Ping River Research Articles

Schistura maejotigrina, a new stream loach (Pisces: Nemacheilidae) from northern Thailand

Schistura maejotigrina, new species, is described from Maechaem River, a tributary of Ping River, in the upper Chao Phra-ya River drainage, Chiang Mai Province, Thailand. It is distinguished from all other species of Schistura in having 21–24dark tiger-stripe black bars on the side of the body and 6½–7½ branched dorsal soft rays. The species is medium-sized,reaching 53.0 mm SL (69.6 mm TL), and is known only from the Maechaem River system, Ping River drainage, northernChao Phraya River basin, Chiang Mai Province, Thailand. It lives in fast running, clear water over a substrate of mixed gravel, small stone and sand.

Monotonic and Cyclic Behavior of Chiang Mai Sand Under Simple Shear Mode

Record of damages and casualties caused by earthquakes in Thailand reveals that Chiang Mai, the second largest province of Thailand, has faced the great threat among other provinces. Triaxial tests, standard penetration tests, and multichannel analysis of surface wave have been recently performed to understand the dynamic response of Chiang Mai ground. However, the cyclic simple shear test, which could convincingly represent the real seismic ground shaking under repeated horizontal shear force, has not been conducted yet. Therefore, this paper aims to characterize the behaviors of Chiang Mai sand under monotonic and cyclic loadings using a direct simple shear apparatus. Sand specimens taken from the Ping River were prepared by dry deposition technique. The mobilized friction angle at the critical state measured by the direct simple shear test is equal to 37.3° which is 9 % less than that measured by direct shear box test. This paper also provides the appropriate dynamic properties of Chiang Mai sand with the shear strain level <2 % for any practical purpose. Test results showed that the normalized shear modulus agrees well with other investigators while the damping ratio is noticeably smaller than the lower-bound range for sand reported in the past studies.

Modifiers and Amplifiers of High and low Flows on the Ping River in Northern Thailand (1921–2009): The Roles of Climatic Events and Anthropogenic Activity

We analyse an 89-year streamflow record (1921–2009) from the Upper Ping River in northern Thailand to determine if anomalous flows have increased over time (Trenberth, Clim Res 47:123–138, 1999; Trenberth, Clim Chang 42:327–339, 2011). We also relate the temporal behavior of high and low flows to climatic phenomena and anthropogenic activities. Peak flows have not increased significantly since 1921. However, minimum flows showed a very significant downward trend over the study period (α = 0.01). Annual and wet season discharge show significant downward trends (α = 0.05). All flow variables appear to be more variable now than 90 years ago especially annual peak flows. Both annual peak and minimum flows are correlated with annual and wet season rainfall totals. Minimum flow is also sensitive to the length of the monsoon season and number of rainy days in the previous monsoon season. Peak flow activity is driven predominantly by climate phenomena, such as tropical storm activity and monsoon anomalies, but the relationship between peak flows and ENSO phenomena is unclear. In general, annual discharge variables did not correspond unequivocally with El Nino or La Nina events. Minimum flows show a major decline from the mid-1950s in line with major anthropogenic changes in the catchment. The plausible intensification of the hydrological cycle that may accompany global warming is of concern because of the potential to affect tropical storm activity and monsoon anomalies, phenomena that are linked with very high flows in this river system. The obvious effect of human activities such as reservoir management on low flows calls for careful management to prevent droughts in the future.

Impact of large‐scale reservoir operation on flow regime in the Chao Phraya River basin, Thailand

AbstractThe Chao Phraya River basin, the largest basin in Thailand, is located in the centre of the northern part of the country. This basin has two large‐scale reservoirs: the Bhumibol Reservoir on the Ping River and the Sirikit Reservoir on the Nan River. A comparison of the annual and monthly flow regimes downstream from the reservoirs before and after reservoir development showed a constant increase in low flow and a drastic decrease in high flow. The spectrum of the daily discharge was analysed using the fast Fourier transform on data collected in the area of Nakhon Sawan and immediately downstream from the Bhumibol Reservoir after the reservoir was constructed. The flow at Nakhon Sawan had a periodic characteristic of 7 days. The water released from the Bhumibol Reservoir at hydrological station P.12 also had a periodic characteristic of 7 days. Reservoir operations have a significant impact on the hydrological cycles. The effect of human activities is evident in the spectrum analysis of recorded historical discharge data. Copyright © 2012 John Wiley &amp; Sons, Ltd.

The Impact Assessment of Water Resource Management in Rainfed Area in the Upper Ping River Basin, Chiang Mai, Thailand

Water resources sustainability has crucial for the existence of farming system which is dependent on the cropping pattern practices. This paper concerns the studies of existing water resource management and determines factors affecting decision making of water resource management in rainfed area. In these cases, a multi criteria decision making model has been determined that aims at allocating efficient water and land resources to farms in the Upper Ping River basin in Chiang Mai, by optimizing a set of important socio- economic objectives which depend on sustainable agricultural and rural development. The solution was found by the using two analytical steps as follows: single objective optimization and compromise programming. In rainfed areas, the model cropping pattern advises farmers to grow the in-season rice, tobacco and longan. If the farmers follow the model cropping pattern even the gross margin increases insignificantly and water using increases slightly from the up to now existing water on farm consumption. The water resource management in rainfed areas the farmers store the scarce water in small reservoirs and water tanks on their farms for saving it for the dry season because the water on-farm security is an indispensable prerequisite in decide making upon the next year crop.

Co-infection with Opisthorchis viverrini and Haplorchis taichui detected by human fecal examination in Chomtong district, Chiang Mai Province, Thailand

Diseases caused by the liver fluke, Opisthorchis viverrini and the minute intestinal fluke, Haplorchis taichui, are clinically important, especially in the Northeast and North regions of Thailand. It is often difficult to distinguish between these trematode species using morphological methods due to the similarity of their eggs and larval stages both in mixed and co-infections. A sensitive, accurate, and specific detection method of these flukes is required for an effective epidemiological control program. This study aimed to determine the prevalence of O. viverrini and H. taichui infections in human feces by using formalin–ether sedimentation and high annealing temperature random amplified polymorphic DNA (HAT-RAPD) PCR methods. Fecal specimens of people living along the Mae Ping River, Chomtong district were examined seasonally for trematode eggs using a compound microscope. Positive cases were analyzed in HAT-RAPD, DNA profiles were compared with adult stages to determine the actual species infected, and specific DNA markers of each fluke were also screened. Our results showed that out of 316 specimens, 62 were positive for fluke eggs which were pre-identified as O. viverrini and H. taichui. In addition, co-infection among these two fluke species was observed from only two specimens. The prevalence of H. taichui infections peaked in the hot-dry (19.62%), gradually decreased in the rainy (18.18%), and cool-dry seasons (14.54%), respectively. O. viverrini was found only in the hot-dry season (6.54%). For molecular studies, 5 arbitrary primers (Operon Technologies, USA) were individually performed in HAT-RAPD-PCR for the generation of polymorphic DNA profiles. The DNA profiles in all 62 positives cases were the same as those of the adult stage which confirmed our identifications. This study demonstrates the mixed infection of O. viverrini and H. taichui and confirms the extended distribution of O. viverrini in Northern Thailand.

Effects of land cover on runoff coefficient

Summary Land cover is considered to have significant influence on the hydrologic response of a river basin. In this study, we assessed how changes in land cover over time affected flood behaviour from 1988 to 2005, in the Upper Ping River Basin, northern Thailand. We correlated the types of land cover with rainfall–runoff behaviour for smaller and larger flood events taking place during this period. To quantify land cover, nine Landsat 5 TM images taken during the dry season (January or February) were obtained and processed to examine inter-annual land cover changes. From the networks of daily read rainfall data and stream gaugings available across the basin, 68 rainfall and 11 runoff stations were selected to evaluate peak flow rate and runoff coefficient for flood events. For individual sub-catchments, strong non-linear correlations were found between the overall runoff coefficient and peak flow rates for flood events. These runoff coefficients to peak flow relationships varied from year to year with different land cover for each sub-catchment. From these relationships within a particular sub-catchment, we determined relationships between different types of land cover and runoff coefficient for the 2, 5, 10 and 15 year Annual Recurrence Interval (ARI) peak flood events. We found that runoff coefficient increased with increasing forest proportion for these specified peak flood conditions, on nine out of eleven sub-catchments. On the other hand, the runoff coefficient associated with these peak flood events decreased as agricultural and disturbed forest areas increased. The influence of land cover on runoff coefficient was, however, found to be very different between smaller (lower than ∼2 year ARI) and larger flood events (larger than ∼2 year ARI). Runoff coefficient is higher for high forest cover during larger flood events; but for smaller flood events, runoff coefficient is lower when forest cover is high. This is due to the fact that for smaller flood events, rainfall loss rate for the forest area is normally higher than that of the non-forest area according to higher evapotranspiration and soil moisture capacity. Forests have proved to potentially offer flood mitigation benefits for smaller flood events. However, for larger flood events the situation of the basin can be different, especially on a basin with higher antecedent soil moisture or even under saturation stage. Antecedent soil moisture from the previous storms could be better retained within the forest area than the non-forest area due to deeper rote zone and higher soil moisture holding capacity of the forest area compared to non-forest area. For the larger flood events, forest area tends to produce more runoff than non-forest area as found in this study. These findings gave us a more thorough understanding of the effect of land cover types on flood behaviour at different stages of soil moisture conditions, and the severity of storm events. It can be useful for land use and flood management of the river basin.

Two new species of Rhabdochona (Nematoda: Rhabdochonidae) from freshwater fishes in Thailand

Two new species ofrhabdochonid nematodes are described from the intestine of freshwater fishes in Chiang Mai Province, northern Thailand: Rhabdochona (Rhabdochona) pseudomysti sp. n. from the catfish Pseudomystus siamensis (Regan) (Bagridae, Siluriformes) in the Fang Brook, a tributary of the Kok River (the Mekong River basin), Fang District and Rhabdochona (Globochona) thaiensis sp. n. from the cyprinid Mystacoleucus marginatus (Valenciennes) (Cyprinidae, Cypriniformes) in the Ping River (the Chao Phraya River basin), Muang District. Rhabdochona pseudomysti is mainly characterized by simple, leaf-like oval deirids (a unique feature among Rhabdochona spp.), a prostom with 14 anterior teeth, the presence of basal prostomal teeth, the length ratio of the muscular and glandular portions of oesophagus (1:2.1-2.6), an unusually long left spicule (1.10-1.22 mm), length ratio of spicules (1:11.5-14.7), arrangement of genital papillae, and conspicuously elevated vulval lips. Rhabdochona thaiensis differs from other representatives of the subgenus Globochona Moravec, 1972 possessing caudal projections on the tail tip in that it has only 2 claw-shaped projections located ventrally on the tail tip of both males and females; the species is mainly characterized by the presence of distinct pseudolabia, 8 anterior prostomal teeth, absence of basal teeth, bifurcated deirids, length ratio of the muscular and glandular portions of oesophagus (1:11.3-11.9), conspicuously short (135-141 microm) left spicule, arrangement of genital papillae, and somewhat elevated vulval lips. Fully developed eggs of R. pseudomysti and R. thaiensis remain unknown. These are the first nominal species of Rhabdochona reported from Thailand.

Observations on two nematode species parasitizing freshwater fishes in Thailand, including Spinitectus thaiensis sp. nov. (Cystidicolidae) from Pseudomystus siamensis (Bagridae)

AbstractOne new and one already known species of parasitic nematodes are described from the intestine of freshwater fishes in Chiang Mai Province, northern Thailand: Spinitectus thaiensis sp. nov. (Cystidicolidae) from the catfish Pseudomystus siamensis (Regan) (Bagridae, Siluriformes) in the Fang Brook, a tributary of the Kok River (the Mekong River basin), Fang District and Oceanicucullanus chitwoodae Le-Van-Hoa et Pham-Ngoc-Khue, 1971 (Cucullanidae) from the cyprinid Mystacoleucus marginatus (Valenciennes) (Cyprinidae, Cypriniformes) in the Ping River (the Chao Phraya River basin), Muang District. The new species, S. thaiensis, is very similar to S. petrowi Belous, 1965, differing from it, in addition to some biometrical differences, mainly in having simple cuticular spines (instead of transversely oriented peg-like spines with rounded ends) on the ventral surface of the female tail; the spicules are 156–171 and 66–72 μm long, the vulva is situated at 74% of female body length, and the entire oesophagus including the vestibule represents 14–15% of body length in the male and 12% in the female. The latter species, O. chitwoodae, was studied for the first time by scanning electron microscopy, which enabled to recognize some previously unrecorded morphological details in this species. The finding of O. chitwoodae in M. marginatus in Thailand represents new host and geographical records for this nematode.

MEASURING THE BENEFITS OF RIVER QUALITY IMPROVEMENT USING THE CONTINGENT VALUATION METHOD: THE CASE OF THE PING RIVER, CHIANG MAI, THAILAND

Rivers provide us with general life support, water supply, transportation, waste assimilation, and a wide array of recreation and tourism activities. However, due to undervaluation of the functions of rivers and river ecosystems, rivers of the world have been overexploited or degraded. To tackle the problem of undervaluation, this study measures the benefits of Ping River quality improvement using the contingent valuation method (CVM). The study estimates the lower-bound and higher-bound annual benefits gained by the residents of Chiang Mai District from the river quality improvement as 42,453,000 THB (1.25 million USD) and 102,835,317 THB (3 million USD), respectively. Moreover, in an attempt to explain the determinants of willingness to pay (WTP) statements, it was found that both behavioural and attitudinal factors affect WTP positively. The study also found distance decay, where WTP statements decreased with increased distance. And rather interestingly, male respondents tend to pay more than their female counterparts. Two other socioeconomic factors which affected WTP positively and significantly are education, partly because it can lead to a well paying and stable job, and normally raises the awareness of citizens towards environmental conservation, as well as income.

Exploring perspectives of environmental best management practices in Thai agriculture: an application of Q-methodology

SUMMARYIn Thailand, horticultural practices are a significant source of non-point source (NPS) pollution, and the government is considering best management practices (BMPs) as control measures for reducing agricultural NPS pollution to water. A prevailing assumption that farmers’ reactions to regulations will be homogenous is not based on underlying insights into attitudinal positions that may explain alternative behavioural responses. This paper uses Q-methodology to identify attitudinal discourses relating to BMP uptake. The approach combines the strengths of qualitative and quantitative research in order to explore subjectivity. The study is conducted with citrus growers in the Ping river basin, where farmers are facing increasing competition from alternative water uses. Four ‘discourses’ or viewpoints are identified, namely conservationist, traditionalist, disinterested and risk-averse. The different attitudes of these four groups are likely to be associated with distinctive behavioural reactions to the adoption of alternative policy instruments for pollution control. These discourses could usefully inform targeted policies for the control of NPS pollution from agriculture.

Hydropower development priority using MCDM method

Hydropower is recognized as a renewable and clean energy sources and its potential should be realized in an environmentally sustainable and socially equitable manner. Traditionally, the decision criteria when analyzing hydropower projects, have been mostly a technical and economical analysis which focused on the production of electricity. However, environmental awareness and sensitivity to locally affected people should also be considered. Multi-criteria decision analysis has been applied to study the potential to develop hydropower projects with electric power greater than 100 kW in the Ping River Basin, Thailand, and to determine the advantages and disadvantages of the projects in five main criteria: electricity generation, engineering and economics, socio-economics, environment, and stakeholder involvement. There are 64 potential sites in the study area. Criteria weights have been discussed and assigned by expert groups for each main criteria and subcriteria. As a consequence of weight assignment, the environmental aspect is the most important aspect in the view of the experts. Two scenarios using expert weight and fair weight have been studied to determine the priority for development of each project. This study has been done to assist policy making for hydropower development in the Ping River Basin.

Women Farm Fish: Gender and Commercial Fish Cage Culture on the Upper Ping River, Northern Thailand

Studies from around the world underline the work of women in household-based aquaculture. Many extension and rural development programs and some commercial activities target women. Over the past decade, a tilapia fish cage industry has emerged on the Upper Ping River in northern Thailand. We interviewed 38 fish farmers, both women and men, about their practices and decision-making behavior and exploring gender relations. In addition, we collected quantitative data from 275 fish farms that allowed comparison of farming practices of women and men, and in a second survey compared 200 households that have farmed fish with 200 that have not to explore gender issues in access and decision-making. Women are frequently engaged in a day-to-day management of fi sh farms, most often working as part of a household team, but sometimes in senior management positions. Women attend trainings, and their experience and skills are largely recognized by male counterparts. Fishfarms managed by men, women, or jointly yield similar profits. Women who farm fish for commercial profit are often empowered by such engagement within households. But empowerment in one arena does not easily translate into decision-making authority in others; few women hold real authority in community affairs and those who do so have primarily risen to prominence within women’s groups or with respect to women’s issues. Successful engagement in aquaculture, arguably, contributed to such success, but also benefi ted from a social position relative to both women and men.

Floodplain sediment from a 100-year-recurrence flood in 2005 of the Ping River in northern Thailand

Abstract. The tropical storm, floodwater, and the floodplain-sediment layer of a 100-year recurrence flood are examined to better understand characteristics of large monsoon floods on medium-sized rivers in northern Thailand. Storms producing large floods in northern Thailand occur early or late in the summer rainy season (May–October). These storms are associated with tropical depressions evolving from typhoons in the South China Sea that travel westward across the Indochina Peninsula. In late September, 2005, the tropical depression from Typhoon Damrey swept across northern Thailand delivering 100–200 mm/day at stations in mountainous areas. Peak flow from the 6355-km2 drainage area of the Ping River upstream of the city of Chiang Mai was 867 m3s−1 (river-gage of height 4.93 m) and flow greater than 600 m3s−1 lasted for 2.5 days. Parts of the city of Chiang Mai and some parts of the floodplain in the intermontane Chiang Mai basin were flooded up to 1-km distant from the main channel. Suspended-sediment concentrations in the floodwater were measured and estimated to be 1000–1300 mg l−1. The mass of dry sediment (32.4 kg m-2), measured over a 0.32-km2 area of the floodplain is relatively high compared to reports from European and North American river floods. Average wet sediment thickness over the area was 3.3 cm. Sediment thicker than 8 cm covered 16 per cent of the area, and sediment thicker than 4 cm covered 44 per cent of the area. High suspended-sediment concentration in the floodwater, flow to the floodplain through a gap in the levee afforded by the mouth of a tributary stream as well as flow over levees, and floodwater depths of 1.2 m explain the relatively large amount of sediment in the measured area. Grain-size analyses and examination of the flood layer showed about 15-cm thickness of massive fine-sandy silt on the levee within 15-m of the main channel, sediment thicker than 6 cm within 200 m of the main channel containing a basal coarse silt, and massive clayey silt beyond 200 m. The massive clayey silt would not be discernable as a separate layer in section of similar deposits. The fine-sand content of the levee sediment and the basal coarse silt of sediment within 200 m of the main channel are sedimentological features that may be useful in identifying flood layers in a stratigraphic section of floodplain deposits.

Climatological Z-R relationship for radar rainfall estimation in the upper Ping river basin

Weather radar can potentially provide high-resolution spatial and temporal rainfall estimates bringing more accuracy to flood estimations as well as having some other applications in areas with insufficient rainfall stations like Thailand. Weather radar cannot be used to measure the rainfall depth directly; so an empirical relationship between the reflectivity ( Z) and rainfall rate (R), called the Z-R relationship (Z = AR b ), is generally used to assess the rainfall depth using radar. In this study, an optimization approach was used to find a suitable climatological Z-R relationship for the upper Ping river basin, Northern Thailand. The reflectivity data between June and October in 2003 and 2004 at the Omkoi radar station located in Chiangmai Province, together with the daily rainfall depths at fifty rainfall stations located in and around the basin during the same periods were used. A climatological Z-R relationship in the form Z = 74R 1.6 shows acceptable statistical indicators, making it suitable for radar rainfall prediction for the upper Ping river basin.

Spatial disaggregation of bias-corrected GCM precipitation for improved hydrologic simulation: Ping River Basin, Thailand

Abstract. Global Climate Models (GCMs) precipitation scenarios are often characterized by biases and coarse resolution that limit their direct application for basin level hydrological modeling. Bias-correction and spatial disaggregation methods are employed to improve the quality of ECHAM4/OPYC SRES A2 and B2 precipitation for the Ping River Basin in Thailand. Bias-correction method, based on gamma-gamma transformation, is applied to improve the frequency and amount of raw GCM precipitation at the grid nodes. Spatial disaggregation model parameters (β,σ2), based on multiplicative random cascade theory, are estimated using Mandelbrot-Kahane-Peyriere (MKP) function at q=1 for each month. Bias-correction method exhibits ability of reducing biases from the frequency and amount when compared with the computed frequency and amount at grid nodes based on spatially interpolated observed rainfall data. Spatial disaggregation model satisfactorily reproduces the observed trend and variation of average rainfall amount except during heavy rainfall events with certain degree of spatial and temporal variations. Finally, the hydrologic model, HEC-HMS, is applied to simulate the observed runoff for upper Ping River Basin based on the modified GCM precipitation scenarios and the raw GCM precipitation. Precipitation scenario developed with bias-correction and disaggregation provides an improved reproduction of basin level runoff observations.

Foundational Study on Water Use and Flood Control Effect by the Large Scale Reservoir

The goal of our study is to clarify the effect of the human activities on water resources and water circulation. The Chao Phraya River basin was selected for this study. The Chao Phraya River basin, the largest basin in Kingdom of Thailand is located in central and northern part of Thailand. This basin has two large-scale dams named Bhumibol Dam across the Ping River and Sirikit Dam across the Nan Riven This large storage dams are beneficial to the country for generating electricity and discharging water for the irrigation project areas and flood mitigation on both banks of the Ping, Nan and the Chao Phraya rivers.This paper has evaluated the water usage and flood control facilities of Bhumibol Dam. As the results of comparing the annual change of monthly runoff before and after dam construction, the minimum runoff increased drastically and the maximum runoff decreased.As the results of numerical analysis, it is clarified the water usage has become stable and the high water has decreased by the operation of Bhumibol Dam.

Effect of Large Scale Dams on Hydrological Regime in the Chao Phraya River Basin, Kingdom of Thailand

The purpose of this paper is to evaluate the effect of the human activities on water resourcesand hydrological cycle. The Chao Phraya River basin was selected for this study. The Chao Phraya River basin, the largest basin in Kingdom of Thailand is located in central and northern part of Thailand. This basin has two large-scale dams named Bhumibol Dam across the Ping River and Sirikit Dam across the Nan River. This large storage dams are beneficial to the country for generatingelectricity and discharging water for the irrigation project areas and flood mitigation on both banks of the Ping, Nan and the Chao Phraya rivers.There is no the long-term increase and decrease tendency of the precipitation. As the results of comparing the annual change of monthly runoff before and after dam construction, the minimum runoff increased and the maximum runoff degreased.As the results of spectrum analysis using FFT, after the Bhumibol dam was constructed, the daily runoff in Nakhon Sawan had period characteristics in 3.5days and 7days and the released water from the Bhumibol dam had period characteristics in 2.5days, 3.5 days and 7days. Dam operation effected on the hydrological cycle considerably.

Possible impact of dam reservoirs and river diversions on material fluxes to the Gulf of Thailand

Thai people have always been agricultural-based, although rainwater is not enough to sustain year-round agricultural practice. The first earth-filled dam was built across a valley near Sukhothai over 700 years ago. Now, there are six major multipurposed dam reservoirs, among which the largest is the Sri Nakarind (SN) built across the Kwae Yai River, the main branch of the Mae Klong River in the western part of Thailand. The first multipurposed dam reservoir built on the Chao Phraya (largest) River System is the Bhumibhol Dam on the Ping River. In this paper, the two Mae Klong River Dam Reservoirs and their biology and chemistry are discussed. Also investigated are the historical records of material fluxes to the Gulf of Thailand in down-core sediment profiles and in 40-year bands of coral, Porites lutea, taken from the Upper Gulf of Thailand near Si Chang Island. Sediment cores studied did not show clear decreases in the biogenic silica concentration in the Upper Gulf area after the building of dams. Part of the reasons might be the higher rate of dissolution of silica in tropical waters bioturbation of surface layers or the constant disturbance of the bottom sediment by fishermen using bottom trawls. The record in the coral bands seems to be more promising in reflecting the material flux change due to dam construction. An attempt to detect changes in diatom population with time due to the expected decrease in siliceous material discharge was not possible because there was a change from the use of 70 μm mesh size to 20 μm mesh size resulting in the increase of species and biomass, although the diatom percentage remained above 80% in all estuarine samples.

Prediction of monthly discharge in ungauged catchments under agricultural land use in the Upper Ping basin, northern Thailand

The present paper describes a methodology proposed for surface runoff modelling in gauged and ungauged subcatchments of northern Thailand. Gauged catchments are modelled using calibration against measured flow data, whereas streamflow in the ungauged subcatchments is simulated by a disaggregation procedure utilising measured streamflow data from a larger gauged catchment in which the ungauged subcatchment may be nested. The disaggregation technique is based on the assumption that the streamflow contribution from each subcatchment to the total catchment yield is proportional to a ratio of the catchment area and its average slope. The Mae Chaem catchment in the Upper Ping River basin was selected as a case study for applying the approach. The model testing performed in two subcatchments, where the modelled streamflow was compared with the measured data, showed that the first pass approach algorithm provides the accuracy of 13–17% of the relative error for the monthly time step.