Kamo River Basin Research Articles

Trend Analysis of Hydroclimatic Variables in the Kamo River Basin, Japan

Understanding long-term trends in hydrological and climatic variables is of high significance for sustainable water resource management. This study focuses on the annual and seasonal trends in precipitation, temperature, potential evapotranspiration, and river discharge over the Kamo River basin from the hydrological years 1962 to 2017. Homogeneity was examined by Levene’s test. The Mann–Kendall and a modified Mann–Kendall test as well as Sen’s slope estimator were used to analyze significant trends (p < 0.05) in a time series with and without serial correlation and their magnitudes. The results indicate that potential evapotranspiration calculated by the Penman–Monteith equation was highly related to temperature, and significantly increased in the annual and summer series. Annual river discharge significantly decreased by 0.09 m3/s. No significant trend was found at the seasonal scale. Annual, autumn, and winter precipitation at Kumogahata station significantly increased, while no significant trend was found at Kyoto station. Precipitation was least affected by the modified Mann–Kendall test. Other variables were relatively highly autocorrelated. The modified Mann–Kendall test with a full autocorrelation structure improved the accuracy of trend analysis. Furthermore, this study provides information for decision makers to take proactive measures for sustainable water management.

Assessment of hydrological extremes in the Kamo River Basin, Japan

ABSTRACTA suite of extreme indices derived from daily precipitation and streamflow was analysed to assess changes in the hydrological extremes from 1951 to 2012 in the Kamo River Basin. The evaluated indices included annual maximum 1-day and 5-day precipitation (RX1day, RX5day), consecutive dry days (CDD), annual maximum 1-day and 5-day streamflow (SX1day, SX5day), and consecutive low-flow days (CDS). Sen’s slope estimator and two versions of the Mann-Kendall test were used to detect trends in the indices. Also, frequency distributions of the indices were analysed separately for two periods: 1951–1981 and 1982–2012. The results indicate that quantiles of the rainfall indices corresponding to the 100-year return period have decreased in recent years, and the streamflow indices had similar patterns. Although consecutive no rainfall days represented by 100-year CDD decreased, continuous low-flow days represented by 100-year CDS increased. This pattern change is likely associated with the increase in temperature during this period.EDITOR D. KoutsoyiannisASSOCIATE EDITOR E. Gargouri

Impact assessment of rainfall scenarios and land‐use change on hydrologic response using synthetic Area IDF curves

AbstractIn combination with land use change, climate change is increasingly leading to extreme weather conditions and consequently novel hydrologic conditions. Rainfall Area intensity‐duration‐frequency (IDF) curves, commonly used tools for modeling hydrology and managing flood risk can be used to assess hydrologic response under extreme rainfall conditions. We explore the influence of land use change on hydrologic response under designed extreme rainfall over the period 1976 to 2006 in the Kamo River basin. Run‐off for all six designed rainfall shapes under 2006 land use is higher than that under 1976 land use, but the timing of peak discharge under 2006 land use occurs at roughly the same time as that under 1976 land use. Results indicate that run‐off under 2006 land use yielded higher discharge than under 1976 land use, and rainfall shape six leads to the most extreme hydrologic response and most dangerous conditions from the perspective of urban planning and flood risk management. Future hydrologic response will differ from present due both to changes in land cover and changes in extreme rainfall patterns requiring modification to Area IDF curves for catchments.

Integrated Assessment of Hydro-Climatology Variability in Kamo River Basin: Confronting Climate and Extremes

Integrated Assessment of Hydro-Climatology Variability in Kamo River Basin: Confronting Climate and Extremes

Reconstruction assessment of historical land use: A case study in the Kamo River basin, Kyoto, Japan

Reconstruction assessment of historical land use can be useful for understanding historical conditions and the impact of long-term land-use change. This study establishes a new method to estimate historical land use based on a set of basic rules generated from the comparison of present land-use and historical documents. This method has been formalized in the paleo-land-use reconstruction (PLUR) program, allowing users to quickly reconstruct historical land use using historical information. The 1843, 1902 and 1927 historical land use conditions were generated using the PLUR model for the Kamo River basin (KRB). Our results show that between 1902 and 1976, three golf courses (Ohara Public course, Kamigamo course and Funayama course) replaced forest land in the KRB. As a result of agricultural development, the area occupied by paddy fields in 1843 was 2.48km2 less than that in 1902. Urban areas increased from 1843 to 1976, mainly reflecting declining coverage of paddy fields after 1902. The approach presented in this study can be used to support land-use change analyses and reconstruction of paleo-hydrology. This study also provides a discussion of the major drivers of land use change.

Palaeoflood simulation of the Kamo River basin using a grid‐cell distributed rainfall run‐off model

AbstractLand‐use change and human activities have dramatic implications for water resources, especially through impacts on hydrology and water quality. We characterise the impact of land‐use change on floods through the reconstruction of palaeoflood events and the estimation of discharge during extreme rainfall events under the historical environment using the grid‐Cell Distributed Rainfall Run‐off Model Version 3 (CDRMV3). Historical land use maps were digitised using the Palaeoland‐Use Reconstruction (PLUR) programme as the input data for CDRMV3. Palaeoflood simulations show the delay and the reduction of the peak discharge under 1902 land use in the Kamo River basin because of increases in coverage of forest and paddy fields compared with 1976 land use. Lower discharge and earlier peak discharge time are estimated under historical land use and compared with conditions under present land use. The results of the palaeoflood simulations under extreme rainfall events create a better understanding of palaeoenvironmental conditions and their potential impact on flood management while suggesting important implications for resource management under land use and climate change.

Environmental Valuation of Up and Down Stream Regions

In a basin, the environment along the waterside in upstream and downstream regions is very different. For example, depopulation and conservation of forests are serious problems in upstream regions. In downstream regions, access to water is important. Therefore, it is necessary to consider the differences among regions in environmental management along the waterside. The environmental valuation by local residents is also important in environmental management. We clarified the environmental valuation along the waterside through the impressions of local residents to consider differences among regions in environmental management. According to Cramer's coefficient of contingency and factor analysis, the environmental valuation along the waterside is composed of ‘the components of impression', ‘impression' and ‘common factors'. Second, this study clarified characteristics of the regions by conducting a survey of the Kamo River Basin. Regions for implementation of a social survey are chosen based on the characteristics ofregions. A social survey was implemented to clarify problems and characteristics of the regions and impressions of the local resident along the waterside. In this study, it was shown that this valuation can be applied to the environmental valuation by taking into account the characteristics of up and down stream regions. It was also clear that the impression analysis also contributes to environmental management along the waterside. Finally, environmental management along the waterside should be done with consideration for ‘diversity and integration'.JEL Classification: Q51, Q57, R10, R53

都市河川流域におけるエストロゲン様汚染の把握と評価

A survey study for estrogens, nonylphenol (NP) and its precursors (nonylphenol ethoxylates and nonylphenol ethoxy acetates) was conducted for water and sediment of the Kamo River and its inflow waterways. 17β-estradiol (β-E2), estrone (E1) and 17α-estradiol were detected in river water and sediment up to the levels near their highest concentrations detected in the nationwide surveys. β-E2 concentration in water at almost all sampling sites was higher in winter and spring and lower in summer and autumn, suggesting more active decomposition of β-E2 by microorganisms at high water temperature. E1 showed the largest contribution to estrogenic activity of water among the examined compounds. However, NP accounted for a large part in estrogenic activity of sediment. The average emission loads of β-E2 and E1 estimated in the Kamo River basin were 12 and 75 nmol/cap/day, respectively. These values corresponded to a comparatively high amount estimated in the effluents from sewage treatment plants.

Analysis of parameter variations in L–Q equations for river runoff processes from the viewpoint of spatial and temporal conditions

This study aims to find out variation characteristics of the parameters of 'a' and 'b' in L = a x Q(b), an empirical equation for run-off loading (L) and flow rate (Q), by evaluating the effects of flow conditions and regional properties of the watersheds on the values. We selected the Kamo River basin (155 km2) as a study field, and conducted various kinds of investigations, such as 80 day high frequency observations, continuous monitoring for more than 2 years, storm event surveys, and simultaneous surveys of 39 stations. Then, we obtained 7-170 data in each of 39 sampling stations. The main results obtained are as follows: (1) L-Q equation with a range of 'a' can express L-Q relation in most of the WQIs (water quality indices); (2) 'a' receives temporal (flow condition) effects more in SS, VSS and Al, while it receives regional effect more in inorganic carbon, TN, Ca and Fe; (3) both of flow change in storm events, and base flow levels affect the L-Q relation, and their effects can classify the WQIs into several groups; (4) the effects of regional properties were obviously observed in 'a', and quantitatively evaluated, especially for density of population.

Estimation of annual pollutant loadings in two small catchments and examination of their differences caused by regional properties

A series of runoff surveys was conducted for more than one year in two small catchments of the Kamo River basin (75.4 km2) and the Takano River basin (66.8 km2) in Kyoto, Japan, which adjoin each other, and may have the same precipitation pattern. The investigation consisted of a high-frequency periodic survey, a long-term regular survey and a storm event survey. The survey results were compared with the regional properties of the basins, and the following results were obtained. (1) Pollutant loadings were successfully estimated as two portions of base discharge and storm events discharge from the survey results. (2) Estimated annual loading of the sites was 2.9-4.5, 1.3-1.8, 17-27, 1.3-2.2, 0.076-0.97 t/km2/y, respectively for COD(Mn), DOC, SS, TN and TP. (3) 52-53% of the whole flow, which was caused by rainfall events, conveyed 81-87, 68-73, 92-95, 64-67, 76-81% of the whole loading, respectively for COD(Mn), DOC, SS, TN and TP. (4) Differences of regional properties in two basins cause different runoff patterns, but the differences in runoff patterns also depend on the rainfall patterns. In general, a more urbanized basin receives early and strong influence of precipitation on the storm event runoff.

STUDY ON FLOOD HAZARD IN RIVER RECREATION SITE DUE TO HEAVY RAINFALL

A mathematical model which can simulate inundation process in river recreation site due to heavy rainfall has been developed. This model comprises the runoff model by the kinematic wave method and the 2-D inundation flow model based on the generalized curvilinear coordinate system. This model was applied to Hiragino park area in the Kamo river basin, Kyoto city. It was found out that under the same rainfall condition that caused the flood disaster at Tanigawadake in August 2000, the park area can become very dangerous. Also, the flood hazard possibility is expressed by the rainfall intensity and the time taken for rise of water depth or river velocity.