Southeastern Afghanistan, Wardak Province, Aunkhi Valley, Gorbat Watershed Restoration
Area Plan
Henry F. Shovic, PhD
June 21, 2011
Completed under CERP contract 20101227034827 for RC-East
The purpose of this analysis is to systematically inventory a small watershed in
Afghanistan and to complete input for a statement of work for watershed restoration in the
Gorbat River area near Baghak and Chingay villages (42SVC6371950610 MGRS). Its objective
is to promote agricultural uses in the watershed by increasing infiltration on hillslopes and
improving water availability via maintenance of Karez (subsurface irrigation) and an extensive
canal irrigation system.. These treatments are restricted to areas contributing to the Karez
irrigation systems and erosion near settlements.
The task order included the following:




Determine watershed conditions and potentials on four watersheds in the Wardak
Province.
Provide maps and documents.
Recommend areas having the highest restoration potential
Using client input, provide watershed restoration plans and designs for selected areas.
This project plan addresses the fourth task.
Objectives of this project:




Increasing groundwater infiltration on upper slopes that feed irrigation systems on the
alluvial fan.
Reducing flooding potential on streams on that fan
Improving existing irrigation systems
Reducing surface erosion on slopes
Methods of analysis include use of QuickBird satellite imagery (copyright Digital
Globe, Inc) at 1 m resolution, digital terrain data at 5 m resolution, and available geologic, soils,
and infrastructure data. The entire area was canvassed at scales of 1:400 to1:2000. ARCMAP
and ARCGLOBE are used for planar and perspective analysis. Images are rendered in colorinfrared for vegetation and soil analysis.
The Gorbat drainage is primarily mountainous with little agriculture and no local
villages. Slopes are steep and rocky with shallow soils. Streams are flashy, incised, and
unstable. No reforestation needs are probable. A small amount of terrace maintenance may be
beneficial. See the D-sized map titled: "SE Afghanistan, Southern Wardak Province, Wardak
Watershed Area: Initial Restoration Review of Gorbat Drainage", for an overview.
Though the drainage itself has low potential for restoration , villages and agricultural
land at its base have a very high potential. Therre are at least four villages nearby which can
provide a labor source. Landscapes are broad and open, enhancing security. The agricultural
area served by the Gorbat drainage is large (907 ha), and the infiltration area contributing to its
water is 514 ha. Hydrologically, the Gorbat drainage or "collection" part of the area has shallow
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soils and rapid runoff. The "infiltration" part of the area has rolling hills with generally deeper
soils feeding deep, gently-sloping alluvial fans. The "depositional" area is primarily irrigated
agriculture on gently-sloping fans and floodplains.
There is an extensive and complex set of irrigation canals serving the agricultural area.
About 90% of these systems is served by surface or near surface water produced by diversion
dams, feeder canals and streams, and Karez systems from the Gorbat and locally-associated
watersheds. The remaining 10% is served by diversion dams on the main river on the eastern
boundary. Streams in the area have wide, braided floodways and are intermittent. There is
evidence of flooding damage to canals and fields.
Proposed projects include canal cleaning and maintenance, karez improvements and
maintenance, hillside ditches to increase infiltration in higher slopes, de-silting of irrigation
ponds, and check dams to improve infiltration in ephemeral stream drainages. The improvement
in water delivery through canal and pond improvements, the increase in available water through
hillside ditches and check dams, and the reducing of flooding (via increase in infiltration) should
radically improve water utilization in this area. A potential side effect of this effort may be less
groundwater recharge to the main river at the eastern edge of the project area.
Candidate features were mapped at a scale of 1:400 to 1:1,200. See the map " SE
Afghanistan, Southern Wardak Province, Aunkhi Valley: Gorbat Watershed Restoration Project
Overview" for an overall look at the project.
Mapping of Karez Systems
Karez systems are both in lateral (across drainage) and linear (parallel with stream)
positions. Access pits average 30 in spacing. Apparently abandoned Karez systems were not
mapped (extreme northern edge of the infiltration area).
Mapping of Canals
Only major canals were mapped (those serving more than 3 fields). Smaller canals
(ditches) are probably generally maintained by farmers, and in any case, can not be reliably
identified on imagery. Tree and large shrubs cover about 30% of canals. Use of Color Infrared
(CIR) imagery greatly enhanced accuracy. This imagery covered 80% of the area. The
remainder (the western 20%) was extrapolated from gray scale imagery and the nearby CIR
imagery. The identification of canals was conservative, so there may be up to 10% more canals
not considered certain.
Mapping of Point Features
Where possible, all sources for canals were identified. Diversions, source or storage
ponds, Karez outlets, and dams were mapped. Large canal leaks were mapped.
Mapping of Infiltration Areas for Treatments
Criteria include:
 Contribute to active mapped Karez or other irrigation systems.
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



Slopes greater than 10%, and less than 40%. Slopes less than 10% were judged to have
adequate infiltration, and those over 40% are outside design specifications.
Not directly above or in the immediate vicinity of reservoirs or dwellings, to prevent
potential sedimentation if failure occurs.
Not in badlands, on bare rock slopes, or in active intensive agricultural areas.
Not in narrow, low-sight distance valleys.
Hillside ditches and rock bunds are for increasing infiltration. Bunds (rock barriers) are
prescribed if slopes have a rock source and soils are apparently too shallow for ditching.
Check dams are normally used for gully restoration and there are few gullies in this
project area. However, there are many ephemeral drainageways that could benefit from check
dams to increase infiltration by slowing water flow. These are not specified in intermittent or
perennial stream channels, because of potential hydrologic disturbance of the channel and
washout potential. Check dams are only specified in areas <40% slope. Candidate
drainageways average 20% slope.
Recommendations
Infiltration Treatments
Hillside ditch (for deep soils) and rock bunds (for shallow soils) are estimated . Hillside Ditch
length is based on an average shape ratio of 5:1 for a master shape, and an average slope for that
polygon based on Standard Operating Procedures. Table 1). Rock bunds (stone contour lines)
are placed at the same spacing for this project. Rock bunds are used where it is judged soils are
too shallow for ditching. This estimate may need to be adjusted during contract administration in
the field.
Hillside Treatment
Areas
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AREA
AVE
(m2) Slope (%)
81,425
29
6
7
8
133000
57450
30900
18
22
30
9
10
49125
138700
26
22
11
92525
22
ID
Treatment
Linear Ditch(m)
Rock Bund Hillside
Treatment
Hillside Ditch Treatment
Hillside Ditch Treatment
Rock Bund Hillside
Treatment
Hillside Ditch Treatment
Hillside Ditch Treatment
(50%)
Rock Bund Hillside
Treatment (50%)
Rock Bund Hillside
Linear Rock Bund (m)
10,178
16,625
5,745
3,862
6,140
6,935
6,935
9,252
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Hillside Treatment
Areas
ID
AREA
AVE
(m2) Slope (%)
12
19550
23
13
26000
25
14
38500
17
15
19250
21
16
17
38625
103325
16
25
19
20
51075
68650
17
28
21
10925
30
Treatment
Linear Ditch(m)
Treatment
Rock Bund Hillside
Treatment
Rock Bund Hillside
Treatment
Rock Bund Hillside
Treatment
Rock Bund Hillside
Treatment
Hillside Ditch Treatment
Rock Bund Hillside
Treatment
Hillside Ditch Treatment
Rock Bund Hillside
Treatment
Rock Bund Hillside
Treatment
Total
Linear Rock Bund (m)
1,955
3,250
3,850
1,925
3,862
12,915
5,107
8,581
1,365
44,415
64,068
Water Delivery Treatments
Project Area
Gorbat
Agricultural Area
Gorbat Infiltration
Area
Total
Check Dam
Drainageway
Length (m)
0
Karez Systems
(m)
Major Canals
(m)
3,993
55,934
4,645
4,017
16,818
8,010
72,752
The streams in this area are not highly-silt laden, so cleaning canals may noticeably
improve delivery for some time. De-silting, removal of bushes or trees (about 30% of the linear
m), debris cleaning, breach-filling, and rebuilding weak sections look like good activities. I don't
recommend canal lining in this project, because of lack of material availability, but part of the
project could be identifying areas where excess seepage could be reduced, or on main-line canals
that are a choke-point for other downstream canals.
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Karez systems need maintenance, such as removal of collapsed material, smoothing of
channels, repair of delivery boxes, and adjustment of grade. A total of 8,010 m of Karez was
mapped.
Check dams are beneficial in infiltration increase and reduction of surface flow. With
4,645 m of candidate drainageways, estimated at 3 m in average linear width and a 1 m high
dam (based on imagery), and an average slope of 20%, spacing is 9 m. Therefore, 516 check
dams are estimated.
Other watershed improvements
This may include desilting of 18 irrigation ponds (see map for locations). Many appear to have
high sediment levels, reducing capacity. There are five major canal leaks that should be
repaired, and one leak on a road crossing (Road Irrigation Conflict).
See the maps " "SE Afghanistan, Southern Wardak Province, Aunkhi Valley:
Gorbat Watershed Restoration Project Overview" and the set of detailed maps of the same area.
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