3.3 Field measurements
3.2.2
53
Quantity: Chill´ on River
Rough estimations of the flow rates of the Chill´on River in Chuquitanta during the upstream rainy period (Dec. - Apr.) and the upstream dry period (May - Nov.) can be made based on monthly average river flow rates recorded between 2007 and 2008 in Obrajillo (100 km upstream of Chuquitanta, in the Canta Province near Canta City) [90], data from ANA on the amount of water diverted from the Chill´on River for use in irrigation or for drinking water production in the Lima Province each month from 2008 to 2009 [7], estimations of monthly average precipitation rates based on monthly precipitation volumes in Lima Province in 2009 [43], and an estimation of the rate of evapotranspiration from the river between Obrajillo and Chuquitanta. Inflow to the river outside of precipitation is assumed negligible. Where Q is flow rate, ET is evapotranspiration and PR is precipitation, in general QChuquitanta = QObrajillo − Qirrigation/drinking
water
+ P R − ET.
Assuming an average monthly evapotranspiration in central coastal Pacific Per´ u of 70.13 mm [81], the average evaporation rate over a 100-km stretch of the Chill´on River with an average width of 20 m was estimated as 100 km length 1000 m 1m ∗ ET = (70.13 mm ) 1000 mm 1 1 km 0.05 m3 1 month = . (20 m width) 30 d ∗ 24 h ∗ 3600 s s
Monthly average precipitation rates were estimated similarly using the area of the Lima Province. Determining QChuquitanta for each month using the equation above and averaging results over the corresponding period led to estimated flow rates for the Chill´on River in Chuquitanta of 6250 L/s from Dec. through Apr. and 2400 L/s from May through Nov. These estimations are likely high, and could be made more precise if they were able to include data about river water losses due to infiltration and seepage as well as the amount of water diverted from the Chill´on River for irrigation in the Canta Province between Obrajillo and the border with the Lima Province.
3.3
Field measurements
Audit data which was not collected using either of the two methods above was determined via field sampling and laboratory testing. As mentioned, the groundwater pumping station is not considered in Phase III because SMP plans to use this water in expanded irrigation network to irrigate green spaces throughout the district. However, the decision was nonetheless made to carry out audit testing only (i.e., no collection of