Interannual variability of yanze river surface level and its effect on water

Abstract

Despite efforts deployed by the Republic of Rwanda to increase the national water supply rate from an approximate of 50% by 2000 to 100% by 2020, Kigali, the capital city of Rwanda is facing a challenging problem of water supply and sanitation. The city is supplied with water by three water treatment plants namely: Nzove, Karenge and Kimisagara Water Treatment Plant (WTP) which are under WASAC. In this study, water level observed during 2011 to 2014 in Yanze River were collected, and the method of variation coefficient was applied to analyze the dynamic characteristics of water level. On the other side, rainfall, temperature and water production at Kimisagara WTP were analyzed to evaluate their relationship with water level fluctuations in Yanze River. The results showed that, (1) between 2011- 2014, the maximum average water level was 0.875143 m in November 2012 and the minimum was 0.453889 m in July 2012 and the maximum rainfall, temperature and water production were 304mm in March 2013, 22.83oc in January 2012, 71401m3 in July 2013 respectively, and the minimum rainfall value observed was 0 mm in June and July for each year except in June 2011 while minimum temperature and water production were 20.86oc May 2012, and 546957m3 in February 2011 respectively;(2) correlation between water level and precipitation was positive (R=0.75) while that of temperature and water production with water level was negative with correlation coefficients corresponding to (R=-0.32) and (R=-0.30) respectively;(3) finally, the studied parameters showed small and moderate variability during 2011-2014. The plant should find measures of diverting excess of sediments at river diversion intake to prevent clogging at the intake. In addition, there is need of extension of the storage capacity in accordance with water level variability to prevent the diversion of excess water at the intake back to the river and there is also need of sustainable management of Yanze watershed in order reduce the effect of erosion on water production.Furthermore, there is need for analysis of water level fluctuations of other sources of water used by other water treatment plants in particular those which supply water in Kigali city