Looking back: 2016 Kenya fieldwork

from Gro for Good newsletter 2

A comprehensive and efficient environmental monitoring network has been set up for the study area collecting relevant, timely and cost-effective data on rainfall, river flow and groundwater level and recharge. Data will be used in the development and running of a Groundwater Risk Management Tool, which will include a hydrogeological model. The model will be able to simulate and predict the effects of different levels of extraction and rainfall on the system, helping Kwale County to make plans to ensure that it has a good and sustainable water supply for people and industry.

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The project is making use of data on temperature, rainfall, humidity, air pressure, wind speed and direction from a number of automatic weather stations (AWS) installed in the project region. Much of the instrumentation has been provided by the Trans-African Hydro Meteorological Observatory (TAHMO) project, hosted in this region by Kenya Meteorological Services.

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River Flow Monitoring and Measurement

To understand the amount of water available in rivers and dams in the study area, various water level and discharge monitors have been installed. In particular, streamflow on the Mukurumudzi and Ramisi Rivers is being monitored to determine the water balance of the rivers at different points, enabling the researchers to understand and model groundwater inputs along these water courses.

River monitoring has been a great example of cooperation between project partners. As well as the existing staff gauge used by WRMA and Base Titanium to monitor flow in the Mukurumudzi River, the project has installed automatic water level loggers (Heron Logger) at two locations on the Mukurumudzi ((3KD06 – Shimba Hills – upstream and Irrigation Intake Works near Bomani Shopping Centre – downstream) and one on the Ramisi River at Eshu Bridge. These are complemented with manual staff gauges provided by WRMA Sub-regional Office in Mombasa. The instruments and staff gauges were installed jointly with WRMA/WRUA, Base Titanium, KENHA and the community. Flow in Ramisi River used to be monitored at Mwachande Bridge (3KD01) stage gauge by WRMA but the gauge has been vandalized and is not in operation.

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River Cross Section and Topographical Survey

A topographical survey was carried out at the river flow monitoring points at the Irrigation Intake Works (on the Mukurumudzi River) and at Eshu Bridge (on the Ramisi River) and measurements of cross section of the river were taken.

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The information will be used to facilitate flow measurement and permit the researchers to develop a Flow Rating Equation and Curve for each site, a key element of the hydrological model.

Surveyors and Survey Equipment at Eshu Bridge during cross section and topographical survey, May 2016 Cross-section of 3KD06 Weir on Mukurumudzi River, Shimba Hills. The figure below is the result of the river cross-section survey at the weir where water
flow is monitored and estimated for the Mukurumudzi River (by Base Titanium, WRMA
and Gro for Good) to aid water resources planning and decision-making. The weir structure also enables the consented abstraction of water by Shimba Hills Community Water Supply project which provides water to Shimba Hills shopping centre and its environs.

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Groundwater hydrochemistry

The chemical composition of groundwater provides useful information about the flow of water into and through the underground aquifers. Chemical and biochemical analysis also allow us to monitor substances which affect the safety and taste of drinking water. Three groundwater sampling campaigns have now been completed, involving the collection and analysis of water from open wells, rivers, handpumps and deep boreholes.

The first campaign was in September 2015 (wet season after the short rains; 81 sampling sites), the second was in March 2016 (dry season, fewer points sampled due to some wells/boreholes being dry) and the final sampling campaign in June 2016 at the end of the wet season (long rains), thus providing information about seasonal variation in water quality and on the process by which the aquifers are recharged following rain. A total of 43 groundwater sites are under fortnightly monitoring for groundwater static level, pH, temperature and conductivity.

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Sample pH, electrical conductivity, temperature, dissolved oxygen and redox potential (ORP) were measured during fieldwork using a flow cell so that the water did not come into contact with air. Other parameters analysed in situ were alkalinity, ammonia levels and faecal bacteria. Samples were also taken to Spain for laboratory analysis to indicate major ions, trace metals, water isotopes (deuterium and oxygen 18) and Total Organic Carbon.

Only very few points contained ammonia, nitrates or trace metals. However, most of the open wells contained high levels of faecal bacteria. The results will be explained in detail in the next newsletter.

Geophysics

by Julius Odida, PhD candidate, University of Nairobi

Geophysical methods (ground-based physical sensing techniques) are used to provide information about sub surface geology. The Gro for GooD project is using both electrical resistivity tomography (ERT) and vertical electric sounding (VES) to identify and characterize the aquifers (water-saturated sub-surface rocks) which lie beneath Kwale County. Over the past year, a number of geophysical surveys have been conducted by a team from University of Nairobi, WRMA and Rural Focus Ltd. The study involved four phases: planning/desktop studies, reconnaissance, actual data acquisition and report writing. Lower resistivity may indicate water saturation and/or fracture zones in the rock. We present a preliminary interpretation of some results below.

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