640 1750 733 518 366 226 156 130 102 15 110 184 1180 1470 1930 693 468 337 218 154 130 100 16 106 208 3230 1350 2020 677 436 311 215 156 129 100 4010 612 94 17 103 221 4010 1260 1640 701 410 303 212 156 129 110 18 102 239 3660 1250 1340 745 383 293 209 154 130 123

1995-96 19 101 628 2900 1210 1190 753 439 282 206 152 129 129 20 108 614 2480 1180 1220 952 598 289 202 162 128 126 21 115 955 2590 1120 1140 1240 507 283 202 163 127 126 22 125 837 2730 1080 1050 1520 475 282 199 158 126 129 23 129 729 2370 1050 946 1880 425 273 196 156 125 130 24 121 653 2170 985 883 1810 392 268 195 154 125 127 25 116 649 2070 930 838 1450 374 269 192 152 123 116 26 116 671 1910 1030 859 1190 360 265 189 150 122 113 27 130 708 1510 1410 1040 1160 344 259 186 151 124 111 28 155 723 1300 1120 938 1140 346 257 183 149 124 109 29 197 741 1410 935 904 859 336 256 183 148 127 108 30 195 780 1350 933 922 955 331 255 182 146 108 31 892 1020 843 325 180 144 108 Max 197 955 4010 2680 2020 1880 1430 628 254 181 145 130 Mean 117 420 1753 1521 1087 938 570 305 218 160 131 114 Median 108 209 1335 1410 938 763 495 286 215 158 130 111 Min 94 163 936 930 740 677 325 255 180 144 122 100

34 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1996-97 19 20 21 22 23 24 25 26 27 28 29 30 31 Max Mean Median Min 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1997-98 19 20 21 22 23 24 25 26 27 28 29 30 31 Max Mean Median Min

35 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 1682 1189 435 271 185 123 95 80 2 1682 996 436 267 183 124 94 78 3 2164 1173 418 273 181 123 94 77 4 1897 1469 404 268 179 118 92 77 5 1844 1354 396 260 177 118 92 77 6 1614 1284 380 255 174 116 92 76 7 1252 1137 360 247 172 114 91 76 8 1097 972 354 253 170 114 91 74 9 1032 839 345 247 170 115 91 74 10 1046 749 345 240 168 111 89 74 11 983 678 331 237 164 111 88 73 12 1090 655 325 236 161 111 88 73 13 824 568 330 229 159 109 88 72 14 884 531 331 224 157 109 87 72 15 975 496 312 222 155 108 87 71 16 1105 461 307 218 154 107 87 69 2164 366 65 17 1056 432 296 215 153 105 85 69 18 1409 400 292 213 151 105 85 69

1998-99 19 1332 416 291 211 149 104 84 68 20 1082 391 423 210 147 104 84 68 21 1210 384 504 207 145 105 84 67 22 1093 408 461 206 143 104 82 67 23 945 427 401 204 143 103 81 66 24 863 532 373 199 141 100 81 67 25 858 572 343 197 141 100 81 67 26 1013 527 332 194 139 98 81 66 27 1163 486 353 189 137 98 81 66 28 1073 478 322 183 135 98 80 65 29 1025 479 304 190 129 97 66 30 1021 452 291 188 124 97 69 31 1112 279 122 95 71 Max 2164 1469 504 273 185 124 95 80 Mean 1207 698 357 225 155 108 87 71 Median 1090 531 345 220 154 107 87 71 Min 824 384 279 183 122 95 80 65 1 69 202 479 1078 453 1109 621 427 239 155 117 93 2 66 197 408 1398 478 1101 618 416 236 153 120 93 3 66 196 477 1485 553 1134 604 407 230 140 121 94 4 77 197 385 1634 480 1138 613 401 225 139 126 94 5 73 201 340 1301 407 1136 636 393 229 141 124 91 6 71 279 302 1315 372 1135 616 379 227 138 117 91 7 74 208 266 1064 358 1175 600 363 222 138 115 91 8 78 178 250 1003 347 1135 590 364 219 141 119 92 9 84 164 235 994 336 896 677 354 216 144 115 93 10 93 151 225 1349 384 870 612 347 209 144 112 92 11 84 141 221 1791 458 884 644 333 204 132 115 93 12 83 131 223 1473 496 848 621 328 207 131 114 95 13 72 128 238 1540 613 809 568 322 207 131 115 91 14 68 127 427 1421 804 804 547 315 205 128 116 91 15 80 127 649 1331 780 762 516 307 202 126 118 91 16 116 131 578 1179 710 730 514 301 198 126 104 91 2090 426 66 17 112 135 577 1055 702 765 472 298 193 126 104 90 18 87 129 479 943 658 749 611 295 188 124 106 94 19 83 116 433 1153 1068 719 623 289 193 124 109 95 1999-2000 20 77 110 435 1128 975 675 990 286 191 124 99 91 21 73 106 517 957 1083 641 1005 280 189 128 107 89 22 73 102 593 838 1140 671 782 274 188 131 97 89 23 86 108 626 701 1278 610 707 269 184 124 97 89 24 104 153 1018 861 1466 588 617 266 177 122 97 88 25 96 339 1457 691 2090 589 575 261 171 124 96 88 26 145 267 1121 628 1883 609 539 258 180 121 95 87 27 148 234 821 597 1895 839 512 253 180 120 93 83 28 208 229 960 610 1494 751 491 250 177 119 92 84 29 169 236 1156 602 1322 673 473 247 177 116 93 87 30 160 247 1085 585 1258 632 462 242 167 119 87 31 342 527 1159 444 156 119 86 Max 208 342 1457 1791 2090 1175 1005 427 239 155 126 95 Mean 96 181 566 1072 887 839 610 317 200 131 109 90 Median 83 164 478 1064 710 784 611 304 198 128 112 91 Min 66 102 221 527 336 588 444 242 156 116 92 83

36 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 82 324 596 1243 830 1028 574 258 193 148 106 86 2 92 271 549 1452 1220 999 547 255 196 147 104 86 3 105 257 597 1656 2149 972 519 252 193 130 103 84 4 148 295 579 1474 2708 966 492 252 188 130 104 82 5 157 259 571 1266 2807 1017 500 248 188 135 102 79 6 160 234 576 1381 2468 1022 523 249 185 137 100 78 7 128 222 689 1497 1925 1145 490 249 184 128 98 79 8 112 228 1101 1216 1755 1280 489 269 178 128 98 78 9 117 247 1253 1212 1832 1295 517 261 171 126 98 79 10 117 211 1293 1139 1527 1261 522 257 180 126 96 78 11 126 205 1088 1097 1417 1187 455 261 174 124 96 73 12 127 201 1569 965 1391 1099 456 253 174 125 95 72 13 126 192 1478 732 1387 955 422 249 171 124 95 72 14 122 193 1459 714 1338 957 407 258 171 122 93 72 15 120 197 1337 701 1604 951 360 260 168 120 93 70 16 113 201 1162 714 1767 1069 344 254 165 120 93 72 2807 509 62 17 121 237 1073 572 1548 1143 330 243 163 118 92 74 18 136 324 881 563 1474 1285 314 230 163 116 89 65

2000-01 19 169 378 859 519 1291 1113 303 235 163 115 87 65 20 154 330 874 464 1172 1006 311 229 161 113 86 64 21 145 346 1063 422 1124 862 320 226 158 112 88 62 22 153 357 1746 515 1077 811 278 226 158 113 86 62 23 189 387 2512 472 1016 754 281 223 155 110 85 62 24 218 359 2057 398 1060 865 273 218 154 110 97 67 25 265 325 1793 390 1161 1049 267 213 148 110 96 67 26 283 323 1703 390 1064 978 260 211 150 108 93 67 27 257 427 1781 476 1147 872 273 208 151 112 89 65 28 209 569 1630 500 1226 777 284 205 149 110 87 64 29 206 601 1292 476 1134 756 277 204 149 107 62 30 307 595 1182 613 1109 689 266 202 150 108 62 31 542 633 1060 261 149 108 67 Max 307 601 2512 1656 2807 1295 574 269 196 148 106 86 Mean 159 317 1211 834 1477 1006 384 239 168 121 95 71 Median 140 295 1172 701 1338 1003 344 249 165 120 95 72 Min 82 192 549 390 830 689 260 202 148 107 85 62 1 93 192 709 549 1186 861 881 403 239 142 123 88 2 98 179 670 508 1405 968 680 377 234 151 125 87 3 92 168 610 523 1398 918 816 361 231 148 122 85 4 81 164 865 503 1214 1083 802 372 229 142 118 83 5 77 179 784 481 1153 1280 922 368 222 144 116 83 6 78 207 745 451 1075 1330 1075 369 216 144 114 81 7 77 211 956 430 1040 1402 870 356 210 142 112 81 8 73 192 984 416 959 1399 754 359 215 140 111 82 9 72 186 981 406 713 1407 701 326 205 137 110 80 10 70 216 871 404 699 1413 693 337 210 135 108 85 11 70 208 733 450 700 1410 880 329 208 135 106 81 12 72 201 583 465 702 1441 1034 323 213 133 104 80 13 93 202 575 593 781 1416 1012 315 201 131 102 78 14 150 183 605 536 730 1434 807 312 207 129 100 78 15 126 167 562 520 721 1447 735 305 202 127 101 78 16 118 165 515 569 851 1364 706 285 207 135 98 74 1447 440 67 17 139 227 458 717 847 1351 653 293 197 144 96 74 18 139 198 458 762 885 1337 625 291 187 138 96 74

2001-02 19 134 183 505 672 960 1243 602 287 192 142 94 74 20 133 192 738 610 934 914 572 281 182 137 93 71 21 134 207 830 596 925 943 543 275 175 135 91 69 22 134 235 759 609 934 964 517 270 185 133 92 70 23 148 341 659 593 953 901 497 257 183 131 95 67 24 141 380 639 540 1225 985 477 267 178 131 96 77 25 136 461 628 530 1191 1040 460 264 167 128 91 87 26 132 558 572 637 955 949 444 258 173 127 89 97 27 130 432 518 772 833 917 426 250 173 125 89 105 28 148 365 568 806 887 881 404 248 162 122 87 105 29 183 303 603 929 912 877 402 245 171 129 115 30 186 296 579 1151 938 866 398 231 166 127 120 31 576 1180 876 404 154 127 120 Max 186 576 984 1180 1405 1447 1075 403 239 151 125 120 Mean 115 257 675 610 954 1158 671 307 197 135 103 85 Median 128 207 633 549 934 1163 680 299 201 135 100 81 Min 70 164 458 404 699 861 398 231 154 122 87 67

37 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 129 225 232 790 960 648 755 239 156 134 93 102 2 148 241 245 918 939 635 784 238 156 134 92 99 3 166 242 254 852 993 644 543 234 154 115 92 94 4 156 253 248 812 882 681 492 231 154 114 91 90 5 149 255 311 809 794 505 465 230 154 113 91 87 6 140 235 387 852 754 504 445 229 152 110 92 82 7 140 205 442 915 712 490 429 228 152 110 92 82 8 137 196 387 879 687 474 428 215 152 109 92 85 9 137 186 375 864 729 463 433 212 150 109 91 84 10 135 169 362 868 718 458 374 208 150 108 91 82 11 147 169 339 832 713 466 348 201 150 107 89 81 12 156 167 389 1044 792 470 340 198 150 106 90 84 13 166 155 470 1068 790 480 335 198 148 104 87 80 14 158 145 565 981 755 487 328 197 148 103 87 78 15 132 137 537 983 753 506 317 194 148 102 88 79 16 126 195 543 803 721 617 310 191 146 105 89 77 1278 352 77 17 123 183 515 738 724 630 301 190 146 103 88 78 18 131 177 510 1084 763 601 324 187 144 102 86 85

2002-03 19 137 195 615 1196 818 468 331 183 142 100 87 117 20 191 202 625 1119 858 437 315 178 142 99 83 123 21 222 208 610 1189 1038 420 299 181 140 97 89 127 22 219 224 541 1177 785 436 293 178 140 97 88 128 23 229 207 517 1129 743 488 285 175 140 99 85 132 24 229 209 521 1072 722 586 283 172 138 97 82 131 25 208 210 517 1278 782 655 292 169 136 94 79 123 26 188 205 496 1263 786 763 274 166 136 94 77 124 27 212 186 531 1196 876 720 267 165 136 93 99 118 28 241 206 532 1145 830 716 268 166 134 91 104 119 29 244 246 555 1067 747 843 271 163 134 90 116 30 232 251 713 1046 698 799 265 159 136 96 113 31 234 1038 658 240 136 95 112 Max 244 255 713 1278 1038 843 784 239 156 134 104 132 Mean 171 204 463 1000 791 570 369 196 145 104 89 100 Median 156 205 512 1038 763 506 324 192 146 103 89 94 Min 123 137 232 738 658 420 240 159 134 90 77 77 1 123 266 357 1159 1403 785 744 435 204 203 160 133 2 150 250 337 1698 1217 750 746 449 200 200 158 140 3 288 246 319 1502 1144 787 711 422 199 198 156 136 4 291 233 300 1587 1080 728 686 400 189 196 154 133 5 270 232 299 1876 983 773 633 389 182 193 152 131 6 256 209 306 1639 924 808 592 365 178 191 150 129 7 261 194 322 1456 893 802 542 355 171 186 148 129 8 267 208 380 1727 874 809 563 342 167 184 148 127 9 273 214 448 2174 1012 707 577 325 166 182 148 125 10 258 218 582 2149 1144 657 994 305 162 182 148 124 11 254 205 499 1889 1207 627 952 292 168 180 146 127 12 239 199 518 1652 1202 642 772 284 167 177 146 129 13 234 185 541 1624 1069 634 776 287 162 175 144 138 14 226 180 584 1529 995 652 687 279 156 175 142 142 15 294 171 672 1433 977 672 625 271 157 173 140 138 16 313 236 752 1342 960 729 595 260 154 171 140 136 2174 499 123 17 343 255 694 1342 1005 863 561 252 152 171 138 134 18 375 292 600 1335 1227 941 513 248 148 171 138 133

2003-04 19 390 316 516 1337 1273 1034 487 243 146 169 138 134 20 383 337 479 1386 1116 988 466 248 144 169 138 134 21 372 331 440 1437 1080 1109 452 242 142 166 136 133 22 368 320 500 1482 910 989 420 240 140 166 136 144 23 372 314 623 1327 854 868 420 237 138 164 136 175 24 162 311 785 1239 983 803 417 235 136 162 136 180 25 155 344 929 1113 927 849 415 230 203 162 136 175 26 164 378 885 1054 1002 891 493 224 200 160 134 171 27 194 419 1123 1050 848 793 602 212 198 166 134 160 28 311 381 1185 1171 820 882 567 211 196 171 134 150 29 342 335 1042 1093 779 989 527 209 208 166 133 144 30 325 352 1104 1276 738 832 481 208 220 162 140 31 383 1508 730 455 210 160 136 Max 390 419 1185 2174 1403 1109 994 449 220 203 160 180 Mean 275 275 604 1471 1012 813 596 290 173 176 143 141 Median 271 255 530 1437 995 802 567 265 167 171 140 136 Min 123 171 299 1050 730 627 415 208 136 160 133 124

38 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 133 210 495 1039 877 965 719 364 247 2 133 208 471 1017 827 807 700 357 242 3 138 196 443 1000 823 790 702 364 239 4 146 189 416 979 773 798 778 368 236 5 148 184 439 1186 807 742 773 357 234 6 150 177 452 1390 771 827 866 346 231 7 150 171 419 1703 730 1072 848 337 228 8 144 166 384 1971 687 1381 1154 333 226 9 146 173 467 2185 695 1916 1190 323 223 10 220 184 655 2435 701 1848 952 317 220 11 213 205 598 2762 659 1474 844 313 218 12 198 244 517 2877 657 1268 763 307 215 13 196 208 516 2688 635 1105 726 304 215 14 213 232 552 2190 622 987 672 297 210 15 228 339 556 1857 618 932 606 294 210 16 236 611 534 1862 572 862 555 289 208 2877 643 133 17 244 454 571 1919 561 764 515 282 205 18 247 430 651 1693 554 731 477 276 203

2004-05 19 258 546 694 1874 590 769 451 270 200 20 247 548 831 1989 572 789 420 304 198 21 220 523 1148 2158 562 704 419 294 198 22 218 519 1140 1936 548 684 406 282 198 23 244 484 1113 1679 518 692 396 276 196 24 282 498 1323 1502 504 821 381 270 196 25 313 489 1075 1433 531 1044 368 267 193 26 273 496 1068 1327 554 952 359 261 191 27 247 584 1184 1244 763 862 351 258 191 28 226 597 1267 1160 951 849 326 256 189 29 218 551 1171 1028 1124 748 316 253 186 30 213 547 1232 982 909 750 305 250 184 31 517 935 905 295 184 Max 313 611 1323 2877 1124 1916 1190 368 247 Mean 208 370 746 1677 697 964 601 302 210 Median 218 430 585 1693 659 838 555 296 208 Min 133 166 384 935 504 684 295 250 184 1 205 120 98 2 205 127 102 3 203 124 100 4 202 123 98 5 151 120 98 6 149 117 96 7 149 114 94 8 148 113 92 9 148 118 93 10 146 116 91 11 146 113 90 12 145 112 88 13 150 109 88 14 148 108 87 15 143 105 85 16 141 112 85 205 115 73 17 137 111 84 18 134 108 84

2005-06 19 144 106 83 20 142 105 82 21 138 105 81 22 136 105 81 23 134 111 75 24 130 108 74 25 128 107 74 26 138 104 73 27 136 102 75 28 131 101 81 29 128 79 30 125 74 31 121 73 Max 205 127 102 Mean 148 111 86 Median 143 111 85 Min 121 101 73

39 Table-A.2: Mean Daily Discharge (m3/s) of Dudhkumar River at Pateswari

Hydrological Month Date Max Mean Min Year Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1 71 100 607 885 588 521 641 260 185 162 131 136 2 70 103 674 846 569 480 603 274 188 162 129 148 3 73 127 700 887 628 448 660 257 191 162 129 152 4 78 149 666 818 604 435 763 227 194 164 127 156 5 75 156 651 781 590 423 868 208 196 164 127 160 6 84 163 663 806 706 418 768 206 199 164 133 152 7 95 160 687 1229 726 474 703 216 167 162 136 131 8 107 150 514 1473 662 611 631 224 170 160 136 129 9 101 142 526 1176 731 956 578 233 172 158 134 127 10 98 151 545 832 631 975 548 244 177 156 133 124 11 103 165 601 713 549 860 536 255 182 154 133 122 12 100 184 759 735 459 944 489 269 190 152 131 120 13 96 204 871 712 466 1095 467 281 195 150 133 120 14 92 213 793 685 390 1063 478 296 163 150 138 118 15 89 192 733 708 353 1040 458 307 165 148 142 117 16 86 180 688 768 330 923 433 217 167 146 144 117 1473 362 70 17 91 168 643 804 414 879 413 216 169 146 144 115 18 95 154 628 696 390 860 385 214 171 144 140 115

2006-07 19 90 149 580 673 373 846 406 211 174 144 138 113 20 120 159 554 698 363 816 374 210 176 144 136 113 21 128 153 555 726 354 774 342 213 148 142 133 112 22 114 150 492 688 349 733 324 213 149 140 129 113 23 110 147 466 666 371 751 310 197 151 138 127 112 24 113 146 478 716 350 897 297 198 152 138 125 110 25 108 158 612 775 334 1019 285 201 153 138 124 108 26 102 169 873 874 337 913 276 201 155 136 122 108 27 110 188 964 866 351 847 266 202 156 136 120 112 28 113 213 1306 772 354 806 318 203 171 136 134 115 29 106 261 1386 690 359 756 305 206 169 134 117 30 103 598 1189 658 417 690 293 183 166 133 117 31 666 621 494 284 164 131 118 Max 128 666 1386 1473 731 1095 868 307 199 164 144 160 Mean 97 194 713 806 471 775 468 228 172 148 132 123 Median 99 159 657 768 414 831 433 215 170 146 133 117 Min 70 100 466 621 330 418 266 183 148 131 120 108 Overall Max 659 1540 4010 7190 6990 4670 9250 628 260 220 163 180 Overall Mean 121 253 693 1188 1128 946 531 245 168 129 105 92 Overall Median 104 206 542 1000 921 796 436 235 167 129 102 89 Overall Min 42 63 103 208 262 233 125 89 76 65 65 56