workshop 1 mutinda munguti.pptx

The International Symposium on Rainwater Harvesting and Resilience: Sand

dams as a 3R Best Practice . Dire Dawa

Tuesday, June 23, 2015 @ 2015 SASOL Foundation 1

J. Mu&nda Mungu&, CEO-‐SASOL, +254713402186, mungu&jm@sasolfounda&on.co.ke, www.sasolfounda&on.co.ke

Why Sand dams? �  The global food security is at stake. The world is grappling with

soaring food prices. The effect is worse in Africa especially Sub-Saharan Africa where dwindling supplies, expanding demand, and changing weather patterns have adverse implications……

�  Unreliability of the seasonal rainfalls in the ASALs greatly contributes to poor crop and pasture production hence contributing to cyclic food insecurity.

�  To buffer the unreliability of rainfall, food production hinges on water retention (recharge & reuse) and moisture conservation. This is what this entire presentation is all about- SAND DAMS; a SMART technology that enhance water retention for improved crop and livestock production to end extreme hunger and poverty.

Tuesday, June 23, 2015 @ 2015 SASOL Founda&on 2

What is a sand dam? �  A sand storage dam (or sand dam) is a weir build on and

into the riverbed of a seasonal sand river. �  The functioning of a sand dam is based on sedimentation of

coarse sand upstream of the structure, by which the natural storage capacity of the riverbed aquifer is enlarged. The aquifer fills with water during the wet season, resulting from surface runoff and groundwater recharge within the catchment.

�  When the riverbed aquifer is full, usually within one or two large rainfall events, the river starts to flow as it does in the absence of the dam. However, the groundwater flow through the riverbed is now obstructed by the sand dam, creating additional groundwater storage for the community.


The History of Sand dams �  The history of sand dams is as controversial as the name. �  There are claims that sand dams were used during the Roman &mes, throughout the Middle East history and lately in the 1800’s in Southwest US and Northern Mexico.

�  In 1928, Nzamba, an ex-‐WW1 soldier, built Mung’eto wa Nzamba in Mathima, Kitui, Kenya.

�  The African Land Development Board built a few sand dams all over Kenya between 1948 and 1963

� A_er independence, the new government also built several isolated cases in Kenya.


Major contributors in Kenya 1.  Utooni Development Organiza&on (UDO) 2.  ASAL Consultants 3.  SASOL and Partners ( MCC/CFGB, & RAIN) 4.  Excellent Development 5.  African Sand Dam Founda&on (ASDF) 6.  Caritas/CRS 7.  Prac&cal Ac&on 8.  Anglican Development Services/UCCS


Pictorial presentation


A newly constructed sand dam filled with flash water

New vs Mature


How to Construct Sand dams: A PRA Approach

@ 2015 SASOL Founda&on Tuesday, June 23, 2015 8

Needs assessment �  Seeks to identify and

prioritize water needs ; �  Assesses the possible

and sustainable water source options;

�  Explores the maintenance cost and community capacity;

�  Agree on the technology.


Site selection and Siting ◊  Site Selection

◊  Topography-Gradient of the stream at the point of interest; ◊  River morphology-checks the alignment(>50m) and nature of bank

material ; ◊  Accessibility during development & utilization time; ◊  Participatory confirmation of the site. ◊  Carrying out site measurement.

◊  Sitting; Check: ◊  Height of the banks(Hb)-Adequate enough to accommodate river flow; ◊  Firm soil formation-To support the structure and withstand abrasion. ◊  The slope of the stream should be ≤ 2m. to provide for adequate throw-back. ◊  Existence of natural water indicators or possibility of an underground aquifer. ◊  Presence of sand deposits; Coarse sand preferred. ◊  Previous channel shift from its original position. ◊  Presence of firm basement through probing.


Construction ◊ This entails:-

◊  Marking out of the proposed point. ◊  Excavation up to firm basement. ◊  Laying out of reinforcement. ◊  Filling of the trench with mortar/hardcore/concrete. ◊  Construction of superstructure.


Hydraulic consideration ◊  This provides for the safety and usefulness of the sand

dam; ◊  Parameters of interest:

◊  C/d cross sectional dimensions,. ◊  Q-Flow rate, ◊  Qd-Design discharge, ◊  S-Gradient ,

◊  The dam and spillway can be designed with the above parameters at hand.

◊  Stilling basin component is designed against the falling water hammer subject to: ◊  Qd-design discharge ◊  Gf-Gross freeboard.


Design calculations ◊  Sand dams are designed against:-

◊  Hydraulic & ◊  Structural failure.

◊  The hydraulic & structural design component looks into: ◊  The spillway dimensions-height and length. ◊  The height of the useful part of the dam-up to spillway ◊  The height of the gross freeboard for dam safety. ◊  The length of the dam. ◊  The sufficiency of the stilling basin/rip-rap. ◊  Forces acting on the dam.

◊  The design discharge is computed by use of the manning formula(Q(m3/s)=AR2/3 S1/n ) from the slope, cross-sectional dimensions.

◊  The spillway dimensioning is developed from the discharge by the discharge equation (Qmann=CLH3/2)

◊  Structural design focuses on vertical and horizontal forces which checks against sliding and overturning.


Sand Dams as a 3R Best Practice 3R = Retention+ Recharge+ (Re)use q  3R is a practical IWRM concept which

looks into :- q injection of more water into the buffer q Increased retention time for outflow and raised

water table and.. q Recirculation of water into the system.

◊ Sand Dams Greatly promotes: q  MUS (Multiple Use Systems) q  Natural re-generation; q  Ground water replenishment. q  Groundwater salinity amelioration.

Tuesday, June 23, 2015 14 @ 2015 SASOL Founda&on

Upscalling: Hinged on Sustainability principles; FIETS �  Financial �  Ins&tu&onal �  Environmental �  Technological �  Social



MUS

Parting shot: Choice to fail or succeed!

“The significant problems we face today cannot be solved at the same level of thinking we were at when we created them”

Albert Einstein


workshop 1 mutinda munguti.pptx

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