Assessment of Streamflow Characteristics in a Watershed Using Flow

Duration Curves and Hydrograph Analysis

Deepa Varghese G. S.

, Mohandas Chadaga

, U. A. Lathashri

, Surumi Rasia Salim

Atma Jyoti

and Som Pant

Department of Civil Engineering, Manipal Academy of Higher Education, Dubai, U.A.E.

Department of Civil Engineering, Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal, India

surumi.rasia@manipaldubai.com, atmajyoti00@gmail.com, sompant98@gmail.com

Keywords: Baseflow, Base Flow Index, Flow Duration Curves, Hydrograph Analysis.

Abstract: Assessment of streamflow characteristics can be considered as one of the most important evaluations that

need to be performed in a watershed for water use planning, implementation of various restoration projects

and the validation of its effectiveness. Out of the several available methods, flow duration curves (FDC) and

hydrograph analysis can be considered as the most effective and simplest methods to assess the flow

characteristics of a stream. The present study aims to evaluate the seasonal variations in the flow

characteristics of one of the important rivers in central Kerala, India, the Meenachil river. The study was done

by interpreting the Base Flow Index (BFI) values of seasonal FDCs and baseflow separation technique using

data from 4 stream gauging stations in the catchment. As per the analysis, the river presented intermittent

flows with variably gaining and losing river reach along its course. This intermittent nature of the stream was

distinctly revealed through the full time FDCs sustaining flows for 47% of time on the upstream reaches to

72%, 62% and 78% progressing towards the downstream. The baseflow contribution to the stream was

greatest during the SW monsoon season for all the stations, particularly station 4 recording a maximum of

40.8 cumecs. The BFI values calculated using both sliding interval method and FDC were comparable and

presented a very good appraisal on the seasonal variations in the streamflow.

1 INTRODUCTION

The Flow-Duration Curve (FDC) is a cumulative

frequency curve that shows the percentage of time

specified discharges were met or exceeded in a

particular period (Searcy, 2011). In a simpler

definition, the flow-duration curve is a technique of

displaying streamflow data by integrating the flow

characteristics of a stream over a wide variety of

discharge ranges into a single curve. Even though, the

chronological sequence of flows is not reflected, the

flow-duration curve is helpful in many studies (Singh,

2015) such as reservoir sedimentation(Strand and

Pemberton 1982), water quality management

(Searcy, 1959) etc. The curve is made to average the

plotted points of specified discharges against the

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percent of the time they were equaled or surpassed,

rather than the flow distribution within a single year.

As a result, FDCs are excellent instruments for

studying the catchment hydrological behavior and

streamflow characteristics since their shape and slope

indicate the at-site flow variability circumstances, as

well as the catchment's flood-formation dynamics and

low-flow features (Costa et.al., 2020). The flow-

duration curve applies only to the period for which

data is used to create the curve or to the period for

which the curve is strictly altered. FDCs represent the

sustainability of stream flows at a river cross-section

over a specified time interval, commonly a day, week,

or month (Vogal and Fennessey,1994;

Smakhtin, 2001). Complete years of records should

be utilized to generate a full-time flow-duration

S., D., Chadaga, M., Lathashri, U., Salim, S., Jyoti, A. and Pant, S.

Assessment of Streamﬂow Characteristics in a Watershed Using Flow Duration Curves and Hydrograph Analysis.

DOI: 10.5220/0011907500003536

In Proceedings of the 3rd International Symposium on Water, Ecology and Environment (ISWEE 2022), pages 90-95

ISBN: 978-989-758-639-2; ISSN: 2975-9439

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

curve; partial years should be avoided. However,

seasonal data can also be used to generate seasonal

flow-duration curves. The FDCs find its important

application in hydro power potential studies (Hickox

et.al., 1933; Barrows, 1943; Yizhi et.al.,2020). The

upper end of FDCs is widely used in several studies

related to flood assessment (Pettis, 1934; Beard,

1943; Gómez-Llanos et.al.,2018).

Stream hydrograph is a graphical representation

of the total flow carried in a stream against the

duration of streamflow. It is ideally considered to be

representing three components of flow viz., direct

runoff (which is the quick response of streamflow to

precipitation), base flow (which is the contribution

from the adjacent aquifer to the streamflow) and

interflow which is following a shallow subsurface

pathway to the stream (which is usually ignored

assuming that it can be a part of either the surface

runoff or the base flow). Baseflow separation

technique is a very efficient tool which can be used to

separate the baseflow from streamflow (Stewart,

2015). The clear distinction in the baseflow and direct

runoff generation process is very evident in the shape

and slope of the two recession curves generated. This

justifies the requirement of separating the two

components of streamflow (Hewlett, 1967). The

watershed management practices could be dependent

on the contribution of baseflow to the stream

(Wondmyibza et.al., 2021). For example, overdraft

from wells to meet the domestic and agricultural

requirements, deterioration of water quality, pressure

on surface and groundwater resources in drought

prone areas etc. The baseflow contribution to the

Meenachil river is yet unknown. Thus, the main

objective of this paper is to interpret the BFI values

generated using FDCs and hydrograph separation

method to evaluate the seasonal variation in

streamflow. This could be very effective in watershed

management studies.

2 STUDY AREA AND DATA

COLLECTION

Meenachil river originates from the Araikunnumudi

at an elevation of approximately 1100 m above MSL

and finds its way to the Vembanad lake. The

Meenachil watershed, in the district of Kottayam,

Kerala, India, experiences a tropical monsoon climate

receiving excess rainfall during monsoon seasons and

hot conditions in summer. The watershed receives

rainfall primarily during the southwest and northeast

monsoon seasons. The flooding of river during

monsoon seasons is an annual event that occurs from

June to September resulting in over-toping the banks

and inundation of the low-lying lands. The Meenachil

river extends 78 km long draining a total area of

1272km

, stretching between 9° 32’ to 9°50’ N

latitudes and 76°29’ to 76°56’ E longitudes (Deepa

et.al., 2022) (Figure 1). The Meenachil river is

uniquely characterized by human settlement right

from its origin at the Western ghats to its culmination

in the Arabian sea.

Figure 1: Meenachil watershed and location of stream

gauge stations

Daily streamflow data was obtained from

Irrigation Design and Research Board (IDRB),

Trivandrum at four stations viz., station 1 (24 years),

station 2 (22years), station 3 (23 years) and station 4

(25 years). The analysis was done for a period of only

17 years since comparison of results were required to

be done for all the 4 stations using concurrent data.

The years of missing data were excluded from the

analysis.

3 METHODOLOGY

With the aim of presenting a cumulative perspective

on the potential of the river to sustain its flows

through baseflow contribution, the flow data were

analysed using the flow duration curves (FDCs) and

hydrograph separation technique. Using the FDC

method and sliding interval method of hydrograph

analysis, the baseflow index (BFI) was calculated and

compared. For uniformity and easier comparison,

these methods were applied considering concurrent

time periods of data at four steam gauging stations

viz., Station 1, Station 2, Station 3 and Station 4

(Figure 1) in the watershed. The concurrent time

periods selected for the study spanned across four

Assessment of Streamﬂow Characteristics in a Watershed Using Flow Duration Curves and Hydrograph Analysis

seasons viz., pre-monsoon from April to May, south-

west(SW) monsoon from June to August, post

monsoon in September and north-east(NE) monsoon

from October to November.

The following essential points were taken into

consideration for generating the flow duration curves

and baseflow separation using the stream flow data.

(i) The period of data with no missing records,

obtained from the Irrigation Design and Research

Board (IDRB), Trivandrum were used in the

study.

(ii)

The physical conditions in the basin were ensured

to be the same during the period of data collected.

4 RESULTS AND DISCUSSION

4.1 Seasonal Discharge Analysis

The streamflow data at the 4 gauging stations were

carefully reviewed to record the maximum and

minimum discharge values (Table 1).

Table 1: The minimum, average and maximum discharge

recorded at the 4 stations.

Discharge Parameters in cumecs

Season Station Minimum Average Maximum

Pre-

Monsoon

1 0 1.05 59.48

2 0 7.818 224.66

3 0 8.324 181.36

4 0 22.33 443.56

SW-

Monsoon

1 0 11.81 211.72

2 0 43.88 363.8

3 0 43.85 826.82

4 0 116.7 877.06

Post SW

Monsoon

1 0 6.724 98.35

2 4.16 33.34 395.02

3 0 27.56 381.81

4 2.23 78.16 679.83

Monsoon

1 0 3.999 207.63

2 3.03 23.15 341.72

3 0 25.57 392.95

4 2.98 76.48 532.3

Post NE

Monsoon

1 0 0.108 28.61

2 0 2.755 54.38

3 0 1.009 54.92

4 0 3.707 107.3

It is emphasized that, the watershed is

characterized to receive maximum discharge brought

in during the SW monsoon season followed by the NE

monsoon season. The flow detected during the pre-

monsoon season (April- May) are due to the frequent

intense showers, known as summer rains. However,

the river fades away into virtually a barren land in the

post monsoon season shortly after the NE monsoon

rains.

4.2 Baseflow Separation

The under lying assumption in the base flow

separation method is that base flow is equated to the

groundwater contribution which in many cases need

not be valid due to the unseen hydraulic connection

of any other drainage systems. Also, it may be altered

due to many anthropogenic influences like land use

changes due to urbanization, surface water extraction

or groundwater extraction for irrigation etc.

The hydrograph analysis generates an index

namely the base flow index (BFI) which is expressed

as the ratio of base flow to the total streamflow. The

built-in tool, BFI +3.0, of HydroOffice 2012 software

(Gregor, 2010a) was used in this analysis. The long-

term statistics of BFI and baseflow contribution using

the sliding interval method (Table 2) were calculated

and compared for all the 4 seasons. This method also

results in a rapid estimation of baseflow.

Table 2: Long term statistics of BFI and baseflow

contribution (in cumecs) using sliding interval method.

Seasons Indicator

Stations

1 2 3 4

Pre-

Monsoon

BFI 0.07 0.29 0.13 0.16

Base-flow 0.1 2.58 1.01 2.79

Monsoon

BFI 0.33 0.54 0.45 0.48

Base-flow 2.79 17.4 12.9 40.8

Post SW

Monsoon

BFI 0.21 0.61 0.5 0.59

Base-flow 0.81 13.7 10.6 35

Monsoon

BFI 0.13 0.58 0.39 0.43

Base-flow 0.29 10.1 8.99 24.3

The results of the baseflow analysis demonstrates

that the baseflow index (BFI) is highest during the

post monsoon season at all the stations expect

station 1. Thus, in this season the flow in the river is

sustained through strong baseflow contribution. The

rainfall received during the SW monsoon season in

the highland station 1, due to the steep terrain of the

land, gets quickly drained off and thus was not

available for groundwater recharge. Consequently,

ISWEE 2022 - International Symposium on Water, Ecology and Environment

the subsequent post monsoon season displays lesser

BFI portraying the lesser potential of the river to

sustain its flows through baseflow contribution in the

respective season. Moreover, at all the stations, the

amount of baseflow contribution was highest during

the SW monsoon season recording a maximum of

40.8 cumecs at station 4.

4.3 Flow Duration Curves

The percentage duration for which the river flow is

recorded in the gauging station gives an idea about

whether the stream can be classified as perennial,

intermittent or ephemeral (Karen, 2008).

Interpretation of FDC can provide a useful appraisal

on the geological characteristics of the watershed

(Winter, 2007). In this study, the potential of FDCs to

understand the extent of baseflow contribution to

sustain the stream flows in the river is demonstrated.

The flow duration curves were plotted using the daily

discharge values against percentage exceedance of

flow on a semi-logarithmic scale for obtaining a clear

display of the high and low flow values. The built-in

tool, FDC 2.1, of HydroOffice 2012 software

(Gregor, 2010b) was used in this analysis.

Figure 2: Full time series FDC (Station 1 to station 4).

The full time series for flow duration curve including

zero discharge values recorded in the gauging stations

of the watershed are presented in Figure 2. Station 1

carries discharge 47% of time which increases to

72%, 62% and 78% respectively towards downstream

stations 2, 3 & 4. The percentage of time for which

the river carries discharge from station 1 to station 4

reveals the type of hydraulic connection of the river

reach with the underlying aquifer. It was found to be

a variably gaining-losing river reach with dominated

direct runoff flows interposed with base flow events

from station 1 to 3 (Karen, 2008). However, from

station 3 to 4, the river reach could be expected to

change to a baseflow dominated river reach

interposed with direct runoff events.

The generated FDCs exhibited a steep slope

representing low or variable base flow contribution to

the stream. Figure 3 and Figure 4 presents the flow

duration curves across 4 different seasons viz., pre

monsoon, SW monsoon, post monsoon and NE

monsoon excluding the zero flow values. The

seasonal FDCs so developed can be used to determine

the Base flow Index values (BFI) which is the ratio of

(Nathen et.al.,1990) as presented in Table 3.

High values of BFI index imply the potential of the

river to sustain its flows for long duration (R

Mohammed et.al., 2018). The results of the BFI using

FDC method were comparable with the results of

sliding interval method of hydrograph separation.

Figure 3: FDC@ station 1 and 2 across 4 seasons.

Assessment of Streamﬂow Characteristics in a Watershed Using Flow Duration Curves and Hydrograph Analysis

Figure 4: FDC@ station 3 and 4 across 4 seasons.

Table 3: Seasonal BFI (Q

) from upstream to

downstream stations.

Station Season Q

BFI

Station

Pre-Monsoon 0.28 3.34 0.084

SW Monsoon 0.48 4.17 0.115

Post SW

Monsoon

0.36 3.14 0.115

NE Monsoon 0.32 3.19 0.1

Station

Pre-Monsoon 3.63 17.1 0.212

SW Monsoon 3.52 18.91 0.186

Post SW

Monsoon

0.3 17.37 0.017

NE Monsoon 4.19 20.15 0.208

Station

Pre-Monsoon 2.33 16.34 0.143

SW Monsoon 2.3 18.9 0.122

Post SW

Monsoon

2.67 22.57 0.118

NE Monsoon 3 20.1 0.149

Station

Pre-Monsoon 2.31 13.8 0.167

SW Monsoon 26.2 84.58 0.31

Post SW

Monsoon

8.78 46.14 0.19

NE Monsoon 10.94 55 0.199

5 CONCLUSIONS

The present study on assessment of the streamflow

characteristics and the potential of the river to sustain

its flows throughout the year was done using flow

duration curves and hydrograph analysis. The flow

regime in the watershed was evaluated to be a

variability gaining and losing reach across the

seasons. The flow duration curve presenting the

percentage duration in a year for which the river could

sustain its flow along its course varied from 47% of

time on the upstream station 1 to 72%, 62% and 78%

progressing towards downstream station 2, 3 & 4

respectively. This clearly proved the intermittent

nature of the river with alternatively gaining and

losing river reach dominated with direct runoff on the

upstream and baseflow events towards the

downstream. The BFI values (Q

) was found to

be maximum at station 2 for pre monsoon and NE

monsoon seasons and station 4 for SW and post SW

Monsoon seasons. Thus, the potential of the river to

sustain its flows upstream of station 2 and station 4

was also evident.

The shape of the FDC, particularly the lower end,

graphs the general characteristics of the shallow

aquifer. The steep slope exhibited by the curves in the

pre-monsoon and NE monsoon season in the gauging

station 1 represents poor groundwater contribution to

the stream. This is due to its location in the highland

region possessing considerably low groundwater

potential. However, the curve remains horizontal for

the SW and post monsoon seasons at the gauging

station 4. This can be due to high groundwater

contribution to the stream from the underlying

aquifers. A detailed analysis of the discharge data

using FDCs and the hydrograph analysis perceived

the greatest contribution to the stream through

baseflow in the SW and post monsoon seasons.

However, station 4 recorded the maximum of 40.8

cumecs in the SW monsoon season. The baseflow

index (BFI) calculated using the sliding interval

method yielded values increasing from station 1 to

station 4, across all four seasons. These values were

observed to be comparable with the BFI values

generated using FDC method. Thus, the interpretation

of FDC curves and results of baseflow analysis

generated a good insight into streamflow

characteristics and the potential of the river to sustain

its flows through baseflow contribution.

Further studies are required in the watershed for

thorough understanding of surface water and

groundwater resource problems. The study of surface

water groundwater interaction, the impact of

groundwater contribution to the stream under climate

change etc can be listed as few among the important

watershed management studies. The studies listed

above can prove to be very useful in formulating the

storage-outflow relationship between aquifer and

stream. It can also benefit in water resource planning

and development and for adopting watershed

ISWEE 2022 - International Symposium on Water, Ecology and Environment

management practices specifically to the Meenachil

watershed.

ACKNOWLEDGEMENTS

Authors would like to thank Manipal Academy of

Higher Education, Dubai for supporting the study by

providing the Research Grant for data collection.

Authors would also like to thank Irrigation Design

and Research Board (IDRB), Trivandrum for

providing the streamflow data.

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Assessment of Streamﬂow Characteristics in a Watershed Using Flow Duration Curves and Hydrograph Analysis